NASA/TM–2000-209597

USAAMCOM-TR-00-A-006

U.S. Civil Rotorcraft Accidents,

1963 Through 1997

Franklin D. Harris, Eugene F. Kasper, and Laura E. Iseler

December 2000
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NASA/TM–2000-209597

USAAMCOM-TR-00-A-006

U.S. Civil Rotorcraft Accidents,

1963 Through 1997

Franklin D. Harris

F. D. Harris & Associates,

Fountain Hills, Arizona 85264

Eugene F. Kasper

Army/NASA Rotorcraft Division, Aeroflightdynamics Directorate (AMRDEC)

U.S. Army Aviation and Missile Command

Ames Research Center, Moffett Field, California 94035

Laura E. Iseler

Ames Research Center

Moffett Field, California 94035

December 2000

National Aeronautics and

Space Administration

Ames Research Center

Moffett Field, California 94035-1000
Available from:

NASA Center for AeroSpace Information National Technical Information Service

7121 Standard Drive 5285 Port Royal Road

Hanover, MD 21076-1320 Springfield, VA 22161

(301) 621-0390 (703) 487-4650

Acknowledgments

The authors wish to express their appreciation to all those who reviewed and commented on this report,

in manuscript or during oral presentations. We especially acknowledge and thank Sandra G. Hart of

NASA Ames Research Center for her detailed review, editing, and suggestions, without which this report

would be of far poorer quality.
iii

CONTENTS

Section/Paragraph Page

CONTENTS.........................................................................................................................................iii

LIST OF TABLES............................................................................................................................... vii

SUMMARY .......................................................................................................................................... 1

1. EXECUTIVE OVERVIEW........................................................................................................... 3

2. INTRODUCTION......................................................................................................................... 7

2.1 Early History....................................................................................................................... 7

2.2 Recent Developments.......................................................................................................... 8

2.3 Present Study....................................................................................................................... 8

3. ACCIDENT CATEGORIZATION.............................................................................................. 11

4. OVERVIEW OF RESULTS........................................................................................................ 15

4.1 Major Trends ..................................................................................................................... 16

4.2 Accident Statistics............................................................................................................. 16

5. COMMERCIAL SINGLE-PISTON ENGINE HELICOPTERS................................................ 19

5.1 Fleet History and Growth.................................................................................................. 19

5.2 Accident Analysis ............................................................................................................. 20

5.3 Detailed Analysis by Accident Category........................................................................... 24

5.3.1 Loss of Engine Power (1,554 Accidents).............................................................. 24

5.3.1.1 Overall Accident Trends........................................................................ 24

5.3.1.2 Loss of Engine Power by Category....................................................... 24

5.3.1.3 Loss of Engine Power by Activity......................................................... 25

5.3.1.4 Loss of Engine Power by Phase of Operation....................................... 25

5.3.1.5 Power-Off Landing................................................................................ 25

5.3.1.6 Conclusions About Loss of Engine Power Accidents. .......................... 27

5.3.2 In Flight Collision with Object (953 Accidents)................................................... 27

5.3.2.1 Overall Accident Trends........................................................................ 27

5.3.2.2 Collision with Object by Object Hit ..................................................... 28

5.3.2.3 Collision with Object by Cause ............................................................ 28

5.3.2.4 Collision with Object by Phase of Operation........................................ 28

5.3.2.5 Collision with Object by Activity ......................................................... 28

5.3.2.6 Collision with Object by Part Hit.......................................................... 29

5.3.2.7 Conclusions About In Flight Collision with Object Accidents............. 29

5.3.3 Loss of Control (625 Accidents) ........................................................................... 29

5.3.3.1 Overall Accident.................................................................................... 30

5.3.3.2 Loss of Control by Phase of Operation................................................. 30

5.3.3.3 Loss of Control by Activity................................................................... 30

5.3.3.4 Loss of Control by Cause...................................................................... 31

5.3.3.5 Loss of Control by Axis ........................................................................ 31
iv

CONTENTS (Continued)

Section/Paragraph Page

5.3.3.6 Loss of Control by Pilot-in-Command Certification Level .................. 32

5.3.3.7 Conclusions About Loss of Control Accidents ..................................... 32

5.3.4 Airframe/Component/System Failure or Malfunction (639 Accidents) ............... 33

5.3.4.1 Overall Accident Trends........................................................................ 33

5.3.4.2 Airframe Failures by Phase of Operation ............................................. 33

5.3.4.3 Airframe Failures by Activity ............................................................... 33

5.3.4.4 Airframe Failures by System/Component............................................. 34

5.3.4.4.1 Drive train failures by subsystem........................................ 34

5.3.4.4.2 Rotor failures by subsystem................................................ 37

5.3.4.4.3 Control system failures by subsystem................................. 38

5.3.4.4.4 Airframe failures by components........................................ 38

5.3.4.5 Conclusions About Airframe Failure or Malfunction Accidents .......... 40

5.4 Summary Remarks, Conclusions, and Recommended Actions ........................................ 41

6. COMMERCIAL SINGLE-TURBINE ENGINE HELICOPTERS ............................................ 45

6.1 Fleet History and Growth.................................................................................................. 45

6.2 Single-Turbine vs. Single-Piston ...................................................................................... 45

6.3 Accident Analysis ............................................................................................................. 46

6.4 Detailed Analysis by Accident Category........................................................................... 48

6.4.1 Loss of Engine Power (704 Accidents)................................................................. 48

6.4.1.1 Overall Accident Trends........................................................................ 48

6.4.1.2 Loss of Engine Power by Category....................................................... 49

6.4.1.3 Loss of Engine Power by Activity......................................................... 49

6.4.1.4 Loss of Engine Power by Phase of Operation....................................... 49

6.4.1.5 Conclusions About Loss of Engine Power Accidents ........................... 50

6.4.2 In Flight Collision with Object (298 Accidents)................................................... 50

6.4.2.1 Overall Accident Trends........................................................................ 50

6.4.2.2 Collision with Object by Object Hit ..................................................... 50

6.4.2.3 Collision with Object by Cause ............................................................ 50

6.4.2.4 Collision with Object by Phase of Operation........................................ 51

6.4.2.5 Collision with Object by Activity.......................................................... 51

6.4.2.6 Collision with Object by Part Hit.......................................................... 51

6.4.2.7 Conclusions About In Flight Collision with Object Accidents............. 51

6.4.3 Loss of Control (284 Accidents) ........................................................................... 51

6.4.3.1 Overall Accident Trends........................................................................ 51

6.4.3.2 Loss of Control by Axis ........................................................................ 52

6.4.3.3 Loss of Control by Cause...................................................................... 52

6.4.3.4 Loss of Control by Phase of Operation................................................. 53

6.4.3.5 Loss of Control by Activity................................................................... 53

6.4.3.6 Loss of Control by PIC Certification Level .......................................... 53

6.4.3.7 Conclusions About Loss of Control Accidents ..................................... 54
v

CONTENTS (Continued)

Section/Paragraph Page

6.4.4 Airframe/Component/System Failure or Malfunction (282 Accidents) ............... 54

6.4.4.1 Overall Accident Trends........................................................................ 54

6.4.4.2 Airframe Failures by Phase of Operation ............................................. 55

6.4.4.3 Airframe Failures by Activity ............................................................... 55

6.4.4.4 Airframe Failures by System/Component............................................. 55

6.4.4.4.1 Drive train failures by subsystem........................................ 56

6.4.4.4.2 Rotor failures by subsystem................................................ 58

6.4.4.4.3 Control system failures by subsystem................................. 60

6.4.4.4.4 Airframe failures by components........................................ 60

6.4.4.4.5. Conclusions about airframe failure or malfunction

accidents ............................................................................. 61

6.5 Summary Remarks, Conclusions, and Recommended Actions ........................................ 62

7. COMMERCIAL TWIN-TURBINE ENGINE HELICOPTERS ................................................ 67

7.1 Fleet History and Growth.................................................................................................. 67

7.2 Twin turbine vs. Single turbine ......................................................................................... 67

7.3 Accident Analysis ............................................................................................................. 68

7.4. Detailed Analysis by Accident Type ................................................................................. 69

7.4.1 Loss of Engine Power (39 Accidents)................................................................... 69

7.4.1.1 Overall Accident Trends........................................................................ 70

7.4.1.2 Loss of Engine Power by Category....................................................... 70

7.4.1.3 Loss of Engine Power by Activity......................................................... 70

7.4.1.4 Loss of Engine Power by Phase of Operation....................................... 71

7.4.1.5 Conclusions About Loss of Engine Power Accidents ........................... 71

7.4.2 In Flight Collision with Object (43 Accidents)..................................................... 71

7.4.2.1 Overall Accident Trends........................................................................ 71

7.4.2.2 Collision with Object by Object Hit ..................................................... 71

7.4.2.3 Collision with Object by Cause ............................................................ 71

7.4.2.4 Collision with Object by Activity ......................................................... 72

7.4.2.5 Collision with Object by Phase of Operation........................................ 72

7.4.2.6 Collision with Object by Part Hit.......................................................... 72

7.4.2.7 Conclusions About In flight Collision with Object Accidents.............. 72

7.4.3 Loss of Control (40 Accidents) ............................................................................. 72

7.4.3.1 Overall Accident Trends........................................................................ 72

7.4.3.2 Loss of Control by Axis ........................................................................ 72

7.4.3.3 Loss of Control by Cause...................................................................... 73

7.4.3.4 Loss of Control by Phase of Operation................................................. 73

7.4.3.5 Loss of Control by Activity. .................................................................. 73

7.4.3.6 Loss of Control by PIC Certification Level. ......................................... 74

7.4.3.7 Conclusions About Loss of Control Accidents ..................................... 74
vi

CONTENTS (Continued)

Section/Paragraph Page

7.4.4 Airframe/Component/System Failure or Malfunction (89 Accidents) ................. 74

7.4.4.1 Overall Accident Trends........................................................................ 74

7.4.4.2 Airframe Failures by Phase of Operation ............................................. 75

7.4.4.3 Airframe Failures by Activity ............................................................... 75

7.4.4.4 Airframe Failures by System/Component............................................. 75

7.4.4.4.1 Drive train failures by subsystem........................................ 76

7.4.4.4.2 Rotor failures by subsystem................................................ 77

7.4.4.4.3 Control system failures by .................................................. 79

7.4.4.4.4 Airframe specific failures by components. ......................... 79

7.4.4.4.5 Conclusions about airframe failure or malfunction

accidents ............................................................................. 79

7.5 Summary Remarks, Conclusions and Recommended Actions ......................................... 80

8. ALL OTHER ROTORCRAFT TYPES....................................................................................... 85

8.1 Fleet History and Growth.................................................................................................. 85

8.2 Accident Analysis ............................................................................................................. 85

8.3 Detailed Analysis by Accident Category........................................................................... 86

8.4 Summary Remarks, Conclusions, and Recommended Actions ........................................ 87

9. FINAL REMARKS, CONCLUSIONS, AND RECOMMENDATIONS.................................... 89

REFERENCES.................................................................................................................................... 97

LIST OF FIGURES............................................................................................................................. 99

Appendix A NTSB DEFINITIONS............................................................................................ 213

Appendix B ESTIMATION OF ROTORCRAFT FLEET SIZE AND HOURS FLOWN ......... 229

Appendix C AUTOROTATION-RELATED ACCIDENTS........................................................ 253

Appendix D OTHER STATISTICAL DATA TABLES............................................................... 265
vii

TABLES

Table Page

1. SUMMARY ACCIDENT COUNT AND DISTRIBUTION, 1963–1997.................................... 4

2. DATA ELEMENTS IN NTSB MINI-BRIEFS, 1963–1997 ...................................................... 13

3. ACCIDENT DISTRIBUTION BY ROTORCRAFT TYPE, 1963–1997 .................................. 15

4. ACCIDENT COUNT AND DISTRIBUTION, 1963–1997....................................................... 16

5. CAA HELICOPTER CENSUS AT END OF 1957.................................................................... 19

6. SINGLE-PISTON ACCIDENT COUNT AND DISTRIBUTION, 1963–1997 ........................ 21

7. SINGLE-PISTON ACCIDENT DISTRIBUTION, LAST 8 YEARS VS. 1963–1997 .............. 22

8. NTSB FAILURE MODE/SYSTEM MATRIX—SINGLE-PISTON HELICOPTERS ............. 35

9. DRIVE TRAIN FAILURES BY COMPONENTS—SINGLE-PISTON HELICOPTERS....... 35

10. DRIVE TRAIN MAJOR COMPONENT FAILURES—SINGLE-PISTON

HELICOPTERS ......................................................................................................................... 36

11. ROTOR SYSTEM FAILURES BY COMPONENTS—SINGLE-PISTON

HELICOPTERS ......................................................................................................................... 37

12. ROTOR SYSTEM COMPONENTS FAILURE MODE—SINGLE-PISTON

HELICOPTERS ......................................................................................................................... 37

13. CONTROL SYSTEM FAILURES BY COMPONENTS—SINGLE-PISTON

HELICOPTERS ......................................................................................................................... 38

14. AIRFRAME FAILURES BY COMPONENTS—SINGLE-PISTON HELICOPTERS............ 39

15. AIRFRAME COMPONENTS FAILURE MODE—SINGLE-PISTON HELICOPTERS........ 39

16. ACCIDENTS BY ACTIVITY AND PHASE OF OPERATION—SINGLE-PISTON

HELICOPTERS ......................................................................................................................... 41

17. FAA ROTORCRAFT ACTIVITY SURVEY OF 1989.............................................................. 45

18. SINGLE-TURBINE VS. SINGLE-PISTON ACCIDENT COMPARISON, 1963–1997 .......... 47

19. SINGLE-TURBINE ACCIDENT DISTRIBUTION, LAST 11 YEARS VS. 1963–1997......... 48

20. SINGLE-ENGINE-HELICOPTER AIRFRAME FAILURE COMPARISON, 1963–1997...... 56

21. NTSB FAILURE MODE/SYSTEM MATRIX—SINGLE-TURBINE

HELICOPTERS ......................................................................................................................... 57

22. DRIVE TRAIN FAILURES BY COMPONENTS—SINGLE-TURBINE HELICOPTERS.... 57

23. DRIVE TRAIN MAJOR COMPONENT FAILURES—SINGLE-TURBINE

HELICOPTERS ......................................................................................................................... 58

24. ROTOR SYSTEM FAILURES BY COMPONENTS—SINGLE-TURBINE

HELICOPTERS ......................................................................................................................... 58

25. ROTOR SYSTEM COMPONENTS FAILURE MODE—SINGLE-TURBINE HELICOPTERS59

26. CONTROL SYSTEM FAILURES BY COMPONENTS—SINGLE-TURBINE

HELICOPTERS ......................................................................................................................... 60

27. AIRFRAME-SPECIFIC FAILURES BY COMPONENTS—SINGLE-TURBINE

HELICOPTERS ......................................................................................................................... 61

28. AIRFRAME COMPONENTS FAILURE MODE— SINGLE-TURBINE HELICOPTERS ... 62

29. ACCIDENTS BY ACTIVITY AND PHASE OF OPERATION—SINGLE-TURBINE

HELICOPTERS ......................................................................................................................... 63
viii

TABLES

Table Page

30. SINGLE-TURBINE VS. TWIN-TURBINE ACCIDENT DISTRIBUTION COMPARISON,

1963–1997.................................................................................................................................. 68

31. TWIN-TURBINE ACCIDENT DISTRIBUTION, LAST 5 YEARS VS. 1963–1997 .............. 69

32. FATALITIES PER 100 ACCIDENTS BY TYPE OF ENGINE, 1963–1997............................. 70

33. HELICOPTER AIRFRAME FAILURE COMPARISON, 1963–1997...................................... 75

34. NTSB FAILURE MODE/SYSTEM MATRIX—TWIN-TURBINE

HELICOPTERS ......................................................................................................................... 76

35. DRIVE-TRAIN FAILURES BY COMPONENTS—TWIN-TURBINE HELICOPTERS....... 77

36. DRIVE-TRAIN MAJOR COMPONENT FAILURES—TWIN-TURBINE

HELICOPTERS ......................................................................................................................... 77

37. ROTOR SYSTEM FAILURES BY COMPONENTS—TWIN-TURBINE

HELICOPTERS ......................................................................................................................... 78

38. ROTOR SYSTEM COMPONENTS FAILURE MODE—TWIN-TURBINE

HELICOPTERS ......................................................................................................................... 78

39. CONTROL SYSTEM FAILURES BY COMPONENTS—TWIN-TURBINE

HELICOPTERS ......................................................................................................................... 79

40. AIRFRAME SPECIFIC FAILURES BY COMPONENTS—TWIN-TURBINE

HELICOPTERS ......................................................................................................................... 80

41. ACCIDENTS BY ACTIVITY AND PHASE OF OPERATION—TWIN-TURBINE

HELICOPTERS ......................................................................................................................... 81

42. ACCIDENT DISTRIBUTION BY ALL OTHER ROTORCRAFT TYPES,

1963–1997.................................................................................................................................. 86

43. AMATEUR VS. COMMERCIAL ACCIDENT DISTRIBUTION, 1963–1997........................ 86

44. ACCIDENTS BY ACTIVITY AND PHASE OF OPERATION—ALL OTHER TYPES ........ 87

45. SUMMARY OF ROTORCRAFT ACCIDENTS FROM MID-1963 TO THE END

OF 1997...................................................................................................................................... 90
1

U.S. Civil Rotorcraft Accidents, 1963 Through 1997

Franklin D. Harris,1 Eugene F. Kasper2 and Laura E. Iseler3

Ames Research Center

SUMMARY

The narrative summary data produced by the U.S. National Transportation Safety Board (NTSB)

were obtained and analyzed for all 8,436 rotorcraft accidents that occurred from mid-1963 through

1997. This analysis was based on the NTSB’s assignment of each accident into one of 21 “first

event” categories. The number of U.S. civil registered rotorcraft as recorded by the Federal Aviation

Administration (FAA) for the same period were obtained as well. Taken together, these data indicate

the civil rotorcraft accident rate (on a per 1,000 registered rotorcraft basis) decreased by almost a

factor of 10 over the 34-year study period (i.e., from 118 accidents per 1,000 rotorcraft in 1964 to

13.6 per 1,000 in 1997).

Analysis of the accident data indicated that the first event in over 70% of the 8,436 rotorcraft

accidents fell into four categories:

2,408 loss of engine power (28.5%)

1,322 in flight collision with objects (15.7%)

1,114 loss of control (13.2%)

1,083 airframe/component/system failure or malfunction (12.8%).

Because the vast majority of rotorcraft registered over the study period had a single engine (piston or

turbine), these aircraft dominated the accident statistics. Over 985 loss of engine power accidents

were caused by improper fuel/air mixture. Fuel exhaustion was a major, common event in both

piston and turbine helicopter accidents. In-flight collisions with wires and poles accounted for over

700 accidents. Pilots of the commercial fleet lost control of their helicopters regardless of their

certified skill level. Airframe related failures left the commercial helicopter pilot without antitorque

and directional control in 470 accidents. Without significantly increased safety efforts in the

immediate future, the authors project that in the year 2010 there will be about 6 accidents per

1,000 registered rotorcraft. If the fleet doubles in size by 2010, then this accident rate corresponds to

150 accidents per year—about 3 accidents per week.

 

1 F. D. Harris & Associates, Fountain Hills, Arizona 85264

2 Army/NASA Rotorcraft Division, Aeroflightdynamics Directorate (AMRDEC), Moffett Field, California

3 Ames Research Center, Moffett Field, California
2

THIS PAGE INTENTIONALLY BLANK
3

1. EXECUTIVE OVERVIEW

The U.S. civil rotorcraft fleet grew from fewer than 10 in 1946 to 2,196 at the end of 1964 and to

12,911 at the end of December 1997. Throughout this period, the commercially manufactured,

single-engine helicopter dominated the registered fleet. Although the single-piston engine

configuration still sold in quantity, the rotorcraft industry introduced the single-turbine engine

configuration in the mid-1960s. In 1997, nearly equal numbers of single-piston and single-turbine

helicopters were registered (about 5,000 each). The commercially manufactured, twin-turbine

helicopter began selling in quantity in the late 1970s—slightly over 1,200 were registered at the end

of 1997. A growing fleet of registered amateur-built rotorcraft included close to 1,000 helicopters

and 2,000 autogyros in 1997.

During the 34-year period from mid-1963 through the end of 1997, the National Transportation

Safety Board (NTSB) recorded a total of 8,436 rotorcraft accidents. However, because of continuing

emphasis on safety, the rotorcraft industry was able to reduce accidents per year, even though the

registered fleet grew in size. Specifically, annual U.S. civil rotorcraft accidents decreased from

260 in 1964 to 175 in 1997. In broad terms then, the industry succeeded in reducing annual

accidents per 1,000 registered rotorcraft by nearly a factor of 10 over the 34-year period (i.e., from

118 accidents per 1,000 registered rotorcraft in 1964 to 13.6 per 1,000 in 1997). Nevertheless,

accidents over this 34-year period took a heavy toll. The 8,436 accidents directly affected

16,825 people: 2,135 were killed and 1,760 were seriously injured, but 12,930 survived with minor

or no injury. Rotorcraft damage during this period was significant. Of the 8,436 rotorcraft involved,

2,363 (i.e., nearly 20% of today’s registered fleet) were listed as destroyed by the NTSB. Another

5,909 rotorcraft were substantially damaged; 164 received little or no damage.

Analysis of each accident (table 1) showed that accident similarities far outnumbered dissimilarities,

despite obvious differences in the helicopter classes. The major observations are as follows:

1. Single-engine, commercially manufactured helicopters, whether piston- or turbinepowered, experienced the most accidents because of a partial or total loss of engine power. The

primary reason for loss of engine power was directly traced by the NTSB to fuel/air mixture

problems, which accounted for no less than 985 accidents. Fuel exhaustion, fuel starvation, fuel

contamination, and, for the piston engine, carburetor heat were key words repeatedly used by the

NTSB accident investigators. Apparently, many pilots disregarded the need by both engine types for

clean fuel and air in proper proportions—to say nothing about the FAA regulations for fuel reserves.

Engine structural failure accounted for 452 accidents. The power-loss cause was not established in

578 single-engine helicopter accidents. Power-off landing proficiency is not required by the FAA in

order to obtain a helicopter pilot’s certification. This standard appears inconsistent with the number

of accidents caused by loss of engine power. However, it also appears that helicopters—currently in

the civil fleet—provide marginal to inadequate autorotational capability for the average pilot to

successfully complete the final flare and touchdown to a generally unsuitable landing site.
4

TABLE 1. SUMMARY ACCIDENT COUNT AND DISTRIBUTION, 1963–1997

Commercially manufactured

Single

piston

Single

turbine

Twin

turbine

Amateur

types

NTSB first event accident category Count (%) Count (%) Count (%) Count (%)

Loss of engine power 1,554 (28.9) 704 (31.3) 39 (12.9) 111 (21.5)

In flight collision with object 953 (17.7) 298 (13.2) 43 (14.2) 28 (5.43)

Loss of control 625 (11.6) 284 (12.6) 40 (13.2) 165 (32.0)

Airframe/component/system failure/

malfunction 639 (11.9) 282 (12.5) 89 (29.5) 73 (14.1)

Hard landing 483 (8.99) 140 (6.23) 8 (2.65) 25 (4.89)

In flight collision with terrain/water 443 (8.25) 143 (6.36) 16 (5.23) 40 (7.75)

Rollover/nose over 290 (5.40) 119 (5.29) 4 (1.32) 20 (3.88)

Weather 57 (1.06) 85 (3.78) 12 (3.97) 5 (0.97)

Other 327 (6.09) 192 (8.54) 51 (16.9) 49 (9.49)

Total 5,371 2,247 302 516

2. Twin-turbine helicopters significantly reduced loss of engine power accidents (on a

percentage basis). However, 23 of the 39 accidents began with a total loss of power in both engines.

Most discouragingly, 17 of the 39 accidents were caused by fuel/air mixture problems, a finding

similar to that for single-engine helicopter accidents.

3. Introducing twin-turbine helicopters reduced loss of engine power accidents, but a very

disturbing trend began with the larger helicopters capable of carrying more people. In the singlepiston helicopter fleet, there were 5,371 accidents, and 683 people were killed. Because of the

2,247 accidents involving single-turbine helicopters, 951 people died. Now, in just 302 twin-turbine

helicopter accidents, there were 321 fatalities.

4. The commercially manufactured helicopter fleet collectively had 1,294 accidents because

of in-flight collisions with objects. Collisions with wires and poles accounted for 720 accidents.

Collisions with trees added another 205 accidents. The major contributor to these in flight collisions

was the single-piston helicopter fleet, most frequently during crop dusting. This helicopter type had

about equal numbers of main- and tail-rotor strikes. The single-turbine helicopter class, which does

relatively little crop dusting, experienced four tail rotor strikes for every three main rotor strikes.

Twin-turbine helicopters had more than twice as many tail rotor strikes than main-rotor strikes.

5. Pilots of commercially manufactured helicopters lost control regardless of their certified

skill level, and this precipitated 12% of the commercial fleets’ 7,920 accidents. Pilots of amateur

built rotorcraft lost control nearly three times as often. The requirement to adequately control
5

antitorque in all flight phases appears as a root problem with the single main rotor helicopter

configuration. Single-piston helicopters (and turbine-powered helicopters to a somewhat lesser

extent) appear to be inordinately difficult to fly; particularly when the average pilot must devote

some attention to any other task or is experiencing a real or imagined emergency. Cross-coupling

between the vertical, power/RPM, and yaw axes is excessive. The handling qualities design

standards applicable to the current helicopter fleet date back to the 1950s. Although generally

tolerated, the resulting helicopter stability and control characteristics now appear quite

unsatisfactory. Equipping some single-turbine and virtually all twin-turbine helicopters with an

electro-hydraulic, automatic stability and control system improved the overall loss of control

situation.

6. Airframe system, subsystem, and component failures or malfunctions were one of the

leading causes of helicopter accidents over the 34-year study period. Pilots of commercially

manufactured helicopters were left without antitorque and directional control in 470 accidents,

virtually 50% of the 1,010 accidents NTSB charged to the airframe category. The tail rotor

driveshaft, which includes the shaft couplings and bearings, failed in 122 accidents. Failure of the

tail rotor control system led to 56 accidents, and blade/hub failures accounted for 186 accidents. The

corresponding main rotor system dynamic components also failed or malfunctioned, which led to

404 additional accidents. Specifically, engine to main rotor gearbox failures caused 137 accidents,

control system failures caused 103, and blade/hub failures caused 112. The commercial helicopter

airframe failure rate strongly suggests that past design standards are inadequate relative to the many

new and varied activities in which this aircraft class is engaged. Pilots did exceed design limits,

required and timely maintenance was skipped, and less than thorough inspections were performed,

but still the current fleet appears, broadly speaking, to be underdesigned in view of today’s

commercial usage.

7. The favorable, downward trend in rotorcraft accidents per year enumerated above was

not linear. During a 15-year period, beginning in 1972 and ending in 1987, the industry experienced

a rash of accidents that drove the annual rate to 327 accidents in 1980 before dropping to

196 accidents in 1987. We believe that the increased accidents per year during this period was

initiated by the 10-year period during which commercial helicopter yearly sales increased by over

50%. The relatively abrupt increase of new helicopters in the U.S. civil fleet was accompanied by a

jump in accidents caused by loss of engine power and failure of airframe systems and components.

8. Single-turbine helicopter accidents per year increased slightly over the last decade of the

period studied. There were 62 accidents in 1987, 65 accidents in 1993 and 73 accidents in 1997,

during which time the registered fleet increased only modestly in size. Most recently, new, singleturbine helicopters were being registered at a rate comparable to that of the 1970s. There is concern,

therefore, that a rapid fleet expansion will prompt an increase in accidents just as it did two decades

ago. We recommend that more intensive safety improvement efforts be quickly initiated by the

industry.

9. The amateur-built helicopter and autogyro fleet experienced approximately the same

accident distribution, based on percentage, as the commercially manufactured helicopter fleet. The

primary exceptions were that loss of control was nearly three times as prevalent and loss of engine

power occurred with two-thirds the frequency. Because the amateur fleet is growing so fast, we
6

believe that major manufacturers, operators, and trade associations must provide considerably more

help to this segment of their industry to lower the risks being taken.

10. There is little doubt that single- or twin-turbine-engine-powered helicopters are safer than

the single-piston-engine helicopter. How much safer can not, in our opinion, be quantified. The

rotorcraft industry is being misguided by accident rate trends that use FAA data for active fleet size,

hours flown, takeoffs made, etc. In fact, we believe it quite likely that the rotorcraft industry will

miss significant safety trends if the currently used methods of computing accident rates remain as

the measure of progress. Unquestionably, the true aviation goal is no fatalities or injuries, in which

case safety rates become meaningless.

This report provides detailed analysis, specific conclusions, and challenging recommendations

relative to each helicopter class. Section 9 provides a concise group of final remarks, conclusions,

and detailed recommendations. Without significantly increased safety efforts in the immediate

future, including implementing the submitted recommendations, it is projected that in the year 2010

there will be about 6 accidents per 1,000 registered rotorcraft. If the fleet doubles in size by 2010,

then this accident rate corresponds to 150 accidents per year—about 3 accidents per week. It is

doubtful that the public will perceive this projection as an indication that pilots and their rotorcraft

are, in fact, becoming safer.
7

2. INTRODUCTION

The gathering, analyzing, and reporting of aviation accident data has played an important part in

making air transportation safer. One of the earliest examples of this safety improvement activity took

place in November 1921, at the Premier Congrés International de la Navigation Aérienne, held in

Paris. During this conference, Albert Tete presented a review of the status of aerial transportation in

France (ref. 1). Additionally, Mayo presented a paper entitled “Aviation and Insurance,” (ref. 2), in

which he discussed the “causes of the many accidents which account for the high insurance rates.”

Specifically, he stated:

The frequent accidents to airplanes employed on air routes have

been due to widely divergent causes. Probably 90% of them were due to

carelessness and could have been avoided, had the necessary precautions

been taken. The principal causes of accidents may be enumerated as

follows:

1. Poor piloting;

2. Engine trouble;

3. Lack of system [organization of personnel];

4. Poorly adapted airplanes;

5. Poor airdromes;

6. Unfavorable meteorological conditions.

With only minor changes, Mayo’s paper could be presented at any “aerial transportation” safety

conference today.

2.1 Early History

In the United States, following World War I, the National Advisory Committee on Aeronautics

(NACA), by request of the Assistant Secretaries for Aeronautics in the Departments of War, Navy,

and Commerce, established a special commission “to prepare a basis for the classification and

comparison of aircraft accidents, both civil and military.” In NACA Technical Report TR-308

(ref. 3), 13 classes of accidents, 4 classes of injuries, and 6 classes of damage to material were

defined. Categories of immediate and underlying accident causes were established and an accident

form was adopted (fig. 1). This approach was used to analyze 1,432 military and 1,400 civilian

accidents that occurred before January 1929 (ref. 4). In June 1936, a further refinement to definitions

and methods of analysis was established in NACA TR-576 (ref. 5). That report, entitled “Aircraft

Accidents, Method of Analysis,” became the standard United States reference on the subject and

formed the foundation for current NTSB aviation accident reporting.

There was an immediate payoff for the efforts of the NACA-led committee. Analysis of the data

revealed major shortcomings in aircraft design and pilot training (e.g., deficiencies in aircraft

stability and control and spin recognition and recovery) for which corrective actions were developed
8

and implemented. It should be noted that solving these problems did not require computing

accidents per flight hour or other ratios that are considered important measures of transportation

safety today. The priority then, as now, was to put an end to accidents.

In October 1944, the U.S. Civil Aeronautics Administration (CAA), the predecessor to the Federal

Aviation Administration (FAA), published the first “Statistical Handbook of Civil Aviation” (ref. 6).

This first of many CAA handbooks pointed out that reported accident statistics were based on

definitions and classifications established by NACA TR-576 (although the Statistical Handbook

incorrectly referenced the NACA TR as “TR-567”). This document summarized aviation statistics

dating back to 1926, including air carrier and private flying accident statistics compiled by the U.S.

Civil Aeronautics Board (CAB), the predecessor to the NTSB. In the introduction, the CAA

acknowledged that, “There are some gaps in the early statistics because fact-gathering machinery

had not been fully organized and it also was extremely difficult to obtain reliable figures from an

industry still inchoate.” With respect to private flying, the CAA noted that, “Because of the

dislocation caused by the War, statistics on the amount of private flying during the war years are

incomplete.” Despite these reservations, the 1944 CAA handbook provided early examples of

detailed tables regarding such aircraft operating statistics as the number of hours flown, miles

covered, and passengers carried. Many of the safety measures using these statistics are still used

today.

2.2 Recent Developments

Today, the NTSB investigates civil aviation accidents and has amassed a database of coded, as well

as narrative, information. Over 32,000 aviation accidents that have occurred since 1982 are

summarized at the NTSB web site (www.ntsb.gov) and at the FAA Office of System Safety

(http://nasdac.faa.gov./asp/asy_ntsb.asp). The FAA Statistics and Forecast Branch publishes a yearly

“Census Of U.S. Civil Aircraft.” The census provides details about the number and types of aircraft

currently operating in the U.S. civil aviation fleet, along with other relevant data. Fleet-size data are

obtained by extrapolating data from a survey questionnaire mailed to a sample of registered owners.

The validity of this extrapolation has been questioned occasionally. Today, there are approximately

350,000 U.S. civil registered aircraft, which makes updating and correcting the census and

registration records a daunting task. Nevertheless, by combining data from the FAA and NTSB, such

statistics as accidents per 100,000 operating hours for each civil aircraft grouping are prepared and

given wide distribution.

2.3 Present Study

The objective of this report is to present and analyze rotorcraft accident trends with the expectation

that areas requiring improvement in rotorcraft design and operation will be identified, and that longand short-term actions will be developed and implemented to reduce the number of accidents. In

contrast to many studies (e.g., ref. 7) that provide snapshots of safety trends over short periods of

time, this study covers a 34-year span from mid-1963 to the end of 1997. This includes the period of

widespread use of matured single-piston-engine helicopters, as well as the introduction and

maturation of single- and twin-turbine powered helicopters. This report also includes a review of

accident trends within the growing amateur rotorcraft (i.e., autogyros and helicopters) fleet. We have
9

chosen not to include extensive statistics on accidents per flight hour, preferring a more in-depth

study of the accidents themselves.

The basic data gathered for this report were compiled from NTSB and FAA records. Although the

CAA/FAA census separated rotorcraft fleet size from fixed wing aviation as early as 1951,

CAB/NTSB accident reports for rotorcraft were only obtained from mid-1963 on.

Regarding the structure of this report, please note the following:

There are 109 figures accompanying this report. A list of these figures

begins on page 99 and figure 1 is placed on page 103. The page number for

any subsequent figure is simply the figure number plus 102.

Tables 1–45 appear at or near the points in the text at which they are cited.

There are 31 supplemental tables enclosed in Appendix D. A supplemental

table is identified by D- as a prefix.
10

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11

3. ACCIDENT CATEGORIZATION

The NTSB defines and categorizes the terms they use in investigating and reporting on accidents.

The key definitions are set down in Part 830 of the Federal Aviation Regulations (FAR). The NTSB

defines an aircraft accident as

An occurrence incident to flight in which “as a result of the operation of an aircraft,

any person (occupant or non-occupant) receives fatal or serious injury or any aircraft

receives substantial damage.”

Fatal, serious, and minor injuries are defined as follows:

“A fatal injury is one that results in death within 30 days of the

accident.”

“A serious injury is one that

1. Requires hospitalization for more than 48 hours,

commencing within 7 days from the date the injury was received,

2. Results in a fracture of any bone (except simple

fractures of the fingers, toes, or nose),

3. Involves lacerations that cause severe hemorrhages,

nerve, muscle, or tendon damage,

4. Involves injury to any internal organ; or

5. Involves second- or third-degree burns, or any burns

affecting more than 5% of body surface.”

“A minor injury is one that does not qualify as fatal or serious.”

Aircraft damage ranges from destroyed to minor; “destroyed means that an aircraft was demolished

beyond economical repair, that is, substantially damaged to the extent that it would be impractical to

rebuild it and return it to an airworthy condition.”

The NTSB notes that this definition of destroyed “may not coincide with the definition of total loss

for insurance purposes. Because of the variability of insurance limits carried and such additional

factors as time on engines and propellers and aircraft condition before the accident, an aircraft may

be totaled even though it is not considered destroyed for accident investigation purposes.”

With respect to substantial damage, the FAR Part 830 states:

1. Except as provided below, substantial damage means

damage or structural failure that adversely affects the structural strength,

performance, or flight characteristics of the aircraft, and that would

normally require major repair or replacement of the affected part.

2. Engine failure, damage limited to an engine, bent

fairings or cowling, dented skin, small puncture holes in the skin or fabric,

ground damage to rotor or propeller blades, damage to landing gear,
12

wheels, tires, flaps, engine accessories, brakes, or wing tips are not

considered “substantial damage.”

The NTSB carefully points out that “As with destroyed above, the definition of substantial for

accident investigation purposes does not necessarily correlate with substantial in terms of financial

loss. Contrary to popular misconception, there is no dollar value that defines substantial damage.

Because of the high cost of many repairs, large sums may be spent to repair damage resulting from

incidents that do not meet the FAR Part 830 definition of substantial damage.” Finally, the NTSB

states that “minor damage is damage that does not qualify as substantial, such as that under

substantial damage above.”

Today, the NTSB uses a number of other definitions, categories, and computer code numbers to

provide a detailed accident report. A sample of this information from the NTSB manual is provided

in appendix A.

In contrast to current NTSB investigation reports, the early NACA aircraft accident analysis form

(fig. 1) categorized accidents in one of four groups: personal, material, miscellaneous, and

undetermined. As time went on, the CAB or NTSB added detail so that today a “mini-brief” of each

complete accident report is available which summarizes the sequence of events leading to the

accident outcome. For purposes of this report, the accidents were categorized based on the first event

in the sequence of events that led to the accident (i.e., the first physical event that adversely affected

the rotorcraft or unusual occurrence the aircrew became aware of). The NTSB has established the

following 21 categories (here presented in order of number of accidents across the entire rotorcraft

fleet):

Loss of engine power

In-flight collision with object

Loss of control

Airframe/component/system failure/malfunction

Hard landing

In-flight collision with terrain/water

Rollover/nose over

Weather

Miscellaneous/other

Propeller/rotor contact to person

Stall/settling with power

Mid-air collision

On ground/water collision with object

Fire/explosion

Abrupt maneuver

Gear collapsed

Undershoot/overshoot

Dragged wing, rotor, pod, float, or tail/skid

Undetermined

On ground/water encounter with terrain/water

Missing aircraft.
13

It is clear from the names of these categories, and by review of accident narrative summaries, that

there is significant overlap among them. This gives the accident investigator leeway for personal

judgment at the cost of possible inconsistency in the assignment of accidents to specific categories.

We noted that different accidents with very similar narratives were assigned to different categories.

Examples include some engine failures being categorized as airframe failures, some in-flight

collisions with terrain being counted as dragged rotors, and other similar cases. It should be noted,

however, that the analysis in this report is based only on the accident narratives provided by the

NTSB and not on the full accident report when it exists.

The amount and character of information contained in the NTSB mini-briefs changed substantially

over the period covered by this report. Four distinct mini-brief forms were used from 1963 to 1971,

1972 to 1981, 1982, and 1983 to 1997. Despite the format differences, the basic data given in table 2

were generally available for each accident studied by the authors.

TABLE 2. DATA ELEMENTS IN NTSB MINI-BRIEFS, 1963–1997

Data element

FAA report reference number

Date and local time of accident

Location of accident

Aircraft make, model, and FAA registration number

Fatalities, serious injuries, minor/no injuries (CX-crew, PX-passengers, OT-others)

Mission type

Pilot-in-command qualification and experience

Aircraft damage

Accident category (i.e., NTSB first event)

Phase of operation during which first event occurred

Probable cause (legal)

Contributing factor(s)

Special weather factors (not included when accident was not weather-related)

Special agricultural operational data (not included when accident was not during agricultural

operations)

Remarks
14

The depth of data in the mini-briefs improved across the 34-year period. As an example of data

available during the period 1963 to 1971, figure 2 shows a mini-brief for an accident in agricultural

operations that involved weather. From 1972 through 1981, the mini-briefs contained essentially the

same information as for 1963 through 1971. The most significant change in 1972 was the addition of

information on the departure point, intended destination, and last en route stop. Figure 3 provides a

mini-brief example for this period.

A major change in the format and data content of the mini-brief took place in 1982. In addition to

more detailed information about the aircraft, engine, environment, and pilot qualification, this

format specifically included a brief narrative of the accident sequence, findings, and the declaration

of which findings constituted the probable cause. This summary format probably contained the most

information of any of the formats encountered during this study. Figure 4 provides a mini-brief

example for this period.

For accidents that occurred after 1982, mini-briefs in two formats are now available through online

resources. At the NTSB web site (www.ntsb.gov/aviation/aviation.htm), the mini-brief format was

changed to emphasize the narrative. This change eliminated information about pilot experience,

weather, and special agricultural data (see fig. 5). The second form of mini-briefs, which can be

obtained through the FAA Office of System Safety web site, has essentially the same information as

the NTSB mini-briefs of 1982 shown in figure 4.

As a final example of available data, figure 6 presents a typical entry as presented on the NTSB web

site. In this format, only identification information and a narrative are included; the user is referred

to the NTSB off-line imaging system for the more complete report. The purpose of these entries

appears to be the rapid dissemination of factual accident information. As accident investigation

progresses from the preliminary through the factual to the final, the entry is modified with additional

data. The example above is for a factual report that does not present formal findings or causes.

Because of the time necessary to investigate an accident and file the final report, we relied on the

information contained in these summaries for many accidents that took place from late 1996 through

1997.

Using these mini-briefs, it was found that the 21 categories paralleled the expanded groupings listed

on the 1936 NACA form (fig. 1) under “Immediate Causes of Accident” and were reasonably

consistent over the 34 years under study. Thus, today’s NTSB first event categories, not to be

confused with the ultimate accident cause, allowed a distribution of the 8,436 accidents within the

21 first event categories. In fact, the bulk of rotorcraft accidents fell into 7 of the 21 NTSB

categories, with 70% in just 4 categories.
15

4. OVERVIEW OF RESULTS

Annual U.S. civil rotorcraft accidents decreased from 260 in 1964 to 175 in 1997 (fig. 7). During

this period, the U.S. registered rotorcraft fleet expanded from 2,196 to 12,911 aircraft (fig. 8). In

broad terms, the industry succeeded in reducing accidents per rotorcraft by nearly a factor of 10 over

this period (i.e., from 118 accidents per 1,000 rotorcraft in 1964 to 13.6 per 1,000 in 1997). The

8,436 accidents that occurred during this 34-year period took a large toll (fig. 9), directly affecting

16,825 people: 2,135 killed, 1,760 seriously injured, and 12,930 with minor or no injuries.

Rotorcraft damage during this period was significant (table D-3). Of the 8,436 rotorcraft involved,

2,363 (i.e., nearly 20% of today’s registered fleet) were listed as destroyed by the NTSB. Another

5,909 rotorcraft were substantially damaged, and only 164 received little or no damage. Of course,

as is well known, helicopter crews and their aircraft have saved more than a million lives. However,

without major safety improvements, the potential exists for an increasing number of rotorcraft

accidents with more people being affected. This could be especially true, as new rotorcraft types

(e.g., civil tilt rotor) become operational.

The distribution of the 8,436 accidents by rotorcraft type for the 34-year period was as shown in

table 3 (which is excerpted from table D-1).

TABLE 3. ACCIDENT DISTRIBUTION BY ROTORCRAFT TYPE, 1963–1997

Commercially manufactured helicopters 7,920

Single piston 5,371

Single turbine 2,247

Twin turbine 302

Other rotorcraft types 516

Commercially built autogyros 50

Amateur built helicopters 137

Amateur built autogyros 261

Unknown/others 68

There was improvement in the safety records of each of these rotorcraft types during the period

under study. However, the improvements were not always uniform. As shown in figure 7, the period

from 1972 to 1987 showed an unfavorable “bubble” relative to the reference trend. There were

“above normal” accidents per year for both matured single-piston helicopters and relatively newer

single-turbine models during this 15-year period. Single-piston helicopters had overly large numbers

of accidents from 1971 to 1983 (fig. 10), whereas single-turbine helicopters showed a similar

increase from 1978 to 1987. Twin-turbine helicopter accidents were relatively rare and did not

markedly influence the broad trend or the 15-year “bubble.” The other rotorcraft types listed above

contributed relatively few accidents per year during the study period (table D-1). Since the singleengine helicopter, piston or turbine, dominates the U.S. civil helicopter fleet, it was not surprising

that it was involved in more accidents per year.
16

4.1 Major Trends

The 21 first event categories used by the NTSB, which should not be confused with the ultimate

accident cause, establishes a reasonably consistent way to group accidents over the period under

study. The distribution of the 8,436 accidents within the 21 first event categories is summarized in

figure 11. The bulk of rotorcraft accidents fell into 7 of the 21 NTSB categories, with 70%

associated with 4 categories (table 4).

TABLE 4. ACCIDENT COUNT AND DISTRIBUTION, 1963–1997

Loss of engine power 2,408 (28.5%)

In-flight collision with object 1,322 (15.7%)

Loss of control 1,114 (13.2%)

Airframe/component/system failure or malfunction 1,083 (12.8%)

Other first event categories 2,509 (29.7%)

Total 8,436

The trend over the 34-year period for these four accident categories is illustrated in figures 12 and 13

using data from table D-4. Figure 12 shows that the first events, loss of engine power and

airframe/components/system failure or malfunction, were major contributors to the 15-year “bubble”

shown in figure 7. In-flight collision with object accidents decreased over the period studied

(fig. 13). However, the number of accidents in the loss of control category virtually doubled in the

last 15 years of the study period relative to the first 15 years.

Single-engine rotorcraft dominated the accident history because they constituted most of the fleet

over the study period; for these aircraft, loss of engine power was the most prevalent first event. The

causes of loss of engine power are shown in figure 14. More than one-half of the loss of engine

power accidents were related to fuel/air mixture. In fact, fuel exhaustion, followed by an inadequate

or otherwise unsuccessful autorotative landing, was the major factor in single-engine rotorcraft

accidents, regardless of whether the rotorcraft was piston or turbine powered. Note that figure 14

shows that there was no confirmed reason for loss of engine power in one-fourth of the 2,408

accidents.

4.2 Accident Statistics

Before detailing accident trends for each rotorcraft type, the applicability of accident statistics needs

to be discussed. Frequently, these statistics are presented as accidents per 100,000 flying hours,

passenger miles, etc. These statistics are relatively accurate for air-carrier operations where there are

statutory requirements for the accurate recording and reporting of such data. The situation is

different for general aviation, which includes most rotorcraft operations. Appendix B and detailed

rotorcraft-type discussions presented below describe the method the FAA uses to obtain data on the

size and composition of the civil aircraft fleet. The FAA yearly aircraft registration data are an

estimate, based on voluntary returns by aircraft owners to an FAA mailing to a sample of recorded
17

owners. In turn, fleet flight hours are a further estimate based on voluntary reporting by the

respondents to the FAA mailing. As a result, we believe that the FAA reported registered fleet size,

despite its shortcomings, is a more reliable measure of annual aircraft use than reported flight hours.

Therefore, we have elected to normalize yearly accident counts by reported registered fleet size and

present accident rates per 1,000 registered aircraft (fig. 15). The accident trend data so normalized

do not highlight the accident “bubble” of figure 7.

Extrapolating the annual accident rate data, it appears that without a substantial effort to improve

rotorcraft safety, the overall trend projects to 6 accidents per 1,000 registered rotorcraft in the year

2010. If the rotorcraft fleet doubles over the next 15 years (i.e., to 25,000 aircraft), the industry will

experience 150 accidents a year—about 3 per week. In short, although the accident rate might

remain constant at 6 per 1,000 registered rotorcraft, the public would likely find the projected

frequency of accidents unacceptable. It is doubtful that the public in the year 2010 would consider

this to be much of an improvement over today’s situation.
18

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19

5. COMMERCIAL SINGLE-PISTON ENGINE HELICOPTERS

5.1 Fleet History and Growth

The modern era of U.S. civil rotorcraft operations officially began on 8 March 1946 with the CAA

certification of the Bell Model 47. In that year, Bell began a first lot production run of 10 rotorcraft.

The two-place Model 47 was followed by the four-place Sikorsky S-51, certificated 17 April 1947.

The S-51 was developed from Sikorsky’s R-5 military helicopter and benefited from experience

gained with the smaller R-4 and R-6 military models. On 14 October 1948, the CAA certificated the

Hiller Model 360, the beginning of the UH-12 series. By the end of 1957, the CAA census reported

540 registered helicopters in the civil fleet (table 5).

TABLE 5. CAA HELICOPTER CENSUS AT END OF 1957a

Manufacturer Model Activeb Inactive Total

Bell Aircraft Corp. 47 246 49 295

Hiller Helicopters UH-12 29 20 49

R-4, R-6, S-51, S-52 14 25 39

S-55 27 12 39

Sikorsky

S-58 21 0 21

All others Various 33 64 97

Total 370 170 540

aThe CAA “Statistical Study of U.S. Civil Aircraft” as of January 1, 1958 (i.e., the end of 1957) was the

earliest the authors found that contained a breakdown by rotorcraft model.

bThe CAA segregated aircraft by “active” and “inactive” based on the following definitions, which are from

the Preface to the January 1964 census: “Active” aircraft, as defined by the FAA, are those which hold a

valid certificate of airworthiness and which have had an approved inspection during the last 12 months and

are eligible to fly. Aircraft classified as “inactive” need not necessarily be in unairworthy condition and may

hold a valid airworthiness certificate, but they have not met the periodic inspection requirement. In later

years, “active” became “eligible” and “inactive” was replaced with “ineligible.” In 1970, the FAA returned

to using “active” and “inactive” descriptions; however, the definitions changed (see text). Regardless of the

words or definitions used, no consistent count of the number of aircraft actually flying appears available.

The size of the single-piston helicopter fleet grew substantially after the type was first introduced

(fig. 16). This growth continued until the early 1980s when the market for new rotorcraft virtually

collapsed.

To obtain the fleet size, FAA census data (ref. 12) were edited by the principal author to correct such

obvious errors as incorrect coding of engine types. Many models were (and still are today) listed as

turbine-powered but are well known in the industry to be piston-powered (refs. 13 and 14). These
20

coding errors, which originated at the FAA’s Mike Monroney Aeronautical Center in Oklahoma

City, illustrate the daunting task of maintaining an accurate, up-to-date database of 350,000 aircraft.

Figure 16 shows a drop of about 350 in the number of single-piston helicopters from 1969 to 1970.

This drop “resulted from changes introduced by a new and improved aircraft data system which will

produce more reliable data pertaining to the nation’s civil aircraft fleet,” according to the Census of

U.S. Civil Aircraft for calendar years 1971/1970 (ref. 12). Approximately 24,000 aircraft in the civil

aircraft fleet of 190,000 were “deregistered” as reported in this 1971/1970 census. Additionally, this

census stated the following:

“Beginning in 1970, the aircraft universe was divided into two major categories:

1. Active—All legally registered civil aircraft for which flight hours were reported or

imputed. (Refer to “Method of Imputation.”)

2. Inactive—All legally registered civil aircraft that do not meet the above-mentioned

criteria.”

This 1971/1970 census report established the FAA’s statistical method for estimating the number of

active and inactive aircraft and the hours flown by the active aircraft. The method was required

because “so many owners failed to furnish aircraft activity on their revalidation forms.” This

statistical process (i.e., the “Method of Imputation” established in 1970) is still used today.

Unfortunately for data collectors and analyzers, the FAA survey questionnaires are mailed to only

about one-tenth of all aircraft owners of record and only about one-half of those respond.

Figure 16 shows that the single-piston helicopter fleet had four distinct growth periods since 1955.

Between 1955 and 1970, the fleet grew, on average, by 127 rotorcraft per year. From 1970 to 1980,

the growth rate increased to 193 per year, a 52% increase. During the 1980’s, the boom collapsed

and the fleet size declined from 1980 to 1989. The fourth period, 1989 through 1997, showed only

modest growth.

Figure 16 also shows single-piston fleet size data published in Air Track’s Rotor Roster (ref. 15), a

recognized source for information about the world’s helicopter fleet. Their records differ from FAA

records because Air Track follows transactions and other detailed data, and “uses multiple sources to

arrive at a conclusion of who and where.” The 1997 listings from the FAA and Air Track were

compared and it was found that about 90% of the data they contained were in agreement. However,

neither the FAA nor Air Track knew how many rotorcraft were actually flying (i.e., active) in any

given year.

5.2 Accident Analysis

The number of reported accidents investigated by the NTSB is not in doubt, however. Despite the

growing number of aircraft in the fleet (fig. 16), the number of single-piston rotorcraft accidents per

year dropped over the 34 years, as figure 10 shows. The accident rate, in accidents per 1,000

registered rotorcraft, generally decreased from 1964 to 1985 (fig. 17). However, a period of no
21

improvement in the rate occurred between 1985 and 1990. This was followed by a return to a

favorable trend from 1990 through 1997.

These accident trends (figs. 10 and 17) for commercially manufactured, single-piston helicopters

raise two questions. First, what caused the increased number of accidents between 1971 and 1983?

Second, what caused the 5-year period of no improvement in accident rates between 1985 and 1990?

To answer these two questions requires more details about how the number of accidents in each first

event category varied with time.

To reiterate, approximately 90% of the 5,371 single-piston helicopter accidents fell into 7 of the 21

NTSB first event categories, as shown in table 6 (see also fig. 18).

TABLE 6. SINGLE-PISTON ACCIDENT COUNT AND DISTRIBUTION,

1963–1997

29% Loss of engine power (1,554 accidents)

18% In-flight collision with object (953)

11% Loss of control (625)

12% Airframe/component/system failure or malfunction (639)

9% Hard landing (483)

8% In flight collision with terrain/water (443)

5% Rollover/nose over (290)

7% Other (384)

100% Total (5,371)

The trends in the number of accidents per year for the top four first event categories are shown in

figures 19 and 20. The “bubble” in total accidents between 1971 and 1983 began with an increase in

loss of engine power and airframe failure accidents (fig. 19). During this period, in-flight collisions

with objects and loss of control accidents remained essentially constant (fig. 20). As a result, the

total number of accidents each year was higher than the long-term trend line. The “bubble” ended

when the trends in loss of engine power, airframe failure, and in-flight collision with object

accidents turned downward. The drop in accidents at the end of the “bubble” would have been

greater had there not been an increase in loss of control accidents starting in 1982 (fig. 20).

Another interpretation of both the “bubble” and the no-improvement periods can be made. Consider

first the “bubble” period. Looking back at the single-piston helicopter fleet growth, shown in

figure 16, the “bubble” between 1971 and 1983 nearly coincides with a boom period in helicopter

fleet size. We suggest that the 52% increase in new helicopters sold to a new and expanding group of

users was the principal cause of the increase in accidents during this period. This interpretation gains

some validity by reexamining the accident rate per 1,000 registered aircraft trend (fig. 21). The

overall trend is reexamined in three periods using exponential regression curve fitting. Using the first

6 years of accident rate data, the regression analysis predicts, when extrapolated 16 years, the most

likely accident rate during the “bubble” period. This extrapolation is shown in figure 21 as the light,
22

solid line. The regression analysis applied to just the “ bubble” period is shown as a dashed line in

figure 21. Comparing these first two trends suggests that had the industry continued its pre-1970

trend, the 1985 accident rate of 30 per 1,000 aircraft could have been nearly halved. The conclusion

to be drawn offers the following cautionary note for the future: When the next rapid expansion of the

fleet occurs, the industry must increase its efforts to improve safety to an extent that is more than

proportional to the fleet growth rate.

Now consider the plateau or “ no improvement period” from 1985 to 1990 shown in figures 10, 17,

and 21. During this period the fleet size remained virtually constant (fig. 16). This apparent plateau

was caused by increased numbers of loss of control accidents coupled with no further reduction in

in-flight collision with object accidents.

From 1990 through 1997, the most commonly occurring first events were again showing a collective

decline in accident rate per 1,000 registered aircraft, as the heavy solid line in figure 21 suggests.

However, over this period, the relative frequencies of first events changed. The distribution of the

top seven accident categories from the past 8 years, in contrast to the past 34-year history, is shown

in table 7.

The positive aspect when comparing the 1990– 1997 distribution to the data over the entire 34 years

is that in-flight collision with object accidents dropped substantially (i.e., from 18% to 12%). The

alarming aspect is that the loss of control category doubled (i.e., 11% to 22%). Furthermore, little

improvement was made in the airframe/component/ system failure or malfunction category and loss

of engine power remained the number one first event.

TABLE 7. SINGLE-PISTON ACCIDENT DISTRIBUTION, LAST 8 YEARS VS. 1963– 1997

Last 8 years Last 34 years

First event category Percent Number Percent Number

Loss of engine power 27 (207) 29 (1,554)

In-flight collision with object 12 (91) 18 (953)

Loss of control 22 (166) 11 (625)

Airframe/component/system failure or

malfunction 10 (80) 12 (639)

Hard Landing 7 (56) 9 (483)

In flight collision with terrain/water 8 (63) 8 (443)

Rollover/nose over 4 (340) 5 (290)

Other 9 (69) 7 (384)

Total 100 (766) 100 (5,371)
23

Most discouraging is the fact that fuel exhaustion (i.e., simply running out of gas) was still the

number one factor in losing engine power. The FARs are quite clear about fuel reserves. For

example, FAR Parts 91.151 and 91.167 state the following:

Sec. 91.151 Fuel requirements for flight in VFR conditions.

(a) No person may begin a flight in an airplane under VFR conditions unless

(considering wind and forecast weather conditions) there is enough fuel to fly to the

first point of intended landing and, assuming normal cruising speed

(1) During the day, to fly after that for at least 30 minutes; or

(2) At night, to fly after that for at least 45 minutes.

(b) No person may begin a flight in a rotorcraft under VFR conditions unless

(considering wind and forecast weather conditions) there is enough fuel to fly to the

first point of intended landing and, assuming normal cruising speed, to fly after that

for at least 20 minutes.

Sec. 91.167 Fuel requirements for flight in IFR conditions.

(a) Except as provided in paragraph (b) of this section, no person may

operate a civil aircraft in IFR conditions unless it carries enough fuel (considering

weather reports and forecasts and weather conditions) to—

(1) Complete the flight to the first airport of intended landing;

(2) Fly from that airport to the alternate airport; and

(3) Fly after that for 45 minutes at normal cruising speed or, for

helicopters, fly after that for 30 minutes at normal cruising speed.

(b) Paragraph (a)(2) of this section does not apply if—

(1) Part 97 of this chapter prescribes a standard instrument approach

procedure for the first airport of intended landing; and

(2) For at least 1 hour before and 1 hour after the estimated time of

arrival at the airport, the weather reports or forecasts or any

combination of them indicate—

(i) The ceiling will be at least 2,000 feet above the airport

elevation; and

(ii) Visibility will be at least 3 statute miles.
24

On this issue of loss of engine power due to fuel exhaustion, Mayo’s November 1921 statement that

“ probably 90% of them [i.e., accidents] were due to carelessness and could have been avoided, had

the necessary precautions been taken” is quite applicable today (ref. 2).

Based on the data from 1990 through 1997 and on analysis that shows that the rotorcraft accident

number and rate histories are examples of statistically stable systems, it is projected that by the year

2010, the annual accident rate for commercially manufactured, single-piston helicopters may still be

above 5 accidents per 1,000 registered aircraft. This projection (fig. 22) assumes “ a business-asusual” approach by the rotorcraft industry and no major changes in the system (e.g., major new

aircraft categories such as tilt rotor or missions). It appears that without the “ bubble” and the “ noimprovement” periods, the industry would already be at this rate.

5.3 Detailed Analysis by Accident Category

Of the 8,436 rotorcraft accidents, single-piston helicopters that were commercially manufactured

had 5,371 accidents. Of these, 3,771 (about 70%) were associated with just four first event

categories. Therefore, an in-depth analysis of these four top categories provides considerable insight

into nearly one-half of all rotorcraft accidents during the 34-year period under study. The next

several paragraphs and associated figures and tables provide detailed analyses gleaned from the

mini-briefs of the four categories (loss of engine power, in-flight collision with objects, loss of

control, and airframe failures).

5.3.1 Loss of Engine Power (1,554 Accidents)

The pilot of any type of single-engine, heavier-than-air aircraft experiences a true emergency

following loss of engine power. However, helicopters provide some safety margin over their fixedwing counterparts because of their inherent ability to glide with a turning rotor (i.e., their

autorotation capability) and their generally slower power-off landing speed. These relative safety

advantages are often negated, however, because helicopter pilots routinely operate their rotorcraft

much closer to the ground where time to react is minimal.

5.3.1.1 Overall Accident Trends. From 1963 through 1997, loss of engine power was implicated

by the NTSB in 1,554 accidents involving commercially manufactured, single-piston helicopters.

Accidents that occurred during this 34-year period took a large toll (table D-24). The 1,554

accidents directly affected 2,621 people: 106 were killed and 234 were seriously injured; 2,281

survived with minor or no injuries. Of the 1,554 helicopters involved, 265 were listed as destroyed

by the NTSB. Another 1,286 helicopters were substantially damaged, and only 3 received little or no

damage. Figure 19 shows that the overall trend in accidents per year for this first event category

decreased over the last 17 years. As a rate of accidents per 1,000 registered single-piston helicopters,

accidents initiated by the loss of engine power showed steady improvement, as seen in figure 23.

However, loss of engine power constantly accounted for approximately 30% of the accidents over

the 34-year period (fig. 23).

5.3.1.2 Loss of Engine Power by Category. The NTSB cited the reason for loss of engine power

in 1,157 of the 1,554 accidents they investigated. Table D-12 shows that 18 primary reasons lay

behind the 1,157 accidents. When the 18 reasons are grouped by major subsystems, fuel/air mixture
25

problems caused 686 of the 1,157 accidents (fig. 24). A closer inspection of figure 24 and the

associated mini-briefs reveals that fuel exhaustion, fuel starvation, fuel contamination, etc., were

repetitive examples of the “ poor piloting” discussed by Mayo (ref. 2). In fact, simply running out of

gas was the number one reason for loss of engine power throughout the 34-year period under study.

Both figure 24 and table D-12 indicate that over 100 accidents were incorrectly charged to loss of

engine power. For example, when the final determination was made, 53 accidents attributed to loss

of engine power were actually rotor drive system component failures, more correctly charged to the

airframe/component/system failure or malfunction first event category. Other subcategories, which

accounted for 54 accidents, were more generally found in the loss of control first event category. On

the other hand, several accidents attributed to airframe failure, for example, were actually engine

failures.

5.3.1.3 Loss of Engine Power by Activity. The commercially manufactured helicopter, powered

by a single-piston engine, has been the breadwinner in the rotorcraft industry, as recounted in

reference 16. The most intensive activity as a “ breadwinner” has been aerial application

(i.e., agricultural operations). This activity has always been high-risk and led to the most accidents

in the loss of engine power first event category, as figure 25 shows.

Aerial application operations are conducted at extremely low heights above the ground (on the order

of 100 feet or less). This frequently requires flight in the "avoid" regions of the helicopters'

height/velocity diagram and offers little time and height for the pilot to perform a successful

autorotation. Other activities in which single-piston helicopters engage are generally conducted

between 500 and 1,500 feet above ground level (AGL). Loss of engine power in this height range

should allow the practiced pilot time to enter autorotation and perform a safe power-off landing.

Unfortunately, as will be discussed shortly, the average pilot proficiency in accomplishing this task

appears insufficient in view of the number of destroyed and substantially damaged helicopters.

5.3.1.4 Loss of Engine Power by Phase of Operation. Loss of engine power was experienced in

every phase of operation in which the single-piston helicopter operated, as figure 26 shows. Not

unexpectedly, the overwhelming loss of engine power situations occurred in cruise flight, which

reflects the general aviation character of helicopter use. The high power required in takeoff and

climb evidently accounted for this subcategory being the second most common phase of flight in

which accidents occurred. The helicopter inherently allows low-speed, low-altitude maneuvering,

which generally requires operation at high power. Therefore, it is reasonable that the 328 accidents

in this flight phase could be combined with the 280 accidents in takeoff and the 53 accidents in

hover. This suggests a total of 661 accidents during high-power operations vs. 607 accidents during

cruise. Since the helicopter has been designed and marketed for hovering and for slow, low-altitude

flight, the ratio of 661 to 607 or 108% does not appear unreasonably high for this type of aircraft.

5.3.1.5 Power-Off Landing. Apparently, the power-off landing that follows a loss of engine power

is considered “successful” by the industry today if (1) there is no serious injury and (2) the main

rotor blades are destroyed while severing the tailboom or when the helicopter rolls over. In other

words, “ If you can walk away from it, it’s successful.” This conclusion was arrived at after several

informal conversations with members of the insurance industry, instructional and high-time pilots

(both civil and military), and operations personnel from one firm primarily engaged in helicopter

pilot training. Today’s initial or recurring training of helicopter pilots rarely includes completion of
26

the simulated power-off landing to touchdown. Rather, the average pilot is well schooled in the

transition from powered to unpowered autorotational flight, proper gliding techniques, and the flare

maneuver required just prior to touchdown. At this point, the pilot under instruction (perhaps with

instructor assistance) generally increases power to end up in a hover. The industry premise appears

to be that if the average pilot can successfully accomplish the maneuver to the flare point, the odds

are that the final outcome in a real emergency will be “successful,” albeit with the possible level of

damage listed above.

This standard for power-off landing training was initially adopted by U.S. Army Aviation during the

Vietnam War. That war’s requirement for many new helicopter pilots led to a high accident rate

when training military students to complete the power-off autorotational landing to touchdown. The

cost of these training accidents was deemed greater than the benefit during emergency experiences

in the field and the training syllabus was changed accordingly. Today, the FAA Practical Test

Standards* (pp. 2– 13, par. 4 C, Task— Power Plant Failure, Single engine helicopter) also reflect this

proficiency standard associated with a pilot’s certification.

The NTSB’s mini-briefs provide any number of narratives describing the recurring events following

loss of engine power. For example, the narrative for a loss of engine power accident that occurred

3 February 1982 (NTSB File No. 0059) states:

“ THE ENGINE LOST POWER DURING A NIGHT FLIGHT WHILE ENROUTE

TO OBTAIN FUEL. THE LOW RPM AUDIO AND WARNING LIGHT WERE

NOTED WHEN THE LOSS OF POWER OCCURRED. THE PILOT ENTERED

AN AUTOROTATIVE DESCENT AND TURNED TO LAND ON AN

INTERSTATE HIGHWAY. AS HE STARTED TO DECELERATE FOR LANDING,

POWER LINES BECAME VISIBLE IN HIS FLIGHT PATH. HE DUMPED THE

NOSE AND DOVE UNDER THE POWER LINES, THEN FLARED AND

TOUCHED DOWN AT ABOUT 25 TO 30 MPH. DURING THE LAST PART OF A

GROUND SLIDE, THE MAIN ROTOR STRUCK A POLE FOR AN OVERHEAD

SIGN AND A SPEED LIMIT SIGN. NO PRE-ACCIDENT ENGINE FAILURES

WERE FOUND.” [Note: The pilot was not injured and the damage to the helicopter

was substantial.]

The recurring theme from the 1,554 loss of engine power narratives was that if the engine quit, the

pilot was most probably over the most unsatisfactory terrain for an emergency landing. The minibrief narratives continually suggested that even near-perfect pilot technique would most likely only

minimize damage. The subsequent autorotative landing by the average pilot was almost invariably a

hard one. The rate of decent and/or forward speed were rarely zeroed out prior to touchdown. The

helicopter frequently was flared too high above the ground, causing the tail skid to hit the ground

first. This caused the helicopter to rock forward as the main skids touched down and the main rotor

tip path plane to tilt aft, severing the tailboom. In many other cases, if the emergency landing area

was soft, the helicopter slid, dug a skid into soft ground, and rolled over. In other cases, the pilot

caused the main rotor to tilt aft and sever the tailboom in attempting to brake the slide with full aft

cyclic stick. The preceding sequences reflect our analyses of the 1,554 mini-brief narratives that

were read in the course of this work.

 *This document can be found at www.mmac.jccbi.gov/afs/afs600/akt.html#pts.
27

Taken in total, it appears that helicopters in the current civil fleet have insufficient stored energy for

the average pilot to successfully complete the final autorotational flare and touchdown, in most

cases. To be sure, skilled pilots frequently demonstrate the helicopter’s inherent autorotation

capability following loss of engine power by softly landing on a paved surface with near zero

forward motion. However, this is not a good measure of what the average pilot, under emergency

conditions, can do in day-to-day operations in the field.

Appendix C provides additional discussion concerning accidents involving autorotations.

5.3.1.6 Conclusions About Loss of Engine Power Accidents. Of the 8,436 rotorcraft accidents

recorded by the NTSB during the 34-year period from mid-1963 through the end of 1997, 5,371

accidents involved commercially manufactured, single-piston helicopters. Of these, 1,554, or

roughly 30%, were attributed to loss of engine power. No fewer than 686 accidents were directly

traced to fuel/air mixture problems. Virtually every one of the 686 accidents was caused by human

error. Fuel exhaustion, fuel starvation, and fuel contamination accounted for over 400 of the 686

accidents. Apparently, many pilots disregarded the engine’s need for clean fuel and air in proper

proportions— to say nothing about the FAA regulations for fuel reserves.

Structural failure of the single-piston engine caused 263 accidents, and the reason for the loss of

engine power was not established in 397 accidents.

Virtually every one of the 1,554 loss of engine power accidents resulted in a substantially damaged

or destroyed helicopter. Therefore, the fact that power-off landing proficiency is not required by the

FAA to obtain a helicopter pilot’s certification appears inconsistent with the number of accidents. It

also appears that helicopters currently in the civil fleet provide marginal to inadequate autorotational

capability for the average pilot to successfully complete the final flare and touchdown to a generally

unsuitable landing site. Clearly, training in full autorotation landings— even to a prepared landing

site— is avoided because of both real and perceived risks.

5.3.2 In Flight Collision with Object (953 Accidents)

One of the most widely known advantages that helicopters have over fixed-wing aircraft is their

capability to hover, fly slow and low, and operate in confined areas. Thus, they are routinely used in

just this manner and therefore encounter a more hostile environment that is full of objects such as

wires and towers that are hard to see. Hence, it is not unexpected that accidents involving in-flight

collision with objects constitute a large portion of rotorcraft accidents. Depending on the severity of

the collision, a pilot may or may not be able to recover. If the helicopter’s main rotor control is lost

from a blade strike, or if the altitude is insufficient for autorotation, recovery, and safe landing may

not be possible. If directional control is lost following a tail rotor strike, any recovery at all becomes

extremely difficult.

5.3.2.1 Overall Accident Trends. The NTSB cited in-flight collision with object as the first event

in 953 single-piston helicopter accidents from mid-1963 through 1997. These collision with object

accidents affected 1,416 people: 166 were killed and 205 suffered serious injuries;

1,045 survived with minor injuries or no injuries at all. Of the 953 helicopters involved, 327 were

listed as destroyed by the NTSB. Another 620 helicopters were substantially damaged; only 6

received little or no damage. Figure 20 shows that the overall trend in accidents per year for this first
28

event category decreased substantially during the first 17 years of the 34-year study period.

However, as figure 27 shows, in-flight collision with object accidents leveled off at about 12% of the

annual single-piston helicopter accidents. In terms of annual accidents per 1,000 registered singleengine helicopters, the trend in the later years shows no substantial reduction (fig. 27).

5.3.2.2 Collision with Object by Object Hit. Figure 28 lists the type of objects that were hit in the

first event category, referred to as in-flight collision with object. Unquestionably, wires and the

combination of wire/pole were the most prevalent objects hit. Together, these two objects account

for 507 (53%) of the 953 accidents. With respect to collisions with trees, the mini-briefs frequently

were unclear whether the pilot descended into a forest of trees (and would have hit whatever was

between the aircraft and the ground) or clipped a branch of one tree from the side. The latter might

have been a result of misjudging distance or not correcting for drift. Most of the other objects were

man-made. Of the 32 accidents associated with the airport/helipad facility objects, most of these

facilities were oil rigs. Conventional heliport design, therefore, did not appear to be an issue.

5.3.2.3 Collision with Object by Cause. The accidents were further subdivided by the condition

that resulted in an object strike. We chose the 12 categories shown in figure 29. It is evident that an

improper decision, which includes poor planning, inadequate training and misjudging clearances,

was the most common cause, followed by the two least descriptive categories; Failure to see and

avoid and undetermined. Failure to see and avoid was used as a “ catchall” category for accidents in

which more specific detail was not available in the mini-brief. For the agricultural application or

crop dusting activity, failure to see and avoid was the most frequently reported cause. Since most

accidents in agricultural operations do not result in fatalities, reports were often sketchy. Quite often,

however, “ crop dusters” appeared to know where the obstacles were relative to a field, but for some

reason (e.g., fatigue, sun glare, misjudging distance, etc.) still collided with them.

Degraded visibility encompassed fog, instrument meteorological conditions, snow, rotorwash

brownout and whiteout darkness, and sun glare; most of these accidents involved sun glare, however.

Not surprisingly, the most frequent condition found for external load and proximity to obstacle work

was precisely the nature of the task: proximity to obstacles. This was followed by improper decision

and performance or RPM issues. For emergency operations, the most frequent cause of collision

with objects was inadequate RPM, followed by wind drift and diverted attention.

5.3.2.4 Collision with Object by Phase of Operation. The phase of operation during which

collision with object accidents occurred is shown in figure 30. As might be expected, collisions

occurred most frequently during maneuvering, a typical phase of flight for aerial application

operations. Aerial application involves extensive maneuvering to ensure complete coverage of the

field being treated. Takeoff, cruise, and landing (taken to together) accounted for 335 of the

953 collision with object accidents. Cruise in a helicopter generally occurs at low altitude and at

relatively high speed, which makes it more difficult to avoid wires that are difficult to see in the first

place.

5.3.2.5 Collision with Object by Activity. The mini-briefs were analyzed to determine the activity

in which a pilot was engaged when a collision with object accident occurred. The activities were

extracted from the narratives based on FAR paragraph numbers and the verbal description of the
29

activity. The accidents were placed into 10 activity groups, 7 of which accounted for over 95% of

the total. The distribution by activity is shown in figure 31.

This activity analysis overlapped the phase of operation analysis in revealing that accidents occurred

most frequently during aerial application and general utility operations, which includes, for

example, aerial surveying, herding, and hunting. The activities involving passenger service,

personal, and business use accounted for 237 of the 953 collision with object accidents. The

frequency of accidents that occurred during instruction clearly showed that student pilots, by

necessity, focused their attention more on learning to operate the aircraft than on avoiding obstacles.

Student pilots were also relatively inexperienced in judging distances, maintaining RPM and

avoiding drift. The pilots flying personal flights may have also been inexperienced in these areas and

may have suffered from lack of regular practice.

5.3.2.6 Collision with Object by Part Hit. The part of the helicopter involved in a collision was

rarely mentioned in NTSB summary reports. The statistics available on this subject are shown in

figure 32. For the 228 (23.9%) of the 953 single-piston helicopter collision with object accidents in

which such data were reported, the most frequent rotorcraft components involved in collisions were

the tail and main rotor blades. The main rotor collisions differed from tail rotor collisions: the

rotorcraft were, more often, in forward flight when a main rotor strike occurred. In contrast, tail

rotor strikes occurred, most often, when the pilot “ dragged the tail” or was backing up. These

components together accounted for 170 (75%) of the 228 accidents in which the part hit was

reported, but it is not clear whether this statistic can be extrapolated to the total of 953 accidents.

5.3.2.7 Conclusions About In-Flight Collision with Object Accidents. Of the 8,436 rotorcraft

accidents recorded by the NTSB during the 34-year period from mid-1963 through the end of 1997,

5,371 involved commercially manufactured, single-piston helicopters. Of these, 953, or roughly

18%, were attributed to in-flight collisions with objects. Nearly one-half (471) of the 953 accidents

occurred during aerial application (i.e., crop spraying) activities. Wire, wire/pole and trees

accounted for 655 of the accidents. Wire strikes, agricultural operations, and main and tail rotor

strikes were the dominant characteristics of collision with object accidents. The unique

characteristics of rotorcraft and the missions flown (e.g., proximity to obstacles, frequent lowaltitude flight) were reflected in the types of objects with which helicopters collided.

To adequately address and reduce the number of collision with object accidents, systematic changes

must be implemented in the human (e.g., improved training and ongoing pilot development), the

aircraft (e.g., less sensitivity to environmental conditions, more robust controllability), and

associated equipment (e.g., proximity sensors, enhanced visibility devices).

5.3.3 Loss of Control (625 Accidents)

Helicopters (particularly the small, single main rotor with antitorque tail rotor configuration) are

generally perceived to be difficult to fly. Unlike pilots of their fixed-wing counterparts, the

helicopter pilot must constantly maintain control of four primary axes that are frequently tightly

coupled. The control of vertical position requires a collective pitch control stick. Roll and pitch are

controlled with a cyclic stick, which is comparable to the fixed-wing stick or yoke. Left and right

pedals control antitorque and directional heading. Finally, constant control of engine RPM with a

motorcycle-like twist-grip throttle attached to the end of the collective stick is required. A pilot
30

must, therefore, use both feet and both hands, as well as a left-wrist twist motion to fly most pistonpowered helicopters successfully.

In and near hover, the helicopter is inherently unstable in both roll and pitch. Constant movement of

the cyclic stick in all directions is required to maintain an upright attitude above a desired point.

Early helicopters, such as those manufactured by Hiller and Bell, incorporated mechanical devices

to reduce roll and pitch instability. Those devices became known as the “ Hiller servo paddle” and

the “ Bell bar.” The primary control coupling that increases pilot workload involves balancing

antitorque so the aircraft generally maintains the desired heading. The antitorque balance is altered

whenever collective pitch or engine RPM is altered.

At typical cruise speeds, the helicopter’s positive stability is quite similar to that of a fixed-wing

aircraft. Little attention to the collective stick and the twist-grip throttle is required. The pilot is

required to coordinate only cyclic stick and pedals to maintain trim and comfortable control of the

aircraft.

To date, no commercially manufactured helicopter, powered by a single-piston engine, is available

with stability augmentation or an autopilot, either of which could reduce pilot workload and enhance

safety.

5.3.3.1 Overall Accident Trends. From 1963 through 1997, the NTSB cited loss of control in

625 accidents involving commercially manufactured, single-piston helicopters. Accidents that

occurred during this 34-year period took a large toll (table D-24). The 625 accidents directly

affected 1,048 people: 92 were killed, 105 were seriously injured, and 851 survived with minor or

no injuries. Of the 625 helicopters involved, 194 were listed as destroyed by the NTSB. Another

428 helicopters were substantially damaged; only 3 received little or no damage. Figure 20 shows

that loss of control accidents per year decreased over the first 17 years of the study period. However,

this type of accident showed a rapid increase in 1982, remained at a relatively high level until 1991,

and then dropped. Figure 33 shows that loss of control accounted for a growing percentage of

single-piston helicopter accidents from 1980 through 1997. When expressed as the number of

accidents per 1,000 registered single-piston helicopters, accidents initiated by loss of control showed

little improvement during the last 17 years (fig. 33).

5.3.3.2 Loss of Control by Phase of Operation. Considering the phase of operation in which loss

of control occurred, the accidents fell into the 11 categories shown in figure 34. As might be

expected, loss of control occurred most frequently during the hover and takeoff phases of a flight.

The control input precision required for hovering, combined with a lack of time and altitude to react

to abnormal conditions and aircraft sensitivity to environmental inputs (e.g., winds, density altitude)

combined to put the greatest demands on a pilot. Most rotorcraft powered by a piston engine require

considerable throttle manipulation, which adds additional workload, particularly during

maneuvering.

5.3.3.3 Loss of Control by Activity. The accident records were analyzed to determine the

frequency distribution of loss of control accidents by flight activity. The activity was extracted from

the narrative based on FAR paragraph numbers and verbal description in the NTSB mini-brief.

Eleven activities dominated, as shown in figure 35. Single-piston helicopters had the most loss of

control accidents during instructional, agricultural, and personal-use operations. It appears that the
31

lower cost of purchasing and operating single-piston helicopters made them more attractive for the

individual and agricultural operator. Furthermore, most basic civilian rotorcraft pilot training takes

place in single-piston helicopters.

Instructional flights were the most prevalent activity in which loss of control occurred. Considering

instructional flights that resulted in accidents, approximately 43% occurred during dual flights and

about 28% during solo flights. The remainder occurred during general instruction (17%), practice

(11%), or check rides. These statistics illustrate the difficulty of piloting rotorcraft and the extreme

demands placed on both student and instructor during training activity. This, in turn, emphasizes the

importance of proper training, evaluation, and professional development of the rotorcraft instructor

corps. Not only does the quality of instruction and instructor directly affect the quality of the newly

trained helicopter pilot, but also the demands of instruction itself require the highest professional

standards.

The second largest number of loss of control accidents occurred during agricultural flying. These

operations require constant low-altitude maneuvering in close proximity to obstacles, frequent lowspeed and downwind flight, service from unprepared areas (e.g., fields, landing trailers), flight at

night (especially in hot climate areas), and extensive travel from job site to job site. These factors,

among many others, resulted in a higher risk of control problems occurring in flight with little or no

time for the pilot to recover.

Personal-use flights were the third most frequent type of activity when vehicle loss of control

occurred. However, the specific flying tasks ranged from point-to-point transportation to high-risk

maneuver practice. The range of aircraft and maintenance characteristics varied from ownermaintained to rentals from a commercial aircraft enterprise.

5.3.3.4 Loss of Control by Cause. The accident mini-briefs were further analyzed in an effort to

understand the conditions that were associated with the control loss. We consolidated reasons that

appeared to precipitate the control loss into 12 categories, as shown in figure 36.

Improper operation of the flight controls was the single factor most frequently implicated in loss of

control accidents. Although it is tempting to assert that “ pilot error” must, therefore, be the biggest

single problem, this conclusion is not fully supported. Since aircraft control is the result of both

pilot capability and aircraft design, any effort to address the “ improper operation of controls”

problem must address both factors. Human-centered actions (e.g., improved training, stricter

currency/proficiency requirements) will be relatively ineffective if airframes are designed and

certificated with known adverse flying characteristics (e.g., an unusual tendency toward loss of tail

rotor effectiveness or extreme control sensitivity in one or more axes). Conversely, even inherently

safe designs may fail if pilots are inadequately trained or lack safety consciousness.

5.3.3.5 Loss of Control by Axis. In an attempt to determine which control axis might be the most

difficult for the pilot, it was noted that only 338 of the 625 single-piston helicopter accidents were

described in sufficient detail to permit such a distinction. The distribution that did emerge is shown

by figure 37. In many cases, loss of control appeared to begin with a loss of rotor RPM, which

occurred for a variety of reasons. Therefore, figure 37 provides the noted problems in each axis

(pitch, roll, yaw, and vertical) where low rotor RPM was not involved. Many mini-briefs stated the

axis and also noted that low rotor RPM was a factor. Thus, to interpret figure 37’s total loss of yaw
32

control count, one adds the 21 accidents with low rotor RPM to the 95 accidents without low rotor

RPM for a total of 116 yaw axis-related accidents.

Figure 37 indicates that pilots experienced the most loss of control accidents in the yaw axis and

vertical axes, most frequently during the hover and takeoff phases of a flight. Of the 338 accidents,

235 involved loss of yaw and/or vertical control. Because the yaw and vertical axes are quite coupled

in today’s single-piston helicopter fleet, this is not an unexpected result. There were 103 main rotor

cyclic-related (i.e., pitch and roll) loss of control accidents. Thus, loss of directional control and

vertical position accounted for nearly 70% of the loss of control accidents in single-piston

helicopters.

5.3.3.6 Loss of Control by Pilot-in-Command Certification Level. The last characteristic of loss

of control accidents analyzed in detail was the reported certification level of the pilot in command

(PIC). The authors examined only mini-briefs from 1963 through 1982 in detail for the PIC data.

Cross-checking was made against data from 1993, 1994, and 1995 that was available at the NTSB

web site.* Therefore, only 461 of the 625 single-piston helicopter mini-briefs were examined. The

data reviewed yielded the distribution provided in figure 38. The most striking finding was that the

PIC held at least a commercial rating in well over 60% of loss of control accidents. It should also be

noted that loss of control accidents involved student pilots (55), private pilots (77), and pilots with

no certificates (12). Since we do not know how many pilots there were at each certification level, we

cannot draw any conclusions about the relationship between certification and accidents. However, it

is clear that loss of control accidents involved pilots of all certification and experience levels.

5.3.3.7 Conclusions About Loss of Control Accidents. Of the 8,436 rotorcraft accidents recorded

by the NTSB during the 34-year period from mid-1963 through the end of 1997, 5,371 accidents

involved commercially manufactured, single-piston helicopters. Of these, 625, or roughly 12%, were

attributed to loss of control. In the 338 accidents for which the control axis loss was specified, 235

involved loss of yaw and/or vertical control. Current single-piston helicopters appear to have a

highly coupled vertical/yaw/power/RPM flight characteristics that, potentially, led to as many as

two-thirds of the loss of control accidents.

Loss of control accidents occurred most frequently during instructional and training activities (152).

However, aerial application, general utility, and personal-use activities together accounted for

347 accidents. This suggests that no activity was immune to a loss of control accident. Loss of

control accidents occurred with pilots of all certification and experience levels at the controls.

The overall impression from the large number of loss of control accidents is that the single-piston

helicopters currently in the registered fleet are inordinately difficult to fly, particularly when the

pilot must devote some attention to any other task. Clearly, given today’s technology, the handling

qualities of this helicopter type could be substantially improved.

 *The information can be found on the web at http://nasbac.faa.gov/asp/asy_ntsb.asp. Access to this site allows a search

by each specific NTSB accident document number.
33

5.3.4 Airframe/Component/System Failure or Malfunction (639 Accidents)

In the United States, the single main rotor with antitorque tail rotor configuration has dominated the

civil fleet. Since 1946, this configuration’s field experience has been the basis for the industry’s

engineering and manufacturing experience. The many lessons learned have allowed the industry to

slowly improve its product.

The helicopter requires a number of airframe systems and components not found on fixed-wing

aircraft. For example, comparably sized airplanes connect the propeller directly to the engine. In

helicopters, a much more complicated drive train is required to transmit power to the main rotor.

This drive train includes a coupling from the engine to a speed-reducing gearbox that outputs power

to a main rotor mast to which the main rotor is attached. The helicopter’s main rotor has two or

more blades that are quite flexible compared to an airplane propeller and continually flex as they

turn. In fact, many helicopter systems and components are subjected to continuous vibration and

flexing, which has forced the industry to become a leader in understanding failure of materials in

fatigue. Put simply, many airframe failures deal with this kind of question: How many times can you

bend and unbend a paper clip before it breaks?

The helicopter’s overall complexity, the different materials used, and the several different ways in

which these materials can fail (i.e., failure modes) are important factors in accidents related to the

NTSB first event category of Airframe/component/system Failure or Malfunction.

5.3.4.1 Overall Accident Trends. The NTSB cited airframe/component/system failure or

malfunction (referred to from here on as simply airframe failure) as the first event in

639 accidents experienced by the single-piston helicopter fleet during the study period. Accidents

that occurred during this 34-year period took a large toll (table D-24). The 639 accidents directly

affected 1,051 people: 153 were killed, 109 were seriously injured, and 789 survived with minor

injuries or no injuries at all. Of the 639 helicopters involved, 212 were listed as destroyed by the

NTSB, and 422 helicopters were substantially damaged; only 5 received little or no damage.

Figure 19 shows that the overall trend in accidents per year for this first event category remained

relatively constant for the first 17 years of the study period. However, airframe failure accidents

showed a rapid decrease in 1982 and remained at a relatively low level through 1997. Figure 39

shows that airframe failure from 1980 through 1997 accounted for a nearly constant percentage of

single-piston helicopter accidents. As a rate of annual accidents per 1,000 registered single-piston

helicopters, accidents initiated by airframe failures showed further reduction during the last 10 years

of the study period (fig. 39).

5.3.4.2 Airframe Failures by Phase of Operation. Considering the phase of operation during

which airframe failures occurred, the accidents fell into 11 categories, as figure 40 shows. Airframe

failures occurred most frequently during the cruise phase of a flight. The large number of airframe

failure accidents associated with maneuvering occurred primarily during aerial application activity.

5.3.4.3 Airframe Failures by Activity. The accident records were analyzed to determine the

frequency distribution of airframe failure accidents by flight activity. The activity was extracted

from the narrative based on FAR paragraph numbers and verbal description in the NTSB mini-brief.

Ten activities dominated, as figure 41 shows.
34

Figure 41 shows that single-piston helicopters had the most airframe failure accidents during

agricultural operations and general utility use. These activities require (1) constant low-altitude

maneuvering in proximity to obstacles, (2) frequent low-speed and downwind flight, (3) service

from unprepared areas (e.g., fields, landing trailers), (4) flight at night (especially in hot climate

areas), and (5) extensive travel from job site to job site. These five factors alone suggest that

maintenance may suffer.

5.3.4.4 Airframe Failures by System/Component. For the 639 accidents involving commercially

manufactured, single-piston helicopters, failures in over 70 systems/components resulted in

accidents. These 70 specific failures are combined into the 10 major categories shown in figure 42.

It is evident from figure 42 that the rotor drive system (both main and tail rotors combined) was the

most significant airframe failure for this aircraft class. Over 38% of the 639 accidents caused by

airframe failures involved problems in transmissions, drive shafts, couplings, clutches, and other

components of the rotor drive trains. Since drive train failure usually required an autorotative

landing (frequently with degraded control when the failure occurred in the tail rotor drive), the

consequences were often very serious. When the tail rotor (i.e., blades and hub), its drive train, and

its control system are considered as one category, then over 40% of the 639 airframe failure

accidents led to loss of directional control.

The accident count is matrixed by major airframe system and failure mode terminology in table 8.

The failure mode terminology used by NTSB accident investigators may lack a certain precise

engineering statement from which redesign might be initiated; however, the meaning implied by

each mode becomes clearer when related to a specific system that failed. For example, failures of

rotor system components owing to fatigue loads are hardly unexpected in the rotorcraft world.

Slippage, when associated with drive systems, suggests a belt, clutch or freewheeling unit

malfunction. Material failure and failed are, of course, less informative and could be taken as the

same. On the other hand, overload could imply under-designed components or improper flight

techniques that exceeded aircraft limits flown. Foreign object damage (FOD) and rotor system are

clear enough. Lack of lubrication and drive system suggest gearbox problems.

Figure 42 offers a convenient outline from which more detail about each system, subsystem,

component or part failure or malfunction can be examined.

5.3.4.4.1 Drive train failures by subsystem: Figure 42 shows that the drive train from the

engine to the main and tail rotors was implicated in a total of 246 (i.e., 38% of the 639) accidents

involving single-piston helicopters during the study period. These accidents, caused by drive-train

failures, are distributed to a lower subsystem level, as shown in table 9.

Failure to transmit power from the engine to the main rotor gearbox accounted for 96 of the

127 main rotor drive train accidents (table 9). Failure to transmit power along the tail rotor drive

shaft caused 73 of the 119 tail rotor drive train-related accidents. Taken together, component failures

in these two subsystems caused 169 accidents.
35

TABLE 8. NTSB FAILURE MODE/SYSTEM MATRIX— SINGLE-PISTON HELICOPTERS

Failure mode

Drive

system

Rotor

system

Control

system

Airframe

LG All other Total

Fatigue 28 74 21 23 0 146

Improper assembly, installation,

maintenance 50 20 33 26 0 129

Material failure 60 19 12 9 0 100

Undetermined/not reported 16 7 5 7 15 50

Failed 26 1 9 10 1 47

Separated 6 13 8 5 0 32

Foreign object damage 4 18 1 0 0 23

Overload 8 6 5 2 1 22

Pilot action/operational issue 2 4 0 5 6 17

Lack of lubrication 16 0 0 0 0 16

Slippage 16 0 0 0 0 16

Disconnected 8 1 5 0 0 14

Blade-airframe strike 0 9 1 0 0 10

Delaminated/debonded 0 7 0 0 0 7

Bearing failure 5 2 0 0 0 7

Bent/binding/jammed 1 0 1 1 0 3

Hydraulic leak/lock 0 0 0 0 0 0

Total 246 181 101 88 23 639

TABLE 9. DRIVE TRAIN FAILURES BY COMPONENTS—

SINGLE-PISTON HELICOPTERS

Drive train— main 127

Engine to transmission drive 96

Main rotor gearbox 20

Main rotor mast 11

Drive train— tail 119

Tail rotor drive shaft 73

Tail rotor gearbox 46
36

The main rotor gearbox was cited in 20 accidents (table 9). Of these 20 accidents, gear failures

dominated. Four of the 11 main rotor mast failures were traced to the thrust bearing. In all, material

failure was cited in 10 cases, and fatigue was implicated in 5 others; one case of a “ bogus”— rather

than manufacture approved part— was identified. Failure within the 46 tail rotor gearboxes was

traced to bearings and gears in about equal numbers.

Table 10 lists the number of accidents caused by components that failed to transmit power between

the engine and the main rotor gearbox or to transmit power from the main rotor gearbox to the tail

rotor gearbox. The clutch assembly accounted for a large number of accidents. In many cases, the

specific part within the assembly that failed was listed by the investigator. Furthermore, the

investigators characterized the failure as “slippage” or “ disconnect.” They frequently pointed to

material failure, wear, and fatigue as the cause of clutch failure. Clearly, the point of power transfer

between the engine and the rotor drive system— the clutch— is a critical component. Possibly, health

and usage monitoring systems (HUMS) and better aircraft inspection techniques/tools could spot

and prevent a potential failure in these component failures.

TABLE 10. DRIVE TRAIN MAJOR COMPONENT FAILURES—

SINGLE-PISTON HELICOPTERS

Engine to transmission drive 96

Clutch assembly 59

Freewheeling unit 16

Torsion coupling 8

Belt 6

Bearing 5

Shaft 2

Tail rotor drive shaft 73

Drive shaft 37

Coupling 28

Hangar bearing 8

Tail rotor drive shaft failures accounted for 73 of the 119 single-piston helicopter accidents

(table 9). Table 10 shows that one or more shaft segments failed in 37 cases, couplings failed in 28

cases, and the investigator specifically identified hanger bearings in 8 accidents. Material factors

accounted for 46 of the tail rotor drive shaft failures (all parts and subsystems). Fourteen were

related to maintenance or manufacture, 8 to operations, and the rest miscellaneous or unreported.

Bogus parts were implicated in two failures. It appears that efforts to reduce tail rotor drive shaft

system problems should concentrate on the design of and materials used for the components of this

system, along with HUMS to detect fatigue, wear, and deterioration.
37

5.3.4.4.2 Rotor failures by subsystem: Figure 42 shows that the main and tail rotor systems

were implicated in a total of 181 of the 639 accidents (i.e., 28%) in single-piston helicopters during

the study period. Table 11 provides the distribution of rotor system failures by accident count to a

lower subsystem and component level. Note that in both the main and tail rotor systems, blade

failures accounted for about 50% of the accidents. Fatigue fractures were the most prevalent failure

mode for both the main and tail rotor systems (table 12).

TABLE 11. ROTOR SYSTEM FAILURES BY COMPONENTS—

SINGLE-PISTON HELICOPTERS

Main rotor 57

Main rotor blade 28

Main rotor hub 16

Main rotor system 12

Other 1

Tail rotor 124

Tail rotor blades 56

Tail rotor hub 32

Tail rotor system 36

TABLE 12. ROTOR SYSTEM COMPONENTS FAILURE MODE—

SINGLE-PISTON HELICOPTERS

Component failure

mode

Main

rotor

blade

Main

rotor

hub

Main

rotor

system Other

Tail

rotor

blade(s)

Tail

rotor

hub

Tail

rotor

system Total

Fatigue fracture 9 8 0 0 34 25 1 77

Material failure 2 2 0 0 8 5 4 21

Separated 4 0 0 0 6 0 9 19

Foreign object damage 0 0 3 0 0 0 15 18

Overload 3 3 0 1 4 1 1 13

Improper assembly 4 2 0 0 2 1 0 9

Not reported 1 1 0 0 1 0 6 9

Blade– airframe strike 0 0 9 0 0 0 0 9

Delamination 5 0 0 0 1 0 0 6

Total 28 16 12 1 56 32 36 181
38

5.3.4.4.3 Control system failures by subsystem: Failure or malfunction of flight control

systems precipitated 101 accidents (fig. 42). Failures in the lower controls (i.e., the nonrotating

components) far outnumbered those in the upper controls (i.e., primarily rotating components) as

shown in table 13. Of the 12 stabilizer bar/paddle failures, 9 were the “ Bell bar” and 3 were the

“ Hiller servo paddle.”

The failure mode in the lower controls of the main rotor was characterized by the accident

investigators in terms such as disconnected/separated, loose or missing bolt, improper assembly,

material failure, overload, and worn. Only eight examples of fatigue failure were noted. The

21 accidents attributed to the tail rotor control cables described the cables as chafed, worn, frayed,

loose, disengaged from pulley, separated, improperly assembled, and crossed.

5.3.4.4.4 Airframe failures by components: Figure 42 shows that failures of the fuselage

structure, landing gear, and other airframe-associated components accounted for 88 of the

639 accidents (i.e., 14%). Table 14 presents the accidents caused by failures at the lower subsystem

and component level. The failure modes of these airframe components is summarized by accident

count in table 15. Ground resonance was the key factor in at least 20 of the 24 landing gear-related

accidents. Lack of maintenance of the landing gear struts was identified as the primary cause of

these accidents. In fact, as table 15 shows, improper assembly, installation, or maintenance

specifically accounted for 16 of the 26 total accidents counted in this grouping. Tailboom failure

caused 26 accidents; one-half of these came about because of a fatigue fracture. NTSB investigators

noted corrosion as a factor in very few fuselage component failures. The six fatigue failures

associated with support assembly led to separation of the main rotor gearbox and rotor system.

TABLE 13. CONTROL SYSTEM FAILURES BY COMPONENTS—

SINGLE-PISTON HELICOPTERS

Main rotor controls 63

Lower controls— cyclic 27

Lower controls— collective 10

Upper controls— swashplate assembly 9

Upper controls— pitch link 3

Upper controls— other 2

Upper controls— stabilizer bar/paddle 12

Tail rotor controls 38

Lower controls— cable 21

Lower controls— other 3

Upper controls— swashplate assembly 2

Upper controls— pitch link 4

Upper controls— other 3

Controls— other 5
39

TABLE 14. AIRFRAME FAILURES BY COMPONENTS—

SINGLE-PISTON HELICOPTERS

Airframe and landing gear 88

Landing gear 24

Tailboom 26

Other systems 8

Support assembly 10

Other systems (engine) 3

Stabilizer— horizontal 9

Miscellaneous equipment 7

Stabilizer— vertical 1

TABLE 15. AIRFRAME COMPONENTS FAILURE MODE—

SINGLE-PISTON HELICOPTERS

Component failure

mode

Landing

gear

Tail

boom

Other

systems

Support

assy

Other

systems

(engine)

Stabilizer

(horizontal)

Misc

equip

Stabilizer

(vertical) Total

Fatigue 0 13 0 6 0 4 0 0 23

Improper assembly,

installation,

maintenance

16 0 4 0 1 2 2 1 26

Failed 0 4 2 1 1 0 2 0 10

Undetermined/not

reported 3 01 1 1 0 1 0 7

Material failure 0 3 0 2 0 2 2 0 9

Pilot action and

operational issues 4 01 0 0 0 0 0 5

Disconnected/separated 0 4 0 0 0 1 0 0 5

Overload 1 1 0 0 0 0 0 0 2

Bent/binding/jammed 0 1 0 0 0 0 0 0 1

Total 24 26 8 10 3 9 7 1 88
40

5.3.4.5 Conclusions About Airframe Failure or Malfunction Accidents. Of the 8,436 rotorcraft

accidents recorded by the NTSB during the 34-year period from mid-1963 through the end of 1997,

5,371 accidents involved commercially manufactured, single-piston helicopters. Of the 5,371

accidents, 639, or roughly 12% of these accidents, were attributed to failure or malfunction of the

airframe or of some system or component associated with the airframe. Drive and rotor system

failures, primarily in the cruise and maneuvering flight phases, accounted for 427 of the 639

accidents. The clutch from the engine to the main rotor gearbox and the tail rotor drive shaft

dominated drive train component failures. Together, these two components accounted for 96 of the

639 accidents. Main and tail rotor blade fatigue failures led to an additional 94 accidents. The pilot

was left without antitorque and directional control in over 300 of the 639 accidents because of

failures or malfunctions of a tail rotor drive train, a tail rotor system, a tail rotor control, or a

tailboom.

Fatigue resulted in more airframe failure accidents in commercially manufactured, single-piston

helicopters than any other cause. Following fatigue failures, material failures, failures without

specific mode stated, and improper assembly, installation, and maintenance contributed the largest

numbers to the accident record. The manufacture and maintenance problem manifested itself by a

wide range of errors: improper servicing, unapproved modifications, missing parts, or installation of

incorrect or unapproved parts, to name several. As discussed above in the context of flight control

problems, improving the quality of design, manufacturing, and maintenance processes is an

important area on which to concentrate industry efforts.

In 60% of the accidents in which there was contact of the rotor blades with other parts of the aircraft

structure, the aircraft was destroyed. This is not surprising because blade-aircraft contact almost

always resulted in loss of part of the main rotor and control systems components. Conversely,

component fatigue, material failure, and improper assembly/installation/maintenance tended to

result in less severe aircraft damage, although it caused more accidents.

In summary, this analysis of airframe failure accidents indicates the following:

1. Airframe failure accidents for commercially manufactured, single-piston-engine-powered

helicopters showed a decreasing trend in accidents per year and in accidents per 1,000 registered

aircraft.

2. Material and assembly/installation/maintenance factors dominated the identified causes

of airframe failure accidents. The large number of system or components identified to have failed

and the large number of failure modes indicate many opportunities for improvement. However, no

small set of problem areas appeared such that, if corrected, accident rates would decrease adequately

to meet national goals.

3. The clutch from the engine to the main rotor gearbox and the tail rotor drive shaft

dominated drive train component failures and led to approximately one-sixth of the airframe-related

accidents.

4. The pilot was left without antitorque and directional control in over 300 of the

639 airframe-related accidents.
41

5.4 Summary Remarks, Conclusions, and Recommended Actions

The number of registered commercially manufactured, single-piston helicopters grew from about

540 at the end of 1957 to over 4,200 at the end of 1997. During the period from mid-1963 through

1997, this growing fleet accounted for 5,371 accidents. The NTSB grouped these accidents into

21 categories; however, as figure 43 shows, 93% of the accidents fell into 7 categories and, in fact,

4 categories accounted for 70% of the accidents.

The summary of accidents by activity and phase of operation, table 16, shows that the overwhelming

number of single-piston helicopter accidents occurred during aerial application. Since crop dusting

requires considerable maneuvering, it is almost a corollary that the most accidents occurred during

some maneuvering operation.

Within the four top accident categories, the following are noted.

1. Loss of engine power because of improper fuel/air mixture caused 686 accidents, of

which 400 were caused by fuel exhaustion, fuel starvation, or fuel contamination.

2. Loss of engine power because of engine structural failure caused 263 accidents.

3. Loss of engine power for undetermined reasons was recorded in 397 accidents.

4. In flight collision with man-made objects accounted for 696 of 953 accidents.

TABLE 16. ACCIDENTS BY ACTIVITY AND PHASE OF OPERATION—

SINGLE-PISTON HELICOPTERS

Activity Phase of operation

Aerial application 1,494 Maneuvering 1,149

Instructional/training 976 Cruise 1,047

General utility 875 Landing 949

Personal use 787 Takeoff 889

Passenger service 421 Hover 450

Business use 338 Approach 241

Ferry/reposition 205 Descent 168

Flight/maintenance test 113 Taxi 164

Public/military use 78 Standing/static 126

Executive/corporate 75 Unknown/other 124

Unknown/not reported 9 Climb 64

Total 5,371 Total 5,371
42

5. In flight collisions with wires and wire/poles accounted for 507 accidents; only 148

accidents involved collisions with trees.

6. Loss-of-control in the vertical/yaw axes contributed to at least 235 accidents and perhaps

to as many as 400 accidents.

7. Loss of control was experienced, regardless of the certification level of the PIC.

8. Drive-train failures caused 246 accidents, of which engine to transmission and tail rotor

drive shaft failures contributed 169 airframe-related accidents.

9. Rotor system failures caused 181 accidents, of which the tail rotor system accounted for

124 accidents.

10. Control system failures caused 101 airframe-related accidents.

11. The pilot was left without antitorque and directional control in 307 of the 639 airframerelated accidents.

12. An autorotation took place in approximately 2,000 of the 5,371 accidents.

The top four— or seven— most common accident categories were not the accident types that caused

the highest fatality rates (i.e., fatalities per 100 accidents). The worst accident severity using that

measure in the single-piston helicopter fleet was midair collisions, of which there were 17 that killed

22 people. Following midair collisions, figure 44 shows, in descending order, fatalities per

100 accidents by other NTSB first event categories. Within this grouping, airframe failure, in flight

collision with object, and loss of control clearly led to a high fatality rate. Note that loss of engine

power, the greatest cause of accidents, had a relatively low fatality rate. Twelve of the

5,371 accidents fell in the undetermined category in which 18 people lost their lives. When ordered

in terms of total fatalities as tabulated in figure 44, in flight collision with object and airframe failure

accidents were the leading causes of fatalities with the single-piston helicopter fleet.

Before discussing single-turbine helicopter accidents, some observations and recommendations are

in order relative to the single-piston helicopter fleet. To begin with, this class of helicopter is sold on

the basis of its unique capability to hover and fly low and slow. This helicopter class has,

historically, provided a cost-effective way to spray crops, to instruct students, and to generally attract

first-time helicopter buyers who have found any number of new personal and utility uses for the

aircraft. In the vast majority of uses, helicopter pilots operate their aircraft in a comparatively hostile

environment when viewed by fixed-wing pilot standards. This environment includes many manmade obstacles.

Helicopters appear to provide some safety margin over fixed-wing aircraft because of their inherent

autorotation capability (i.e., the ability to glide with turning rotor) and their generally slower poweroff landing speed. These relative safety advantages are often negated, however, because helicopter

pilots routinely operate their rotorcraft much closer to the ground where reaction times are minimal

and emergency landing sites are generally unsuitable.
43

In 1997, the commercially manufactured, single-piston helicopter fleet experienced 17 accidents per

1,000 registered rotorcraft. It is projected that, by the year 2010, the annual accident rate for singlepiston helicopters may still be above 5 accidents per 1,000 registered type (fig. 22). This projection

assumes “a business-as-usual” approach by the rotorcraft industry. However, several steps can be

taken now and in the short-term to significantly reduce this projected rate of single-piston engine

helicopter accidents:

1. There is an apparent disregard by many pilots of an engine’s need for clean fuel and air

in proper proportions—to say nothing about the FAA regulations for fuel reserves. The fact that

power-off landing proficiency is not required by the FAA in order to obtain helicopter pilot

certification appears inconsistent with the number of accidents caused by loss of engine power.

However, it also appears that helicopters—currently in the civil fleet—provide marginal to

inadequate autorotational capability to permit the average pilot to successfully complete the final

flare and touchdown to a generally unsuitable landing site. We specifically recommend the

following:

a. Reinforcement of fuel management and mission planning according to current FAA

regulations be immediately initiated.

b. Currently installed fuel quantity measurement and display systems be reexamined

for accuracy and applicability to helicopter applications.

c. Student and recurrent pilot training in full power-off autorotation to touchdown be

reinstated as a pilot certification requirement.

d. Commercial helicopter manufacturers reexamine their current and future product’s

autorotational capabilities with the objective of reducing height-velocity restrictions to a level

consistent with average piloting skills and more representative emergency landing sites.

e. A detailed examination of the 263 accidents caused by piston-engine structural

failure be made with the intent of initiating an engine improvement program.

2. The average pilot’s situational awareness of man-made objects that must be avoided is

significantly impaired because most of the objects are not readily visible. Wires, in particular, are the

best known threat to low flying rotorcraft. It is specifically recommend that:

a. Flying below 750 feet (above ground level) be discouraged by the industry and

regulatory agencies.

b. All man-made objects higher than 500 feet be prominently marked and mapped, to

include electronic databases such as used in Global Positioning System equipment.

c. A low-price proximity spherical sensor be developed and certified. A sensor sphere

of some large radius should, in effect, cocoon the helicopter and provide the pilot with sufficient

warning to avoid obstacles.
44

3. Single-piston helicopters now in the registered fleet appear inordinately difficult to fly,

particularly when the average pilot has to devote some attention to other tasks or is experiencing an

imagined or real emergency. Cross-coupling between the vertical/power/RPM and yaw axes is

excessive. The handling qualities design standards applicable to the current-helicopter fleet date

back to the 1950s. Although generally tolerated, the resulting stability and control characteristics

appear unsatisfactory. Therefore, it is recommended that:

a. Engine RPM management be more fully automated; preferably to the level offered

with turbine engines.

b. A low-price stability augmentation system (in the yaw axis as a minimum) having

at least 10% authority be developed and certified.

c. Handling quality standards for all future helicopters be raised to levels consistent

with what modern technology can provide.

4. The single-piston helicopter fleet has shown that the design standards of the 1950s do not

adequately address the many new and varied activities in which this aircraft class is engaged. This is

particularly true because pilots do exceed design limits, required maintenance is skipped, and less

than thorough inspections are performed. The current fleet appears to be under-designed relative to

today’s use. It is recommended that the industry:

a. Reevaluate design and certification criteria of all components involved in

transmitting power from the engine to the main rotor gearbox with particular attention to clutch and

freewheeling units.

b. Reevaluate design and certification criteria of all components that transmit power to

the tail rotor, with particular attention to the drive shaft and couplings typical of current

configurations.

c. Adopt more conservative fatigue design criteria, particularly for tail rotor blades.

On a final note about the single-piston helicopter fleet, the number of accidents per year decreased

in nearly a linear manner. A representative approximation of this decrease would be from 221

accidents in 1967 to 73 in 1997. However, a significant departure from this favorable trend occurred

between 1971 and 1983 when a rash of accidents created a “bubble” above the generally linear

trend. It is suspected that this bubble was caused by the increase from 127 per year to 193 per year

in newly registered, single-piston helicopters. The conclusion drawn offers the following cautionary

note for the future: When the next rapid expansion of the fleet occurs, the industry must increase all

aspects of its safety improvement efforts, and this increase must be more than proportional to the

fleet growth rate.
45

6. COMMERCIAL SINGLE-TURBINE ENGINE HELICOPTERS

6.1 Fleet History and Growth

The single-turbine helicopter civil fleet began serious growth as the war in Vietnam was coming to

an end. The U.S. military services were the first to demand that gas turbine technology be applied to

their helicopters. With this development support, manufacturers were soon able to offer the turbinepowered helicopter to the civil marketplace. Following the single-piston helicopter trend, the singleturbine helicopter market also experienced a very real collapse in the mid-1980s. A decade later,

growth in the market began again. Today the number of registered single-turbine helicopters is

approximately equal to that of the single-piston fleet (fig. 45 and table D-2). Note that the FAA

census (as edited by the principal author) and the count Air Track, Inc. published in their "Rotor

Roster" are in reasonable agreement.

6.2 Single-Turbine vs. Single-Piston

Contrasts between single-piston and single-turbine helicopters are frequently made, with improved

performance from turbine power being particularly noteworthy. With respect to accident trends,

however, there are more similarities than differences between the two helicopter types. Figure 46

shows that the single-turbine helicopter reduced the single-engine helicopter accident rate per 1,000

registered aircraft relative to the single-piston helicopter. However, the trend shown in figure 46

understates the very real safety improvement obtained with single-turbine helicopters, because it is

based on fleet size as the ratio’s denominator. The relative safety improvement can be examined in

more detail using data from the Rotorcraft Activity Survey of 1989 (ref. 17), which included the

following summary taken from table 2.1 of that survey:

TABLE 17. FAA ROTORCRAFT ACTIVITY SURVEY OF 1989 (From Ref. 17)

Rotorcraft Type

Population

Size

Estimate

of

Number

Active

Estimate of Total

Hours Flown

[in 1989 by

Active Aircraft]

Estimate of Avg.

Hrs. Flown [per Yr.

by Active Aircraft]

Manufacturer Built

Piston Total (1) 3,994 2,684 728,125 277.8

 Single Turbine 3,616 3,248 1,532,270 480.5

Twin Turbine 1,069 984 546,471 551.8

Turbine Total 4,685 4,232 2,078,741 496.5

Manufacturer Total 8,679 6,916 2,806,866 417.3

Amateur Built Total 1,790 572 21,830 38.2

Total − All Rotorcraft 10,469 7,488 2,828,697 390.2

The FAA concluded from these published data that the registered fleets of single-piston and singleturbine rotorcraft were comparable in size. However, the active fleet size of single-turbine

helicopters outnumbered single-piston helicopters by over 20%. The survey estimated that the

single-turbine helicopter fleet flew twice as many hours as the single-piston helicopter fleet
46

(i.e., 1,532,270 vs. 728,125 hours). These differences are very important when accident rates are

computed as ratios of accidents to fleet size, active fleet size, 100,000 hours flown, or departures,

etc. In contrast, the number of reported accidents recorded by the NTSB is reliable for use in the

numerator of any proposed ratio. It is the ratio’s denominator that can be quite misleading or

unreliable. This leads to considerable misgivings about accident statistics in general by the authors;

this issue is discussed in appendix B.

The improved safety of single-turbine relative to single-piston is not exactly clear. The NTSB

recorded during 1989 (tables D-5 and D-6) that the single-piston registered fleet of 3,920 helicopters

experienced 106 accidents and the single-turbine fleet of 3,574 helicopters experienced

72 accidents.* An immediate conclusion might be that the relative safety for the two rotorcraft types

in 1989 was as follows:

Single piston = 106 accidents per 3,920 registered aircraft = 27 per 1,000 aircraft

Single-turbine = 72 accidents per 3,574 registered aircraft = 20 per 1,000 aircraft.

These ratios suggest that the single-turbine helicopter was 1.34 times as safe as the single-piston

helicopter in 1989. When the comparison is made using active aircraft, as estimated by the FAA in

table 17 above, the comparison changes as follows:

Active single piston = 106 accidents per 2,684 active aircraft = 39.5 per 1,000 aircraft

Active single-turbine = 72 accidents per 3,248 active aircraft = 22.2 per 1,000 aircraft.

The relative safety margin of the single-turbine helicopter, in 1989, now becomes 1.78. A last

comparison based on the FAA estimated hours flown in 1989 by the active rotorcraft shows the

following:

Active single piston = 106 per 728,125 hours = 14.5 accidents per 100,000 hours flown

Active single turbine = 72 per 1,532,270 hours = 4.7 accidents per 100,000 hours flown.

Based on accidents per estimated 100,000 hours flown, perhaps the most common safety statistic,

single-turbine helicopters appeared to be about three times safer than single-piston helicopters. At

least this was the case in 1989, if the FAA data can be considered adequately reliable.

We do not suggest extrapolating this conclusion to any other year, because reliable FAA data used in

the denominator do not appear to exist, as explained in appendix B.

6.3 Accident Analysis

That rotorcraft safety improved when the single-turbine-powered helicopter was introduced is hardly

disputable. However, loss of engine power was still the leading NTSB first event category of the

2,247 accidents involving single-turbine helicopters recorded over 34 years, as figure 47 shows. In

 *The FAA count in their reference 17, table 2.1 is 3,994 and 3,616 respectively; but it was found that many pistonpowered helicopters were listed as turbine-powered and vice versa.
47

fact, as the comparison in table 18 summarizes, the percentage distribution of single-turbine

helicopter accidents virtually parallels that for single-piston helicopters. Reduction of in flight

collision with object accidents from 18% to 13% appears as the one difference that stands out in

table 18.

TABLE 18. SINGLE-TURBINE VS. SINGLE-PISTON ACCIDENT COMPARISON,

1963–1997

Single turbine Single piston

NTSB category Count % Count %

Loss of engine power 704 31 1,554 29

In flight collision with object 298 13 953 18

Loss of control 284 12 625 11

Airframe/component/system failure or malfunction 282 12 639 12

Hard landing 140 6 483 9

In flight collision with terrain/water 143 6 443 8

Rollover/nose over 119 5 290 5

Other 227 10 384 7

Total 2,247 100 5,371 100

The trend of single-turbine helicopter accidents per year for the most frequent first event categories

is shown in figures 48 and 49. This rotorcraft type experienced a severe rash of loss of engine power

accidents beginning in 1978 (fig. 48). Apparently, it took 10 years to find and correct a number of

problems. The sum of in flight collision with object and loss of control accidents began to rise in the

same period as engine related accidents, which is shown by the heavy, solid line in figure 49. The

overall picture suggests that it was not until the late 1980s that the single-turbine helicopter fleet

matured, nearly 20 years after this rotorcraft type was introduced into the fleet.

The number of accidents per 1,000 registered single-turbine helicopters decreased until 1986 and

then remained virtually unchanged after 1986 (fig. 46). We suspect that a plateau occurred with the

single-turbine helicopter fleet. Figure 50 projects that, by the year 2010, accidents with singleturbine helicopters may only decrease to about 15 per 1,000 aircraft. The single-turbine helicopter

fleet began to expand after 1993 (fig. 45). This expansion, clearly evident over the last 4 years of the

study period, reflects an abrupt fleet growth of the type experienced by the single-piston helicopter

fleet, as discussed earlier. Therefore, it may be that insufficient emphasis—relative to increased

sales, use, and new missions—is being placed on single-turbine helicopter safety. Without a renewed

emphasis on safety, the projection shown in figure 50 is quite likely to come true.

Over the last 11 years of the study, the distribution of the 841 accidents changed when compared

with the distribution of the 2,247 accidents that occurred over the 34-year period. The comparative

distributions are summarized in table 19. Loss of control and airframe/component/system failure or

malfunction first event categories increased slightly, while loss of engine power and in flight
48

collision with objects decreased. Although the distributions are similar, certain changes occurred

which will be discussed in the detailed analyses below.

TABLE 19. SINGLE-TURBINE ACCIDENT DISTRIBUTION,

LAST 11 YEARS VS. 1963–1997

First event category 1987–1997 1963–1997

Loss of engine power 29% (244) 31% (704)

In flight collision with object 11% (94) 13% (298)

Loss of control 16% (132) 12% (284)

Airframe/component/system failure or malfunction 15% (124) 12% (282)

Hard landing 5% (43) 6% (140)

In flight collision with terrain/water 6% (47) 6% (143)

Rollover/nose over 3% (26) 5% (119)

Other 9% (131) 12% (277)

Total 100% (841) 100% (2,247)

6.4 Detailed Analysis by Accident Category

Of the 8,436 rotorcraft accidents, 2,247 accidents were incurred by single-turbine helicopters that

were commercially manufactured. Of these, 1,568 (about 70%) fell into the top four first event

categories. Therefore, a more in-depth analysis of the four top categories provides considerable

insight into most of the single-turbine helicopter accidents during the 34-year period under study.

The following several paragraphs and associated figures and tables provide further analysis of these

top four categories.

6.4.1 Loss of Engine Power (704 Accidents)

As table 18 shows, the single-turbine helicopter and the single-piston helicopter incurred virtually

the same percentage of accidents in the loss of engine power first event category during the 34-year

period studied. The explanation for this (perhaps surprising) fact is that both engine types need clean

fuel and air in the correct proportions to operate and that fuel problems, especially fuel exhaustion

and starvation, is as prevalent in the single-turbine as in the single-piston helicopter. It appears

many of the poor practices of pilots flying single-piston-engine-powered helicopters appears to have

carried over to the operation of turbine-powered helicopters that cost over five times as much.

Single-turbine helicopters have, in general, more seats than single-piston helicopters. Thus, as

table D-19 enumerates, somewhat fewer numbers of people (1,846 in single-turbine vs. 2,621 in

single-piston) were affected by considerably fewer accidents (704 in single-turbine vs. 1,554 in

single-piston) following loss of engine power.

6.4.1.1 Overall Accident Trends. From mid-1963 through 31 December 1997, the NTSB cited

loss of engine power in 704 accidents involving commercially manufactured, single-turbine

helicopters. The 704 accidents directly affected 1,846 people: 129 were killed, 237 were seriously
49

injured, and 1,480 survived with minor or no injuries (table D-25). Of the 704 helicopters involved,

139 were listed as destroyed by the NTSB, 546 were substantially damaged, and 9 received little or

no damage. Figure 48 shows that the trend in loss of engine power accidents per year improved over

the last 10 years of the study period. Furthermore, as an accident rate in terms of 1,000 registered

aircraft, figure 51 shows that accidents initiated by the loss of engine power steadily decreased.

However, as figure 51 shows, loss of engine power accidents also grew as the fleet grew, resulting in

nearly a constant 30% of the accidents in the 1970s and 1980s. Since 1990, it appears that a

concerted effort was made to correct poor-piloting-related accidents in this first event category.

6.4.1.2 Loss of Engine Power by Category. The NTSB cited the reason for loss of engine power

in 523 of the 704 accident reports. Table D-12 shows that 18 primary reasons lay behind the

704 accidents. Figure 52 shows that when the 18 reasons are grouped by major subsystems, fuel/air

mixture problems caused 299 of the 523 accidents. A closer inspection of figure 52 and the

associated mini-briefs reveals that fuel exhaustion, fuel starvation, fuel contamination, etc., repeated

single-piston helicopter experiences. Again, simply running out of gas was the primary reason for

loss of engine power throughout the 34-year period under study.

Figure 52 and table D-12 indicate that relatively few accidents were incorrectly charged to loss of

engine power by NTSB investigators.

6.4.1.3 Loss of Engine Power by Activity. The commercially manufactured helicopter, powered

by a single-turbine engine, has become the backbone of the helicopter industry (ref. 16). As figure

53 shows, the greatest number of loss of engine power accidents took place during passenger service

(e.g., air taxi) flights.* Agricultural operations contributed proportionally fewer loss of engine power

accidents than single-piston helicopters (see fig. 25). This may reflect the fact that modern, singleturbine helicopters cost so much more than the smaller, single-piston helicopter (ref. 18).

Power-off landings in single-turbine helicopters—currently in the civil fleet—generally were no

more successful than in single-piston helicopters. As table D-19 shows, there were 1,554 loss of

power accidents with the single-piston helicopter; 265 (17%) were destroyed and 1,286 (83%) were

substantially damaged. The corresponding statistics for the single-turbine helicopter were

704 accidents, 139 (20%) destroyed, and 546 (78%) were substantially damaged. Thus, of

2,258 single-engine (piston and turbine) loss of power accidents, all but 22 of the helicopters

involved were either destroyed or substantially damaged. It appears, therefore, that (1) the average

pilot proficiency in accomplishing a full power-off landing in a single-engine helicopter was quite

inadequate and (2) the helicopters themselves offered marginal autorotation capability.

6.4.1.4 Loss of Engine Power by Phase of Operation. Loss of engine power occurred in every

phase of operation in which the single-turbine helicopter operated, as figure 54 shows. Paralleling

single-piston helicopter experience, most losses of power occurred in cruise flight, which reflects the

passenger service, general aviation character of turbine helicopter use. The high power required in

takeoff and hover accounted for this sub-category being the second riskiest operational phase. When

the 104 accidents in takeoff are added to the 84 accidents in maneuvering and the 58 accidents in

hover, 246 accidents occurred during high-power use (vs. 314 accidents during cruise). The ratio of

 *This activity is still serving to expand the helicopter industry in much the same way that the public was introduced to

airline transportation following World War I.
50

accidents that occurred during high-power flight phases to those in cruise (246/314 or 78%) is lower

(78% vs. 108%), but quite comparable to that of single-piston helicopters discussed earlier.

6.4.1.5 Conclusions About Loss of Engine Power Accidents. Of the 8,436 rotorcraft accidents

recorded by the NTSB from mid-1963 through the end of 1997, 2,247 were incurred by singleturbine-engine-powered helicopters that were commercially manufactured. Loss of engine power

was the first event in 704, or roughly 30% of these accidents. No fewer than 299 accidents were

directly traced to fuel/air mixture problems as a consequence of human error. Fuel exhaustion, fuel

starvation, and fuel contamination accounted for over 151 of the 299 accidents. Apparently, despite

the higher cost of single-turbine helicopters, many pilots continued to ignore the engine’s need for

clean fuel and air in proper proportion. Since the single-turbine helicopter is used primarily for

passenger service, running out of fuel will provide the public with reasons to suspect rotorcraft

safety.

The need for training and practice in full touchdown autorotations is as great for pilots of singleturbine helicopters as for pilots of single-piston helicopters. It also appears that the single-turbine

helicopters that are currently in the civil fleet lack sufficient autorotational capability to permit the

average pilot to successfully complete the final flare and touchdown to what is generally

unsatisfactory terrain.

6.4.2 In Flight Collision with Object (298 Accidents)

Single-turbine helicopters demonstrated a 5% reduction in in flight collision with objects accidents

when compared with the single-piston helicopter fleet (table 18). However, many of the trends

observed about single-piston helicopters were also found in the more expensive, single-turbine

helicopter fleet.

6.4.2.1 Overall Accident Trends. The NTSB implicated in flight collision with object in

298 single-turbine helicopter accidents from 1963 through 1997. These accidents affected

688 people: 140 were killed, 106 suffered serious injuries, and the remaining 442 survived with

minor or no injuries. Of the 298 helicopters involved, 114 were listed as destroyed by the NTSB,

182 were substantially damaged, and 2 received little or no damage. The number of accidents per

year for this first event category decreased over the last 17 years of the study period (fig. 49).

However, as figure 55 shows, in flight collision with object accidents appeared to level off at a mean

level of 12% of the total single-turbine helicopter accidents. In terms of annual accidents per 1,000

of the registered single-turbine helicopter fleet, little reduction occurred in the later years (fig. 55).

6.4.2.2 Collision with Object by Object Hit. The objects hit by single-turbine helicopters while in

flight are listed in figure 56, which shows that wires and objects categorized as wire/pole accounted

for 108 plus 24 (i.e., 132) or 45% of the 298 accidents. Pilots of single-turbine helicopters appeared

more successful in avoiding objects when compared to a 55% rate for single-piston helicopters (as

derived from fig. 28).

6.4.2.3 Collision with Object by Cause. The NTSB summary narratives were studied to establish

each accident’s major causes or conditions. This study was somewhat subjective in that frequently

two or more factors were involved. This required that we proportion the cause of some accidents into

several parts; the results are provided in figure 57. Single-turbine helicopter pilots caused the
51

overwhelming number of collisions because of improper decisions, just as for single-piston

helicopters (fig. 29). Improper decisions include poor planning, inadequate training, and misjudging

clearances. Thus, for passenger transport operations (when helicopter safety is most visible to the

public), improper pilot decisions were the most frequent NTSB-reported cause, followed by

degraded visibility and winds.

6.4.2.4 Collision with Object by Phase of Operation. The single-turbine helicopter fleet

experienced nearly an equal number of collisions over all flight phases (fig. 58). This contrasts with

the single-piston helicopter fleet, which experienced an overwhelming number of collisions with

objects while maneuvering (fig. 30). The difference appears related to the different activities in

which these two helicopter classes were engaged.

6.4.2.5 Collision with Object by Activity. The NTSB mini-briefs’ summary narratives were

analyzed to identify the activities that resulted in accidents. The results are summarized in figure 59.

Unlike single-piston helicopters (fig. 31), single-turbine helicopters were engaged in general utility

and passenger service when most of the objects were struck. Single-turbine helicopters did not

appear to engage in significant aerial application activities or, if they did, agricultural operations

were conducted with much greater regard to safety.

6.4.2.6 Collision with Object by Part Hit. Another question regarding collision with object

accidents concerns what part of the helicopter was involved in the collision. The statistics available

on this subject are shown in figure 60. Tail rotor strikes occurred in 43 of the 104 single-turbine

helicopter accidents in which the part hit was reported. Whether this dominates the statistics because

it is noteworthy or because it is truly reflective of all of the collision with object accidents is

unknown.

6.4.2.7 Conclusions About In Flight Collision with Object Accidents. Of the 8,436 rotorcraft

accidents that occurred between mid-1963 and the end of 1997, 2,247 accidents involved singleturbine helicopters that were commercially manufactured. Of these, 298 (or roughly 13%) were

attributed to in flight collision with objects. Even though agricultural activities constituted only a

small percentage of single-turbine helicopter use (compared to single-piston helicopters), three

object struck categories—wire, wire/pole, and trees—accounted for 182 accidents. Main and tail

rotor strikes dominated helicopter components in the collision with object accidents. The data

strongly suggest that pilots lack situational awareness of the tail rotor.

6.4.3 Loss of Control (284 Accidents)

The number of single-turbine helicopter loss of control accidents fluctuated year to year. There was

an improvement relative to the single-piston helicopter fleet, but many of the same problems were

just as evident.

6.4.3.1 Overall Accident Trends. Loss of control was cited by the NTSB in 284 accidents

involving commercially manufactured, single-turbine helicopters. These 284 accidents directly

affected 754 people: 155 lost their lives, 123 were seriously injured, and 476 survived with minor or

no injuries. Of the 284 helicopters involved, 125 were listed as destroyed by the NTSB and 159 were

substantially damaged, while none went undamaged. Figure 49 shows that the trend in accidents per

year for this first event category steadily increased for the first 15 years of the study period. Then,
52

beginning in 1981, loss of control accidents showed a rapid increase, reaching a peak of 20 accidents

in 1984. After 1984, loss of control accidents per year dropped for nearly a decade. However, in

1997, there were again 20 accidents per year attributed to loss of control.

Loss of control accidents accounted for an erratic percentage of single-turbine helicopter accidents

during the 1981 through 1997 period (fig. 61). As a rate of accidents per 1,000 registered singleturbine helicopters, accidents initiated by loss of control showed little improvement over the latter

17 years. The yearly variability in the number of accidents in this category makes statistical analysis

difficult.

The long-term rate of single-turbine helicopter loss of control accidents was 3.83 per 1,000 aircraft.

The rate peaked sharply in the late 1960s, and exceeded its statistical upper control limit of 12.66 in

1969. This implies some systematic change took place, perhaps related to the large-scale

introduction of the single-turbine helicopter into the civil fleet which occurred during that period

(see fig. 45). In addition, since the actual number of registered single-turbine helicopters was still

relatively low during that time, a small change in the number of accidents resulted in a large change

in the rate. However, after 1969, overall accidents per 1,000 aircraft generally decreased, with some

spikes noted (fig. 61).

6.4.3.2 Loss of Control by Axis. Only 145 of the 284 mini-briefs for loss of control accidents

provided information about which axis of control was lost. However, two aspects became clear when

the remaining accidents were evaluated in descending order, as shown in figure 62. Two striking

differences between single-turbine helicopters (fig. 62) and single-piston helicopters (figure 37)

were observed. Low rotor RPM was not a serious problem with the single-turbine helicopter, at least

as a contributing factor to loss of control accidents. This difference can be attributed to the better

engine speed governing provided by turbine engine fuel controls. On the other hand, the singleturbine helicopter fleet suffered more loss of yaw control accidents (i.e., 75 of the 145 for which the

loss of control axis was reported, or 52%). In contrast, loss of yaw control accounted for only 95 of

338 accidents (i.e., 28%) in the single-piston helicopter fleet (fig. 37). Thus, loss of yaw control was

nearly twice as prevalent with single-turbine helicopters as with single-piston helicopters.

This increased percentage may be attributable to the generally higher installed power and associated

higher antitorque corrections required. Alternatively, the higher percentage may be related to “loss

of tail rotor effectiveness” (LTE). Although LTE was directly cited in the accident mini-briefs in

only a few cases, a review of the narratives indicates that LTE was probably involved in many loss of

yaw control accidents. It appears that pilots were not fully aware of the conditions conducive to LTE

or had difficulty interpreting in flight information to determine whether LTE might occur.

Single-turbine helicopters experienced proportionally fewer loss of control accidents in the vertical

axis than did single-piston helicopters. This may be a result of the better engine speed governing

provided by turbine engine fuel controls or the higher, power-to-weight ratios in turbine helicopters,

which minimizes the potential for low rotor RPM and loss of altitude control.

6.4.3.3 Loss of Control by Cause. Loss of control accidents were subdivided into which of the 24

categories brought on the control loss; figure 63 lists the top 12 categories (this information may be

contrasted with single-piston helicopter experience given in fig. 36). As for piston rotorcraft,
53

improper operation of controls again was the most prevalent factor cited by the NTSB in loss of

control accidents. However, the percentage of accidents attributed to this rather vague term was

somewhat lower for single-turbine helicopters (29%) than for single-piston helicopters (33%). This

reduction may be attributed to the generally higher experience level of single-turbine helicopter

pilots, especially since little high-risk civilian initial training was conducted in single-turbine

helicopters. Loss of control accidents involving low rotor RPM were considerably reduced in singleturbine helicopters, primarily for the same reasons given for axis of control lost.

Finally, accidents involving spatial disorientation or loss of visual reference were significantly

higher for single-turbine (13%) than for single-piston (3%) helicopters. This may be a result of the

more frequent operations in unprepared areas that are conducted in single-turbine helicopters and the

consequent higher risk for operations in degraded visual environments.

6.4.3.4 Loss of Control by Phase of Operation. Considering the phase of operation during which

loss of control occurred, the accidents were first subdivided into 18 categories and then condensed

into 11 key groups. As was noted for single-piston helicopters (fig. 34), loss of control occurred

more frequently in single-turbine helicopters during the takeoff and hover phases than during any

other single flight phase (fig. 64).

6.4.3.5 Loss of Control by Activity. The mini-briefs were reviewed to associate loss of control

accidents with the activity in which single-turbine helicopters were engaged. The results are

provided in figure 65. Single-turbine helicopters showed a substantially different activity distribution

than did the single-piston helicopter (fig. 35). First, single-turbine helicopter accidents during

passenger operations were two-and-a-half times those of single-piston helicopters. Conversely,

accidents during personal use operations occurred less than half as frequently. This may be

explained by the relative costs (purchase and ownership) of turbine engine-powered helicopters

compared with the average purchase and ownership costs of piston-engine-powered helicopters;

single-turbine helicopters being more frequently used in commercial operations than for personal

pleasure or convenience. Second, figure 65 shows the far lower percentage of loss of control

accidents during agricultural operations. This can be attributed to the fact that agricultural flying was

a more important role for single-piston helicopters than for single-turbine helicopters.

Finally, note that no accidents related to instructional flights appear in figure 65. Little civilian initial

rotorcraft flight training was conducted in single-turbine helicopters. Thus, even pilots transitioning

into turbine types for the first time were, presumably, experienced in the principles and practices of

helicopter flight.

6.4.3.6 Loss of Control by PIC Certification Level. The last characteristic of loss of control

accidents analyzed was the reported certification level of the PIC. The results are shown in figure 66.

For loss of control accidents involving single-turbine helicopters, an overwhelming majority of

accidents involved PICs with commercial or higher certified ratings at the controls. This statistic

supports the analysis by activities, which concluded that the difference in mission-type distribution

was due to the greater use of single-turbine helicopters for commercial purposes than single-piston

helicopters.

6.4.3.7 Conclusions About Loss of Control Accidents. Of the 8,436 rotorcraft accidents recorded

by the NTSB from mid-1963 through the end of 1997, 2,247 involved single-turbine-engine-
54

powered helicopters that were commercially manufactured. Of these, 284 (or roughly 13%) were

attributed to loss of control.

There is little evidence that low rotor RPM was a serious problem with the single-turbine helicopter,

at least as a contributing factor to loss of control accidents. This improvement, relative to the singlepiston helicopter, is attributed to the better engine speed governing provided by turbine-engine fuel

controls. However, loss of yaw control was nearly twice as prevalent with the single-turbine

helicopter fleet as it was with the single-piston helicopter fleet. On the positive side, single-turbine

helicopters experienced proportionally fewer loss of control accidents in the vertical axis than the

single-piston helicopters.

There were significant differences in loss of control accidents involving single-turbine helicopters

and piston-engine helicopters. Single-turbines experienced proportionally more loss of control

accidents during commercial operations and fewer in training or personal use operations.

The accident rate per 1,000 registered aircraft showed an extremely high peak during the time this

helicopter type was coming into wide civil aviation use. Since then, the rate shows an irregularly

decreasing trend. The raw numbers of loss of control accidents jumped in the early 1980s and

remained high through 1997.

6.4.4 Airframe/Component/System Failure or Malfunction (282 Accidents)

The introduction of helicopters powered by a single-turbine engine required the rotorcraft industry

to engineer and manufacture an aircraft with a much higher power-to-weight ratio. Virtually every

component found on the lower power, piston-engine helicopter required strengthening. Adequately

designing for fatigue loads became even more important. Increased system complexity, such as

adding hydraulic boosted controls, became more prevalent.

The single-turbine helicopter allowed an expanded flight envelope in speed, altitude, and

maneuvering capability. Frequently, within this expanded flight envelope, operational experience

showed the new aircraft to be under-designed, which required the industry to retrofit various

components and parts. In addition, the industry saw that the user community had found new

applications for its helicopters, and many of these new applications had not been considered in the

design of first-generation, single-turbine helicopters.

6.4.4.1 Overall Accident Trends. The NTSB cited airframe/component/system failure or

malfunction (again referred to from here on as airframe failure) in 282 accidents involving the

single-turbine helicopter fleet during the 34-year study period. These accidents directly affected 705

people: 157 were killed, 110 were seriously injured, and 438 survived with minor or no injuries. Of

the 282 helicopters involved, 111 were listed as destroyed by the NTSB, 163 were substantially

damaged, and 8 received little or no damage. Figure 48 shows that the number of airframe failure

accidents per year grew in a nearly linear manner during the first 17 years of the study period. This

trend is a partial measure of the industry’s problems as the first-generation single-turbine helicopters

grew to maturity. After a peak in 1982, airframe failure accidents began to drop and than leveled off.

Following the widespread introduction of single-turbine helicopters in the early 1970s, airframe

failure accidents (as a percentage of all single-turbine helicopter accidents) grew from about 10% in
55

1971 to over 15% in 1997 (fig. 67). Accidents per 1,000 registered single-turbine helicopters showed

continuous improvement from 1972 until 1991. After 1991, however, airframe failures remained

constant at about 2.5 per year per 1,000 registered single-turbine helicopters (fig. 67). This is

believed to be a reflection of the increased maturity of single-turbine engine helicopter designs and

the increasing familiarity of designers, manufacturers, and maintainers with this aircraft class.

6.4.4.2 Airframe Failures by Phase of Operation. The single-turbine helicopter fleet experienced

the most airframe failures while in cruise (fig. 68). These 107 accidents accounted for 38% of the

282 accidents, slightly more than the single-piston helicopter fleet's 33% (fig. 40). Accidents during

the maneuvering flight phase were relatively infrequent for the single-turbine helicopter. This

contrasts with single-piston helicopters, which are used more extensively in aerial application

activities. There were 83 accidents in the hovering and takeoff flight phases of passenger service and

general utility activities (fig. 68).

6.4.4.3 Airframe Failures by Activity. Figure 69 shows that the single-turbine helicopter fleet had

the most airframe failure accidents while engaged in general utility and passenger service activities.

This was in sharp contrast to the single-piston helicopter fleet experience (fig. 41). As noted earlier,

aerial application did not appear to be an activity for which modern single-turbine helicopters were

extensively used.

6.4.4.4 Airframe Failures by System/Component. For the 282 airframe failure accidents

involving commercially manufactured, single-turbine helicopters, the many detailed categories were

combined into the 10 major categories shown in figure 70. These 10 categories compare directly to

those for the single-piston helicopter fleet (fig. 42). When compared on a percentage basis, as

presented in table 20, it becomes clear that both single-engine helicopter types experienced virtually

the same airframe failure problems. If anything, single-turbine helicopters had more main rotor,

fuselage, and other subsystem failures than single-piston helicopters.

It is evident from figure 70 and table 20 that the drive system—to both main and tail rotors

combined—and the two rotor systems were the most significant problem areas in airframe failure

accidents with the single-turbine helicopter fleet. Over 67% of the 282 airframe failure accidents

were caused by transmissions, drive shafts, blades, and hub failures. As discussed earlier, the change

from piston to turbine engine improved helicopter safety. It is not evident from table 20, however,

that corresponding improvements to the remaining major airframe systems were achieved.

The failure mode terminology used by NTSB accident investigators is matrixed with the major

rotorcraft systems in table 21 to summarize the airframe accident count. (A comparable summary

for the single-piston helicopter was provided in table 8.)
56

TABLE 20. SINGLE-ENGINE-HELICOPTER AIRFRAME FAILURE COMPARISON,

1963–1997

Single piston Single turbine

Airframe major systems Count % Count %

Drive train—main 127 19.9 49 17.3

Drive train—tail 119 18.6 54 19.1

Main rotor 57 8.9 36 12.8

Tail rotor 124 19.4 52 18.4

Control system—main 63 9.9 29 10.3

Control system—tail 38 5.9 11 3.9

Airframe (fuselage, other subsystems) 64 10.0 41 14.5

Landing gear 24 3.8 2 0.7

Engine 7 1.1 3 1.1

Undetermined/other 16 2.5 5 1.8

Total 639 100 282 100

Following the earlier discussion format used to examine the single-piston helicopter airframe

failures, figure 70 offers a convenient outline from which more detail about each system/

subsystem/component/part failure or malfunction can be examined. Consider first the number of

accidents caused by failures in the main and tail drive trains.

6.4.4.4.1 Drive train failures by subsystem: Figure 70 shows that the drive train from the

engine to the main and tail rotors was implicated in a total of 103 (i.e., 36%) of the 282 accidents

involving single-turbine helicopters during the study period. Table 22 gives the number of accidents

caused by lower-level-subsystem failures within the drive train.

Failure to transmit power from the engine to the main rotor gearbox accounted for 35 of the 49 main

rotor drive train accidents (table 22). Failure to transmit power along the tail rotor drive shaft caused

32 of the 54 tail rotor drive train accidents charged to this subsystem. Taken together, component

failures in these two subsystems caused 67 accidents. This approximately parallels single-piston

helicopter experience shown in table 9.

The components most frequently failing to (1) transmit power between the engine and the main rotor

gearbox and (2) transmit power from the main rotor gearbox to the tail rotor gearbox caused the

number of accidents shown in table 23.

It should be noted that the clutch assembly accounted for the largest number of single-piston

helicopter accidents, as enumerated in table 10. Clearly, improvement in this component’s design

and operation was achieved, as table 23 shows. In contrast, relatively little improvement (on a

percentage basis) was achieved in the tail rotor drive shaft components.
57

TABLE 21. NTSB FAILURE MODE/SYSTEM MATRIX—SINGLE-TURBINE

HELICOPTERS

Failure mode

Drive

system

Rotor

system

Control

system

Airframe

LG

All

other Total

Fatigue 26 21 5 17 1 70

Improper assembly, installation,

maintenance 15 5 14 4 1 39

Material failure 0 30 0 0 0 30

Undetermined/not reported 6 6 5 7 2 26

Failed 15 3 1 5 0 24

Separated 13 3 4 1 1 22

Foreign object damage 8 11 0 2 0 21

Overload 9 0 2 0 0 11

Pilot action/operational issue 2 0 1 5 3 11

Lack of lubrication 0 6 0 0 0 6

Slippage 1 0 5 0 0 6

Disconnected 4 0 0 1 0 5

Blade-airframe strike 1 0 2 1 0 4

Delaminated/debonded 1 3 0 0 0 4

Bearing failure 2 0 0 0 0 2

Bent/binding/jammed 0 0 1 0 0 1

Hydraulic leak/lock 0 0 0 0 0 0

Total 103 88 40 43 8 282

TABLE 22. DRIVE TRAIN FAILURES BY COMPONENTS—

SINGLE-TURBINE HELICOPTERS

Drive train—main 49

Engine to transmission drive 35

Main rotor gearbox 8

Main rotor mast 6

Drive train—tail 54

Tail rotor driveshaft 32

Tail rotor gearbox 22
58

TABLE 23. DRIVE TRAIN MAJOR COMPONENT FAILURES—

SINGLE-TURBINE HELICOPTERS

Engine to transmission drive 35

Clutch assembly 8

Freewheeling unit 9

Torsion coupling 13

Shaft 5

Tail rotor drive shaft 32

Driveshaft 16

Coupling 13

Hang bearing 3

The tail rotor gearbox was the second largest contributor to tail rotor drive train failures for singleturbine helicopters (table 22). Failures occurred within the gear train and its rotating components.

Failures in the gearbox case and aircraft mounting points were frequently noted. The primary failure

mode of drive train components was fatigue.

The basic similarity in failure modes for the single-turbine and single-piston helicopter fleets

implies that general improvements in materials and component design will be applicable to and

benefit both of these major rotorcraft types.

6.4.4.4.2 Rotor failures by subsystem: Figure 70 shows that the main and tail rotor systems

were implicated in a total of 88 single-turbine helicopter accidents (i.e., 31% of the 282) during the

period studied. The accident count of rotor system failures at a lower subsystem/component level is

provided in table 24. Table 25 summarizes the accidents in relation to the prevalent failure mode for

both main and tail rotors.

TABLE 24. ROTOR SYSTEM FAILURES BY COMPONENTS—

SINGLE-TURBINE HELICOPTERS

Main rotor 36

Main rotor blade 12

Main rotor hub 14

Main rotor system 10

Tail rotor 52

Tail rotor blades 12

Tail rotor hub 5

Tail rotor system 35
59

TABLE 25. ROTOR SYSTEM COMPONENTS FAILURE MODE—

SINGLE-TURBINE HELICOPTERS

Subsystem/component failure

mode

Main

rotor

blade

Main

rotor

hub

Main

rotor

system

Tail

rotor

blades

Tail

rotor

hub

Tail

rotor

system Total

Foreign object damage 0 0 4 0 0 26 30

Fatigue fracture 3 9 0 6 3 0 21

Separated 3 1 0 3 0 4 11

Not reported 1 1 0 1 0 4 7

Material failure 3 1 0 0 2 0 6

Blade-airframe strike 0 0 6 0 0 0 6

Delamination 2 1 0 2 0 0 5

Improper assembly 0 1 0 0 0 1 2

Overload 0 0 0 0 0 0 0

Total 12 14 10 12 5 35 88

The contrast between this single-turbine helicopter experience (tables 24 and 25) and single-piston

helicopter experience is provided in tables 11 and 12. For example, where main rotor blades

accounted for 49% of the 57 single-piston helicopter main rotor failures, only 33% of the 36 singleturbine accidents were attributable to this component. In fact, main rotor hub failures accounted for

most of this subsystem’s failures for single-turbine helicopters.

Foreign object damage (FOD) to the tail rotor was a significant problem in the operation of singleturbine helicopters (table 25). In the 26 accidents, 6 involved external loads or associated equipment,

6 involved unsecured items from the aircraft cabin, 1 involved the loss of an aircraft exit hatch, 1

was caused by flight through the debris cloud of a planned motion picture production explosion, and

12 were unspecified. Approximately the same number of accidents involved the main rotor head as

the main rotor blades. Fatigue, material failures, and delamination were the major blade problems

that resulted in accidents, especially for the main rotor hub. This distribution is similar to that of the

single-piston helicopters (table 12). However, improper assembly was a less significant problem for

single-turbine helicopters. This may be the result of more stringent maintenance procedures and

oversight for the more complex (and expensive) turbine fleet as opposed to that of the relatively

simpler piston aircraft. As was discussed for single-piston helicopter accidents, main rotor system

failures associated with blade-to-airframe strikes tended to be very severe and generally resulted in

fatalities.

Finally, just as for single-piston helicopters, improvements in the design, construction, and

maintenance of main rotor system components represent an important opportunity for reduction of

serious helicopter accidents.
60

6.4.4.4.3 Control system failures by subsystem: Forty single-turbine helicopter accidents

were attributed to failures or malfunctions in the main and tail rotor flight control systems (fig. 70).

A breakdown to lower level subsystems/components is provided by accident count in table 26.

TABLE 26. CONTROL SYSTEM FAILURES BY COMPONENTS—

SINGLE-TURBINE HELICOPTERS

Main rotor controls 29

Lower controls—cyclic 9

Lower controls—collective 1

Upper controls—swashplate assembly 4

Upper controls—pitch link 2

Upper controls—other 3

Hydraulic 10

Tail rotor controls 11

Lower controls—cable 5

Lower controls—other 1

Upper controls—swashplate assembly 2

Upper controls—pitch link 3

Upper controls—other 0

Controls—other 0

No modern single-turbine helicopter was found that uses stabilizer bar/paddle such as the “Bell bar”

or the “Hiller servo-paddle.” Instead, the rotorcraft industry moved to hydraulically boosted control

systems. As table 13 summarizes, 12 stabilizer bar/paddle failures occurred out of 63 main rotor

flight control accidents with the single-piston helicopter fleet. In a sense then, the 10 of 29 main

rotor flight control accidents with the single-turbine helicopter fleet represents a substantial step

backward. Nevertheless, the lower pilot workload offered by boosted controls is considered by the

industry as a plus.

As was the case with single-piston helicopters, improper assembly or installation—primarily in the

lower controls—was the most frequent factor identified for single-turbine helicopter flight control

system failure accidents. This issue was discussed in some detail for single-piston helicopter flight

control failures, and the conclusions and recommendations are equally applicable to single-turbine

helicopters.

6.4.4.4.4 Airframe failures by components: Figure 70 shows that failures of the fuselage

structure, landing gear, and other airframe-associated components accounted for 43 (i.e., 15%) of the

282 single-turbine helicopter accidents during the 34-year study period. Table 27 shows that

tailboom failures and subsystems that support operation of other major systems (i.e., engine, etc.)

were major contributors to this category. Evidently, the increase in complexity of single-turbine
61

helicopters was accompanied by an increase in accidents. Although the percentage of airframe

failures was comparable to that of single-piston helicopters’ experience (table 14), decreased

numbers of landing-gear-related accidents (from 24 to 2) was substantial; earlier ground resonance

accidents (caused primarily by inadequate maintenance) were virtually eliminated.

TABLE 27. AIRFRAME-SPECIFIC FAILURES BY COMPONENTS—

SINGLE-TURBINE HELICOPTERS

Airframe and landing gear 43

Landing gear 2

Tailboom 10

Other systems 6

Support assembly 6

Other systems (engine) 11

Stabilizer-horizontal 0

Miscellaneous equipment 3

Stabilizer-vertical 5

Tailboom failure caused 10 accidents, one-half of which were caused by fatigue fractures. NTSB

investigators noted corrosion as a factor in very few of the fuselage component failures. The six

fatigue failures associated with main gearbox support assemblies led to complete separation of main

rotor gearbox and rotor system from the helicopter.

A substantial reduction in failures caused by improper assembly, installation, and maintenance was

achieved with the single-turbine-helicopter fleet, as the accident count shows (table 28). This can be

seen when compared with similar failures in single-piston helicopters (table 15). With that

exception, fatigue failures were, on a percentage basis, quite comparable for the two helicopter

types.

6.4.4.4.5. Conclusions about airframe failure or malfunction accidents: Of the 8,436

rotorcraft accidents recorded by the NTSB from mid-1963 through the end of 1997, 2,247 accidents

involved commercially manufactured, single-turbine-engine-powered helicopters. Of these, 282, or

12%, were attributed to failure or malfunction of the airframe, or some system or component

associated with the airframe. Drive and rotor system failures, primarily in the hover, takeoff, and

cruise flight phases, accounted for 191 of the 282 accidents.

Single-turbine and single-piston helicopters show quite comparable airframe failures on a

percentage basis. The engine to transmission and the tail rotor drive systems (i.e., shaft and gearbox)

accounted for 89 of the 103 drive system related accidents. Main and tail rotor system failures,

primarily caused by fatigue, led to an additional 88 accidents. The pilot was left without antitorque

and directional control in over 125 of the 282 accidents, because a tail rotor drive train, rotor system,

rotor control, or a tailboom failed or malfunctioned.
62

TABLE 28. AIRFRAME COMPONENTS FAILURE MODE—

SINGLE-TURBINE HELICOPTERS

Subsystem/component

failure mode

Landing

gear

Tail

boom

Other

systems

Support

assy

Other

systems

(engine)

Stabilizer

(horizontal)

Misc

equip

Stabilizer

(vertical) Total

Fatigue 2 4 2 3 1 0 0 5 17

Improper assembly,

install, maintenance 0 1 0 0 3 0 0 0 4

Failed 0 1 0 1 1 0 2 0 5

Undetermined/not

reported 0 0 1 0 5 0 1 0 7

Material failure 0 0 0 1 0 0 0 0 1

Pilot action and

operational issues 0 3 1 0 1 0 0 0 5

Disconnected/separated 0 0 2 1 0 0 0 0 3

Overload 0 1 0 0 0 0 0 0 1

Bent/binding/jammed 0 0 0 0 0 0 0 0 0

Total 2 10 6 6 11 0 3 5 43

Taking an overall look at the single-turbine helicopter accident history resulting from

airframe/component/system failure or malfunction, the conclusion appears to be that fatigue caused

more airframe failure accidents in single-turbine helicopters than any other single factor. Following

fatigue failures, several other factors contributed in more or less equal proportions to the overall

airframe failure problem.

Lubrication failures in the rotor drive systems were, on a fatal accident percentage basis, the most

severe. Loss of lubrication to the gearboxes, shafts, bearings, and control systems normally resulted

in, at best, a marginally controllable situation and an immediate forced landing. However, these

failures were fairly rare—only 10 over the study period. Again, component fatigue was a serious

problem area. There is evidence that failures caused by operational errors (e.g., intentional repeated

operation of the aircraft beyond its limits) tended to result in severe accidents, both from the aircraft

damage and fatality perspective. As in the case of lubrication failure, operational error accidents

tended to be infrequent, but the toll was high.

6.5 Summary Remarks, Conclusions, and Recommended Actions

The registered fleet of commercially manufactured, single-turbine helicopters grew from fewer than

100 at the end of 1963 to approximately 5,000 by the end of 1997. During this period, this growing

fleet had 2,247 accidents. The NTSB grouped these accidents into 21 different categories. However,

as figure 71 shows, 92% of the accidents fell into eight categories and, in fact, four categories

accounted for 70% of all the accidents.
63

A summary of these accidents by activity and phase of operation, table 29, shows that most singleturbine helicopter accidents occurred during passenger service and general utility activities. Takeoff,

cruise, and landing constituted the primary operations of these activities, and that was when most

accidents occurred.

TABLE 29. ACCIDENTS BY ACTIVITY AND PHASE OF OPERATION—

SINGLE-TURBINE HELICOPTERS

Activity Phase of Operation

Passenger service 642 Cruise 633

General utility 520 Takeoff 353

Business use 209 Landing 301

Personal use 200 Maneuvering 270

Aerial application 150 Hover 247

Ferry/reposition 135 Approach 146

Instructional/training 127 Standing/static 97

Executive/corporate 97 Descent 73

Public/military use 93 Unknown/other 47

Flight/maintenance test 67 Taxi 40

Unknown/not reported 7 Climb 40

Total 2,247 Total 2,247

The following study findings are for the four top accident categories:

1. Loss of engine power because of improper fuel/air mixture caused 299 accidents of

which 151 were caused by fuel exhaustion, fuel starvation, or fuel contamination.

2. Loss of engine power because of engine structural failure caused 189 accidents.

3. Loss of engine power for undetermined reasons was recorded in 181 accidents.

4. In flight collision with man-made objects accounted for 213 of 298 accidents.

5. In flight collisions with wires and wire/poles accounted for 151 accidents; there were

only 50 collisions with trees.

6. Loss of control in yaw contributed no fewer than 75 accidents and, on a percentage basis,

as many as 140 accidents.

7. Loss of directional control was nearly twice as prevalent with single-turbine helicopters

as with single-piston helicopters, on a percentage basis.
64

8. Loss of control was experienced regardless of the PIC certification.

9. Drive train failures caused 103 accidents, of which engine to transmission and tail rotor

drive shaft failures contributed 67 airframe failure accidents.

10. Rotor system failures caused 88 accidents, of which the tail rotor system accounted for

52 accidents.

11. Control system failures caused 40 airframe failure accidents.

12. The pilot was left without antitorque and directional control in 127 of the 282 airframe

failure accidents.

13. An autorotation took place in about 800 of the 2,247 accidents.

The most frequently occurring accident types were not the accident types that caused the highest

fatality rate (i.e., fatalities per 100 accident). The greatest risk of fatality was in midair collisions, of

which 37 occurred killing 66 people. Figure 72 shows the number of fatalities per 100 accidents by

NTSB first event category. Airframe failure, in flight collision with object, and loss of control

accidents clearly had the highest fatality rate. Note that loss of engine power, the greatest cause of

accidents, had a relatively low fatality rate. When ordered in terms of total fatalities, as tabulated in

figure 72, airframe failures were the leading cause of fatalities with the single-turbine helicopter

fleet.

Before discussing twin-turbine helicopter fleet accidents, several observations and recommended

actions relative to the single-turbine helicopter fleet can be set forth. Unquestionably, single-turbine

helicopters have an improved safety record over that of single-piston helicopters. The most reliable

evidence, gathered in 1989, suggests that the improvement amounts to a reduction by a factor of 3 in

accidents per 100,000 fleet flight hours (i.e., 14.5 single-piston helicopter accidents per 100,000

flight hours vs. 4.7 single-turbine helicopter accidents per 100,000 flight hours).

This safety improvement is impressive, but there is little evidence suggesting that single-turbine and

single-piston helicopters differ in the distribution of first event accident cause. For example, loss of

engine power was the first event in approximately 30% of the accidents for both types of helicopters.

Fuel exhaustion, fuel starvation, or fuel contamination were just as prevalent with each helicopter

type, on a percentage of total accidents basis. The apparent disregard by many pilots of the engine’s

need for clean fuel and air in proper proportions (to say nothing about the FAA regulations for fuel

reserves) was just as characteristic of the single-turbine helicopter fleet as it was of the single-piston

helicopter fleet. Despite the different types of activities in which the two single engine helicopter

types engaged, loss of control in yaw was equally likely, on a percentage of total accidents basis.

However, there were considerably fewer in flight collisions with man-made objects with the singleturbine helicopter, probably because single-turbine helicopters were less frequently used in

agricultural operations.

In 1997, there were 15 accidents per 1,000 registered commercially manufactured, single-turbine

helicopters, a rate similar to that of the average of 18 accidents per 1,000 aircraft from 1986 through

1996. However, the single-turbine helicopter experience virtually paralleled that of the single-piston
65

helicopter (on a percentage of total fleet basis). Therefore, it is projected that little improvement will

occur by the year 2010 if no more than “a-business-as-usual” effort is made by the rotorcraft

industry. Therefore, it is recommended that all but one of the several specific corrective actions for

single-piston helicopters (sec. 5.4) be directly applied to the single-turbine helicopter fleet. The one

exception is automated RPM control already incorporated in turbine engine fuel control systems.

On a final note, single-turbine helicopter accidents per year increased slightly over the last decade of

the period studied: there were 62 accidents in 1987, 65 in 1993, and 73 in 1997, during which time

the registered single-turbine helicopter fleet increased only modestly in size. Most recently, new

single-turbine helicopters were being registered at a rate comparable to that of the 1970s. There is

concern, therefore, that a rapid fleet expansion will prompt an increase in accidents just as it did

with the single-piston helicopter fleet. For this reason, it is recommended that more intensive safety

improvement efforts be quickly initiated by the industry.
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THIS PAGE INTENTIONALLY BLANK
67

7. COMMERCIAL TWIN-TURBINE ENGINE HELICOPTERS

7.1 Fleet History and Growth

Helicopters powered by two turbine engines were introduced into the civil fleet in 1961. At that

time, several helicopter airlines operated scheduled mail and passenger service. Each hoped that

Sikorsky S-61s, S-62s, or Vertol 107s would dramatically lower their operating costs from the level

experienced using the piston-powered Bell 47s, Sikorsky S-51s, S-55s, S-58s, and Vertol V-44Bs.* In

fact, the introduction of twin-turbine helicopters was not immediately followed by great demand and

the civil fleet grew relatively slowly (fig. 73). In the early 1970s, following a number of widely

publicized, high-fatality accidents, and the termination of government mail subsidies, the Part 121

helicopter airlines ceased operations. In 1972, Bell began delivering its 212 series (based on the

military UH-1N), followed shortly by Aerospatiale’s SA-330J Puma series and MBB’s BO-105

series. Sikorsky’s S-76 series became available in 1977 and by 1980 Boeing Vertol offered its 40–45

passenger Model 234, based on the U.S. Army’s CH-47 Chinook. This significant growth in the

twin-turbine helicopter fleet during the 1980s was fueled by primarily corporate and offshore oil

customers. However, after almost 40 years and substantially improved twin-turbine-powered

helicopters, a flourishing scheduled helicopter airline industry in the U.S. has yet to be established.

7.2 Twin turbine vs. Single turbine

Twin-turbine-engine helicopters were developed for two reasons. First, in many cases, no singleturbine engine of sufficient power was available to meet the payload requirements of larger

helicopters. Second, there was an industry-wide perception that two engines would improve safety.

This perception is potentially misleading, if not even false, whenever the twin-engine helicopter is

unable to continue flight with one engine inoperative. Fortunately, modern twin-engine helicopters

offer adequate one-engine-inoperative performance.

Twin-turbine helicopters demonstrated further improvement in annual accidents per 1,000 registered

aircraft when compared with single-turbine helicopters (fig. 74). Although this statement may not

apply to the first 15 years of its civil use, experience since 1990 seems indisputable. Twin-turbine

accidents plateaued during the 1990s suggesting that 10 accidents per 1,000 registered aircraft might

be a minimum, given current technology and operations. This might, however, be an unfortunate

conclusion based on figure 74.

The distribution, over the NTSB’s 21 first event categories, of the 302 twin-turbine accidents over

the 34-year period of this study is provided in figure 75. Loss of engine power ceased to be the

leading accident factor for helicopters powered by two turbine engines. Rather, the 302 accidents in

this rotorcraft class were dominated by airframe and system failures. Twin-turbine helicopters also

experienced a significantly different accident first event category distribution than did the single

engine (piston or turbine) helicopter fleet. This point is illustrated in table 30.

 *Reference 19 notes that this early experience with piston-powered helicopters operating in a mail, freight, and

passenger carrying mode was anything but profitable for Chicago Helicopter Airways, Los Angeles Airways, and New

York Airways, and later San Francisco and Oakland Helicopter Airlines.
68

TABLE 30. SINGLE-TURBINE VS. TWIN-TURBINE ACCIDENT DISTRIBUTION

COMPARISON, 1963–1997

Single turbine Twin Turbine

NTSB category Count % Count %

Loss of engine power 704 31 39 13

In flight collision with object 298 13 43 14

Loss of control 284 12 40 13

Airframe/component/system failure or malfunction 282 12 89 29

Hard landing 140 6 8 9

In flight collision with terrain/water 143 6 16 5

Rollover/nose over 119 5 4 1

Other 277 12 63 21

Total 2,247 100 302 100

The top four first event accident categories remained the same for the two helicopter classes, as table

30 shows; but a different order appeared. Engine malfunctions and airframe failures reversed

themselves on a percentage basis. The top four categories accounted for 70% of the accidents for

each helicopter type, but the remaining categories were quite different. For example, “other”

increased from 10% to 21% (with more detail provided by comparing figure 75 to figure 47). A

more meaningful comparison on a percentage basis (fig. 76) shows that in 17 first event categories,

twin-turbine helicopter accidents exceeded single-turbine helicopter accidents. Although gear

collapsed might easily be reclassified as an airframe failure, the differences in on ground/water

collision with object, propeller/rotor contact to person, and fire/explosion are of concern.

7.3 Accident Analysis

Twin-turbine helicopter accident trends are shown in figure 77. Since 1992, a favorable trend

occurred in the top four categories as a group. Accidents in the other 17 categories were randomly

distributed, averaging 3 to 4 a year. Table 31 contrasts twin-turbine accident counts from 1992

through 1997 with the entire 34-year study period. On a percentage basis, only minor changes

appear evident.

The overall picture suggests that the twin-turbine helicopter demonstrated its maturity in civil

operations by the very early 1990s, approximately 15 years after second-generation models, such as

Bell 212s, Aerospatiale’s SA-330J Puma, and MBB’s BO-105 became operational. Based on the 12

years from 1985 through 1997, it appears that yearly twin-turbine helicopter accidents per 1,000

registered aircraft will drop below 5 per year by 2010 (fig. 78). The implication is that the 1991–

1997 rates do not represent a minimum, as figure 74 might suggest, but rather a broad point in the

12-year experience.
69

TABLE 31. TWIN-TURBINE ACCIDENT DISTRIBUTION, LAST 5 YEARS VS. 1963–1997

1992–1997 Last 34 years

NTSB category Count % Count %

Loss of engine power 14 10 39 13

In flight collision with object 19 13 43 14

Loss of control 21 15 40 13

Airframe/component/system failure or malfunction 39 27 89 29

Hard landing 3 2 8 3

In flight collision with terrain/water 11 8 16 5

Rollover/nose over 1 1 4 1

Other 35 25 63 21

Total 143 100 302 100

7.4. Detailed Analysis by Accident Type

Commercially manufactured, twin-turbine helicopters accounted for 302 of the 8,436 rotorcraft

accidents. Approximately 70% were associated with four first event categories, paralleling singleengine helicopter experience. Therefore, a more in-depth analysis of the four top categories provides

considerable insight into the differences between single and twin configurations from 1963 through

1997. The next several paragraphs analyze these top four categories in some depth, even though

302 accidents is a relatively small sample of experience from which to infer trends.

7.4.1 Loss of Engine Power (39 Accidents)

As table 30 shows, introduction of twin-turbine helicopters to the civil fleet dramatically reduced the

percent of loss of engine power accidents from 31% to 13%. However, table 32 suggests that a very

disturbing trend began when larger helicopters capable of carrying more people were introduced:

any serious accident affects more people and likely receives greater attention by the public. This

trend exactly parallels the situation faced by the fixed-wing industry as they moved from the 1920s

Ford Tri-motor to modern day, large jet airliners, such as the Boeing 747.
70

TABLE 32. FATALITIES PER 100 ACCIDENTS BY TYPE OF ENGINE, 1963–1997

Engine type

Loss of engine power

accidents Fatalities

Fatalities per

100 accidents

Single piston 1,554 106 7

Single turbine 704 129 18

Twin turbine 39 16 41

7.4.1.1 Overall Accident Trends. From 1963 through 1997, loss of engine power was the first

event in 39 of the 302 accidents involving twin-turbine helicopters. The 39 accidents directly

affected 140 people; 16 were killed, 26 were seriously injured, and 98 survived with minor or no

injuries. Of the 39 helicopters involved, 13 were listed by the NTSB as destroyed, 21 were

substantially damaged, and 5 received little or no damage. Twin-turbine helicopter yearly accidents

per 1,000 registered aircraft remained relatively constant from 1990 through 1997 (fig. 74). A

contributing factor to this apparent plateau was the increase in loss of engine power accidents, as

shown in figure 79.

7.4.1.2 Loss of Engine Power by Category. The NTSB cited the reason for loss of engine power

in 33 of the 39 accidents. Table D-12 lists 18 primary reasons for the 39 accidents, and figure 80

groups them by major subsystems. Fuel/air mixture problems caused 17 of the 33 accidents. A

closer inspection of figure 80 and the associated mini-briefs reveals that fuel exhaustion, fuel

starvation, fuel contamination, etc. were, on a percentage basis, just as prevalent with twin-turbine

helicopters as with single-piston and single-turbine helicopters.

Total or partial loss of engine power is a key issue for twin-engine-powered helicopters. Pilots of

twin-turbine helicopters, faced with performing a total power-off landing, appeared no more

successful at the task than pilots of single-engine helicopters. From 1963 through 1997, 23 of the

39 accidents (i.e., nearly 60%) began with a total loss of power from both engines. In fact, even with

partial loss of power in 16 of the 39 accidents, 5 helicopters were destroyed, 10 received substantial

damage, and only 1 was landed with minor damage.

Pilot proficiency in accomplishing total or partial power-off landings appears insufficient. A possible

explanation is that the chances of a dual-engine failure are perceived to be very low and, in many

cases, the approved aircraft flight manual does not permit touchdown autorotations. If power-off

landings are practiced at all, they are practiced in simulators of questionable fidelity.

7.4.1.3 Loss of Engine Power by Activity. Most twin-turbine helicopter loss of power accidents

occurred during passenger service and general utility activities (fig. 81). The twin-turbine

configuration allowed the rotorcraft industry to expand passenger service beyond the capability

provided by single-turbine helicopters (ref. 16). This, in many ways, is how the public was

introduced to airline transportation when single- and multi-engine airplanes from World War I were

converted from military to civilian use.
71

7.4.1.4 Loss of Engine Power by Phase of Operation. Loss of engine power was experienced

during every flight phase (fig. 82). Although most (13) occurred in cruise flight, high-power

operations (low-speed/low-altitude maneuvering, takeoff, and hover), taken together, accounted for

18 loss of engine power accidents. Neither single-piston (see fig. 26) nor single-turbine helicopters

(see fig. 54) had the same pattern of loss of engine power accidents in high-power situations vs.

cruise.

7.4.1.5 Conclusions About Loss of Engine Power Accidents. Of the 8,436 rotorcraft accidents

recorded between mid-1963 and the end of 1997, 302 involved commercially manufactured, twinturbine helicopters. Of the 302 accidents, 39, or roughly 13%, of these accidents were attributed to

partial (16) or total (23) loss of engine power. No fewer than 17 accidents, roughly 44%, were

directly traced to fuel/air mixture problems paralleling experiences of both single-piston and singleturbine helicopters. However, there have been relatively few loss of engine power accidents with

twin-turbine helicopters. Therefore, statistically meaningful trends remain open to question.

7.4.2 In Flight Collision with Object (43 Accidents)

The twin-turbine helicopter fleet demonstrated no reduction (on a percentage basis) of in flight

collision with objects accidents when compared with the single-turbine helicopter fleet (table 30).

Furthermore, many of the trends observed about single-turbine helicopters were also found with the

more expensive twin-turbine helicopters.

7.4.2.1 Overall Accident Trends. The NTSB implicated in flight collision with object in 43 twinturbine helicopter accidents from 1963 through 1997. These accidents affected 175 people:

35 received fatal injuries, 29 suffered serious injuries, and the remaining 111 survived with minor or

no injuries. Of the 43 helicopters involved, 16 were listed by the NTSB as destroyed, 25 were

substantially damaged, and 2 received little or no damage. As figure 83 shows, in flight collision

with object accidents leveled off at about 12% of twin-turbine helicopter accidents, but with

significant year-to-year variability. From 1987 through 1997, the trend was one to two accidents per

year per 1,000 registered aircraft.

7.4.2.2 Collision with Object by Object Hit. Figure 84 shows that pilots of twin-turbine

helicopters were—on a percentage basis—nearly as prone to hitting wires and trees as pilots of

single-engine helicopters (see figs. 28 and 56). What stands out in figure 84 are the 12 collisions

associated with airport/helipad facilities. Upon reviewing the 12 mini-briefs listing these collision

with object accidents, nine objects were protuberances around the heliport (six on offshore oil rig

platforms, one stairwell at a hospital, one crane at a building site, one jetway gate). A tail rotor was

swung into a hanger, a barge rising and falling was an inadequate heliport, and the object was

unspecified in the last mini-brief reviewed.

7.4.2.3 Collision with Object by Cause. Figure 85 shows that improper pilot decision-making was

the cause of most collision with object accidents, although more than one factor was often involved.

This required proportioning one accident into part causes. The corresponding interpretation of the

results for single-engine helicopters is provided in figures 57 and 29. Improper decision includes

poor planning, inadequate training, and misjudging clearances.
72

7.4.2.4 Collision with Object by Activity. The twin-turbine helicopter fleet rapidly became the

helicopter of choice for passenger transport operations. Thus, it is not surprising that 44% of 43

accidents occurred during passenger service activity (fig. 86). Note that ferry and repositioning

accounted for another 16% of the 43 accidents.

7.4.2.5 Collision with Object by Phase of Operation. Figure 87 shows that operation during

takeoff and landing accounted for a total of 21 of the 43 accidents. Preparations prior to takeoff,

such as taxi and hover, accounted for another 11 accidents. Actual cruise flight was a relatively lowrisk phase of operation.

7.4.2.6 Collision with Object by Part Hit. The NTSB mini-briefs provided information about the

part of the helicopter that struck the object in only 14 cases. For those 14 examples, 75% were tail

rotor strikes (fig. 88). Only four cases of main rotor strikes were noted.

7.4.2.7 Conclusions About In flight Collision with Object Accidents. Of the 8,436 rotorcraft

accidents recorded by the NTSB during the 34-year period from mid-1963 through the end of 1997,

302 accidents involved commercially manufactured, twin-turbine helicopters. Of the 302 accidents,

43, or roughly 14%, were attributed to in flight collision with object. This experience directly

parallels single-turbine helicopter experience when compared as a percentage of total accidents.

Most collisions occurred while the twin-turbine helicopter was engaged in passenger service to and

from offshore oil rigs. There were 13 wire-strike accidents and 12 objects attached to the

airport/helipad landing site were struck. Limited data suggest that twin-turbine helicopters were at

least twice as prone to tail rotor strikes as main rotor strikes.

7.4.3 Loss of Control (40 Accidents)

Twin-turbine helicopters constituted only about 10% of the total rotorcraft fleet in 1997. Thus, as

might be expected, the number of loss of control accidents involving twin-turbine helicopters was a

small fraction of the total number of loss of control accidents—a little over one per year. The

number of twin-turbine helicopter accidents in this first event category grew slowly and irregularly

as the twin-turbine fleet increased.

7.4.3.1 Overall Accident Trends. The NTSB cited loss of control as the first event in 40 twinturbine helicopter accidents of the 302 total (13%) from 1963 through 1997. The number of

accidents by year (fig. 89) appears nearly random, both as a percentage of total annual accidents and

in annual accidents per 1,000 registered twin-turbine helicopters. Long term, there were 3.93

accidents per 1,000 aircraft, quite similar to the single-turbine helicopter rate of 3.83 per 1,000

aircraft. Although the twin-turbine helicopter rate showed considerable variation about its mean

since the mid-1970s, the rate remained generally below the rate of the total rotorcraft fleet. This

highlights the importance of increased safety efforts as new aircraft types are introduced.

7.4.3.2 Loss of Control by Axis Lost. Figure 90 shows that the axis about which control was lost

was not identified in 20 of the 40 accidents. The available data indicate that loss of control was

nearly equally distributed about all axes. Unlike single engine helicopters, yaw coupled with vertical

was not an obvious problem.
73

Because of the small number of twin-turbine helicopter loss of control accidents, the differences

between twin-turbine and single-turbine helicopters (see fig. 62) may not be significant. The

proportionally lower number of unknown/not reported accidents for the twin-turbine helicopter fleet

may be related to the more thorough accident investigations required for high-cost aircraft and the

higher proportion of fatalities in twins. Otherwise, it remains evident that loss of control accidents

involved all aircraft axes.

7.4.3.3 Loss of Control by Cause. As was done for single-piston and single-turbine helicopters

(figs. 36 and 62, respectively), the loss of control accidents for twin-turbine helicopters were

subdivided by cause. The results are shown in figure 91.

Again, because of the small number of twin-turbine helicopter loss of control accidents, statistical

comparison with overall rates or with the accident history of any other rotorcraft type is premature.

However, some qualitative observations can be made. First, improper operation of controls was not

the clearly leading precipitating event in loss of control for twin-turbine helicopters as it was for

single-piston or single-turbine helicopters. This may be a result of the higher experience level of the

pilots involved, the preference for multi-pilot operations, or the more general use of stability

augmentation systems. The relatively increased importance of flight control failure may reflect the

increased dependence on control augmentation; if the control system malfunctions, the chance for an

accident increases. The proportionally greater incidence of accidents attributed to loss of visual

references and/or spatial disorientation may be a result of more planned operations into instrument

meteorological conditions or in other degraded visual conditions.

7.4.3.4 Loss of Control by Phase of Operation. The 40 accidents fell into 11 phase of operation

categories (fig. 92). The distribution of loss of control accidents for twin-turbine helicopters

appeared distinctively different from the distributions for single-engine helicopters (see figs. 34 and

64). However, the small number of twin-turbine helicopter accidents makes direct statistical

comparison problematical. The two most obvious differences were (1) the relatively low percentage

of accidents that occurred in hover, 12.5% for twin-turbine helicopters and 23% for the singleengine helicopter fleet; and (2) the relatively higher percentage of accidents that occurred in the

traffic pattern or approach phases of flight, 24% for twins and 12% for singles. Improved hover

controllability may be credited to the wider use of stability augmentation systems in the twin-turbine

helicopter class or, perhaps, better inherent stability with the generally greater size of these aircraft.

With respect to the increased percentage of approach accidents, there was a broad range of

contributory factors. For the seven traffic-pattern/approach accidents, two were attributed to FOD,

two to downwind approaches, and one each to pilot impairment because of alcohol, a cyclic flight

control failure, and spatial disorientation.

7.4.3.5 Loss of Control by Activity. The frequency distribution of activities that resulted in loss of

control accidents is shown in figure 93. For the twin-turbine helicopter, it was found that the general

utility activity was primarily emergency medical service (EMS) missions. Air passenger operations,

along with ferry and reposition activities, showed accidents in similar proportions to single-turbine

helicopter experience (see fig. 65). These data point out the preferential use of turbine helicopters

for commercial passenger transportation. The discussion presented regarding the relative use of

single-turbine and piston-powered helicopters for personal and instructional missions applies to

twins as well.
74

7.4.3.6 Loss of Control by PIC Certification Level. All loss of control accidents involving twinturbine helicopters, for which a PIC certification level was stated, involved pilots with commercial

or higher ratings. Therefore, a figure comparable to that for the single engine helicopters (figs. 38

and 66) is not included.

7.4.3.7 Conclusions About Loss of Control Accidents. Of the 8,436 rotorcraft accidents recorded

by the NTSB during the 34-year period from mid-1963 through the end of 1997, 302 accidents

involved commercially manufactured twin-turbine helicopters. Of these, 40 (or roughly 13%) were

attributed to loss of control. This directly parallels single-turbine helicopter statistics as a percentage

of total accidents.

Loss of control was relatively evenly distributed about all axes. Where pilots of single-engine

helicopters clearly experienced loss of yaw control, the electronic stability and control augmentation

offered with twin-turbine helicopters appears to have considerable benefit.

No single problem (nor small set of problems) can be identified, which, if solved, would

immediately reduce the accident rates in this first event category. However, the “spikes” in the

annual accident numbers and rates (which occurred when second-generation, twin-turbine

helicopters were introduced into the civil fleet) reinforce the observations made for the singleturbine helicopter: it is absolutely necessary to understand the possible consequences of introducing

new aircraft types (e.g., civil tilt rotor) and ensure that the entire aviation system (design,

manufacture, training, professional development, use, etc.) is prepared to address the resulting

systematic changes.

7.4.4 Airframe/Component/System Failure or Malfunction (89 Accidents)

With few exceptions, modern, twin-turbine helicopters evolved from successful, single-turbine

designs. Manufacturers “simply” added an engine, redesigned associated components/systems and

incorporated other product improvements derived from single-engine helicopter field experience. No

major configuration changes in drive train or rotor systems appear to have been made, although

more advanced materials were substituted in many cases. With a comparatively small fleet having

accumulated relatively few flight hours, it is probably premature to assess the effects of all of the

changes made in progressing from the single- to the twin-turbine helicopter. Furthermore,

89 airframe failure accidents is a small number from which to draw major conclusions.

7.4.4.1 Overall Accident Trends. The NTSB cited airframe/component/system failure or

malfunction (again referred to from here on as airframe failure) in 89 twin-turbine helicopter

accidents from 1965 through 1997. These relatively few accidents took a large toll however

(table D-26). The accidents directly affected 452 people: 148 were killed in 27 accidents, 37 were

seriously injured, and 267 survived with minor or no injuries. Of the 89 helicopters involved

34 were listed by the NTSB as destroyed, 40 were substantially damaged, and 15 received little or

no damage.

Airframe failures accounted for a higher proportion of twin-turbine helicopter accidents (29.5% of

302) than for accidents involving single-piston (12.8% of 2,247) or single-turbine (11.7% of 5,371)

helicopters. This is primarily because of a lower proportion of loss of engine power accidents with

the twin-turbine helicopter fleet. Figure 94 suggests that accident rates in this first event category
75

decreased, both as a percentage of total accidents and per 1,000 registered aircraft. It is believed that

many airframe failure accidents reflect the twin-turbine helicopter fleet’s relative immaturity.

7.4.4.2 Airframe Failures by Phase of Operation. Fifty-two percent of the airframe failures

experienced by twin-turbine helicopters occurred in cruise (fig. 95). The accident distribution by

phase appears consistent with twin-turbine helicopter passenger carrying service. However, takeoff

and climb-out (when taken together) accounted for 24 accidents.

7.4.4.3 Airframe Failures by Activity. Figure 96 shows that most airframe failure accidents

involving twin-turbine helicopters occurred while those aircraft were engaged in passenger service

activities. Note that ferry and repositioning accident experience with the twin-turbine helicopter

was, percentage wise, similar to that of the single-engine helicopter fleet (see figs. 41 and 69). Twinturbine helicopters do not appear to be engaged in significant aerial application operations a sharp

contrast to the single-engine helicopter fleet experience examined in figure 41.

7.4.4.4 Airframe Failures by System/Component. The 89 airframe failure accidents were

grouped into 10 major categories (fig. 97). These 10 categories compare directly with those used for

the single-piston and single-turbine helicopter fleets (see figs. 42 and 70, respectively). When

compared on a percentage basis (table 33), it is clear that single-engine helicopter types and twinturbine helicopters experienced virtually the same airframe failure problems. The significant

reduction in tail rotor blade and hub failures was promising. It should be remembered that these

comparative data are based on experience with a relatively small fleet of twin-turbine helicopters.

TABLE 33. HELICOPTER AIRFRAME FAILURE COMPARISON, 1963–1997

Single piston Single turbine Twin turbine

Airframe major systems Count % Count % Count %

Drive train—main 127 19.9 49 17.3 13 14.6

Drive train—tail 119 18.6 54 19.1 19 21.3

Main rotor 57 8.9 36 12.8 19 21.3

Tail rotor 124 19.4 52 18.4 10 11.2

Control system—main 63 9.9 29 10.3 11 12.3

Control system—tail 38 5.9 11 3.9 7 7.9

Airframe (fuselage, other subsystems) 64 10.0 41 14.5 8 9.0

Landing gear 24 3.8 2 0.7 2 2.2

Engine 7 1.1 3 1.1 0 0

Undetermined/other 16 2.5 5 1.8 0 0

Total 639 100 282 100 89 100

It is evident from figure 97 and table 33 that failures in the drive system (to both main and tail rotors

combined) and in the two rotor systems caused most of the airframe failure accidents with the twinturbine helicopter fleet. Over 68% of these 89 airframe failure accidents were caused by problems
76

in transmissions, driveshafts, rotor blades, and hubs. This percentage virtually duplicates that of the

single-turbine helicopter fleet. As discussed earlier, the change from single- to twin-turbine engines

apparently improved helicopter safety (for example, see fig. 74). It is not evident from table 33,

however, that corresponding improvements in the remaining major airframe systems were achieved.

Accident counts by failure mode matrixed with the major rotorcraft systems are provided in table 34.

(Comparable summaries for single-engine helicopters are shown in tables 8 and 21). Fatigue failures

in both drive and rotor systems were just as prevalent in the twin-turbine helicopter fleet as in the

single-turbine fleet. Note also that accidents caused by damage inflicted by foreign objects were

nearly as prevalent.

Figure 97 will be used as the outline from which more detail about each system/subsystem/

component/part failure or malfunction is examined. This duplicates the summary data presentation

for single-piston (fig. 42) and single-turbine helicopter (fig. 70) airframe failures. Consider first the

main and tail drive train failures.

TABLE 34. NTSB FAILURE MODE/SYSTEM MATRIX—TWIN-TURBINE

HELICOPTERS

Failure mode

Drive

system

Rotor

system

Control

system

Airframe

LG Total

Fatigue 13 13 4 3 33

Improper assembly, installation, maintenance 3 1 7 3 14

Material failure 3 2 2 0 7

Undetermined/not reported 1 4 1 1 7

Failed 1 3 2 0 6

Separated 5 0 0 0 5

Foreign object damage 1 4 0 0 5

Overload 2 0 0 2 4

Pilot action/operational issue 1 1 0 1 3

Lack of lubrication 1 0 1 0 2

Slippage 0 1 0 0 1

Disconnected 0 0 1 0 1

Blade–airframe strike 1 0 0 0 1

Total 32 29 18 10 89

7.4.4.4.1 Drive train failures by subsystem: The drive train from the engine to the main and

tail rotors was implicated in 32 (i.e., 36% of the 89) twin-turbine helicopter accidents during the

study period (fig. 97). The distribution of accident count to a lower drive train subsystem level is

provided in table 35. Failure to transmit power from the engine to the main rotor gearbox accounted
77

for 6 of the 13 main rotor drive train accidents. Failure to transmit power along the tail rotor drive

shaft caused 17 of the 19 tail rotor drive-train accidents. Taken together, the components in these two

subsystems caused 23 of the 32 drive-train-related accidents. The number of tail rotor drive shaft

failures was excessive when compared with that of the single-turbine helicopter fleet (refer to

table 23).

Table 36 shows accidents caused by components that most frequently failed to (1) transmit power

between the engine and the main rotor gearbox, and (2) transmit power from the main rotor gearbox

to the tail rotor gearbox. Apparently, clutch assembly and freewheeling unit design and operation

improvements were made. It also appears that, tail rotor drive shaft and associated components

remain relatively unimproved. It should be noted, however, that many of the fleet’s twin-turbine

helicopters were, in fact, derived by simply “twinning” an earlier single-turbine model, an

evolutionary process that attempted to modify the basic design as little as possible.

TABLE 35. DRIVE-TRAIN FAILURES BY COMPONENTS—

TWIN-TURBINE HELICOPTERS

Drive train—main 13

Engine to transmission drive 6

Main rotor gearbox 4

Main rotor mast 3

Drive train—tail 19

Tail rotor drive shaft 17

Tail rotor gearbox 2

TABLE 36. DRIVE-TRAIN MAJOR COMPONENT FAILURES—

TWIN-TURBINE HELICOPTERS

Engine to transmission drive 6

Clutch assembly 0

Freewheeling unit 0

Torsion coupling/input shaft 6

Tail rotor drive shaft 17

Drive shaft 8

Coupling 5

Hangar bearing 4

7.4.4.4.2 Rotor failures by subsystem. Figure 97 shows that the main and tail rotor systems

were implicated in 29 (or 33%) of the 89 twin-turbine helicopter accidents during the study period.

Accidents caused by rotor system failures distributed to a lower subsystem/component level is
78

provided in table 37. Fatigue was the prevalent failure mode for both main and tail rotors (table 38).

Foreign object damage to the tail rotor (a significant problem in the operation of single-turbine

helicopters, as table 25 shows) was not a major factor in twin-turbine helicopter accidents.

TABLE 37. ROTOR SYSTEM FAILURES BY COMPONENTS—

TWIN-TURBINE HELICOPTERS

Main rotor 19

Main rotor blade 7

Main rotor hub 7

Main rotor system 5

Tail rotor 10

Tail rotor blades 7

Tail rotor hub 0

Tail rotor system 3

TABLE 38. ROTOR SYSTEM COMPONENTS FAILURE MODE—

TWIN-TURBINE HELICOPTERS

Component failure mode

Main

rotor

blade

Main

rotor

hub

Main

rotor

system

Tail

rotor

blade(s)

Tail

rotor

hub

Tail

rotor

system Total

Fatigue fracture 4 4 0 4 0 0 12

Separated 1 0 1 2 0 0 4

Foreign object damage 0 0 3 0 0 1 4

Undetermined/not reported 0 1 0 0 0 2 3

Improper assembly 0 2 0 0 0 0 2

Material failure 1 0 0 1 0 0 2

Overload 1 0 0 0 0 0 1

Blade–airframe strike 0 0 1 0 0 0 1

Delamination 0 0 0 0 0 0 0

Total 7 7 5 7 0 3 29
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7.4.4.4.3 Control system failures by subsystem: Eighteen twin-turbine helicopter accidents

were attributed to failures or malfunctions in the main and tail rotor flight control systems (fig. 97).

A breakdown of the accident count to lower-level subsystems/components is provided in table 39.

As with single-engine helicopters, improper assembly or installation—primarily in the lower

controls—was the most frequently identified factor in twin-turbine flight control system failure

accidents. This issue was discussed in some detail for single-piston helicopter flight control failures

(refer to table 13) and the conclusions and recommendations are equally applicable to twin-turbine

helicopters.

7.4.4.4.4 Airframe specific failures by components: Figure 97 shows that failures of the

fuselage structure, landing gear, and other airframe-associated components accounted for 10 of the

89 twin-turbine helicopter accidents during the study period. Subsystems that support operation of

other major systems (e.g., engine), and the other systems themselves accounted for 6 of the

10 accidents. The failure mode of the major subsystems listed in table 40 was improper assembly

and fatigue in 6 of the 10 accidents.

7.4.4.4.5 Conclusions about airframe failure or malfunction accidents: Twin-turbine

engine powered helicopters accounted for 302 of the 8,436 rotorcraft accidents recorded by the

NTSB from mid-1963 through 1997. Of these, 89, or roughly 29%, involved airframe/component/

system failure or malfunction. This was nearly twice the accident rate of single-engine helicopters

when compared as a percentage of total accidents.

TABLE 39. CONTROL SYSTEM FAILURES BY COMPONENTS—

TWIN-TURBINE HELICOPTERS

Main rotor controls 11

Lower controls—cyclic 3

Lower controls—collective 0

Upper controls—swashplate assembly 2

Upper controls—pitch link 1

Upper controls—other 2

Hydraulic 3

Tail rotor controls 7

Lower controls—cable 2

Lower controls—other 3

Upper controls—swashplate assembly 0

Upper controls—pitch link 1

Upper controls—other 1

Controls—other 0
80

TABLE 40. AIRFRAME SPECIFIC FAILURES BY COMPONENTS—

TWIN-TURBINE HELICOPTERS

Airframe and landing gear 10

Landing gear 2

Tailboom 0

Other systems 4

Support assembly 1

Other systems (engine) 2

Stabilizer—horizontal 1

Miscellaneous equipment 0

Stabilizer—vertical 0

Drive and rotor system failures, primarily in cruise flight, accounted for 61 of the 89 accidents. The

tail rotor drive system dominated drive train component failures and accounted for 19 of the

61 accidents. Failure, primarily in fatigue, of 29 main and tail rotor systems (i.e., blades and hubs)

occurred.

The pilot was left without antitorque and directional control in 36 of the 89 accidents because a tail

rotor drive train, a tail rotor system, or a tail rotor control failed or malfunctioned. On a percentage

basis of total accidents, this experience directly parallels that of single-engine helicopters.

Taking an overall look at the history of twin-turbine helicopter accidents resulting from

airframe/component/system failure or malfunction, the conclusion appears to be that fatigue failures

cause more airframe failure accidents in twin-turbine helicopters than any other single problem.

7.5 Summary Remarks, Conclusions and Recommended Actions

The registered fleet of commercially manufactured, twin-turbine helicopters grew from fewer than

50 at the end of 1963 to approximately 1,200 by the end 1997. During this period, the fleet had 302

accidents, 91% of which fell into the 10 categories shown in figure 98.

The summary of accidents by activity and phase of operation in table 41 shows that the

overwhelming number of twin-turbine helicopter accidents occurred during a passenger carrying or

similar activity. Since point-to-point activities involve relatively long duration, high-speed flight, it is

understandable that most twin-turbine helicopter accidents occurred during a cruise operation.
81

TABLE 41. ACCIDENTS BY ACTIVITY AND PHASE OF OPERATION—

TWIN-TURBINE HELICOPTERS

Activity Phase of Operation

Passenger service 97 Cruise 84

General utility 49 Takeoff 36

Ferry/reposition 46 Landing 35

Executive/corporate 31 Hover 32

Business use 23 Maneuvering 30

Flight/maintenance test 16 Approach 26

Instructional/training 13 Standing/static 22

Public/military use 12 Taxi 15

Personal use 6 Climb 14

Unknown/not reported 5 Descent 6

Aerial application 4 Unknown/other 2

Total 302 Total 302

The following study findings relate to the four top accident categories.

1. Total loss of engine power occurred in 23 of the 39 (60%) loss of engine power accidents

experienced by the twin-turbine helicopter fleet. The cause of 17 of these 23 accidents was attributed

to improper fuel/air mixture. Fuel exhaustion, fuel starvation, or fuel contamination occurred in the

twin-turbine helicopter fleet, just as they did in single-engine helicopters.

2. Loss of engine power because of engine structural failure caused 15 accidents.

3. Loss of engine power for undetermined reasons was recorded in six accidents.

4. In flight collision with man-made objects accounted for 34 of 43 accidents.

5. In flight collisions with 13 wires occurred and 12 objects attached to the airport/helipad

landing site were struck.

6. Loss of control was relatively evenly distributed about all axes.

7. Airframe failures caused nearly 30% (89) of the 302 total twin-turbine helicopter

accidents.

8. Drive train failures caused 32 accidents, of which 19 were tail rotor drive shaft failures.

9. Rotor system failures caused 29 accidents, of which the tail rotor system accounted for

10 accidents.
82

10. Control system failures caused 18 airframe failure accidents.

11. The pilot was left without antitorque and directional control in over 36 of the 89 airframe

failure accidents.

12. An autorotation took place in approximately 50 of the 302 accidents.

The top 4—or 10—most common accident categories were not the accident types that caused the

highest fatality rate (i.e., fatalities per 100 accidents). The greatest risk of fatality in twin-turbine

helicopter accidents occurred in midair collisions; there were six midair collisions in which 13

people were killed. Figure 99 shows, in descending order, fatalities per 100 accidents by NTSB first

event category. On ground/water collision with object, airframe failure, weather, and in flight

collision with terrain/water led to the highest fatality rates. When ordered in terms of total fatalities,

as tabulated on figure 99, airframe failures were the leading cause of fatalities with the twin-turbine

helicopter fleet.

Before discussing accidents that all other rotorcraft types had, several observations and

recommendations relative to the twin-turbine helicopter fleet are offered. From 1990 through 1997,

the twin-turbine helicopter fleet demonstrated an improved safety record over that of the singleturbine helicopter fleet by nearly a factor of 2. Single-turbine helicopters had 17.2 accidents per

1,000 registered aircraft and twin-turbine helicopters had 9.5. However, the improvements due to

fewer loss of engine power accidents were offset by an increase in airframe failure accidents. There

is little evidence to suggest that the twin-turbine helicopter significantly improved in any of the other

first event accident categories.

In 1997, the commercially manufactured, twin-turbine helicopter fleet experienced 8.2 accidents per

1,000 registered rotorcraft. It is projected here that this accident rate will drop below 4 accidents per

1,000 registered rotorcraft by the year 2010 (fig. 78). To ensure that this projection is achieved, it is

recommended that design and certification criteria and standards applicable to the airframe be

raised. The tail rotor drive train and tail rotor system should receive immediate attention.

Most of the recommendations applicable to the single-engine helicopter fleet are also applicable to

twin-turbine helicopters. However, these further suggestions are offered:

1. Begin a detailed review of the basic causes of loss of aircraft control for twin-turbine

helicopters. Review transition and refresher training, currency requirements, and evaluation criteria

for pilots of twin-turbine helicopters. In particular, address issues of aircraft handling, especially in

marginal weather conditions.

2. Incorporate into the fleet an alert system that effectively warns the pilot that aircraft

operational limits are being approached (e.g., maximum power available, conditions conducive to

loss of tail rotor effectiveness, avoid areas of the aircraft height-velocity diagram). Control force

cueing or cockpit displays should be considered as a means of alerting the pilot.

3. Examine the information and flying task requirements for EMS and commercial

passenger transportation operations to improve crew selection and training. Ensure that required

operational information is provided clearly to the crew and properly acted upon.
83

4. Examine aircraft certification criteria to ensure that time/cycle part-change requirements

provide adequate safety margins and are based on sound materials science and operational

experience.

5. Develop requirements and standards for health and usage monitoring systems. Continue

and intensify research and development efforts leading to widespread fielding of prototype HUMS

and analysis of data obtained.
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8. ALL OTHER ROTORCRAFT TYPES

8.1 Fleet History and Growth

A large and growing number of registered rotorcraft are classified by the FAA as amateur built (i.e.,

principally homebuilt from kits). This group began with small, single-place autogyros modeled after

larger autogyros manufactured by de la Cierva, Pitcairn, and Kellett before World War II. Igor

Bensen pioneered the early amateur autogyros in the mid-1950s. Ten years later, Air & Space

America developed and began selling its M-18A series. Amateur single-place helicopters became

available from Rotorway in the early 1970s. In 1997, a large number of kit rotorcraft were offered to

the homebuilt market, as reference 20 notes. This fleet of amateur built rotorcraft grew at a steady

pace (fig. 100). (Note, however, the substantial drop in fleet count from 1969 to 1970 when the FAA

introduced its revised aircraft data system.) Amateur built helicopters accounted for approximately

one-third of the homebuilt rotorcraft fleet by the end of 1997. The amateur rotorcraft fleet, whether

autogyro or helicopter, is dominated by single-piston engine power plants. Although virtually all of

these rotorcraft are single-seat, some kit manufacturers have recently begun to offer multi-place

versions.

8.2 Accident Analysis

The annual accidents per 1,000 registered amateur rotorcraft dropped steadily from 1963 through

1997, as shown in figure 101. It might be argued that the amateur fleet was the safest group of all

rotorcraft based solely on this figure. However, the Rotorcraft Activity Survey of 1989 (ref. 17),

suggests that this would be an incorrect presumption. Out of a fleet of 1,790, only 572 were active

and this small group flew only 21,830 hours (table 17). The estimated average annual hours flown

during 1989 by active amateur rotorcraft was only 38.2. This was about 14% of the activity of the

single-piston helicopters sold by manufacturers. Table D-1 indicates that the NTSB recorded 17 “All

Other Types” accidents in 1989. Therefore, a more realistic accident rate comparison between

commercially built and amateur homebuilt single-piston rotorcraft for 1989 would be as follows:

Active commercially built = 106 per 728,125 hours = 14.5 accidents per 100,000 hours flown

Active amateur built = 17 per 21,830 hours = 77.9 accidents per 100,000 hours flown.

This sobering statistic suggests that amateur homebuilt rotorcraft were over five times as accident

prone as commercially built rotorcraft. The NTSB investigated 516 All Other Types accidents over

the study period (table 42).
86

TABLE 42. ACCIDENT DISTRIBUTION BY ALL OTHER ROTORCRAFT TYPES,

1963–1997

All other types Count Reference

Manufacturer—autogyro 50 Table D-8

Amateur helicopter 137 Table D-9

Amateur autogyro 261 Table D-10

Unknown configuration 68 Table D-11

Total 516

8.3 Detailed Analysis by Accident Category

The 516 accidents are charted by first event category in figure 102. Approximately 90% of the

accidents fell into 7 of the 21 NTSB categories; a comparison summary to single-piston rotorcraft

sold by manufacturers is provided in table 43. Loss of control was the leading cause of accidents in

the homebuilt fleet. Although this might be expected, given the “amateur” character assigned to the

group, the homebuilt fleet was notably safer in almost all other first event accident categories. In

particular, the loss of engine power category shows that the amateur fleet had a much better safety

record.

TABLE 43. AMATEUR VS. COMMERCIAL ACCIDENT DISTRIBUTION, 1963–1997

Single piston

amateur

Single piston

manufacturer

NTSB category Count % Count %

Loss of engine power 111 21 1,554 29

In flight collision with object 28 5 953 18

Loss of control 165 32 625 11

Airframe/component/system failure or malfunction 73 14 639 12

Hard landing 25 5 483 9

In flight collision with terrain/water 40 8 443 8

Rollover/nose over 20 4 290 5

Other 54 10 384 7

Total 516 100 5,371 100

Figures 103 through 106 provide a review of the four top first event categories. From figure 103, it is

quite evident that the amateur fleet was just as susceptible to fuel/air mixture problems that caused

loss of engine power as the rest of the rotorcraft fleet; 40 of the 111 loss of engine power accidents.

Pilots of amateur built rotorcraft were as prone to colliding with wires, poles, and trees as pilots of
87

commercially manufactured helicopters (fig. 104). Figure 105 suggests that, after construction, the

pilots tried to teach themselves to fly with very little assistance and—too often—without success.

Finally, every major subsystem associated with the main rotor was a potential problem for amateurs

(fig. 106).

8.4 Summary Remarks, Conclusions, and Recommended Actions

There were approximately 3,000 homebuilt and a few experimental rotorcraft as of 31 December,

1997. Nearly 1,000 of these rotorcraft were single-rotor helicopters, with the rest being autogyros.

From mid-1963 through 1997, this fleet accumulated 516 accidents. The NTSB grouped these

accidents into 21 different categories. However, 80% of the accidents fell into five categories (fig. 107).

The summary of accidents by activity and phase of operation in table 44 shows that the

overwhelming number of accidents occurred during personal use. Takeoff was the most critical

phase of flight for builders/pilots of amateur rotorcraft.

Observations from the most common first events:

1. Loss of control was the leading cause of amateur rotorcraft accidents. No fewer than 165

of the 516 accidents were attributed to this cause by the NTSB.

2. Loss of engine power because of improper fuel/air mixture caused 40 of the 111 loss of

engine power accidents.

3. Loss of engine power because of engine structural failure caused 28 accidents.

TABLE 44. ACCIDENTS BY ACTIVITY AND PHASE OF OPERATION—

ALL OTHER TYPES

Activity Phase of Operation

Personnel use 358 Takeoff 127

Instructional/training 82 Cruise 93

Flight/maintenance test 43 Landing 74

General Utility 13 Maneuvering 70

Business use 11 Approach 54

Aerial application 4 Hover 28

Ferry/reposition 3 Unknown/other 24

Passenger service 1 Taxi 19

Unknown/not reported 1 Descent 12

Executive/corporate 0 Climb 10

Public/military use 0 Standing/static 5

Total 516 Total 516

4. Loss of engine power for undetermined reasons was recorded in 25 accidents.
88

5. In flight collision with object (e.g., wires, wire/poles, and trees) accounted for relatively

few accidents (i.e., 28 out of 516).

6. Drive train and rotor system failures caused 33 of the 73 airframe-related accidents.

Control system failures caused an additional 11 airframe failure accidents.

As before, the most common first event accident categories were not the accident types that caused

the highest fatality rate (i.e., fatalities per 100 accidents). There was one midair collision that killed

the pilot. Beyond this one accident, figure 108 shows, in descending order, the high-risk accident

categories for amateur rotorcraft.

There is considerable evidence that the amateur built fleet will continue to grow by approximately

80 to 120 rotorcraft per year. The number of amateur built helicopters has been increasing at a rate

of approximately 40 per year for the last 5 years, and interest appears very high considering the

relatively low selling price. From the projection shown in figure 109, it is estimated that the amateur

fleet will have two to three accidents per 1,000 registered aircraft by the year 2010 if concerns about

safety are not raised above today’s level.

The projection shown in figure 109 could easily be optimistic by a factor of 2, and perhaps even 3.

Taking a pessimistic view, there could be as many as 35 amateur rotorcraft accidents per year by

2010 (given the enthusiasm of the members of this segment of aviation, the likely increase in active

aircraft count and flying hours per active fleet). Thus, the situation now being experienced in

England (ref. 9, Vol. 22, No. 4, pg. 102), could happen in the U.S. in 2010.
89

9. FINAL REMARKS, CONCLUSIONS, AND RECOMMENDATIONS

The civilian rotorcraft fleet registered in the United States by the FAA includes, principally,

helicopters and autogyros. Commercially manufactured helicopters dominate the fleet, followed by

amateur built autogyros and helicopters. Periodically, experimental rotorcraft of either type are

added to the FAA registry for a short time. The most common helicopter configuration follows the

Igor Sikorsky arrangement (i.e., a large main rotor for lift and propulsion and a small, propeller-like

rotor at the tail for antitorque and directional control). Since no scheduled airline-type (i.e., Part 121)

operations are currently flown with rotorcraft, the FAA includes rotorcraft in its general aviation

class.

This civil rotorcraft fleet grew from fewer than 10 in 1946 to 2,196 in 1964 to 12,911 by the end of

1997. Single-engine helicopters dominated the registered fleet throughout this period. While the

single-piston-engine configuration still sold in quantity, the rotorcraft industry introduced the singleturbine-engine configuration in the mid-1960s. In 1997, nearly equal numbers of single-piston and

single-turbine helicopters were registered (about 5,000 each). The commercially manufactured,

twin-turbine helicopter began selling in quantity in the late 1970s and, by the end of 1997, slightly

over 1,200 were registered. A growing fleet of registered amateur built autogyros and helicopters

numbered close to 3,000 at the end of 1997.

The NTSB recorded 8,436 rotorcraft accidents between mid-1963 and the end of 1997. Because of

continuing emphasis on safety, the industry reduced accidents per year from 260 in 1964 to 175 in

1997, even as the registered fleet grew. Per 1,000 registered rotorcraft, accidents were reduced by

nearly a factor of 10 over this period (i.e., from 118 in 1964 to 13.6 in 1997). Nevertheless, these

accidents took a large toll, directly affecting 16,825 people: 2,135 were killed, 1,760 were seriously

injured, while 12,930 survived with minor or no injuries. Of the 8,436 rotorcraft involved, 2,363

(i.e., nearly 20% of the 1997 registered fleet) were listed by the NTSB as destroyed, 5,909 were

substantially damaged, and 164 received little or no damage.

The favorable downward trend in rotorcraft accidents per year enumerated above was not linear.

During a 15-year period, beginning in 1972 and ending in 1987, the industry experienced a rash of

accidents that drove the annual rate to 327 accidents in 1980 before dropping to 196 accidents in

1987. We believe that the increase in accidents per year during this period was initiated by the

10-year period during which commercial helicopter yearly sales increased by over 50%. The

relatively abrupt increase of new helicopters in the U.S. civil fleet was accompanied by a jump in

accidents caused by (1) loss of engine power and (2) failure of airframe systems and components. It

is clear, therefore, that when the next rapid expansion of the fleet occurs, the industry must increase

all aspects of its safety improvement efforts. This increase must be more than proportional to the

fleet growth rate.

Table 45 summarizes rotorcraft accidents over the study period. Analysis of the 8,436 rotorcraft

accidents recorded by the NTSB showed that approximately 90% of the accidents were precipitated

by only 7 of the NTSB’s 21 first event accident categories.
90

TABLE 45. SUMMARY OF ROTORCRAFT ACCIDENTS FROM MID-1963 TO THE END

OF 1997

Commercially manufactured

Single

piston

Single

turbine

Twin

turbine

Amateur

types

NTSB first event accident category Count (%) Count (%) Count (%) Count (%)

Loss of engine power 1,554 (28.9) 704 (31.3) 39 (12.9) 111 (21.5)

In flight collision with object 953 (17.7) 298 (13.2) 43 (14.2) 28 (5.43)

Loss of control 625 (11.6) 284 (12.6) 40 (13.2) 165 (32.0)

Airframe/component/system failure/

malfunction 639 (11.9) 282 (12.5) 89 (29.5) 73 (14.1)

Hard landing 483 (8.99) 140 (6.23) 8 (2.65) 25 (4.89)

In flight collision with terrain/water 443 (8.25) 143 (6.36) 16 (5.23) 40 (7.75)

Rollover/nose over 290 (5.40) 119 (5.29) 4 (1.32) 20 (3.88)

Weather 57 (1.06) 85 (3.78) 12 (3.97) 5 (0.97)

Miscellaneous/other 74 (1.38) 42 (1.87) 9 (2.98) 9 (1.74)

Stall/settling with power 67 (1.25) 2 (0.09) 1 (0.33) 13 (2.52)

Propeller/rotor contact to person 33 (0.61) 35 (1.56) 8 (2.65) 3 (0.58)

Midair collision 17 (0.32) 37 (1.65) 6 (1.99) 1 (0.19)

On ground/water collision with object 26 (0.49) 18 (0.80) 10 (3.31) 2 (0.39)

Fire/explosion 28 (0.52) 15 (0.67) 5 (1.66) 2 (0.39)

Abrupt maneuver 12 (0.22) 8 (0.36) 2 (0.66) 10 (1.94)

Undetermined 12 (0.22) 13 (0.58) 2 (0.66) 1 (0.19)

Gear collapsed 16 (0.23) 3 (0.13) 6 (1.99) 2 (0.39)

Dragged wing/rotor, pod, float, or tail/skid 20 (0.37) 2 (0.09) 1 (0.33) 1 (0.19)

Undershoot/overshoot 16 (0.23) 4 (0.18) 1 (0.33) 3 (0.58)

On ground/water encounter with terrain/

water 5 (0.09) 12 (0.53) 0 (0) 2 (0.39)

Missing 1 (0.02) 1 (0.05) 0 (0) 0 (0)

Total 5,371 2,247 302 516
91

Detailed analyses of these accidents showed that similarities far outnumbered differences. The three

commercially manufactured helicopter types are viewed by the industry as quite different, but they

shared many common accident causes. The major similarities observed are discussed below:

1. Thirty percent of single-piston or single-turbine helicopter accidents were caused by a

partial or total loss of engine power. The primary reason for the loss of power was not engine

structural failure, which only accounted for 452 accidents. Rather, the primary cause for the loss of

power was directly traced by the NTSB to fuel/air-mixture problems, which accounted for no fewer

than 985 accidents. Virtually every one of the 985 accidents was caused by human error. Fuel

exhaustion, fuel starvation, fuel contamination, and, for the piston-engine, improper use of

carburetor heat were key words repeatedly used in the NTSB accident reports. Apparently, many

pilots disregarded the need by both engine types for clean fuel and air in proper proportions—to say

nothing about the FAA regulations for fuel reserves.

Power-off landing proficiency is not required by the FAA in order to obtain a helicopter pilot’s

certificate. This standard appears inconsistent with the number of accidents caused by loss of engine

power (also see ref. 21). Virtually all of these accidents resulted in substantially damaged or

destroyed helicopters. It therefore appears that helicopters currently in the civil fleet provide

marginal to inadequate autorotational capability for the average pilot to successfully complete the

final flare and touchdown to what is usually an unsuitable landing site. Lastly, training in full

autorotation landings—even to a prepared landing site—is apparently avoided because of both real

and perceived risks. Based on these findings, the following are recommended:

• Immediate reinforcement of fuel management and mission planning according to

current FAA regulations.

• Reexamination of currently installed fuel quantity measurement and display hardware

for accuracy and applicability to rotorcraft operations.

• Reinstatement of full power-off autorotation to touchdown as an industry standard for

students and recurrent pilot training as soon as possible.

• Reexamination by commercial helicopter manufacturers of their current and future

product’s autorotational capabilities with the objective of reducing height-velocity

restrictions to a level consistent with average piloting skills, and more representative

emergency landing sites.

• Reexamination in detail of the accidents caused by piston-engine structural failure for

the purpose of initiating an engine improvement program.

2. Although twin-turbine helicopters appear to have significantly reduced loss of engine

power accidents on a percentage basis, 23 of the 39 accidents were caused by a total loss of power in

both engines. The other 16 accidents followed a partial loss of power. Most discouragingly, 17 of the

39 accidents were caused by fuel/air-mixture problems similar to those encountered in single-engine

helicopters. Clearly, the rotorcraft industry is dealing with a situation where approximately 50% of

loss of engine power accidents (regardless of the type of engine) are caused by improper fuel/air

mixture. Approximately, 25% to 30% of the loss of engine power accidents are related to engine

structural failure.
92

3. In flight collision with object accidents were common with all types of helicopters.

Commercially manufactured helicopters are sold primarily because they perform well flying low and

slow. Unfortunately, this flight regime places the helicopter pilot in a very hostile environment,

populated by many natural and man-made objects. The commercial helicopter fleet collectively had

1,294 collision with object accidents. There were 720 accidents involving collisions with wires and

poles, and 205 involving trees. The major contributor to these in flight collisions was the singlepiston helicopter fleet, which was most frequently involved in an agricultural operation (e.g., crop

dusting). This helicopter type had about equal numbers of main and tail rotor strikes. The singleturbine helicopter class, used relatively less in aerial applications, experienced four tail rotor strikes

for every three main rotor strikes. Twin-turbine helicopters experienced more than twice as many tail

rotor strikes as main rotor strikes. The average pilot’s situational awareness of objects that must be

avoided was significantly impaired because most of the objects were not readily visible. Wires, in

particular, are well-known threats to low flying by all aircraft types. Based on these findings, the

authors recommend that:

• Flying below 750 feet (above ground level) be discouraged by the industry and

regulatory agencies.

• All man-made objects higher than 500 feet be marked, mapped, and included in

electronic databases, such as used in Global Positioning System equipment.

• A low-price proximity spherical sensor be developed and certified; a sensor sphere of

some large radius should, in effect, cocoon the helicopter and provide the pilot with

sufficient warning to avoid obstacles.

4. Pilots of the commercial fleet lost control of their helicopters—regardless of their

certification level—causing 12% of the commercial fleet’s 7,920 accidents. Pilots of amateur

rotorcraft lost control nearly three times as often. The requirement to adequately control antitorque

in all flight phases appeared to be the root problem with the single main rotor helicopter

configuration. This was particularly true with the single-piston helicopter, where fluctuations in

engine RPM occurred because of the reciprocating engine’s governing system. The turbine engine

RPM governing system virtually removed this cause of accidents. However, on a percentage basis,

pilots of single-turbine helicopters lost directional control twice as often as pilots of single-piston

helicopters, which suggests a design deficiency. Equipping some single-turbine and virtually all

twin-turbine helicopters with an automatic stability and control system generally improved the

overall loss of control situation.
93

Current single-piston helicopters (and turbine-powered helicopters to a somewhat lesser extent)

appeared inordinately difficult to fly; particularly when the average pilot had to devote attention to

another task, or had a real or imagined emergency. Cross-coupling between the vertical/power/RPM

and yaw axes appeared excessive. The handling qualities design standards applicable to the current

helicopter fleet date back to the 1950s. Although generally tolerated, the resulting helicopter

stability and control characteristics now appear quite unsatisfactory. Therefore, the authors

recommend that:

• Piston-engine RPM management be more fully automated, to the level offered with

turbine engines, if possible.

• A low-price stability augmentation system (in the yaw axis as a minimum), having at

least 10% authority, be developed and certified.

• Handling quality standards for all future helicopters be raised to levels consistent

with what modern technology can provide.

• A detailed review of the basic causes of loss of aircraft control for single- and twinturbine helicopters be initiated.

• Transition and refresher training, currency requirements, and evaluation criteria for

pilots of twin-turbine helicopters be reviewed, with particular emphasis on aircraft

handling issues, especially in marginal-weather conditions.

• Aircraft certification criteria be reviewed and modified to ensure that undesirable

flying characteristics encountered in real-world operational use are included in precertification testing and corrected before final certification.

• Current certification and currency requirements for rotorcraft flight instructors be

reviewed with the intent of improving selection and training of instructors, thus

ensuring ongoing professional development, while providing a higher level of

instruction to future pilots.

5. Airframe system, subsystem, and component failures or malfunctions were one of the

leading causes of helicopter accidents. With the commercial helicopter fleet, the pilot was left

without antitorque and directional control in 470 accidents related to airframe failure or malfunction

(nearly 50% of 1,010 accidents). The failure or malfunction occurred in the tail rotor system

dynamic components (i.e., drive train, control system, and blades and hub). More specifically,

failures in the tail rotor drive train (which includes the shafts, couplings, bearings, and gearboxes)

caused 192 accidents. Failure of the tail rotor control system caused 56 accidents, and tail rotor

blade/hub failures caused 186 accidents. Tailboom failures accounted for the remaining 36

accidents. The corresponding main rotor system dynamic components also failed or malfunctioned,

which led to 404 accidents. Specifically, engine to main rotor gearbox failures caused 137 accidents,

control system failures caused 103, and blade/hub failures caused 112. Transmission and mast

failures caused 52 accidents.
94

The accident record of the commercial helicopter fleet shows that past design standards are

inadequate relative to the many new and varied activities in which this aircraft class is engaged.

Even considering that pilots did exceed design limits, that required and timely maintenance was

skipped, and that less than thorough inspections were performed, the current fleet appears, broadly

speaking, to be under-designed when faced with its commercial use. Therefore, the authors

recommend that the industry:

• Reevaluate design and certification criteria of all components involved in transmitting

power from the engine to the main rotor gearbox, with particular attention to clutch

and freewheeling units.

• Reevaluate design and certification criteria of all components that transmit power to

the tail rotor with particular attention to the drive shaft and couplings typical of

current configurations.

• Adopt more conservative fatigue design criteria (both loads and material allowables),

particularly for tail rotor blades and hubs.

• Incorporate into the fleet an alert system that effectively tells the pilot when aircraft

operational limits (e.g., maximum power available, conditions conducive to loss of

tail rotor effectiveness, “avoid” areas of the aircraft height-velocity diagram) are

being approached, perhaps by control force cueing or cockpit displays.

• Develop a reliable, low-priced health and use monitoring system with the intent of

requiring that such a system be installed on all future turbine-engine-powered

helicopters.

• Review certification and currency requirements for helicopter manufacturing, and

maintenance workers with the intent of raising standards.

• Raise aircraft design and certification standards to permit reduced maintenance and

incorporate additional system fail-safe modes.

• Continue research and development of better structural materials that are more

practical, more resistant to fatigue, and more affordable than the materials currently

in use.

6. The amateur helicopter and autogyro fleet experienced an accident distribution similar to

that of the commercial fleet, based on percentage. The primary exceptions were that loss of control

was nearly three times as prevalent and loss of engine power occurred one-third less often. Because

the amateur fleet is growing so fast, major manufacturers, operators, and trade associations must

provide considerably more help to this segment of their industry in an effort to lower the risks being

taken.

7. Single-turbine helicopter accidents per year increased slightly over the last decade of the

period studied. A measure of this unfavorable trend is that there were 62 accidents in 1987, 65 in

1993, and 73 in 1997, while the registered fleet increased only modestly in size. Most recently, new,
95

single-turbine helicopters were being registered at a rate comparable to that of the 1970s. There is

concern, therefore, that a rapid fleet expansion will prompt an increase in accidents, just as it did

with the single-piston helicopter fleet. We recommend that more intensive safety improvement

efforts be quickly initiated by the industry.

8. Introducing twin-turbine helicopters reduced loss of engine-power accidents, but a very

disturbing trend began with the larger helicopters capable of carrying more people. In the singlepiston helicopter fleet, there were 5,371 accidents and 683 fatalities. In the 2,247 accidents involving

single-turbine helicopters, 951 people died. In 302 twin-turbine helicopter accidents, 321 people

were killed.

9. There is little doubt that helicopters powered by turbine engines are safer than those

powered by a single-piston engine. How much safer can not, in the our opinion, be quantified. The

rotorcraft industry is being misguided by accident rate trends that use FAA data for active fleet size,

hours flown, takeoffs made, etc. In fact, it is quite likely that the rotorcraft industry will miss

significant safety trends if the currently used methods of computing accident rates remain as the

measure of progress. Unquestionably, the true goal of any aviation safety effort is no fatalities or

injuries.

10. Without significantly increased industry-wide safety efforts in the immediate future,

including implementing the above recommendations, it is projected that in the year 2010 there will

be about 6 accidents per 1,000 registered rotorcraft. Should the rotorcraft fleet size double by 2010,

there will be 150 accidents per year—about 3 accidents per week. It is not likely that the public will

perceive this projection as an indication that pilots and their rotorcraft are, in fact, becoming safer.

Rather, the perceived dangers of rotorcraft operations will make it more likely that rotorcraft will be

restricted, if not prohibited, from many areas and, as a result, rotorcraft will not be allowed to

perform a significant role in the U.S. air transportation system.
96

THIS PAGE INTENTIONALLY BLANK
97

REFERENCES

1. Tete, Albert: Organization and Exploitation of Regular Aerial Transportation Lines.

NACA TM-83, 1922.

2. Mayo, R. H.: Aviation and Insurance. NACA TM-93, 1922.

3. Aircraft Accidents, Method of Analysis. NACA TR-308, 1928.

4. Aircraft Accidents, Method of Analysis. NACA TR-357, 1930.

5. Aircraft Accidents, Method of Analysis. NACA TR-576, 1936.

6. Statistical Handbook of Civil Aviation. Civil Aeronautics Administration, Washington, D.C.,

1944.

7. Fox, Roy G.: Helicopter Accident Trends. AHS/FAA/HAI National Specialists Meeting on

Vertical Flight Training Needs and Solutions, Arlington, Texas, September 1987.

8. Persinos, John, ed.: Rotor & Wing (various monthly issues), Phillips Business Information,

Inc., Potomac, Maryland.

9. Rees, Elfan, ed.: Helicopter International (various bimonthly issues), Avia Press Associates,

Somerset, England.

10. McKinnis, Marilyn, ed.: Rotor (various quarterly issues), Helicopter Association

International, Alexandria, Virginia.

11. Healey, Andrew, ed.: Helicopter World (various monthly issues), The Shephard Press,

Burnham, Bucks, England.

12. Census of U.S. Civil Aircraft. Statistical Analysis Branch, Management Standards and

Statistics Division of the CAA/FAA, Washington, D.C., 1957–1994.

13. Lambermont, Paul; and Pirie, Anthony: Helicopters and Autogyros of the World. Second

edition, A. S. Barnes and Company, Inc., Cranbury, New Jersey, 1970.

14. The Official Helicopter Blue Book (various calendar years), HeliValue$, Inc., Lincolnshire,

Illinois.

15. Rotor Roster (various calendar years), Air Track, Hilliard, Florida.

16. McGuire, Francis G.: Helicopters, 1948–1998. Helicopter Association International,

Alexandria, Virginia, 1998.

17. Rotorcraft Activity Survey Summary Report: 1989 Data. Executive Resource Associates, Inc.

and Adsystech, Inc., Arlington, Virginia, 1989. (Also DTIC No. AD-A236698.)
98

18. Harris, Franklin D.; and Scully, Michael P.: Rotorcraft Cost Too Much. Journal of the

American Helicopter Society, vol. 43, no. 1, January 1998.

19. The Helicopter and Other V/STOL Aircraft in Commercial Transport Service: Growth to

Date and Forecasted Growth to 1965 and 1970. Economics Branch, Office of Plans, Federal

Aviation Agency, Washington, D.C., November 1960.

20. Martin, Dave, ed.: Kitplanes, Annual Directory of Kit Aircraft. Primedia Publication,

vol. 15, no. 12, 1998.

21. Prouty, Raymond W.: Unrealistic Practice Autorotations. Rotor & Wing, December 1999,

p. 45.

22. Final Report of the Helicopter Accident Analysis Team. Army/NASA Rotorcraft Division,

Ames Research Center, Moffett Field, California, July 1998.

23. Workshop on Near Term Gains in Rotorcraft Safety-Strategies for Investment. Army/NASA

Rotorcraft Division, Ames Research Center, Moffett Field, California, July 1998.
99

LIST OF FIGURES

The 109 figures contained in this document are sequenced by the rotorcraft class. That is,

after 15 figures that give a picture of the total rotorcraft fleet, 29 figures then deal with the

commercially manufactured single-piston engine powered helicopter. Next, 28 figures relate to the

single-turbine, commercially manufactured helicopter followed by another 28 figures devoted to the

commercially manufactured twin-turbine helicopter. All other rotorcraft types are dealt with by 10

figures. Figure 1 is found on page 103. In like manner, the page number for any figure which follows

is simply the figure number + 102.

Total Rotorcraft Fleet

Figure 1. NACA accident form, ca 1936

Figure 2. Accident mini-brief, 1963–1971

Figure 3. Accident mini-brief, 1972–1981

Figure 4. Accident mini-brief, 1982

Figure 5. Accident mini-brief, 1983–1997

Figure 6. Accident mini-brief, NTSB web site summary

Figure 7. Rotorcraft accidents per Year: 1964–1997 (total registered rotorcraft fleet)

Figure 8. FAA registered rotorcraft count: 1951–1997 (total registered rotorcraft fleet)

Figure 9. Injuries and fatalities caused by rotorcraft accidents: 1963–1997 (total registered rotorcraft fleet)

Figure 10. Rotorcraft accidents per year: 1964–1997 (total registered rotorcraft fleet)

Figure 11. Rotorcraft accident count by first event category (total registered rotorcraft fleet)

Figure 12. Loss of engine power and airframe/component/system failure or malfunction accidents (total registered

rotorcraft fleet)

Figure 13. In flight collision with object and loss of control accidents (total registered rotorcraft fleet)

Figure 14. Factors related to loss of engine power accidents (total registered rotorcraft fleet)

Figure 15. Rotorcraft accidents per 1,000 registered aircraft: (total registered rotorcraft fleet)

Commercial, Single-Piston Engine Helicopters

Figure 16. Single-piston helicopter fleet size (commercially manufactured))

Figure 17. Accidents per 1,000 registered aircraft: single-piston helicopters (commercially manufactured)

Figure 18. Accident count by first event category: single-piston helicopters (commercially manufactured

Figure 19. Loss of engine power and airframe failure or malfunction accidents: single-piston helicopters

(commercially manufactured)

Figure 20. In flight collision with object and loss of control accidents: single-piston helicopters (commercially

manufactured)

Figure 21. Accidents per 1,000 registered aircraft: 1964–1997: single-piston helicopters (commercially

manufactured)

Figure 22. Accidents per 1,000 registered aircraft projected to 2010: single-piston helicopters (commercially

manufactured)

Figure 23. Loss of engine power yearly accident standards: single-piston helicopters (commercially manufactured)

Figure 24. Loss of engine power by category: single-piston helicopters (commercially manufactured)

Figure 25. Loss of engine power by activity: single-piston helicopters (commercially manufactured)

Figure 26. Loss of engine power by phase of operation: single-piston helicopters (commercially manufactured)

Figure 27. In flight collision with object yearly accident statistics: single-piston helicopters (commercially

manufactured)

Figure 28. In flight collision with object by object hit: single-piston helicopters (commercially manufactured)

Figure 29. In flight collision with object by cause: single-piston helicopters (commercially manufactured)

Figure 30. In flight collision with object by phase of operation: single-piston helicopters (commercially

manufactured)

Figure 31. In flight collision with object by activity: single-piston helicopters (commercially manufactured)

Figure 32. In flight collision with object by part hit: single-piston helicopters (commercially manufactured)

Figure 33. Loss of control yearly accident statistics: single-piston helicopters (commercially manufactured)

Figure 34. Loss of control accidents by phase of operation: single-piston helicopters (commercially manufactured)
100

Figure 35. Loss of control accidents by activity: single-piston helicopters (commercially manufactured)

Figure 36. Loss of control accidents by cause: single-piston helicopters (commercially manufactured)

Figure 37. Loss of control accidents by axis lost: single-piston helicopters (commercially manufactured)

Figure 38. Loss of control accidents by pilot in command certification: single-piston helicopters (commercially

manufactured)

Figure 39. Airframe failure yearly accident statistics: single-piston helicopters (commercially manufactured)

Figure 40. Airframe failure accidents by phase of operation: single-piston helicopters (commercially manufactured)

Figure 41. Airframe failure accidents by activity: single-piston helicopters (commercially manufactured)

Figure 42. Airframe failure accidents by system: single-piston helicopters (commercially manufactured)

Figure 43. Summary accident statistics, mid-1963 through 1997: single-piston helicopters (commercially

manufactured)

Figure 44. Fatalities per 100 accidents, mid-1963 through 1997: single-piston helicopters (commercially

manufactured)

Commercial, Single-Turbine Engine Helicopters

Figure 45. Single-turbine helicopter fleet size (commercially manufactured)

Figure 46. Accidents per 1,000 registered aircraft: single-turbine helicopters (commercially manufactured)

Figure 47. Accident count by first event category: single-turbine helicopters (commercially manufactured)

Figure 48. Loss of engine-power and airframe failure or malfunction accidents: single-turbine helicopers

(commercially manufactured)

Figure 49. In flight collision with object and loss-of-control accidents: single-turbine helicopters (commercially

manufactured)

Figure 50. Accidents per 1,000 registered aircraft projected to 2010: single-turbine helicopters (commercially

manufactured)

Figure 51. Loss of engine power yearly accident statistics: single-turbine helicopters (commercially manufactured)

Figure 52. Loss of engine power accidents by category: single-turbine helicopters (commercially manufactured)

Figure 53. Loss-of engine power accidents by activity: single-turbine helicopters (commercially manufactured)

Figure 54. Loss of engine power accidents by phase of operation: single-turbine helicopters (commercially

manufactured)

Figure 55. In flight collision with object yearly accident statistics: single-turbine helicopters (commercially

manufactured)

Figure 56. In flight collision with object accidents by object hit: single-turbine helicopters (commercially

manufactured)

Figure 57. In flight collision with object accidents by cause: single-turbine helicopters (commercially manufactured)

Figure 58. In flight collision with object accidents by phase of operation: single-turbine helicopters (commercially

manufactured)

Figure 59. In flight collision with object accidents by activity: single-turbine helicopters (commercially

manufactured)

Figure 60. In flight collision with object accidents by part hit: single-turbine helicopters (commercially

manufactured)

Figure 61. Loss of control yearly accident statistics: single-turbine helicopters (commercially manufactured)

Figure 62. Loss of control accidents by axis lost: single-turbine helicopters (commercially manufactured)

Figure 63. Loss of control accidents by cause: single-turbine helicopters (commercially manufactured)

Figure 64. Loss of control accidents by phase of operation: single-turbine helicopters (commercially manufactured)

Figure 65. Loss-of-control accidents by activity: single-turbine helicopters (commercially manufactured)

Figure 66. Loss-of-control accidents by pilot-in-command certification: single-turbine helicopters (commercially

manufactured)

Figure 67. Airframe failure yearly accident statistics: single-turbine helicopters (commercially manufactured)

Figure 68. Airframe failure accidents by phase of operation: single-turbine helicopters (commercially

manufactured)

Figure 69. Airframe failure accidents by activity: single-turbine helicopters (commercially manufactured)

Figure 70. Airframe failure accidents by system: single-turbine helicopters (commercially manufactured)

Figure 71. Summary accident statistics, mid-1963 through 1997: single-turbine helicopters (commercially

manufactured)
101

Figure 72. Fatalities per 100 accidents, mid-1963 through 1997: single-turbine helicopters (commercially

manufactured)

Commercial, Twin-Turbine-Engine Helicopters

Figure 73. Twin-turbine helicopter fleet size (commercially manufactured)

Figure 74. Accidents per 1,000 registered aircraft: twin-turbine helicopters (commercially manufactured)

Figure 75. Accident count by first event category: twin-turbine helicopters (commercially manufactured)

Figure 76. Other first event categories: twin-turbine helicopters (commercially manufactured)

Figure 77. Accidents by first-event categories: twin-turbine helicopters (commercially manufactured)

Figure 78. Accidents per 1,000 registered aircraft projected to 2010: twin-turbine helicopters (commercially

manufactured)

Figure 79. Loss of engine-power yearly accident statistics: twin-turbine helicopters (commercially manufactured)

Figure 80. Loss of engine power accidents by category: twin-turbine helicopters (commercially manufactured)

Figure 81. Loss of engine power accidents by activity: twin-turbine helicopters (commercially manufactured)

Figure 82. Loss of engine power accidents by phase of operation: twin-turbine helicopters (commercially

manufactured)

Figure 83. In flight collision with object yearly accident statistics: twin-turbine helicopters (commercially

manufactured)

Figure 84. In flight collision with object accidents by object hit: twin-turbine helicopters (commercially

manufactured)

Figure 85. In flight collision with object accidents by cause: twin-turbine helicopters (commercially manufactured)

Figure 86. In flight collision with object accidents by activity: twin-turbine helicopters (commercially manufactured)

Figure 87. In flight collision with object accidents by phase of operation: twin-turbine helicopters (commercially

manufactured)

Figure 88. In flight collision with object accidents by part hit: twin-turbine helicopters (commercially manufactured)

Figure 89. Loss of control yearly accident statistics: twin-turbine helicopters (commercially manufactured)

Figure 90. Loss of control accidents by axis lost: twin-turbine helicopters (commercially manufactured)

Figure 91. Loss of control accidents by cause: twin-turbine helicopters (commercially manufactured)

Figure 92. Loss of control accidents by phase of operation: twin-turbine helicopters (commercially manufactured)

Figure 93. Loss of control accidents by activity: twin-turbine helicopters (commercially manufactured)

Figure 94. Airframe failure yearly accident statistics: twin-turbine helicopters (commercially manufactured)

Figure 95. Airframe failure accidents by phase of operation: twin-turbine helicopters (commercially manufactured)

Figure 96. Airframe failure accidents by activity: twin-turbine helicopters (commercially manufactured)

Figure 97. Airframe failure accidents by system: twin-turbine helicopters (commercially manufactured)

Figure 98. Summary accident statistics, mid-1963 through 1997: twin-turbine helicopters (commercially

manufactured)

Figure 99. Fatalities per 100 accidents, mid-1963 through 1997: twin-turbine helicopters (commercially

manufactured)

All Other Rotorcraft Types

Figure 100. All other rotorcraft types fleet Size

Figure 101. Accidents per 1,000 registered aircraft: all other rotorcraft types

Figure 102. Accident count by first event category: all other rotorcraft types

Figure 103. Loss of engine power accidents: all other rotorcraft types

Figure 104. In flight collision with object accidents: all other rotorcraft types

Figure 105. Loss of control accidents: all other rotorcraft types

Figure 106. Airframe failure accidents: all other rotorcraft types

Figure 107. Summary accident statistics, mid-1963 through 1997: all other rotorcraft types

Figure 108. Fatalities per 100 accidents, mid-1963 through 1997: all other rotorcraft types

Figure 109. Accidents per 1,000 registered aircraft projected to 2010: all other rotorcraft types
102

THIS PAGE INTENTIONALLY BLANK
103

Figure 1. NACA accident form, ca. 1936.
104

2-0342 (1)

64/5/14 TIME - 1030 (2

BRYANT WASH (3)

BRANTLY B2 N5900X (4)

CR- 0 0 1

PX- 0 0 0, (5)

OT- 0 0 0

COMMERCIAL AERIAL APPLICATION (6)

COMMERCIAL, AGE 42, 8177 TOTAL HOURS, 52 IN TYPE NOT INSTRUMENT RATED. (7)

DAMAGE-SUBSTANTIAL (8)

TYPE OF ACCIDENT (9)

ENGINE FAILURE OR MALFUNCTION

ROLL OVER

PHASE OF OPERATION (10)

IN FLIGHT: STARTING SWATH RUN

LANDING: POWER-OFF AUTOROTATIVE LANDING

PROBABLE CAUSE(S) (11)

MISCELLANEOUS ACTS,CONDITIONS - ICE-CARBURETOR

MISCELLANEOUS ACTS,CONDITIONS - ANTI-ICING/DEICING EQUIPMENT-IMPROPER OPERATION OF/OR FAILED TO USE

FACTOR(S) (12)

WEATHER - CONDITIONS CONDUCIVE TO CARB./INDUCTION SYSTEM ICING

COMPLETE POWER LOSS - COMPLETE ENGINE FAILURE/FLAMEOUT-1 ENGINE

EMERGENCY CIRCUMSTANCES - FORCED LANDING OFF AIRPORT ON LAND

SKY CONDITION CLEAR (13)

CEILING AT ACCIDENT SITE UNLIMITED

VISIBILITY AT ACCIDENT SITE 5 OR OVER(UNLIMITED)

TEMPERATURE-F 60

WIND DIRECTION-DEGREES 270

WIND VELOCITY-KNOTS 5

TYPE OF WEATHER CONDITIONS VFR

TYPE OF FLIGHT PLAN NONE

SPECIAL DATA (14)

TOTAL HOURS IN CROP CONTROL - 1750

KIND OF OPERATION - SPRAYING FORESTS

KIND OF CROP - FOREST-TREES

TYPE OF CHEMICAL USED - LIQUID CHEMICAL-NONTOXIC

PILOT' S SEAT BELT -FASTENED-PROPERLY

GLOVES - NOT USED

GOGGLES - NOT USED

CRASH HELMET - NOT AVAILABLE

COCKPIT CRASHPAD - NOT INSTALLED

CRASH BAR - NOT INSTALLED

TANK/HOPPER-LOCATION - BELLY

ELEVATION-AREA BEING TREATED-FEET - 680

REMARKS (15)

FORCED LANDING ON UNSUITABLE TERRAIN

Figure 2. Accident mini-brief, 1963–1971.
105

3-0196

 72/1/9 TIME - 1415

HILLSBOROUGH,NC

ENSTROM F-28A N426RD

CR- 0 0 1

PX- 0 0 1

OT- 0 0 0

COMMERCIAL CTR PASSG-D

COMMERCIAL, AGE 38, 5750 TOTAL HOURS, 38 IN TYPE, INSTRUMENT RATED.

DAMAGE-SUBSTANTIAL

DEPARTURE POINT HILLSBOROUGH,NC

INTENDED DESTINATION LOCAL

TYPE OF ACCIDENT

 ENGINE FAILURE OR MALFUNCTION

 HARD LANDING

PHASE OF OPERATION

TAKEOFF: INITIAL CLIMB

LANDING: POWER-OFF AUTOROTATIVE LANDING

PROBABLE CAUSE(S)

 POWERPLANT - MISCELLANEOUS: POWERPLANT FAILURE FOR

UNDETERMINED REASONS

 PILOT IN COMMAND - MISJUDGED SPEED AND ALTITUDE 

 PARTIAL POWER LOSS - PARTIAL LOSS OF POWER - 1 ENGINE

 EMERGENCY CIRCUMSTANCES - PRECAUTIONARY LANDING OFF AIRPORT

 UNUSUAL NOISE

REMARKS

ENG CKD OK.PLT RPRTD LOUD BANG,ENG RPM INCRD TO 3300.ENTERED AUTO

FM LOW ALT,T/R BLDS HIT TLCONE.

Figure 3. Accident mini-brief, 1972–1981.
106

FILE NO. - 0069 2/10/82 URBANA,IL A/C Reg. No. N2256G Time (Lcl) - 1400 CST

------------------------------------------------------------------------------------------------------------------------------------

----Basic Information----

 Type Operating Certificate-NONE (GENERAL AVIATION) Aircraft Damage Injuries

 Substantial Fatal Serious Minor None

 Type of Operation -OTHER Fire Crew 0 0 0 2

 Flight Conducted Under -14 CFR 91 NONE Pass 0 0 0 0

 Accident Occurred During -LANDING

------------------------------------------------------------------------------------------------------------------------------------

----Aircraft Information----

 Make/Model - SIKORSKY UH-19B Eng Make/Model - WRIGHT R-1300 ELT Installed/Activated - NO -N/A

 Landing Gear - Tailwheel-all fixed Number Engines - 1 Stall Warning System - UNK/NR

 Max Gross Wt - 7200 Engine Type - Reciprocating-carburetor Weather Radar - NO

 No. of Seats - 4 Rated Power - 600 HP

------------------------------------------------------------------------------------------------------------------------------------

----Environment/Operations Information----

 Weather Data Itinerary Airport Proximity

 Wx Briefing - No record of briefing Last Departure Point On airport

 Method - N/A HOMER,IL

 Completeness - N/A Destination Airport Data

 Basic Weather - VMC URBANA,IL RESTRICTED HELIPORT

 Wind Dir/Speed- 180/005 KTS Runway Ident - UNK/NR

 Visibility - 12.0 SM ATC/Airspace Runway Lth/Wid - UNK/NR

 Cloud Conditions(1st) - NONE Type of Flight Plan - None Runway Surface - Concrete

 Cloud Conditions(2nd) - NONE Type of Clearance - None Runway Status - Snow - dry

 Obstructions to Vision- None Type Apch/Lndg - Visual full circuit

 Precipitation - None

 Condition of Light - Daylight

------------------------------------------------------------------------------------------------------------------------------------

----Personnel Information----

 Pilot-In-Command Age - 48 Medical Certificate - Valid medical-waivers/limit

 Certificate(s)/Rating(s) Biennial Flight Review Flight Time (Hours)

 Private,Commercial Current - YES Total - 561 Last 24 Hrs - 0

 SE land Months Since - 1 Make/Model- 53 Last 30 Days- UNK/NR

 Helicopter Aircraft Type - UNK/NR Instrument- 12 Last 90 Days- 38

 Multi-Eng - 64 Rotorcraft - 291

 Instrument Rating(s) - None

----Narrative----

THE PILOT AND A MEDICAL ATTENDANT WERE ON A FLIGHT TO URBANA TO MAKE A MEDICAL EVACUATION. THE

PILOT STATED THAT JUST PRIOR TO TOUCHDOWN, THE HELICOPTER BEGAN TO ROTATE TO THE LEFT. HE

REPORTED THAT HE LANDED IMMEDIATELY, CUT THE POWER, AND STOPPED THE ROTATION OF THE MAIN

ROTOR AS QUICKLY AS POSSIBLE AFTER TOUCHDOWN. DURING THE LANDING, A MAIN ROTOR BLADE HIT THE

TAIL CONE AND TAIL ROTOR DRIVE SHAFT, AND FLYING PARTS STRUCK THE FUSELAGE.

Occurrence #1 HARD LANDING

Phase of Operation LANDING - FLARE/TOUCHDOWN

Finding(s)

 1. ALTITUDE - MISJUDGED - PILOT IN COMMAND

 2. DISTANCE - MISJUDGED - PILOT IN COMMAND

 3. ROTORCRAFT FLIGHT CONTROLS - IMPROPER USE OF - PILOT IN COMMAND

----Probable Cause---- is/are finding(s) 1,2,3

Figure 4. Accident mini-brief, 1982.
107

Public 02/25/83 1518 MKC83FA073 COUNCIL BLUFFS ,IA:

HUGHES TH-55A N1040S

IOWA WESTERN COMMUNITY

COLLEGE /

 0 0 1 1

ACC / On Airport/ COUNCIL BLUFFS MUNICIPAL (CBF) Substantial

91 Instruction

THE STUDENT, WHO WAS A RATED HELICOPTER PLT, AND A HELICOPTER

INSTRUCTOR (CFI) WERE ON A DUAL INSTRUCTIONAL FLT. AFTER TAKEOFF, THE

AIRCREW REMAINED IN A RIGHT TRAFFIC PATTERN FOR RWY 13 , INTENDING FOR

THE STUDENT TO MAKE A 180 DEG AUTOROTATION TO A PARALLEL TAXIWAY. THE

STUDENT OVERSHOT THE AUTOROTATIVE TURN & THE CFI INSTRUCTED HIM TO

CONTINUE THE APCH TO A GRASS AREA BETWEEN THE TAXIWAY & RWY. THE CFI

REPORTED THAT THE TOUCHDOWN WAS SMOOTH WITH ZERO AIRSPEED. HOWEVER,

THE HELICOPTER BEGAN VIBRATING & TURNED TO THE LEFT. REPORTEDLY, THE

MAIN ROTOR BLADES HAD SEVERED THE TAIL BOOM.

No Occ Phs Subj Mod Pers

-- --- --- ----- ---- ----

 1 200 571 Hard landing Landing - flare/touchdown

 F 24545 3141 4103 Emergency procedure <> Simulated <> Pilot in command(CFI)

 F 24520 3135 4101 Autorotation <> Performed <> Dual student

 C 24523 3120 4101 Distance <> Misjudged <> Dual student

 C 24518 3120 4101 Altitude <> Misjudged <> Dual studen

 C 24627 3115 4103 Supervision <> Inadequate <> Pilot in command(CFI)

Figure 5. Accident mini-brief, 1983–1997.
108

NTSB Identification: MIA98LA051. The docket is stored in the (offline) NTSB Imaging System.

Accident occurred JAN-03-98 at BUNNELL, FL

Aircraft: Bell 47D1, registration: N59326

Injuries: 1 Uninjured.

The student pilot was on a supervised solo flight in the traffic pattern, practicing landings and

takeoffs. At an altitude of about 300 feet above the airport, the helicopter's engine lost power. The

student autorotated to an open field, and the helicopter was damaged during a forced landing. The

student said when he checked the fuel gauge during preflight, it indicated "5/8" of a tank, which

was confirmed by a "dip stick test." When he next checked the fuel gauge after doing some pattern

work, it indicated "3/8" tank. According to an FAA Inspector's statement, "...the fuel tank was

drained and less than 12 ounces of fuel remained in the undamaged fuel tank...no other

maintenance discrepancies were found which may have contributed to the accident." The flight was

about 1 hour and 10 minutes in duration.

Probable Cause

the student pilot's improper planning/decision, which resulted in fuel exhaustion, loss of engine

power, and a forced landing.

The helicopter was released to the owner's representative.

MIA98LA051

On January 3, 1998, about 0840 eastern standard time, a Bell 47D1 helicopter, N59326, registered

to a private owner, operating as a 14 CFR Part 91, local instructional flight, crashed during a forced

landing near Bunnell, Florida. Visual meteorological conditions prevailed and no flight plan was

filed. The helicopter was substantially damaged. The student pilot was not injured. The flight

originated about 0730.

The student pilot was on a solo flight in the traffic pattern, practicing landings and takeoffs when

the engine lost power. The pilot autorotated to an open field. The pilot said when he checked "the

fuel indicator [it] was on 5/8 tank (sic), which was confirmed by the dip stick test." When he next

checked the fuel gauge after doing some pattern work, it indicated "3/8 tank (sic)."

According to the FAA Inspector's statement, the student pilot was on a supervised instructional

flight, and at an altitude of about 300 feet above the airport the helicopter's "engine stopped." The

inspector stated, "...the fuel tank was drained and less then 12 ounces of fuel remained in the

undamaged fuel tank...no other maintenance discrepancies were found which may have contributed

to the accident."

Figure 6. Accident mini-brief, NTSB web site summary.
 109

0

50

350300250200150100

1960 1965 1970 1975 1980 1985 1990 1995 2000

Rotorcraft

accident

count

each

year

End of year

All rotorcraft

Reference

trend line

Accident

"bubble"

period

Figure 7. Rotorcraft accidents per year: 1964–1997 (total registered rotorcraft fleet).

Accident

"bubble"
 110

0

8,0006,0004,0002,000

14,00012,00010,000

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Registered

rotorcraft

fleet

size

End of year

Total

rotorcraft

fleet

Commercial

helicopter

manufacturers

only

All

other

types

Figure 8. FAA registered rotorcraft count: 1951–1997 (total registered rotorcraft fleet).
 111

0

500

2,5002,0001,5001,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Rotorcraft cumulative accident count over 34 years

Fatalities

and

injuries

(cumulative)

8,436

People involved 16,825 Fatal 2,135 Serious 1,760 Minor + None 12,930

Fatal

2,135

Serious

1,760

Figure 9. Injuries and fatalities caused by rotorcraft accidents: 1963–1997 (total registered rotorcraft fleet).
 112

0

50

350300250200150100

1960 1965 1970 1975 1980 1985 1990 1995 2000

Rotorcraft

accident

count

each

year

End of year

Single

piston

Single

turbine

Twin

turbine

All rotorcraft

Figure 10. Rotorcraft accidents per year: 1964–1997 (total registered rotorcraft fleet).
 113

2,408

1,322

1,114

1,083

656

642

433

159

134

79

83

61

56

50

32

27

2424

28

19

2

0 500 1,000 1,500 2,000 2,500

Loss of engine power

In flight collision with object

Loss of control

Airframe/component/system failure/malfunction

Hard landing

In flight collision with terrain/water

Rollover/noseover

Weather

Miscellaneous/other

Propeller/rotor contact to person

Stall/settling with power

Midair collision

On ground/water collision with object

Fire/explosion

Abrupt maneuver

Gear collapsed

Undershoot/overshoot

Dragged wing, rotor, pod, float or tail/skid

Undetermined

On ground/water encounter with terrain/water

Missing

NTSB accident count 

Figure 11. Rotorcraft accident count by first event category (total registered rotorcraft fleet).

Total of 8,436 accidents

from mid-1963 through 1997
 114

0

80604020

120100

1960 1965 1970 1975 1980 1985 1990 1995 2000

Rotorcraft

accident

count

each

year

End of year

Loss of engine power

(all rotorcraft)

Airframe/component/

system failure/malfunction

(all rotorcraft)

Figure 12. Loss of engine power and airframe/component/system failure or malfunction accidents (total registered rotorcraft fleet).
 115

0

8070605040302010

1960 1965 1970 1975 1980 1985 1990 1995 2000

Rotorcraft

accident

count

each

year

End of year

Loss of control

(all rotorcraft)

Figure 13. In flight collision with object and loss of control accidents (total registered rotorcraft fleet).

In flight collision with object

(all rotorcraft)
 116

609

65

62

135

10

36

76

79

107

145

417

495

172

0 100 200 300 400 500 600 700

Other Sub-categories

Undetermined/Other

Rotor Drive System

Other Engine Systems

 Fuel improper

 Induction air system

 Carburetor heat

 Fuel control

 Fuel starvation

 Fuel contamination

 Fuel system

 Fuel exhaustion

Engine structure

NTSB accident count

1,042

Fuel / air 

mixture

related

accidents

Figure 14. Factors related to loss of engine power accidents (total registered rotorcraft fleet).
 117

0

908070605040302010

130120110100

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Accidents

per

1,000

registered

rotorcraft 

End of year

Figure 15. Rotorcraft accidents per 1,000 registered aircraft: (total registered rotorcraft fleet).

1964 through 1997

accident experience 

trend-line extrapolated to 2010

(exponential)
 118

0

500

5,0004,5004,0003,5003,0002,5002,0001,5001,000

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Registered

singlepiston

helicopters

End of year

FAA data,

(edited by Harris)

Rotor Roster data,

from Air Track

Growth rate

127 per year

Growth rate

193 per year

Figure 16. Single-piston helicopter fleet size (commercially manufactured).
 119

0

908070605040302010

150140130120110100

1960 1965 1970 1975 1980 1985 1990 1995 2000

Accidents

per

1,000

registered 

rotorcraft

End of year

Figure 17. Accidents per 1,000 registered aircraft: single-piston helicopters (commercially manufactured).
 120

1,554

953

625

639

483

443

290

57

74

33

67

17

26

28

12

1616

20

12

5

1

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800

Loss of engine power

In flight collision with object

Loss of control

Airframe/component/system failure/malfunction

Hard landing

In flight collision with terrain/water

Rollover/noseover

Weather

Miscellaneous/other

Propeller/rotor contact to person

Stall/settling with power

Midair collision

On ground/water collision with object

Fire/explosion

Abrupt maneuver

Gear collapsed

Undershoot/overshoot

Dragged wing, rotor, pod, float or tail/skid

Undetermined

On ground/water encounter with terrain/water

Missing

NTSB accident count

Figure 18. Accident count by first event category: single-piston helicopters (commercially manufactured).

Total of 5,371 accidents

from mid-1963 through 1997
 121

0

908070605040302010

1960 1965 1970 1975 1980 1985 1990 1995 2000

Singlepiston

helicopter

accident

count

End of year

Loss of engine power

Airframe/component/

system failure or 

malfunction

Figure 19. Loss of engine power and airframe failure or malfunction accidents: single-piston helicopters (commercially manufactured).
 122

0

8070605040302010

1960 1965 1970 1975 1980 1985 1990 1995 2000

Singlepiston

helicopter

accident

count

End of year

Loss of control

In flight collision with object

Figure 20. In flight collision with object and loss of control accidents: single-piston helicopters (commercially manufactured).
 123

0

908070605040302010

160150140130120110100

1960 1965 1970 1975 1980 1985 1990 1995 2000

Accidents

per

1,000

registered 

rotorcraft

End of year

Figure 21. Accidents per 1,000 registered aircraft: 1964–1997: single-piston helicopters (commercially manufactured).

1964 through 1969

accident experience 

trend-line extrapolated to 1985

(exponential)

1970 through 1985

accident experience 

trend-line

(exponential) 1990 through 1997

accident experience 

trend-line

(exponential)
 124

50

353025201510

1985 1990 1995 2000 2005 2010

Accidents

per

1,000

registered

rotorcraft

End of year

Figure 22. Accidents per 1,000 registered aircraft projected to 2010: single-piston helicopters (commercially manufactured).

1990 through 1997

accident experience 

trend-line extrapolated to 2010

(exponential)
 125

50

4540353025201510

1960 1965 1970 1975 1980 1985 1990 1995 2000

Loss of

engine

power

statistics

End of year

Percentage of

total single-piston

accidents

Accidents per 1,000

registered

 single-piston

Figure 23. Loss of engine power yearly accident statistics: single-piston helicopters (commercially manufactured). 
 126

397

53

54

101

66

70

42

72

97

326

263

67

0 50 100 150 200 250 300 350 400 450

Other Sub-categories

Undetermined/Other

Rotor Drive System

Other Engine Systems

 Fuel improper

 Induction air system

 Carburetor heat

 Fuel control

 Fuel starvation

 Fuel contamination

 Fuel system

 Fuel exhaustion

Engine structure

NTSB accident count

686

Fuel / air 

mixture

related

accidents

Figure 24. Loss of engine power accidents by category: single-piston helicopter (commercially manufactured).
 127

2

26

27

30

80

97

173

117

231

277

494

0 100 200 300 400 500 600

Unknown/not reported

Public/military use

Executive/corporate

Flight/maintenance test

Ferry/reposition

Business use

Instructional/training

Passenger service

Personal use

General utility

Aerial application

NTSB accident count

Figure 25. Loss of engine power accidents by activity: single-piston helicopters (commercially manufactured).
 128

3

1

10

18

35

72

60

53

87

280

328

607

0 100 200 300 400 500 600 700

Standing/static

Unknown

Taxi

Climb

Other

Landing

Descent

Hover

Approach

Takeoff

Maneuvering

Cruise

NTSB accident count

Figure 26. Loss of engine power accidents by phase of operation: single-piston helicopters (commercially manufactured).
 129

50

40353025201510

1960 1965 1970 1975 1980 1985 1990 1995 2000

In flight

collision

with

object

statistics

End of year

Percentage of

total single-piston

accidents

Accidents per 1,000

registered

 single-piston

Figure 27. In flight collision with object yearly accident statistics: single-piston helicopters (commercially manufactured).
 130

8

10

8

7

14

27

19

3535

30

26

32

47

148

197

310

0 50 100 150 200 250 300 350

Miscellaneous

Unspecified object

Bird strike

Electronic tower

Building

Aircraft

Crop

FOD

Vehicle

Rock/brush/terrain

Fence/fence post

Airport/helipad facility

Pole/pipe

Tree(s)

Wire/pole

Wire

NTSB accident count

Figure 28. In flight collision with object accidents by object hit: single-piston helicopters (commercially manufactured).
 131

188

20

20

22

39

52

54

68

83

87

157

165

0 20 40 60 80 100 120 140 160 180 200

Undetermined

Obstacle Proximity

Incorrect Information

Insuff Clearance for Turn

Concealed in Terrain

Wind causes drift

Diverted Attention

End of Day - Fatigue

Inadequate RPM/perf 

Degraded Visibility

Failure to See & Avoid

Improper Decision

NTSB accident count

Figure 29. In flight collision with object accidents by cause: single-piston helicopters (commercially manufactured).
 132

2

5

4

15

36

50

55

75

106

96

133

376

0 50 100 150 200 250 300 350 400

Unknown

Standing/static

Climb

Descent

Other

Taxi

Approach

Hover

Landing

Cruise

Takeoff

Maneuvering

NTSB accident count

Figure 30. In flight collision with object accidents by phase of operation: single-piston helicopters (commercially manufactured).
 133

3

10

11

12

31

62

69

98

70

168

419

0 50 100 150 200 250 300 350 400 450

Flight/maintenance test

Unknown/Not reported

Public/military use

Executive/corporate

Ferry/Reposition

Instructional/training

Personal use

Business use

Passenger service

General utility

Aerial application

NTSB accident count

Figure 31. In flight collision with object accidents by activity: single-piston helicopters (commercially manufactured).
 134

33

5

12

35

83

87

0 10 20 30 40 50 60 70 80 90 100

Cabin

Main rotor mast

Tail boom

External Load

Landing gear

Main rotor blades

Tail rotor

NTSB accident count

Figure 32. In flight collision with object accidents by part hit: single-piston helicopters (commercially manufactured).
 135

50

3025201510

1960 1965 1970 1975 1980 1985 1990 1995 2000

Loss

of

control

statistics

End of year

Percentage of

total single-piston

accidents

Accidents per 1,000

registered

 single-piston

Figure 33. Loss of control early accident statistics: single-piston helicopters (commercially manufactured).
 136

8

5

6

9

23

21

37

43

79

96

150

148

0 20 40 60 80 100 120 140 160

Other

Standing/static

Climb

Descent

Taxi

Approach

Unknown

Cruise

Landing

Maneuvering

Hover

Takeoff

NTSB accident count

Figure 34. Loss of control accidents by phase of operation: single-piston helicopters (commercially manufactured).
 137

1

4

10

22

16

33

40

133

98

152

116

0 20 40 60 80 100 120 140 160

Unknown/Not reported

Executive/corporate

Public/military use

Ferry/Reposition

Flight/maintenance test

Business use

Aerial application

Passenger service

General utility

Instructional/training

Personal use

NTSB accident count

Figure 35. Loss of control accidents by activity: single-piston helicopters (commercially manufactured).
 138

29

13

12

21

20

29

33

38

44

72

209

105

0 50 100 150 200 250

Miscellaneous

Inadequate preflight planning

Airframe/comp./sys. fail. or malf.

Unqualified operator

Loss of visual ref./spatial disorient.

Weight/CG

Attached/snagged to grd. equip.

Flight control failure/deficiency

Undetermined

Winds

Low rotor RPM

Improper operation of controls

NTSB accident count

Figure 36. Loss of control accidents by cause: single-piston helicopters (commercially manufactured).
 139

56

231

30

3

70

25

94

21

95

 0

0 50 100 150 200 250

Not Reported But Low Rotor

RPM

Not Reported

Pitch & Low Rotor RPM

Pitch

Roll & Low Rotor RPM

Roll

Vertical & Low Rotor RPM

Vertical

Yaw & Low Rotor RPM

Yaw

NTSB accident count

Figure 37. Loss of control accidents by axis lost: single-piston helicopters (commercially manufactured).
 140

1

5

7

12

16

17

55

77

96

175

0 50 100 150 200

Military Only

Other/Unknown/Not Reported

No Rating Specified-CFI

None

ATP-CFI

Airline Transport Pilot

Private

Student

Commercial-CFI

Commercial

NTSB accident count

Figure 38. Loss of control accidents by pilot in command certification: single-piston helicopters (commercially manufactured).
 141

86420

201816141210

1960 1965 1970 1975 1980 1985 1990 1995 2000

Airframe/

component/

system

failure

or

malfunction

statistics

End of year

Percentage of

total single-piston

accidents

Accidents per 1,000

registered

 single-piston

Figure 39. Airframe failure yearly accident statistics: single-piston helicopters (commercially manufactured).
 142

8

5

13

14

26

13

31

36

41

99

137

216

0 50 100 150 200 250

Unknown

Other

Taxi

Descent

Standing/static

Climb

Approach

Landing

Hover

Takeoff

Maneuvering

Cruise

NTSB accident count

Figure 40. Airframe failure accidents by phase of operation: single-piston helicopters (commercially manufactured).
 143

1

7

1414

25

55

73

75

55

191

129

0 50 100 150 200 250

Unknown/Not reported

Public/military use

Flight/maintenance test

Executive/corporate

Ferry/Reposition

Business use

Instructional/training

Personal use

Aerial application

Passenger service

General utility

NTSB accident count

Figure 41. Airframe failure accidents by activity: single-piston helicopters (commercially manufactured).
 144

16

7

24

64

38

63

124

57

119

127

0 20 40 60 80 100 120 140

Undetermined/Other

Engine

Landing gear

Airframe

Control system-Tail

Control system-Main

Tail rotor

Main rotor

Drive train-Tail

Drive train-Main

NTSB accident count

Figure 42. Airframe failure accidents by system: single-piston helicopters (commercially manufactured).
 145

0

6,0005,0004,0003,0002,0001,000

0 3 6 9 12 15 18 21

1,554 Loss of engine power 953 In flight collision with object 639 Airframe/component/system failure/malfunction 625 Loss of control 483 Hard landing 443 In-flight collision with terrain/water 290 Rollover/nose-over 4,987 Accidents from first 7 categories 384 Accidents from other 14 categories 5,371 Total

7 Categories account for 93 % of accidents

4 Categories account for 70 % of accidents

NTSB major categories

Singlepiston

helicopter

accident

count

Figure 43. Summary accident statistics, mid-1963 through 1997: single-piston helicopters (commercially manufactured).
 146

1

3

4

7

7

9

10

11

13

15

18

17

24

37

42

42

 0 0

0 5 10 15 20 25 30 35 40 45

Gear collapsed

On ground/water encounter with terrain/water

Hard landing

Rollover/noseover

On ground/water collision with object

Loss of engine power

Fire/explosion

Stall/settling with power

Dragged wing, rotor, pod, float or tail/skid

In flight collision with terrain/water

Undershoot/overshoot

Loss of control

In flight collision with object

Miscellaneous/other

Airframe/component/system failure/malfunction

Weather

Abrupt maneuver

Propeller/rotor contact to person

Fatalities per 100 accidents

Figure 44. Fatalities per 100 accidents, mid-1963 through 1997: single-piston helicopters (commercially manufactured).

Fatalities First-event category

 166 In flight collision with object

 153 Airframe/component/system failure/malfunction

 106 Loss of engine power

 92 Loss of control

 47 In flight collision with terrain/water

 22 Midair collision

 21 Weather

 14 Propeller/rotor contact to person

 62 Undetermined/miscellaneous/other

 683 Total
 147

0

500

5,0004,5004,0003,5003,0002,5002,0001,5001,000

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Registered

singleturbine

helicopters

End of year

Rotor Roster Data,

from Air Track

Figure 45. Single-turbine helicopter fleet size (commercially manufactured).

FAA data,

(edited by Harris)
 148

0

908070605040302010

150140130120110100

1960 1965 1970 1975 1980 1985 1990 1995 2000

Accidents

per

1,000

registered

rotorcraft

End of year

Singlepiston

(fig. 17)

Single

turbine

Figure 46. Accidents per 1,000 registered aircraft: single-turbine helicopters (commercially manufactured).
 149

704

298

284

282

140

143

119

85

42

35

2

37

18

15

8

3

4

2

13

12

1

0 100 200 300 400 500 600 700 800

Loss of engine power

In flight collision with object

Loss of control

Airframe/component/system failure/malfunction

Hard landing

In flight collision with terrain/water

Rollover/noseover

Weather

Miscellaneous/other

Propeller/rotor contact to person

Stall/settling with power

Midair collision

On ground/water collision with object

Fire/explosion

Abrupt maneuver

Gear collapsed

Undershoot/overshoot

Dragged wing, rotor, pod, float or tail/skid

Undetermined

On ground/water encounter with terrain/water

Missing

NTSB accident count

Figure 47. Accident count by first event category: single-turbine helicopters (commercially manufactured). 

Total of 2,247 accidents

from mid-1963 through 1997
 150

0

605040302010

1960 1965 1970 1975 1980 1985 1990 1995 2000

Singleturbine

helicopter

accident

count

End of year

Loss of engine power

Airframe/component/

system failure/malfunction

Figure 48. Loss of engine power and airframe failure or malfunction accidents: single-turbine helicopters (commercially manufactured). 
 151

50

40353025201510

1960 1965 1970 1975 1980 1985 1990 1995 2000

Singleturbine

helicopter

accident

count

End of year

Loss of control

In flight collision with object

In flight collision with object

Plus

Loss of control

Figure 49. In flight collision with object and loss of control accidents: single-turbine helicopters (commercially manufactured). 
 152

50

25201510

1980 1985 1990 1995 2000 2005 2010

Accidents

per

1,000

registered

rotorcraft

End of year

Figure 50. Accidents per 1,000 registered aircraft projected to 2010: single-turbine helicopters (commercially manufactured). 

1986 through 1997

accident experience 

trend-line extrapolated to 2010

(exponential)
 153

0

70605040302010

1960 1965 1970 1975 1980 1985 1990 1995 2000

Loss of

engine

power

statistics

End of year

Percentage of

total single-turbine

accidents

Accidents per 1,000

registered

 single-turbine

Figure 51. Loss of engine power yearly accident statistics: single-turbine helicopters (commercially manufactured). 
 154

181

11

7

17

3

26

27

26

43

82

189

0

92

0 20 40 60 80 100 120 140 160 180 200

Other Sub-categories

Undetermined/Other

Rotor Drive System

Other Engine Systems

 Fuel improper

 Induction air system

 Carburetor heat

 Fuel control

 Fuel starvation

 Fuel contamination

 Fuel system

 Fuel exhaustion

Engine structure

NTSB accident count

299

Fuel / air 

mixture

related

accidents

Figure 52. Loss of engine power accidents by category: single-turbine helicopters (commercially manufactured). 
 155

3

16

33

26

53

71

15

215

58

162

52

0 50 100 150 200 250

Unknown/Not reported

Public/military use

Executive/corporate

Flight/maintenance test

Ferry/reposition

Business use

Instructional/training

Passenger service

Personal use

General utility

Aerial application

NTSB accident count

Figure 53. Loss of engine power accidents by activity: single-turbine helicopters (commercially manufactured). 
 156

1

2

0

5

15

24

33

58

64

104

84

314

0 50 100 150 200 250 300 350

Standing/static

Unknown

Taxi

Climb

Other

Landing

Descent

Hover

Approach

Takeoff

Maneuvering

Cruise

NTSB accident count

Figure 54. Loss of engine power accidents by phase of operation: single-turbine helicopters (commercially manufactured). 
 157

50

25201510

1960 1965 1970 1975 1980 1985 1990 1995 2000

In flight

collision

with

object

statistics

End of year

Percentage of

total single-turbine

accidents

Accidents per 1,000

registered

 single-turbine

Figure 55. In flight collision with object yearly accident statistics: single-turbine helicopters (commercially manufactured).
 158

1

2

7

9

4

5

13

1

4

11

2020

19

50

24

108

0 20 40 60 80 100 120

Miscellaneous

Unspecified object

Bird strike

Electronic tower

Building

Aircraft

Crop

FOD

Vehicle

Rock/brush/terrain

Fence/fence post

Airport/helipad facility

Pole/pipe

Tree(s)

Wire/pole

Wire

NTSB accident count

Figure 56. In flight collision with object accidents by object hit: single-turbine helicopters (commercially manufactured). 
 159

11

12

13

14

15

16

18

21

32

34

37

77

0

0 10 20 30 40 50 60 70 80 90

Incorrect Information

Insuff Clearance for Turn

Inadequate RPM/perf 

Equipmt snag

Obstacle Proximity

Concealed in Terrain

End of Day - Fatigue

Wind causes drift

Diverted Attention

Failure to See & Avoid

Degraded Visibility

Undetermined

Improper Decision

NTSB accident count

Figure 57. In flight collision with object accidents by cause: single-turbine helicopters (commercially manufactured). 
 160

2

1

2

9

10

15

16

41

30

50

57

65

0 10 20 30 40 50 60 70

Unknown

Standing/static

Climb

Descent

Other

Taxi

Approach

Hover

Landing

Cruise

Takeoff

Maneuvering

NTSB accident count

Figure 58. In flight collision with object accidents by phase of operation: single-turbine helicopters (commercially manufactured).
 161

11

13

17

12

4

33

26

71

83

37

0 10 20 30 40 50 60 70 80 90

Flight/maintenance test

Unknown/Not reported

Public/military use

Executive/corporate

Ferry/Reposition

Instructional/training

Personal use

Business use

Passenger service

General utility

Aerial application

NTSB accident count

Figure 59. In flight collision with object accidents by activity: single-turbine helicopters (commercially manufactured). 
 162

00

3

11

13

34

43

0 10 20 30 40 50

Cabin

Main rotor mast

Tail boom

External Load

Landing gear

Main rotor blades

Tail rotor

NTSB accident count

Figure 60. In flight collision with object accidents by part hit: single-turbine helicopters (commercially manufactured). 
 163

50

25201510

1960 1965 1970 1975 1980 1985 1990 1995 2000

Loss

of

control

statistics

End of year

Percentage of

total single-turbine

accidents

Accidents per 1,000

registered

 single-turbine

Figure 61. Loss of control yearly accident statistics: single-turbine helicopters (commercially manufactured). 
 164

8

139

11

38

13

75

 0 0 0 0

0 20 40 60 80 100 120 140 160

Not Reported But Low Rotor

RPM

Not Reported

Pitch & Low Rotor RPM

Pitch

Roll & Low Rotor RPM

Roll

Vertical & Low Rotor RPM

Vertical

Yaw & Low Rotor RPM

Yaw

NTSB accident count

Figure 62. Loss of control accidents by axis lost: single-turbine helicopters (commercially manufactured). 
 165

22

5

7

6

36

1414

30

32

28

82

8

0 10 20 30 40 50 60 70 80 90

Miscellaneous

Inadequate preflight planning

Airframe/comp./sys. fail. or malf.

Unqualified operator

Loss of visual ref./spatial disorient.

Weight/CG

Attached/snagged to grd. equip.

Flight control failure/deficiency

Undetermined

Winds

Low rotor RPM

Improper operation of controls

NTSB accident count

Figure 63. Loss of control accidents by cause: single-turbine helicopters (commercially manufactured). 
 166

2

5

2

44

9

20

34

30

39

61

74

0 10 20 30 40 50 60 70 80

Other

Standing/static

Climb

Descent

Taxi

Approach

Unknown

Cruise

Landing

Maneuvering

Hover

Takeoff

NTSB accident count

Figure 64. Loss of control accidents by phase of operation: single-turbine helicopters (commercially manufactured). 
 167

9

19

11

8

30

74

13

79

11

30

0

0 10 20 30 40 50 60 70 80 90

Unknown/Not reported

Executive/corporate

Public/military use

Ferry/Reposition

Flight/maintenance test

Business use

Aerial application

Passenger service

General utility

Instructional/training

Personal use

NTSB accident count

Figure 65. Loss of control accidents by activity: single-turbine helicopters (commercially manufactured). 
 168

3

11

13

34

43

104

194

298

00

0 50 100 150 200 250 300 350

Military Only

Other/Unknown/Not Reported

No Rating Specified-CFI

None

ATP-CFI

Airline Transport Pilot

Private

Student

Commercial-CFI

Commercial

NTSB accident count

Figure 66. Loss of control accidents by pilot-in-command certification: single-turbine helicopters (commercially manufactured). 
 169

86420

201816141210

1960 1965 1970 1975 1980 1985 1990 1995 2000

End of year

Percentage of

total single-turbine

accidents

Accidents per 1,000

registered

 single-turbine

Airframe/

component/

system

failure

or

malfunction

statistics

Figure 67. Airframe failure yearly accident statistics: single-turbine helicopters (commercially manufactured). 
 170

0

6

1

7

6

16

1414

47

36

28

107

0 20 40 60 80 100 120

Unknown

Other

Taxi

Descent

Standing/static

Climb

Approach

Landing

Hover

Takeoff

Maneuvering

Cruise

NTSB accident count

Figure 68. Airframe failure accidents by phase of operation: single-turbine helicopters (commercially manufactured). 
 171

2

10

6

10

17

25

8

16

73

25

90

0 10 20 30 40 50 60 70 80 90 100

Unknown/Not reported

Public/military use

Flight/maintenance test

Executive/corporate

Ferry/Reposition

Business use

Instructional/training

Personal use

Aerial application

Passenger service

General utility

NTSB accident count

Figure 69. Airframe failure accidents by activity: single-turbine helicopters (commercially manufactured). 
 172

5

3

2

41

11

29

52

36

54

49

0 10 20 30 40 50 60

Undetermined/Other

Engine

Landing gear

Airframe

Control system-Tail

Control system-Main

Tail rotor

Main rotor

Drive train-Tail

Drive train-Main

NTSB accident count

Figure 70. Airframe failure accidents by system: single-turbine helicopters (commercially manufactured). 
 173

0

500

2,5002,0001,5001,000

0 3 6 9 12 15 18 21

 704 Loss of engine power 298 In flight collision with object 284 Loss of control 282 Airframe/component/system failure/malfunction 143 In flight collision with terrain/water 140 Hard landing 119 Rollover/nose-over 85 Weather 2,055 Accidents from first 8 categories 192 Accidents from other 13 categories 2,247 Total

8 Categories account for 92 % of accidents

4 Categories account for 70 % of accidents

NTSB major categories

Singleturbine

helicopter

accident

count

Figure 71. Summary accident statistics, mid-1963 through 1997: single-turbine helicopters (commercially manufactured). 
 174

2

11

18

21

33

34

47

50

55

56

73

88

126

178

00

0

0

0 20 40 60 80 100 120 140 160 180 200

On ground/water encounter with terrain/water

On ground/water collision with object

Gear collapsed

Dragged wing, rotor, pod, float or tail/skid

Hard landing

Rollover/noseover

Miscellaneous/other

Loss of engine power

Fire/explosion

Propeller/rotor contact to person

In flight collision with object

Undershoot/overshoot

Loss of control

Airframe/component/system failure/malfunction

In flight collision with terrain/water

Abrupt maneuver

Weather

Midair collision

Fatalities per 100 accidents

Figure 72. Fatalities per 100 accidents, mid-1963 through 1997: single-turbine helicopters (commercially manufactured). 

Fatalities First-event category

 157 Airframe/component/system failure/malfunction

 155 Loss of control

 140 In flight collision with object

 129 Loss of engine power

 107 Weather

 104 In flight collision with terrain/water

 66 Midair collision

 93 Undetermined/miscellaneous/other

 951 Total
 175

0

800600400200

1,4001,2001,000

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Registered

twinturbine

helicopters

End of year

FAA data,

(edited by Harris)

Rotor Roster data,

from Air Track

Figure 73. Twin-turbine helicopter fleet size (commercially manufactured). 
 176

0

908070605040302010

100

1960 1965 1970 1975 1980 1985 1990 1995 2000

Accidents

per

1,000

registered

rotorcraft

End of year

Twinturbine

Singleturbine

(Fig. 46)

Figure 74. Accidents per 1,000 registered aircraft: twin-turbine helicopters (commercially manufactured).
 177

39

43

40

89

8

16

4

12

9

8

1

6

10

5

2

6

11

2

 0 0

0 10 20 30 40 50 60 70 80 90 100

Loss of engine power

In flight collision with object

Loss of control

Airframe/component/system failure/malfunction

Hard landing

In flight collision with terrain/water

Rollover/noseover

Weather

Miscellaneous/other

Propeller/rotor contact to person

Stall/settling with power

Midair collision

On ground/water collision with object

Fire/explosion

Abrupt maneuver

Gear collapsed

Undershoot/overshoot

Dragged wing, rotor, pod, float or tail/skid

Undetermined

On ground/water encounter with terrain/water

Missing

NTSB accident count

Figure 75. Accident count by first event category: twin-turbine helicopters (commercially manufactured).

Total of 302 accidents

from mid-1963 through 1997
 178

3.8

1.9

1.6

0.1

1.6

0.8

0.7

0.4

0.1

0.2

0.1

0.6

0.5

4.0

3.0

2.6

0.3

2.0

3.3

1.7

0.7

2.0

0.30.3

0.7

0.0

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

Weather

Miscellaneous/other

Propeller/rotor contact to person

Stall/settling with power

Midair collision

On ground/water collision with object

Fire/explosion

Abrupt maneuver

Gear collapsed

Undershoot/overshoot

Dragged wing, rotor, pod, float or tail/skid

Undetermined

On ground/water encounter with terrain/water

Single Turbine Helicopter (2,247 Total Accidents)Twin Turbine Helicopter (302 Total Accidents)

Percent of totals by NTSB first event category

Figure 76. Other first event categories: twin-turbine vs. single-turbine helicopters (commercially manufactured).

Single-turbine helicopter (2,247 total accidents)Twin-turbine helicopter (302 total accidents)
 179

86420

1816141210

1960 1965 1970 1975 1980 1985 1990 1995 2000

Twinturbine

helicopter

accident

count

End of year

Sum of first four categoriesa. Loss of engine powerb. In flight collision with objectc. Loss of controld. Airframe/component/system  failure/malfunction

Sum of all 17

other categories 

Figure 77. Accidents by first event categories: twin-turbine helicopters (commercially manufactured).
 180

50

201510

1980 1985 1990 1995 2000 2005 2010

Accidents

per

1,000

registered

rotorcraft

End of year

Figure 78. Accidents per 1,000 registered aircraft projected to 2010: twin-turbine helicopters (commercially manufactured).

1986 through 1997

accident experience 

trend-line extrapolated to 2010

(exponential)
 181

50

504540353025201510

1960 1965 1970 1975 1980 1985 1990 1995 2000

Loss of

engine

power

statistics

End of year

Percentage of

total twinturbine

Accidents per 1,000

registered

 twin-turbine

Figure 79. Loss of engine power yearly accident statistics: twin-turbine helicopters (commercially manufactured).
 182

6

1

4

3

5

11

15

000

3

0

0 2 4 6 8 10 12 14 16

Other Sub-categories

Undetermined/Other

Rotor Drive System

Other Engine Systems

 Fuel improper

 Induction air system

 Carburetor heat

 Fuel control

 Fuel starvation

 Fuel contamination

 Fuel system

 Fuel exhaustion

Engine structure

17

NTSB accident count

Fuel / Air 

mixture

related

accidents

Figure 80. Loss of engine power accidents by category: twin-turbine helicopters (commercially manufactured).
 183

33

5

4

11

1

11

1

000

0 2 4 6 8 10 12

Unknown/Not reported

Public/military use

Executive/corporate

Flight/maintenance test

Ferry/reposition

Business use

Instructional/training

Passenger service

Personal use

General utility

Aerial application

NTSB accident count

Figure 81. Loss of engine power accidents by activity: twin-turbine helicopters (commercially manufactured).
 184

000

222

8

2

8

2

13

0

0 2 4 6 8 10 12 14

Standing/static

Unknown

Taxi

Climb

Other

Landing

Descent

Hover

Approach

Takeoff

Maneuvering

Cruise

NTSB accident count

Figure 82. Loss of engine power accidents by phase of operation: twin-turbine helicopters (commercially manufactured).
 185

50

25201510

1960 1965 1970 1975 1980 1985 1990 1995 2000

In flight

collision

with

object

statistics

End of year

Percentage of

total twin-turbine

accidents

Accidents per 1,000

registered

 twin-turbine

Figure 83. In flight collision with object yearly accident statistics: twin-turbine helicopters (commercially manufactured).
 186

22

111

2

12

2

7

13

00

0

000

0 2 4 6 8 10 12 14

Miscellaneous

Unspecified object

Bird strike

Electronic tower

Building

Aircraft

Crop

FOD

Vehicle

Rock/brush/terrain

Fence/fence post

Airport/helipad facility

Pole/pipe

Tree(s)

Wire/pole

Wire

NTSB accident count

Figure 84. In flight collision with object accidents by object hit: twin-turbine helicopters (commercially manufactured).
 187

0.50.5

111

22

2.52.5

3.53.5

5

8

0123456789

Concealed in Terrain

Inadequate RPM/perf 

Diverted Attention

End of Day - Fatigue

Equipmt snag

Failure to See & Avoid

Undetermined

Obstacle Proximity

Insuff Clearance for Turn

Incorrect Information

Wind causes drift

Degraded Visibility

Improper Decision

NTSB accident count

Figure 85. In flight collision with object accidents by cause: twin-turbine helicopters (commercially manufactured).
 188

1

4

3

7

1

2

19

5

1

 0

 0

0 2 4 6 8 10 12 14 16 18 20

Flight/maintenance test

Unknown/Not reported

Public/military use

Executive/corporate

Ferry/Reposition

Instructional/training

Personal use

Business use

Passenger service

General utility

Aerial application

NTSB accident count

Figure 86. In flight collision with object accidents by activity: twin-turbine helicopters (commercially manufactured).
 189

00000

5

1

6

10

4

11

6

0 2 4 6 8 10 12

Unknown

Standing/static

Climb

Descent

Other

Taxi

Approach

Hover

Landing

Cruise

Takeoff

Maneuvering

NTSB accident count

Figure 87. In flight collision with object accidents by phase of operation: twin-turbine helicopters (commercially manufactured).
 190

00000

4

10

0 2 4 6 8 10 12

Cabin

Main rotor mast

Tail boom

External Load

Landing gear

Main rotor blades

Tail rotor

NTSB accident count

Figure 88. In flight collision with object accidents by part hit: twin-turbine helicopters (commercially manufactured).
 191

50

25201510

1960 1965 1970 1975 1980 1985 1990 1995 2000

Loss

of

control

statistics

End of year

Percentage of

total twin-turbine

accidents

Accidents per 1,000

registered

 twin-turbine

Figure 89. Loss of control yearly accident statistics: twin-turbine helicopters (commercially manufactured).
 192

20

3

5

1

4

7

 0 0

 0 0

0 5 10 15 20 25

Not Reported But Low Rotor

RPM

Not Reported

Pitch & Low Rotor RPM

Pitch

Roll & Low Rotor RPM

Roll

Vertical & Low Rotor RPM

Vertical

Yaw & Low Rotor RPM

Yaw

NTSB accident count

Figure 90. Loss of control accidents by axis lost: twin-turbine helicopters (commercially manufactured).
 193

5

0

1

0

7

0

6

3

4

5

8

1

0123456789

Miscellaneous

Inadequate preflight planning

Airframe/comp./sys. fail. or malf.

Unqualified operator

Loss of visual ref./spatial disorient.

Weight/CG

Attached/snagged to grd. equip.

Flight control failure/deficiency

Undetermined

Winds

Low rotor RPM

Improper operation of controls

NTSB accident count

Figure 91. Loss of control accidents by cause: twin-turbine helicopters (commercially manufactured).
 194

0

3

00

11

8

6

2

8

5

6

0123456789

Other

Standing/static

Climb

Descent

Taxi

Approach

Unknown

Cruise

Landing

Maneuvering

Hover

Takeoff

NTSB accident count

Figure 92. Loss of control accidents by phase of operation: twin-turbine helicopters (commercially manufactured).
 195

1

2

7

33

9

2

9

22

0

0 1 2 3 4 5 6 7 8 9 10

Unknown/Not reported

Executive/corporate

Public/military use

Ferry/Reposition

Flight/maintenance test

Business use

Aerial application

Passenger service

General utility

Instructional/training

Personal use

NTSB accident count

Figure 93. Loss of control accidents by activity: twin-turbine helicopters (commercially manufactured).
 196

0

70605040302010

1960 1965 1970 1975 1980 1985 1990 1995 2000

End of year

Percentage of

total twin-turbine

accidents

Accidents per 1,000

registered

 twin-turbine

Airframe/

component/

system

failure

or

malfunction

statistics

Figure 94. Airframe failure yearly accident statistics: twin-turbine helicopters (commercially manufactured).
 197

1

0

1

2

3

9

5

4

6

9

3

46

0 5 10 15 20 25 30 35 40 45 50

Unknown

Other

Taxi

Descent

Standing/static

Climb

Approach

Landing

Hover

Takeoff

Maneuvering

Cruise

NTSB accident count

Figure 95. Airframe failure accidents by phase of operation: twin-turbine helicopters (commercially manufactured).
 198

11

7

1313

6

1

34

13

 0

 0

0 5 10 15 20 25 30 35 40

Unknown/Not reported

Public/military use

Flight/maintenance test

Executive/corporate

Ferry/Reposition

Business use

Instructional/training

Personal use

Aerial application

Passenger service

General utility

NTSB accident count

Figure 96. Airframe failure accidents by activity: twin-turbine helicopters (commercially manufactured).
 199

2

8

7

11

10

1919

13

 0 0

0 2 4 6 8 10 12 14 16 18 20

Undetermined/Other

Engine

Landing gear

Airframe

Control system-Tail

Control system-Main

Tail rotor

Main rotor

Drive train-Tail

Drive train-Main

NTSB accident count

Figure 97. Airframe failure accidents by system: twin-turbine helicopters (commercially manufactured).
 200

0

50

350300250200150100

0 3 6 9 12 15 18 21

 89 Airframe/component/system failure/malfunction 43 In flight collision with object 40 Loss of control 39 Loss of engine power 16 In flight collision with terrain/water 12 Weather  10 On ground/water collision with object 9 Miscellaneous/other 8 Hard landing 8 Propeller/rotor contact to person  274 Accidents from first 10 categories 28 Accidents from other 11 categories  302 Total

10 Categories account for 91 % of accidents

4 Categories account for 70 % of accidents

NTSB major categories

Twinturbine

helicopter

accident

count

Figure 98. Summary accident statistics, mid-1963 through 1997: twin-turbine helicopters (commercially manufactured).
 201

38

41

50

6767

81

95

100

113

133

166

180

217

 0 0 0

 0

 0

0 50 100 150 200 250

Hard landing

Fire/explosion

Rollover/noseover

Stall/settling with power

Dragged wing, rotor, pod, float or tail/skid

Propeller/rotor contact to person

Loss of engine power

Undetermined

Miscellaneous/other

Gear collapsed

In flight collision with object

Loss of control

Abrupt maneuver

In flight collision with terrain/water

Weather

Airframe/component/system failure/malfunction

On ground/water collision with object

Midair collision

Fatalities per 100 accidents

Figure 99. Fatalities per 100 accidents, mid-1963 through 1997: twin-turbine helicopters (commercially manufactured).

Fatalities First-event category

 148 Airframe/component/system failure/malfunction

 38 Loss of control

 35 In flight collision with object

 18 In flight collision with terrain/water

 18 On ground collision with object  16 Loss of engine power

 16 Weather

 13 Midair collision

 19 Undetermined/miscellaneous/other

 951 Total
 202

0

500

3,0002,5002,0001,5001,000

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

Registered

amateur

helicopters

and

autogyros

End of year

Total

amateur

(edited by Harris)

Amateur

helicopters

(edited by Harris)

Figure 100. All other rotorcraft types fleet size.
 203

0

40302010

1960 1965 1970 1975 1980 1985 1990 1995 2000

Accidents

per

1,000

registered 

rotorcraft

End of year

Figure 101. Accidents per 1,000 registered aircraft: all other rotorcraft types.
 204

111

28

165

73

25

40

20

5

9

3

13

1

22

10

2

3

11

2

0

0 20 40 60 80 100 120 140 160 180

Loss of engine power

In flight collision with object

Loss of control

Airframe/component/system failure/malfunction

Hard landing

In flight collision with terrain/water

Rollover/noseover

Weather

Miscellaneous/other

Propeller/rotor contact to person

Stall/settling with power

Midair collision

On ground/water collision with object

Fire/explosion

Abrupt maneuver

Gear collapsed

Undershoot/overshoot

Dragged wing, rotor, pod, float or tail/skid

Undetermined

On ground/water encounter with terrain/water

Missing

NTSB accident count

Figure 102. Accident count by first event category: all other rotorcraft types.

Total of 516 accidents

from mid-1963 through 1997
 205

25

2

16

1

6

7

44

8

28

0

0

10

0 5 10 15 20 25 30

Other Sub-categories

Undetermined/Other

Rotor Drive System

Other Engine Systems

 Fuel improper

 Induction air system

 Carburetor heat

 Fuel control

 Fuel starvation

 Fuel contamination

 Fuel system

 Fuel exhaustion

Engine structure

NTSB accident count

40

Fuel / air 

mixture

related

accidents

Figure 103. Loss of engine power accidents: all other rotorcraft types.
 206

111

2

11

6

5

10

0000

000

0 2 4 6 8 10 12

Bird strike

Electronic tower

Miscellaneous

Unspecified object

Aircraft

FOD

Fence/fence post

Building

Rock/brush/terrain

Airport/helipad facility

Crop

Vehicle

Pole/pipe

Tree(s)

Wire/pole

Wire

NTSB accident count

Figure 104. In flight collision with object accidents: all other rotorcraft types.
 207

5

1

6

29

0

2

11

0

20

8

70

13

0 10 20 30 40 50 60 70 80

Miscellaneous

Inadequate preflight planning

Airframe/comp./sys. fail. or malf.

Unqualified operator

Loss of visual ref./spatial disorient.

Weight/CG

Attached/snagged to grd. equip.

Flight control failure/deficiency

Undetermined

Winds

Low rotor RPM

Improper operation of controls

NTSB accident count

Figure 105. Loss of control accidents: all other rotorcraft types.
 208

19

3

7

2

18

11

6

7

0

0 2 4 6 8 10 12 14 16 18 20

Other

Landing gear

Tail rotor

Airframe

Main rotor

Control system-Tail

Control system-Main

Drive train-Tail

Drive train-Main

NTSB accident count

Figure 106. Airframe failure accidents: all other rotorcraft types.
 209

0

600500400300200100

0 3 6 9 12 15 18 21

 165 Loss of control 111 Loss of engine power 73 Airframe/component/system failure/malfunction 40 In flight collision with terrain/water 28 In flight collision with object 25 Hard landing 20 Rollover/nose-over  13 Stall/settling with power  475 Accidents from first 8 categories 41 Accidents from other 13 categories 516 Total

5 Categories account for 80 % of accidents

NTSB major categories

All

other

rotorcraft

accident

count

Figure 107. Summary accident statistics, mid-1963 through 1997: all other rotorcraft types.
 210

11

15

20

33

3333

39

47

59

80

100100

0

0

0

000

0

0 20 40 60 80 100 120

Hard landing

Stall/settling with power

Weather

On ground/water collision with object

Gear collapsed

Fire/explosion

Dragged wing, rotor, pod, float or tail/skid

Miscellaneous/other

Loss of engine power

Rollover/noseover

In flight collision with terrain/water

Propeller/rotor contact to person

Undershoot/overshoot

In flight collision with object

Loss of control

Airframe/component/system failure/malfunction

Abrupt maneuver

On ground/water encounter with terrain/water

Midair collision

Fatalities per 100 accidents

Figure 108. Fatalities per 100 accidents, mid-1963 through 1997: all other rotorcraft types.

Fatalities First-event category

 38 Loss of control

 43 Airframe/component/system failure/malfunction

 17 Loss of engine power

 13 In flight collision with terrain/water

 11 In flight collision with object 8 Abrupt maneuver

 4 Rollover/noseover

 2 On ground collision with object 

 5 Undetermined/miscellaneous/other

180 Total
 211

50

3025201510

1970 1975 1980 1985 1990 1995 2000 2005 2010

Accidents

per

1,000

registered 

rotorcraft

End of year

Figure 109. Accidents per 1,000 registered aircraft projected to 2010: all other rotorcraft types.

1972 through 1997

accident experience 

trend-line extrapolated to 2010

(exponential)
212

THIS PAGE INTENTIONALLY BLANK
213

Appendix A

NTSB DEFINITIONS

This appendix provides excerpts from the Federal Aviation Regulations that govern the National

Transportation Safety Board (NTSB) and excerpts from the NTSB manual that guide investigators in

reporting accidents.

A-1. Definitions of Accident/Incident

The following definitions of terms used in this report have been extracted from NTSB Part 830 of

the Federal Aviation Regulations. These regulations are included in most commercially available

FAR/AIM digests and should be referenced for detailed information.

Aircraft Accident—An occurrence incident to flight in which “as a result of the operation of an

aircraft, any person (occupant or non-occupant) receives fatal or serious injury or any aircraft

receives substantial damage.”

A fatal injury is one that results in death within 30 days of the accident.

A serious injury is one that:

1. Requires hospitalization for more than 48 hours, commencing within seven days from the

date the injury was received;

2. Results in a fracture of any bone (except simple fractures of the fingers, toes, or nose);

3. Involves lacerations that cause severe hemorrhages, nerve, muscle, or tendon damage;

4. Involves injury to any internal organ; or

5. Involves second- or third-degree burns, or any burns affecting more than 5% of body

surface.

A minor injury is one that does not qualify as fatal or serious.

Destroyed means that an aircraft was demolished beyond economical repair; that is, substantially

damaged to the extent that it would be impractical to rebuild it and return it to an airworthy

condition.

(This may not coincide with the definition of “total loss” for insurance purposes. Because of the

variability of insurance limits carried and such additional factors as time on engines and propellers

and aircraft condition before the accident, an aircraft may be “totaled” even though it is not

considered “destroyed” for accident investigation purposes.)
214

Substantial Damage:

1. Except as provided below, substantial damage means damage or structural failure that

adversely affects the structural strength, performance, or flight characteristics of the aircraft, and that

would normally require major repair or replacement of the affected part.

2. Engine failure, damage limited to an engine, bent fairings or cowling, dented skin, small

puncture holes in the skin or fabric, ground damage to rotor or propeller blades, damage to landing

gear, wheels, tires, flaps, engine accessories, brakes, or wing tips are not considered “substantial

damage.”

(As with “destroyed” above, the definition of “substantial” for accident investigation purposes does

not necessarily correlate with “substantial” in terms of financial loss. Contrary to popular

misconception, there is no dollar value that defines substantial damage. Because of the high cost of

many repairs, large sums may be spent to repair damage resulting from incidents that do not meet

the NTSB Part 830 definition of “substantial damage.”)

Minor damage is damage that does not qualify as substantial, such as that under “substantial

damage” above.

A-2. Definitions of Kinds of Flying

The purpose for which the aircraft is being operated at the time of the accident:

On-Demand Air Taxi—Revenue flights conducted by commercial air carriers operating under

14 CFR 135 that are not operated in regular scheduled service, such as charter flights, and all nonrevenue flights incident to such flights.

Personal—Flying by individuals in their own or rented aircraft for pleasure or personal

transportation, not in furtherance of their occupation or company business. This category includes

practice flying (for the purpose of increasing or maintaining proficiency) not performed under

supervision of an accredited instructor and not part of an approved flight training program.

Business—The use of aircraft by pilots (not receiving direct salary or compensation for piloting) in

connection with their occupation or in the furtherance of a private business.

Instruction—Flying accomplished in supervised training under the direction of an accredited

instructor.

Executive/Corporate—The use of aircraft owned or leased and operated by a corporate or business

firm for the transportation of personnel or cargo in furtherance of the corporation’s or firm’s

business, and that are flown by professional pilots receiving a direct salary or compensation for

piloting.
215

Aerial Application—The operation of aircraft for the purpose of dispensing any substance for plant

nourishment, soil treatment, propagation of plant life, pest control, or fire control, including flying to

and from the application site.

Aerial Observation—The operation of an aircraft for the purpose of pipeline/powerline patrol, land

and animal surveys, etc. This does not include traffic observation (electronic news gathering) or

sightseeing.

Other Work Use—The operation of an aircraft for the purpose of aerial photography, banner/glider

towing, parachuting, demonstration or test flying, racing, aerobatics, etc.

Public Use—Any operation of an aircraft by any federal, state, or local entity.

Ferry—A non-revenue flight for the purpose of (1) returning an aircraft to base, (2) delivering an

aircraft from one location to another, or (3) moving an aircraft to and from a maintenance base.

Ferry flights, under certain terms, may be conducted under terms of a special flight permit.

Positioning—Positioning of the aircraft without the purpose of revenue.

Other—Any flight that does not meet the criteria of any of the above.

Unknown—A flight whose purpose is not known.

A-3. NTSB Manual Definitions and Codes

PART I—INSTRUCTIONS

Introduction

The NTSB Coding Manual is a source document for codes to be used in the Board’s main frame

computer for storage and retrieval of information concerning the findings of aviation accidents. This

revision of the coding manual contains suggested changes that were received in the Regional

Operations and General Aviation Division (AS-20). Procedures are in effect to update the manual on

a periodic basis. Suggestions for changes or corrections should be forwarded to the Senior

Analyst(s) in AS-20. Suggestions may be forwarded by using the form at the end of this manual or

by telephone.

The codes are normally sent to the main frame computer through a network system by using the

ADMS program. Entry of codes may be made by the individual investigator by using his (or her) PC

or by personnel in AS-20. A computer matrix is provided in the ADMS program for entry of codes.

The codes should be entered in the matrix to correspond with the sequence in which they led to the

accident/incident.
216

Computerized findings are published for each accident and incident in a brief format (Brief-ofAccident or Brief-of-Incident). Each brief includes findings, which are identified in a sequence-ofevents as occurrences, phases, causes, factors, and/or events. A probable cause (PC) statement is also

published to provide a narrative presentation of the NTSB findings.

The codes and respective printout data are listed in the coding manual in an alphabetical order,

within the respective categories, rather than in a sequential or number order. Printout data is listed in

upper-case letters, whereas explanatory notes (that do not print out) are in parenthesis with lowercase wording.

The previous publication of the this manual was in January 1995. Codes that have been added or

changed (since the previous publication) are annotated as follows:

• Pound sign (#) designates a change

• Plus sign (+) designates an addition

• Equal sign (=) designates a code for a subject (printout) that was previously used

before the previous revision

• Less-than symbol (<) interim change to previous revision

• Asterisk (*) references definition in Part II of manual.

General Instructions

As previously noted, the codes in this manual are intended to be used to describe the sequence-ofevents of each accident and/or incident. All entries in the sequence-of-events (and brief narrative)

must be substantiated by information that is documented in the Factual Report or is available in

other accessible documents or publications.

Multiple occurrences, causes, factors and/or events may be used in each sequence-of-events to

describe the findings. Each occurrence is coded separately and a corresponding phase of operation

must be entered with each occurrence; as of the date of this publication, only five occurrences can be

recorded for each mishap. There must be at least one occurrence and one cause identified with each

accident or incident. The occurrences must be chronologically numbered. For accidents with

multiple causes, there is no provision to show the magnitude of each cause with respect to the others.

Likewise, there is no provision to show the relative magnitude of multiple factors. For retrieval

purposes, elements of the PC statement should be coded in the sequence-of-events, if feasible.

The number of findings and the size of the PC statement are limited by the amount of space

available on the second page of the computer printout. Depending on the number of occurrences and

number of lines used in the PC statement, about 15 to 43 causes/factors/events can be listed for any

one accident or incident.

The sequence-of-events matrix (see: Sequence-of-Events Worksheet, Part III) contains entry spaces

for codes in the following sections:
217

1. IA—Primary Non-Person-Related Findings (Aircraft/Environment)

2. IB—Primary Person-Related Findings (Operations/Performance)

3. II—Direct Underlying Events

4. III—Indirect Underlying Events.

Each section of the matrix contains columns of spaces. The spaces in the left column of each section

are for “subject” codes. The long spaces to the right of the subject spaces are for modifiers/persons.

The short spaces in the middle of each section are used to describe whether the subjects are causes

or factors by entering “C” or “F” codes. These may be left blank, if the subject is neither a cause nor

a factor, but merely an event.

Formerly, the main frame (DEC 10) computer (using System 1022) was programmed to allow entry

of restricted information in the database that would not print out in the briefs. This was

accomplished by putting an “X” in the middle space to denote the restricted information. This

information was stored in the computer for use as statistical information only. Currently, there is no

requirement for entry of restricted data, and the VAX/MV-4 computer (using System 1032) has not

been programmed for entry of this information. The database, however, still contains restricted

information that was previously entered via the DEC 10.

Within each section of the matrix, each line entry must be completed in its entirety; i.e., each subject

code must be followed by a modifier and/or person code. Sections IA and IB are used to list the

primary events/findings that led to the accident or incident. Sections II and III are used to further

define or explain a primary event or finding that is listed in Section IA or IB.

Section IA is used to identify the primary non-people-related findings. It contains columns of spaces

to enter non-people-related subjects and modifiers. However, a code is available to allowed the

modifier to be left blank, if needed. The non-people-related subjects are grouped in the following

categories:

Aircraft systems/components

Air traffic facilities

Airport facilities

Terrain conditions

Weather conditions

Light conditions

Object(s).

Section IB identifies the primary finding(s) that are people related. This section normally contains a

subject, modifier, and person, although codes are available for the modifier and person to be left

blank. However, the blank code for a person should only be used when no other person code can be

supported by the factual report. A blank modifier code is only used in conjunction with a blank

person code.
218

Sections II and III are used for the direct and indirect underlying findings. They are normally coded

with a subject and a person (or institution), but codes are available for the person code to be left

blank. Any number of underlying findings can be related to a primary finding in Section IA and/or

IB. However, underlying findings in Section II or III should only be used when they are related to a

primary finding in Section IA and/or IB

The computer system was previously programmed so that when more than one finding was entered

on the same line, findings in sections/columns to the right would be indented to show a relationship.

This feature is no longer available. Print-outs from the codes are now (without indentation),

beginning with the first code entered on the left in line one of the matrix followed by those to the

right and below.

Mandatory Conventions:

The coding manual is designed to provide a great degree of latitude and flexibility in formulating the

findings. However, certain conventions should be followed to logically present some sequences-ofevents.

For NTSB retrieval of multiengine aircraft information, the phrase “TOTAL LOSS OF ENGINE

POWER” and “PARTIAL LOSS OF ENGINE POWER” are to be used in reference to the specific

engine(s) being addressed, rather than to the overall power of the aircraft. Specifically, for a situation

involving total loss of power for mechanical reasons in one engine of a multiengine aircraft, the code

for that occurrence would be 351 (for “LOSS OF ENGINE POWER (TOTAL)—MECH

FAILURE/MALFUNCTION”). Also, codes are provided in the aircraft section to identify the

number of engines affected on multiengine aircraft. The following codes are intended for use with

multiengine aircraft findings:

a. [16905] ONE ENGINE

b. [16906] TWO ENGINES

c. [16907] THREE OR MORE ENGINES

d. [16908] ALL ENGINES.

For occurrences involving loss of engine power in multiengine aircraft, one of the above codes

would normally be used as the first entry (subject) in the sequence-of-events (in Section IA); an

exception would be when the number of engines that lost power was unknown. These (subject)

codes should be modified by Code 1220 (blank code), so that no modifier will print out. Typically,

losses of power in more than one engine would be coded as separate occurrences, except when more

than one engine loses power at the same time for the same reason. If the occurrence resulted in all

engines losing power (i.e., fuel exhaustion), then Code 16908 (ALL ENGINES) should be used

(even if the aircraft had two or three engines, though there are codes for two and three engines).

For example, consider a turbine disk failure of the No. 1 engine of a Boeing 727 that resulted in a

total loss of power of that engine; then shortly thereafter, partial loss of power occurred in the No. 2

and No. 3 engines due to a fuel system problem.
219

In coding this scenario, there would be two occurrences involving loss of power; i.e. the first

occurrence would be coded “LOSS OF ENGINE POWER (TOTAL)—MECH FAILURE/

MALFUNCTION.” The first subject code for this occurrence would be 16905, (ONE ENGINE),

which would be modified by Code 1220 (blank space). Of course, additional findings would follow

to describe the appropriate cause(s) and/or factor(s).

The second occurrence would be coded “LOSS OF ENGINE POWER (PARTIAL)—

MECHANICAL FAILURE/MALF.” The first subject code for the second occurrence would be

16906 (TWO ENGINES) followed by Code 1220 (blank space).

For single-engine aircraft accidents/incidents, there is no reason to provide a code for the number of

engines, since “one engine” would be obvious.

A progressive loss of power may be considered a single event. For example, a bearing failure may

result in a partial loss of power at first, but the power loss could deteriorate until there was a total

loss of power. For all practical purposes, this would be one occurrence.

Whenever an occurrence mandates a forced landing, the next occurrence in the sequence-of-events

would normally be “FORCED LANDING” (180). The associated phase of operation will often be

“EMERGENCY DESCENT/LANDING” (576), but the phase could be “MANEUVERING—TURN

TO LANDING AREA (EMERGENCY)” (583), “EMERGENCY LANDING AFTER TAKEOFF”

(575), “EMERGENCY LANDING” (574), or “LANDING” (570). Forced landings are often

presented with no other findings listed for that occurrence. However, there are some typical findings

that are occasionally used with forced landings, if they are appropriate and substantiated;

i.e., “EMERGENCY PROCEDURE—NOT FOLLOWED—PILOT IN COMMAND” if and when

appropriate, and “AUTOROTATION—PERFORMED—PILOT IN COMMAND” when a helicopter

is involved in an autorotation during a forced landing.

Code 502, “STANDING—STARTING ENGINE(S),” is used for hand propping/runaway accidents.

The typical convention for coding this situation would be as follows:

1st Occurrence—MISCELLANEOUS/OTHER (430)

1st Phase—STANDING-STARTING ENGINE(S) (502)

2nd Occurrence—Usually a collision with object or terrain

2nd Phase—Usually “TAXI” (510), although the aircraft could become airborne before the

second occurrence, result in an in flight collision with terrain or object.
220

For occurrences involving carburetor ice, the sequence-of-events should include the environmental

condition and the events leading to the situation as well as listing the cause/factor(s). The following

is a typical convention for mechanical loss of power due to carburetor heat control failure and

subsequent carburetor ice:

LOSS OF ENGINE POWER (TOTAL)—MECH FAILURE/MALF (351)

1. WEATHER—CARBURETOR ICING CONDITIONS (20000/F/2202)

2. CARB HEAT CONTROL—FAILURE, TOTAL (16400/C/1135)

3. FUEL SYSTEM, CARBURETOR—ICE (15109/C/1146).

For non-mechanical loss of power due to improper use of the carburetor heat by the pilot:

LOSS OF ENGINE POWER (TOTAL)—NON-MECHANICAL (353)

1. WEATHER—CARBURETOR ICING CONDITIONS (20000/F/2202)

2. FUEL SYSTEM, CARBURETOR—ICE (15109/C/1146)

3. CARB HEAT—IMPROPER USE OF—PIC (22304/C/3110/4000).

PART II—DEFINITIONS

ABRUPT MANEUVER: An intentional maneuver that directly results in personal injury or aircraft

damage.

ALTITUDE DEVIATION, UNCONTROLLED: For an occurrence in which there is a loss-ofcontrol that results in a loss or gain in the altitude, but recovery is accomplished (i.e., autopilot

malfunction of airliner that results in altitude deviation & injury to unbelted occupant).

COLLECTIVE BIAS: A mechanism, system, or function of a helicopter that automatically adjusts

engine power to maintain rotor rpm, when an increase or decrease in collective is made. (The

mechanism is also known as a throttle/collective correlator box.)

DITCHING: A planned event in which a flight crew knowingly makes a controlled emergency

landing in water. (Excludes float plane landings in normal water landing areas.)

DRAGGED WING, ROTOR, POD, FLOAT, OR TAIL: Use as a first occurrence only, when this

results in an aircraft accident or incident during taxi, takeoff, or landing. (Not used in conjunction

with a hard landing or after a gear collapse or ground loop/swerve.)

DYNAMIC ROLLOVER: Ground rollover mishap of a helicopter, which results from a cumulative

effect of dynamic forces. These forces cause a roll reaction that results in the helicopter exceeding

its static rollover angle.
221

ENGINE TEARAWAY: An occurrence in which one or more engines are torn away from an aircraft,

but not due to contact with an external object. (Includes tearaway due to internal damage from

foreign object damage.)

FORCED LANDING: An emergency landing involving circumstances in which the pilot does not

have the option to selectively choose the time and appropriate location for landing. (See

“precautionary landing” for circumstances in which the pilot has the time and option to choose an

appropriate landing area.)

GEAR COLLAPSE: Collapse of the landing gear due to mechanical failure other than malfunction

of the retracting system. When the landing gear collapses as a result of a hard landing, the gear

collapse will be the subsequent (second) occurrence.

FIRE/EXPLOSION: Use as an occurrence for fire, explosion, or heavy smoke occurring in flight,

and for aircraft fires occurring on the ground, except those resulting from impact.

GEAR RETRACTION: Retraction of the landing gear (on ground or runway) due to malfunction of

the retraction system, or due to inadvertent or premature retraction by the crew. (Gear retraction on

takeoff will be coded as gear retraction in the takeoff phase, and will not be recorded as a wheels-up

landing. Excludes intentional gear retractions.)

GO-AROUND: A maneuver following an uncompleted approach, which involves transition to a

climbing flightpath.

GROUND LOOP: An involuntary uncontrolled (abrupt) turn of an aircraft, while moving along the

ground (i.e., ground taxiing or moving on the takeoff or landing run).

GROUND RESONANCE: Dangerous natural vibration of a helicopter on the ground, caused by

stiffness and frequency of the landing gear legs, amplifying the primary frequency of the main rotor.

(Includes the self-excited vibration of a helicopter, occurring whenever the frequency of oscillation

of the blades about the lead-lag hinges of an articulated rotor becomes the same as the natural

frequency of the fuselage.)

HARD LANDING: Stalling onto or flying into a runway or other intended landing area with

abnormally high vertical speed. For rotorcraft, includes “tail-down” landings and those where the

main rotor contacts the tail boom on landing.

HEIGHT/VELOCITY CURVE: Fundamental plot of indicated airspeed against altitude, which is

included in the helicopter flight manual; indicates region(s) from which safe autorotative descent is

possible, normally assuming zero wind, sea level, and maximum takeoff weight.

HELIPAD: Prepared area (of land, water or structure) designated as a takeoff/landing area for

helicopters (no facilities other than markings needed); includes truck or trailer that is routinely used

as heliport.

HELIPORT: A facility used for operating, basing, housing, and maintaining helicopters.
222

IN FLIGHT ENCOUNTER WITH WEATHER: Weather encountered that is not normal to the

intended phase of operation. Use as an occurrence only when it leads to an accident or incident.

(Excludes: vortex turbulence and operations in normal crosswind or IFR conditions.)

MISSING AIRCRAFT: For purposes of coding, a missing aircraft is one that is presumed to have

crashed, and the location of the crash is unknown. If credible witness(es) or pieces of wreckage can

reasonably verify the accident and location, then the aircraft would not be considered as missing.

NOSE DOWN: When an aircraft noses down on the ground, water, or runway without going

inverted.

NOSE OVER: When an aircraft goes inverted on the ground, water, or runway, while taxiing or on

takeoff or landing.

NOTAR SYSTEM: Helicopter “No Tail Rotor” System. (For McDonnell Douglas Helicopters:

consists of an enclosed variable pitch fan driven by the transmission, a circulation control tail boom,

direct-jet thruster, and vertical stabilators.)

OCCURRENCE: Distinct major event of relative significance that leads to an accident or incident.

ON-GROUND ENCOUNTER WITH WEATHER: An occurrence involving weather that is not

normal to the phase of operation. (Excludes: vortex turbulence, jet/prop blast, and normal IFR or

crosswind conditions.)

OVERRUN: The continuation of aircraft movement beyond the end of the runway; i.e., overrunning

the intended landing or takeoff area. (Used in takeoff and landing phases.)

PHASE OF OPERATION: The point in aircraft operations during which an occurrence takes place.

PIBAL: Small balloon launched to check wind direction before takeoff of hot air balloon to assist in

visualizing ground track relative to anticipated flightpath.

PRECAUTIONARY LANDING: A landing involving a sense of urgency due to an emergency or

pending emergency, in which the pilot has the option and time to selectively choose an appropriate

landing area.

PROPELLER FAILURE/MALFUNCTION: An occurrence concerning failure or malfunction of a

propeller blade, hub, or related part, including separation or overspeeding of a propeller, or failure of

a propeller system. (Note: When propeller failure results from engine seizure, crankshaft failure,

etc., the occurrence should be coded as an engine failure.)

ROLL OVER: Refers to rotorcraft only. Includes tilting with the main rotor blades striking the

ground.
223

ROTOR FAILURE/MALFUNCTION: An occurrence concerning failure or malfunction of a rotor

blade, hub, or related part, including separation or overspeeding of a rotor or failure of the rotor

drive system.

SETTLING WITH POWER: A condition of helicopter power settling, in which hover power

required exceeds power available, normally resulting from an attempt to hover out of ground effect

with insufficient power available to compensate for elevation, temperature, and/or humidity.

UNAPPROVED PART: A part, component, or material that has not been manufactured in

accordance with the approval procedures in FAR 21.305 or repaired in accordance with FAR Part 43;

does not conform to an approved type design; or does not conform to established industry or U.S.

specifications (standard parts). Examples of an unapproved part include, but are not limited to: (1)

Counterfeit or fraudulently marked parts, components, or materials; (2) Parts shipped directly to

users by a manufacturer, supplier, or distributor who does not hold, or operate under the authority of,

a production approval for the part; and (3) Parts that have been maintained or repaired and returned

to service by persons or facilities not authorized under FAR Parts 43 or 145.

UNDERSHOOT: A condition that occurs during an approach to landing that results in an inadvertent

landing or contact with the ground or an object short of the runway or intended landing area,

normally due to misjudgment of distance, speed, and/or altitude on final approach. For IFR

approaches, an undershoot will occur only after the field or intended landing area is in sight. An

undershoot will always be followed by a subsequent occurrence; i.e., in flight collision-with-object

or terrain, etc. (Does not include occurrences in which the aircraft could not have reached the

intended landing area; i.e. after loss of engine power.)

VORTEX RING STATE: An area of nonuniform and unsteady airflow around a rotating main rotor

or tail rotor in which the rotor is affected by an induced velocity of airflow that approaches or

exceeds the airflow being produced by the affected rotor. It is characterized by a sudden requirement

for increased power and/or rotor pitch when airflow from the affected rotor is forced back through

and around the rotor.

WHEELS-UP LANDING: Code as an occurrence when the landing gear is not lowered and locked

before contact with the ground/runway during a landing. (Excludes inadvertent retraction on the

ground and retractions due to failure or malfunction of the gear assembly and/or retracting

mechanism. Includes intentional wheels-up landing and inability to extend the gear due to

malfunction of the gear extension system.)

VLOF “Lift-off speed”

VMCG “Minimum control speed on the ground” The minimum speed at which, the critical engine

having been made suddenly inoperative at that speed and having been recognized by the pilot, it is

possible to maintain control of the airplane with the engine still inoperative, using primary

aerodynamic controls alone, and thereafter maintain a straight path parallel to that originally

intended.
224

VMCA “Minimum control speed” The minimum speed at which, when the critical engine is

suddenly made inoperative at that speed, it is possible to recover control of the airplane with the

engine still inoperative and to maintain it in a straight flight at a speed, either with zero yaw or with

an angle of bank not in excess of 5o.

VYSE “Best rate-of-climb single-engine speed”

VXSE “Best angle-of-climb single-engine speed”

VS “Stalling speed” The minimum speed in flight at which the airplane can develop a lift equal to

the weight of the airplane.

VSO “The power off stall speed” or minimum steady flight speed in the landing configuration.

VFE “Maximum flap extended speed”

VLO “Maximum landing gear extension/retraction speed”

VLE “Maximum landing gear extended speed”

VA “Design maneuvering speed” The maximum speed for which the aircraft is designed for full

abrupt control deflection without incurring structural damage.

VMO “Maximum operating limit speed”

VNE “Never-exceed speed”

VREF “Landing approach speed” The indicated airspeed that the aircraft should be at 50 feet above

the landing area in the landing configuration. (1.3 × VSO)

VR “Rotation speed”

Vtoss “Takeoff safety speed” (Category A helicopter)

V1 “Takeoff decision speed” (Formerly denoted as critical engine failure speed.) The speed at

which, should the critical engine fail, the pilot could elect to abandon the takeoff or continue.

V2 “Takeoff safety speed” A reference speed obtained after lift-off at which the required oneengine-inoperative climb performance can be achieved.

V2MIN “Minimum takeoff safety speed” (1.15 × VS for two and three engine propeller-driven

aircraft or 1.10 × VS for four engine propeller-driven aircraft or 1.10 × VMCA, whichever is

greater.)
225

PART IV—CODES FOR OCCURRENCES

100 ABRUPT MANEUVER*

130 AIRFRAME/COMPONENT/SYSTEM FAILURE/MALFUNCTION (incld inflt brkup)

131 PROPELLER FAILURE/MALFUNCTION

132 ROTOR FAILURE/MALFUNCTION (main or tail rotor of helicopter)

110 ALTITUDE DEVIATION, UNCONTROLLED (i.e., after auto-plt malfunction)

120 CARGO SHIFT

140 DECOMPRESSION

150 DITCHING*

160 DRAGGED WING, ROTOR, POD, FLOAT OR TAIL/SKID*

355 ENGINE TEARAWAY

170 FIRE/EXPLOSION

172 EXPLOSION

171 FIRE

180 FORCED LANDING

190 GEAR COLLAPSED

194 COMPLETE GEAR COLLAPSED

191 MAIN GEAR COLLAPSED

192 NOSE GEAR COLLAPSED

195 OTHER GEAR COLLAPSED

193 TAIL GEAR COLLAPSED

198 GEAR RETRACTION ON GROUND*

200 HARD LANDING

210 HAZARDOUS MATERIALS LEAK/SPILL (fumes/smoke therefrom)

220 IN FLIGHT COLLISION WITH OBJECT (object modifiers, 20200 series)

230 IN FLIGHT COLLISION WITH TERRAIN/WATER (trrn modfrs, 19200 series)

231 WHEELS DOWN LANDING IN WATER

232 WHEELS UP LANDING

240 IN FLIGHT ENCOUNTER WITH WEATHER* (wx modifiers, 20000 series)

250 LOSS OF CONTROL—IN FLIGHT (includes stall, spin, vmc roll, and inability to ctl acft

after becoming spatially disoriented)

260 LOSS OF CONTROL—ON GROUND/WATER(excludes intentional gnd loop)
226

350 LOSS OF ENGINE POWER (includes loss of power for unknown reason)

352 LOSS OF ENGINE POWER(PARTIAL)—MECH FAILURE/MALF

354 LOSS OF ENGINE POWER(PARTIAL)—NONMECHANICAL

351 LOSS OF ENGINE POWER(TOTAL)—MECH FAILURE/MALFUNCTION

353 LOSS OF ENGINE POWER(TOTAL)—NONMECHANICAL

270 MIDAIR COLLISION (when both aircraft involved are airborne)

271 COLLISION BETWEEN AIRCRAFT (OTHER THAN MIDAIR) (excludes unoccupied acft)

420 MISSING AIRCRAFT*

430 MISCELLANEOUS/OTHER

280 NEAR COLLISION BETWEEN AIRCRAFT

290 NOSE DOWN*

300 NOSE OVER*

310 ON GROUND/WATER COLLISION WITH OBJECT (obj mod, 20200 series)

320 ON GROUND/WATER ENCOUNTER WITH TERRAIN/WATER (trrn/19200 series)

330 ON GROUND/WATER ENCOUNTER WITH WEATHER* (wx mod, 20000 series)

340 OVERRUN*

360 PROPELLER BLAST OR JET EXHAUST/SUCTION

370 PROPELLER/ROTOR CONTACT TO PERSON

380 ROLL OVER (normally associated with helicopter)

390 UNDERSHOOT*

400 UNDETERMINED

410 VORTEX TURBULENCE ENCOUNTERED

PART V—CODES FOR PHASES OF OPERATION

500 STANDING

501 STANDING—PRE-FLIGHT

502 STANDING—STARTING ENGINE(S)

503 STANDING—ENGINE(S) OPERATING

504 STANDING—ENGINE(S) NOT OPERATING

505 STANDING—IDLING ROTORS

510 TAXI (includes runaway while hand-propping)

511 PUSHBACK/TOW
227

512 TAXI TO TAKEOFF

513 TAXI—FROM LANDING

514 TAXI—AERIAL (includes air/hover taxi)

520 TAKEOFF (modify with operational code 24563, if on touch-and-go)

523 TAKEOFF—ABORTED

522 TAKEOFF—INITIAL CLIMB (to 1st power reduction or pattern altitude; includes crosswind

leg)

521 TAKEOFF—ROLL/RUN (ground or water)

530 CLIMB

531 CLIMB—TO CRUISE

540 CRUISE (includes low-altitude straight and level flight)

541 CRUISE—NORMAL

550 DESCENT

551 DESCENT—NORMAL

552 DESCENT—EMERGENCY (plt initiated; i.e., after decompression)

553 DESCENT—UNCONTROLLED

560 APPROACH

561 APPROACH—VFR PATTERN—DOWNWIND

562 APPROACH—VFR PATTERN—BASE TURN

563 APPROACH—VFR PATTERN—BASE LEG/BASE TO FINAL

564 APPROACH—VFR PATTERN—FINAL APPROACH

566 APPROACH—IAF TO FAF/OUTER MARKER (IFR)

567 APPROACH—FAF/OUTER MARKER TO THRESHOLD (IFR)

568 APPROACH—CIRCLING (IFR) (in conjunction with IFR approach)

569 MISSED APPROACH (IFR)

565 GO-AROUND (VFR) (before touchdown)* (refer to 573 for after touchdown)

570 LANDING (modify with operational code 24563, if touch-and-go)

573 LANDING—ABORTED (balked—after touchdown)

571 LANDING—FLARE/TOUCHDOWN

572 LANDING—ROLL

574 EMERGENCY LANDING

575 EMERGENCY LANDING AFTER TAKEOFF (i.e., forced lndg after tkof)
228

576 EMERGENCY DESCENT/LANDING (i.e., with forced landing, except after takeoff or

during landing approach)

580 MANEUVERING (includes buzzing)

581 MANEUVERING—AERIAL APPLICATION (includes swath run)

582 MANEUVERING—TURN TO REVERSE DIRECTION

583 MANEUVERING—TURN TO LANDING AREA (EMERGENCY)

542 MANEUVERING—HOLDING(IFR)

590 HOVER (stationary; excludes aerial taxi)

591 HOVER—IN GROUND EFFECT

592 HOVER—OUT OF GROUND EFFECT

600 OTHER

610 UNKNOWN
229

Appendix B

ESTIMATION OF ROTORCRAFT FLEET SIZE AND HOURS FLOWN

Some often-quoted aviation safety statistics for any given aircraft class are fatalities per 100,000

flight hours and accidents per 100,000 flight hours. These ratios are obtained by dividing two

numbers. The numerator for these ratios, fatalities or accidents for a given year, comes from the

NTSB’s files, which are reliable. The denominator, flight hours per year, comes from the FAA files,

which are frequently questioned because the statistical data are very dependent on (1) the Aircraft

Registration Master File, (2) the aircraft owners’ response to FAA registration and activity requests,

and (3) the FAA statistical methodology. The FAA and its CAA predecessor have—since 1944—

made a yearly effort to publish their Census of U.S. Civil Aircraft.* This census includes results,

since 1977, from the General Aviation Activity and Avionics Survey. Rotorcraft are grouped with

general aviation fixed-wing aircraft in the surveys and reports.

In the early 1980s, the census data for the active aircraft count, as well as hours flown per year by

the active rotorcraft fleet, began to appear erratic, and the rotorcraft industry publicly expressed its

concern (see, for example, ref. 7). Because the FAA groups rotorcraft together with general aviation

fixed-wing aircraft in their yearly census, the rotorcraft industry felt that their unique rotary wing

products—representing anywhere from 3% to 5% of the general aviation fleet—were likely not to be

accurately represented statistically. Should the flight hours per year be substantially in error, for

example, the rotorcraft accidents per 100,000 flight hours would be misleading. In turn, this could,

perhaps, cast the rotorcraft industry’s safety record in a bad light, with obvious consequences. In

response to the rotorcraft industry’s misgivings, the FAA performed a special survey of just the

registered rotorcraft fleet activity in 1989 (ref. 17).

In view of the situation discussed above, an in-depth review of the FAA yearly Census of U.S. Civil

Aircraft reports (1957 through 1994), and the General Aviation Activity and Avionics Survey reports

(1977 through 1997) was completed. Particular attention was paid to the FAA’s one-time-only

Rotorcraft Activity Survey (ref. 17), which was also included in the 1987 General Aviation Activity

and Avionics Survey report. The following discussion offers some insight into several issues

concerning the method for gathering, evaluating, and using FAA rotorcraft fleet activity data.

The Rotorcraft Activity Survey (ref. 17) illustrates the statistical methodology used by the FAA to

arrive at their 1989 reference data. The data bank accumulation process begins with the Aircraft

Registration Master File (maintained by the FAA’s Mike Monroney Aeronautical Center in

Oklahoma City). This Master File is sent to the FAA’s Statistical Analysis Branch in Washington,

D.C., where the surveys are conducted and the data published. The Statistical Analysis Branch

arrives at the number of active aircraft and the number of hours flown by active aircraft by sending

out a questionnaire to registered owners. For example, the Rotorcraft Activity Survey questionnaire

(Form 1800-55) contained 31 blanks to be filled in by respondents to the questionnaire. This

questionnaire specifically asked for “(1) hours by use and the number of landings for the entire

 *The last version of this Census available as a paper copy is for 1994. In 1995, the primary data tables were put on the

World Wide Web. It now looks like a Census for 1996, 1997, 1998, and 1999 will not be published at all. The FAA now

appears to have no staff available for what many consider to be a very valuable service.
230

calendar year, 1989 and (2) total airframe hours and the aircraft’s base location as of December 31,

1989.” The questionnaire was sent out to 10,469 rotorcraft owners/operators. Appendix A of the

Rotorcraft Activity Survey report describes the methodology for the survey in additional detail.

After reading the Rotorcraft Activity Survey and its appendix several times, it is concluded that:

1. The final tally of 10,469 rotorcraft represents some culling from the Aircraft Registration

Master File, which is approximately 10% greater in number. For example, questionnaires were not

sent for rotorcraft registered to dealers; rotorcraft with “Sale Reported” or “Registration Pending”

appearing in the record instead of the owner’s name; rotorcraft with a known, inaccurate owner’s

address; and rotorcraft with missing state of registration, aircraft make-model-series code, or aircraft

type information.

2. The return rate on the 10,469 questionnaires with three mailings was: first mailing,

March 1990 of 10,469 with return of 5,786; second mailing, May 1990 of 4,683 with return of 619;

and third mailing, July 1990 of 2,181 with return of 319.

Thus, the overall response totaling 6,724 was 64% of the 10,469 questionnaires mailed. The second

mailing included a repeat mailing to postal returns from the first mailing. The third mailing excluded

1,883 postal returns. Between these first two factors, a large percentage of the rotorcraft fleet is

unaccounted for. The last sentence in the Survey’s appendix (Paragraph 5.3.2, Non-Sampling Error)

states: “Unfortunately, the high rate of postal returns reflects a seriously out-of-date rotorcraft file.”

With about 275,000 aircraft to keep track of, rotorcraft represented slightly less than 4% of the civil

aircraft fleet.

The Rotorcraft Activity Survey appendix describes, in paragraph 5.2, how the responses from 6,724

owners were extrapolated to the baseline 10,469 population. Apparently, any rotorcraft owner who

answered at least one question on a 31 blank form was counted as a “respondent.” Paragraph 5.2

then goes on to describe a weighting computation based on respondents, “census frame” and

“response rate for a cell,” words that were undefined. Despite other hints about the method, we were

unable to follow the details.* However, the 1989 results of the extrapolation were provided in

table 2.1, chapter II, of the Rotorcraft Activity Survey. The key data from that table are reproduced

below.

Using data from the Rotorcraft Activity Survey as a 1989 reference point, a detailed review of

available census tabulations and surveys from 1964 through 1997 was completed. Based on that

review, the principal author is of the opinion that the rotorcraft industry (representing just one

aircraft type) has every reason to question the validity of the FAA published count of active

rotorcraft—as well as the hours flown by the active rotorcraft fleet—in any given year after 1979. A

basis for the rotorcraft industry concern is given by figures B-1 through B-9 or tables D-20, D-21,

and D-22.

 *A more detailed and helpful explanation of the method is included as an appendix in each General Aviation Activity

and Avionics Survey report. The reports for 1996 and 1997 can be found at Web page

http://api.hq.faa.gov/apo_pubs.htm on the Internet.
231

Rotorcraft type

Population

size

Estimate of

number

active

Estimate of total

hours flown

(in 1989 by

active aircraft)a

Estimate of

average hours

flown (per year by

active aircraft)a

Manufacturer built

Piston total 3,994 2,684 728,125 277.8

Single turbine 3,616 3,248 1,532,270 480.5

Twin turbine 1,069 984 546,471 551.8

Turbine total 4,685 4,232 2,078,741 496.5

Manufacturer total 8,679 6,916 2,806,866 417.3

Amateur built total 1,790 572 21,830 38.2

Total all rotorcraft 10,469 7,488 2,828,697 390.2

aIt is not clear why column three divided by column two does not equal column four in the above table.

As figures B-1 and B-2 suggest, the trend in FAA quoted hours flown by the “active” portion of the

registered rotorcraft fleet in any given year after 1979 appears quite erratic relative to the trend

shown for earlier years. Figure B-1 suggests that the timing of this erratic appearance might be

consistent with the downturn in the rotorcraft industry’s growth in the 1980s (see figs. 8, 16, 45, or

73). However, when yearly hours flown are graphed versus registered fleet size (i.e., active plus

inactive rotorcraft), as shown in figure B-2, an entirely different impression is made. Figure B-2

suggests that registered fleet size growth after 1979 was accompanied by fewer hours flown per year.

This would be at odds with the historical trend shown prior to 1979. One interpretation of figure B-2

might be, that the active fleet (i.e., those rotorcraft that flew at least 1 hour in the year) decreased,

that the active fleet flew fewer hours, and that 1,000 to 2,000 rotorcraft were simply “mothballed.”

(This possible explanation will be discussed shortly.) Similar contradictory impressions are shown

individually by the piston-engine-powered portion of the fleet (figs. B-3 and B-4) and the turbineengine-powered portion of the fleet (figs. B-3 and B-5). In fact, the generally erratic trend in census

and fleet activity borders on the absurd for the piston-powered fleet shown in figure B-4. The post1979 trend (shown by the long dashed line) suggests that when the Aircraft Registration Master File

lists 8,000 piston-powered rotorcraft, all rotorcraft of this type will be “inactive” and the total fleet

will accumulate no flight hours in that year.

The more likely explanation for the picture presented by figures B-1 through B-5 is that the method

of gathering data changed in the 1977-1979 period. A hint that this is exactly what happened is

provided by the FAA Census of U.S. Civil Aircraft for calendar year 1979. In the section entitled

"ACTIVE GENERAL AVIATION AIRCRAFT AND HOURS FLOWN," beginning on page 51,

several key statements are made. These statements (along with comments by the principal author in

brackets) are as follows:

From paragraph 1: These data [tables 3.1 onward] are for the active fleet, as opposed to the

registered fleet data shown in preceding tables.
232

From paragraph 2: Beginning in 1977, General Aviation Aircraft Activity information [where

rotorcraft are grouped] was obtained using the General Aviation Activity and Avionics Survey.

Heretofore, the activity data were collected from each owner of a registered aircraft [principal

author’s italics] using the Aircraft Registration, Eligibility, Identification, and Activity report.

From paragraph 3: [The General Aviation Activity and Avionics Survey, which replaced the

Aircraft Registration, Eligibility, Identification, and Activity report, used a sampling method.] The

sample of 31,208 aircraft was selected from approximately 234,000 registered general aviation

aircraft. The sample is a scientifically designed random sample which represents all general aviation

aircraft registered in the United States.

From paragraph 4: Because the estimates [of active aircraft and hours flown] are derived

from a sample—not the total population of aircraft—a certain amount of sampling error is

introduced. ...Although the exact value of the sample error is unknown, a quantity known as the

standard error is used to approximate it [etc.].

From paragraph 5: If, for example, the estimate for the total number of active piston powered

rotorcraft were 2,658 and the standard error were 176, then the 95% confidence interval would be

2,658 ± 2(176) or (2,306; 3010). One would say that there is a 95% chance that the number of active

piston-powered rotorcraft lies between 2,306 and 3,010.

From last paragraph: More detail estimates and a more detailed discussion of the survey and

its method are available in the 1978 General Aviation Activity and Avionics Survey. [The first

GAAA Survey was conducted in 1978 to examine fleet activity for the calendar year 1977. The

results were published in April 1979 as Report No. FAA-MS-79-5.]

The FAA initiative to unburden the public and save money in the data gathering effort by relying

more heavily on statistical methods than it did in earlier years was not a blind step.* The reliance on

the General Aviation Activity and Avionics Survey appears to have been a smart decision even for

1978 and 1979. However, as figures B-6 and B-7 show (see also tables D-21A, D-21B, and D-21C),

the results throughout the 1980s, and so far in the 1990s, shows a diverging pattern of erratic

behavior that is not reflected in the total registered fleet census data of figures 8, 16, 45, or 73.

In itself, the erratic character of the FAA data shown in figures B-1 through B-7 may be considered

relatively inconsequential by many people. After all, the major rotorcraft manufacturers maintain

much more accurate records of where their rotorcraft are, what they are being used for, and the

status of each type’s fleet hours. However, when potentially misleading FAA data are used as the

denominator in a safety ratio (such as accidents per 100,000 flight hours) and this ratio then creates

a misleading impression—either way—a disservice is being done to the public and to the aviation

industry.

 *The first GAAA Survey states in Paragraph 1.1.2, Background, that “Specifically, the public reporting burden was

reduced by an estimated 13,000 hours annually, and the cost savings to the public and Government were estimated to be

one million dollars annually.” Figures 1.4, 1.5 and 1.6 of this first GAAA Survey show 1977 data obtained by the new

statistical methodology connected quite well with data from 1973, 1974, 1975, and 1976.
233

A more practical view of the statistical situation is given in figures B-8 and B-9. These two figures

show that the error in hours flown using the General Aviation Activity and Avionics Survey method

adopted in 1978 might easily be ±30% for piston-powered rotorcraft and ±25% for turbine-powered

rotorcraft when calculated at constant active rotorcraft fleet size. More specifically, suppose in

figure B-8, the active piston count in 1983 is truly 2,541 rotorcraft. Then the possibility exists that

the hours flown in that year could be as low as 480,000 or as high as 790,000. Now, according to the

NTSB’s report (see table D-1), 150 accidents occurred with piston-powered rotorcraft of all types in

1983. Thus, the safety statistic could be anywhere from 150 accidents per 4.8 hundred thousand

hours (i.e., 31 accidents per 100,000 hours) down to 150 accidents per 7.9 hundred thousand hours

(i.e., 19 accidents per 100,000 hours).

The chronology of this ambiguity—a growing uncertainty of rotorcraft fleet flight hours

accumulated in any given year and the number of rotorcraft actually flying—is documented in the

General Aviation Activity and Avionics Survey reports (1977 through 1997). Table D-22 provides a

data summary from selected GAAA survey yearly reports to examine the chronology. To begin with,

the first GAAA Survey (covering 1977) provided encouragement that a “statistically designed

sample of about 14.4% of the registered general aviation fleet” would be accurate enough for FAA

purposes. Data obtained by the new statistical method correlated reasonably well with data from

1973, 1974, 1975, and 1976. For rotorcraft, instead of sending out 6,845 questionnaires (the census

count after some culling to yield the approximate population), only 1,924 questionnaires were sent,

which defined the “sample size” of 1,924 in table D-22. The 80.5% response rate yielded the

statisticians 1,548 returns from which the total “population’s” activity could be constructed. Results

differentiating piston- from turbine-powered rotorcraft were obtained, but a breakdown to specific

make and model was not published; nor were results comparing single-turbine against multi-turbine

powered rotorcraft.

This first GAAA Survey was actually conducted in 1978 and was published in April 1979. It

contained information of additional note. Again, principal author comments are in brackets.

1. “In 1978, the FAA replaced AC Form 8050-73 with a new system

[Form 1800-54].” The new system changed the mandatory aircraft registration

renewal requirement from once a year to a “triennial registration program.”

(Par. 1.1.2)

2. The sample size was constructed using the Aircraft Registration Master

File as of December 31, 1977. “This file is the official record of registered civil

aircraft in the U.S., containing one record per aircraft. It accurately represents the

current civil air fleet, being updated continuously for new registrations, change in

ownership, etc.” (Par. 1.3.1)

3. The population “consisted of 212,598 general aviation aircraft records

from which 30,643 records were sampled, yielding a 14.4% sample.” “These

[figures] clearly demonstrate the disproportionality of the sample to the population,

an intended result of the sample design to gain efficiency and to control errors.”

(Par. 1.3.1)
234

4. “Errors associated with estimates derived from sample survey results fall

into two categories: sampling and non-sampling errors.” [Reference is made to the

U.S. Dept. of Commerce, Bureau of the Census document entitled Standards for

Discussion and Presentation of Errors in Data, 1974, pp. I1–I4.] “Sampling errors

occur because the estimates are based on a sample—not the entire population. Nonsampling errors arise from a number of sources such as non-response, inability or

unwillingness of respondents to provide correct information [etc.].” (Par. 1.3.3)

5. A second mailing and telephone survey of a sample of non-respondents

were conducted in addition to the original mailing to improve the response rate,

since a low response rate is a major cause of non-sampling error.” “[Ultimately]

80% of those aircraft sampled responded to at least one question of the survey.” (Par.

1.3.3.2)

As figure B-1 and table D-22 strongly suggest, the inadequacy of the “new system” and associated

GAAA Survey method quickly became evident. From 1977 to 1987, response rate dropped from

80% to roughly 50%. The 1987 GAAA Survey, in its Appendix B, paragraph B.1, adequately

summed up the dilemma the new system was creating by stating:

1. Instead of requiring all owners to revalidate and update their aircraft

registration annually, FAA required revalidation for only those owners who had not

contacted the registry for 3 years. The less frequent updating affected the accuracy

of the file and its representativeness. Two major consequences for the survey results

are discussed below:

A. The accuracy of owner’s addresses deteriorated causing the percentage of

questionnaires returned by the post office to almost triple from 1977 to 1982.

Post office returns have since increased to nearly 13% in 1987, of the original

sample of aircraft selected. This partially accounted for the lower survey

response rates experienced since 1977.

B. The [Aircraft Registration Master] file contained a residue of aircraft

which under the old revalidation system would have been deregistered and

purged from the file, but remained under the new system. Consequently, the

population counts were inflated resulting in artificially large increases in the

estimates of the number of active general aviation aircraft from 1977 to 1978,

and from 1978 to 1979.

2. Also during this period the entire Aircraft Registration System was

installed on a new computer system. At the same time, FAA modified many of the

updating and processing procedures. It is quite possible that these changes affected

the registration file, although it is not known in what way.

These three basic themes—points 1 and 1.A and 1.B above—along with a continued unsatisfactory

response rate of around 50% are repeated in each GAAA Survey report from 1987 to 1997. It should

be noted that at no time over this 20-year period did the FAA arbitrarily increase its sample size

from approximately 30,000, which might have offset the reduced response rate and increasing
235

number of post office returns. In 1977, the defined general aviation aircraft population was 212,598

aircraft, 30,643 questionnaires were sent out and about 24,500 (i.e., 80% response rate) respondents

filled in at least 1 blank on Form 1800-54. In 1987, the corresponding numbers were 267,400

aircraft, 29,719, questionnaires and about 18,100 respondents (i.e., 61.1% response rate). By 1996,

the defined population was 247,821 aircraft with 29,952 questionnaires sent out. The Post Office

returned 1,641 envelopes, and 19,362 responses were counted to give a response rate of 68.7%. A

footnote on page A-12 of the 1996 GAAA Survey report states that “The 68.7% response rate is

computed by subtracting the Post Master Returns (1,641) and museum pieces (126) from the total

valid sample size of 29,952.” This method change, among several others, as well as a recompilation

of survey results over the 1987 to 1996 period (to account for a “nonresponse bias”) is discussed in

the 1996 GAAA Survey report. This 1996 report and the 1997 report are available at Web page

http://api.hq.faa.gov/apo_pubs.htm on the Internet.

From the rotorcraft industry point of view shown in table D-22, the statisticians began in 1988 to

deflate the census count given by the Aircraft Registration Master File to arrive at the defined

population. Apparently dealing with an outdated, unpurged Master File was considered

unsatisfactory. How the size of the population and then the sample size were arrived at is, however,

not clear. One thing is clear and that is: to statistically infer the activity of 8,000 to 12,000 rotorcraft

from 750 to 1,500 responses is a very bold extrapolation—regardless of the perceived intentions “to

gain efficiency and to control errors.”

Safety statistics can be constructed, of course, at face value irrespective of the concerns about FAAprovided fleet hours raised in the preceding discussion. Some results, when approached in this

fashion, are provided in figures B-10, B-11, B-12, and B-13, based on the tabulations of table D-23.

These results are provided without further discussion.

A very real danger exists given the possibility that safety statistical trends could be influenced and

varied as much as discussed above. For example, reference 22 notes that on 12 February 1997, the

White House Gore Commission on Aviation Safety issued a report. Based upon the

recommendations of this report, President William J. Clinton announced a national goal of reducing

aviation fatal accident rate 80% over the next 10 years.*

One meaning to the rotorcraft community of this national goal can be interpreted first with

figure B-14 and, perhaps more familiarly in ratio form, with figure B-15. Figure B-14 shows the

number of people who lost their lives each year in civil rotorcraft accidents in the United States.

These are yearly fatalities as recorded by the NTSB—not the number of fatal accidents in the year or

the fatal accident rate referred to by President Clinton. These yearly fatalities are graphed with the

solid-black, circled points shown in the figure. These “data” are associated with the left-hand

vertical scale, as the arrow labeled Fatalities (NTSB) points out. The second set of data is the graph

of hours accumulated in a year of flying by the active rotorcraft fleet in each year from 1965 through

1997. This FAA published data use the × symbol and the right-hand vertical scale that the arrow

labeled Hours (FAA) points to. The hours are in units of 100,000. Note that the last 5 years of FAA

data were abruptly displaced downward relative to the preceding 5 or 7 years by about 25%. This

change reflects the apparent decision to define the rotorcraft population independently of the

 * The actual goal contained in the FAA’s Strategic Plan aims to “ reduce the U.S. aviation fatal accident rate per aircraft

departure, as measured by a 3-year moving average, by 80% from the 3-year average from 1994–1996” by 2007.
236

Aircraft Registration Master File census as discussed above and shown in table D-22 for years 1991,

1992, and 1993.

The statistical ratio of fatalities per 100,000 hours is obtained for each year from figure B-14 by

dividing the number of fatalities by the number of 100,000-hour units. The result of this division is

shown in figure B-15 and table D-23. An exponential trend, shown as the heavy solid line in figure

B-15, gives a sense of how the rotorcraft industry is generally improving despite considerable yearto-year ups and downs. The national goal announced by President Clinton could, in fact, be applied

to the fatality rate (i.e., fatalities per 100,000 hours—not fatal accidents per 100,000 hours). If this

were done, then a reference point for 1997 might be 2.5 fatalities per

100,000 hours, which lies at the end of the exponential trend line. Should the 80% goal then be

applied, it follows that the rotorcraft industry would be striving for less than 0.5 fatalities per

100,000 hours by the year 2007.

Figure B-15 suggests an ambitious goal irrespective of accuracy questions concerning FAA fleet

activity data. Of course, the true aviation goal is—unquestionably—no fatalities or injuries.
 237

0

500,000

3,000,0002,500,0002,000,0001,500,0001,000,000

1960 1965 1970 1975 1980 1985 1990 1995 2000

Total

hours

flown

per year

by the

active

rotorcraft

fleet

Year ending

Figure B-1. Annual hours flown by the active rotorcraft fleet.

Upper trend line

Lower trend line

Annual flight

hours estimated

by the FAA
 238

0

500,000

3,000,0002,500,0002,000,0001,500,0001,000,000

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

1979

Total

hours

flown

per year

by the

active

rotorcraft

fleet

Total registered rotorcraft (active plus inactive)

Figure B-2. Annual hours flown vs. registered rotorcraft yearly count.

1969

1964

1970

1997

1993

1991

Linear

trend

since

1979
 239

0

500,000

3,000,0002,500,0002,000,0001,500,0001,000,000

1965 1970 1975 1980 1985 1990 1995 2000

Total

hours

flown

per year

by

active

rotorcraft

type

Figure B-3. Annual hours flown by rotorcraft type.

Year ending

Piston powered

Turbine powered

Active fleet total 
 240

0

800,000600,000400,000200,000

1,000,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000

1977

1979

Total

hours

flown

per year

by the

active

piston

powered

fleet

Total registered piston powered rotorcraft (active plus inactive)

Figure B-4. Annual hours flown vs. registered piston powered rotorcraft.

1970

1997

Linear

trend

since

1979
 241

0

500,000

2,500,0002,000,0001,500,0001,000,000

0 1,000 2,000 3,000 4,000 5,000 6,000

1979

Total

hours

flown

per year

by the

active

turbine

powered

fleet

Total registered turbine powered rotorcraft (active plus inactive)

Figure B-5. Annual hours flown vs. registered turbine powered fleet.

1970

1997
 242

0

8,0007,0006,0005,0004,0003,0002,0001,000

1960 1965 1970 1975 1980 1985 1990 1995 2000

table D-21Atable D-21Btable D-21C

Active

rotorcraft

fleet

Year ending

Figure B-6. Total active rotorcraft fleet count by year (including revisions).
 243

0

8,0007,0006,0005,0004,0003,0002,0001,000

0 2,000 4,000 6,000 8,000 10,000 12,000 14,000

table D-21Atable D-21Btable D-21C

1979

Active

rotorcraft

fleet

Total registered rotorcraft (active plus inactive)

Figure B-7. Active count vs. total count by year (including revisions). 

1993

1994

1964

1997

Upper trend

of scatter

Lower trend

of scatter
 244

0

800,000600,000400,000200,000

1,000,000

0 500 1,000 1,500 2,000 2,500 3,000 3,500

table D-21Atable D-21Btable D-21C

Active piston fleet count (including revisions)

Figure B-8. Annual hours flown by active piston fleet vs. active piston fleet.

Total

hours

flown

per year

by the

active

piston

fleet

1997

Linear

 trend

Linear trend

plus 30 %

Linear trend

minus 30 %
 245

0

500,000

2,500,0002,000,0001,500,0001,000,000

0 1,000 2,000 3,000 4,000 5,000

table D-21Atable D-21Btable D-21C

Active turbine fleet count (including revisions)

Figure B-9. Annual hours flown by active turbine fleet vs. active turbine fleet.

Total

hours

flown

per year

by the

active

turbine

fleet

Linear

trend

Linear trend

plus 25 %

Linear trend

minus 25 %
 246

0

50

350300250200150100

0 5 10 15 20 25 30

Accidents

per year

for the

total

fleet

Hours flown per year by the total active fleet (100,000 hrs.)

Figure B-10. Annual accident count vs. annual hours flown for the active fleet.

1970

1997

1979

1964

60 Accidents

per 100,000 hrs

12 Accidents

per 100,000 hrs

8 Accidents

per 100,000 hrs
 247

50

40353025201510

1970 1975 1980 1985 1990 1995 2000 2005 2010

Piston

powered

rotorcraft

accidents

per

100,000

hours

Year ending

Figure B-11. An accident statistic for piston powered rotorcraft.

Exponential

trend

1997

92 Accidents

343,841 Hrs.

1996

86 Accidents

591,000 Hrs.

1995

91 Accidents

337,000 Hrs.

1994

116 Accidents

340,189 Hrs.
 248

86420

16141210

1970 1975 1980 1985 1990 1995 2000 2005 2010

Turbine

powered

rotorcraft

accidents

per

100,000

hours

Year ending

Figure B-12. An accident statistic for turbine powered rotorcraft.

Exponential

Trend
 249

0

70605040302010

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Rotorcraft

accidents

per

100,000

hours

Year ending

Figure B-13. An accident statistic for all rotorcraft.

8 accidents per

100,000 hrs

by trend

Exponential

Trend
 250

0

80604020

120100

1965 1970 1975 1980 1985 1990 1995 2000

6050403020100

Year ending

Fatalities

per year

for the

total

fleet

Figure B-14. Rotorcraft trends in fatalities per year and annual hours flown.

Hours

flown

per

year

by the

total

active

fleet

(100,000)

Fatalities (NTSB)

Hours (FAA)

25 %
 251

876543210

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Fatalities

per

100,000

hours

Year ending

Figure B-15. A possible aviation goal for rotorcraft.

Exponential

Trend

2.5 fatalities per

100,000 hrs

in 1997

from trend

Year 2007 Goal

0.5 fatalities per

100,000 hrs
252

THIS PAGE INTENTIONALLY BLANK
253

Appendix C

AUTOROTATION-RELATED ACCIDENTS

A fairly common issue for discussion among rotorcraft pilots, operators, designers,

manufacturers, and regulators is the value of autorotation training. The question, similar to

ongoing discussions regarding spin training in fixed-wing aircraft, is whether autorotation

training (with its inherent risks) would result in a reduction of autorotation accidents in case of

actual emergency. The NTSB database used in this study provides information that interested

parties can use to explore this issue.

For this analysis, accidents from 1987 through 1997 were extracted from the NTSB database.

The accident summaries for the subgroup were searched for the terms “autorotation,”

“autorotational,” and “autorotative.” Summaries with any of those terms were examined; if the

summary showed that the accident involved an autorotation, the information was placed on a new

spreadsheet. After review of all such accidents, a new subgrouping containing autorotationrelated accidents was available for use.

For the 11-year period under consideration (1987 through 1997), 713 accidents were identified

as autorotation related. Of these, 401 (56.2%) involved piston-engine-powered rotorcraft, 295

(41.4%) involved single-turbine-engine helicopters, and 17 (2.4%) involved twin-turbine-engine

helicopters. Annual numbers of autorotation-related accidents for each aircraft type and rates per

1,000 airframes were also extracted and are presented in figures C-1 and C-2.

In figure C-2, the annual rate of autorotation accidents per 1000 aircraft varies about an average

of 8 per 1000 aircraft. What is interesting is that the rates are approximately the same for both

single-piston and turbine helicopters—in other words, this metric does not show an improvement

resulting from the use of turbine engines over piston engines.

The long-term ratio of autorotation-related accidents to all accidents is 0.33 for the entire

rotorcraft fleet, 0.32 for piston-engine rotorcraft, 0.39 for single-turbine helicopters, and 0.14 for

twins (fig. C-3). The yearly ratios for single turbines are consistently above the annual fleet ratio,

whereas the ratios for piston rotorcraft generally remain below those of the entire fleet. The

ratios are remarkably consistent from year to year. Even the twin-turbine ratios remain fairly

close to the long-term type mean if 1993 and 1997 are disregarded. Thus, as a rule of thumb, one

can estimate that 35% of rotorcraft accidents involve an autorotation.

The question, “does the autorotation capability of rotorcraft decrease the severity of accidents

(i.e., increase the survivability)?” may be raised. Figure C-4 shows two comparative ratios of

accidents involving fatalities. The upper curve in figure C-4 gives the ratio of fatal accidents to

all accidents. The lower curve on figure C-4 shows the ratio of fatal autorotation accidents to all

autorotation accidents. The annual ratios of fatal autorotation-related accidents to total

autorotation accidents remain consistently below the corresponding ratio of fatal accidents to all

accidents. The difference in the long-term averages (0.09 for autorotations and 0.19 for all fatal

accidents) represents the survivability advantage provided by the ability to autorotate. In other

words, if the accident sequence permits the pilot to enter autorotation, survival chances improve.
254

What are the reasons pilots enter autorotation? Figure C-5 shows the distribution of precipitating

events that led to autorotation-related accidents. Two major events stand out: engine problems

and practice. The dominance of the single-engine rotorcraft types drives this characteristic.

When flying a single-engine rotorcraft, the pilot normally reacts to any loss of engine power by

entering autorotation. Figure C-5 shows that 21% of autorotations-related accidents take place

during practice of the maneuver. However, it is important to note that this statistic (indeed all the

percentages shown on this chart) does not measure the risk per autorotation event, since, for the

most part, successful autorotations are not reported. In addition, some autorotation accidents that

took place during practice autorotations actually involved some mechanical or operational

problem, which turned the practice maneuver into an actual forced landing. This is also true for

some of the small number of autorotations during test flights. Figure C-6 amplifies figure C-5 by

reallocating these actual forced landings during practice or test into the appropriate reason bin.

When reallocated, practice autorotations account not for 21%, but for 17%.

This reallocation further increases the proportion of autorotation accidents precipitated by some

sort of engine problem (i.e., from 44.18% in fig. C-5 to 47.41% in fig. C-6). It thus appears that

the true proportion of accidents caused by poorly executed practice autorotations is about 17% to

18%. Flight instructors, flight schools, pilot examiners, and regulators should seriously consider

this statistic when evaluating the risk of practice autorotations compared with the benefits it

offers in improved survivability.

Engine problems are further broken down to determine their underlying events in figure C-7.

Mechanical failures are the major causal factor in both engine-problem-related autorotation

accidents and all autorotation accidents. Almost a quarter of all autorotations that resulted in

accidents are due to some mechanical failure of the engines. Further, and troubling, is that the

reasons for one-quarter of the engine problems could not be determined. Additionally, as was

discussed in the main part of this report, fuel exhaustion (the principal problem directly under

the control of the pilot) accounted for nearly one-fifth of the autorotation-related accidents. The

large number of undetermined-cause accidents is troublesome, because without knowing what

actually took place, no corrective action can be proposed.

Figure C-8 depicts the first event categories that virtually describe the end of an unsuccessful

autorotation. Hard landings and collisions with the terrain are the major problems with

autorotative landings. There is a degree of overlap between these categories. A basic distinction

is that a hard landing is normally a result of inadequate flare or collective pitch pull, whereas

collision with the terrain implies either no flare or the existence of a terrain feature the pilot

could not avoid. In any event, it appears that these two problem areas can be considered together

and, taken together, imply that the main difficulty in autorotative landings is judgment and

application of the flare and collective pitch pull. Together, almost two-thirds of the autorotation

accidents involve hard landings or collisions. This is another consideration for instructors, flight

schools, pilot examiners, and regulators in evaluating the benefits of practice autorotations in

reducing errors during actual forced landings.

Further examination of the data led to developing a distribution of problems identified in

autorotation accidents. The results of this examination are shown in figure C-9. A clearly evident

problem is the difficulty in maintaining autorotational RPM. This factor relates to the hard

landing problem since low rotor RPM, especially in the flare, will almost inevitably result in a

hard landing. This leads to a basic question: How can instructors, designers, manufacturers,
255

regulators, and pilots themselves improve RPM awareness and controllability (i.e., how to make

low RPM conditions more difficult to encounter or how to make corrections easier)?

The second major problem area identified by figure C-9 is difficulty in the flare. A successful

flare is the product of awareness of and correction for a wide variety of operational and

environmental factors such as aircraft performance, wind, altitude, presence of obstacles, type of

terrain, and many others. The required situational awareness and judgment develops with

practice. However, as has been discussed above, the practice autorotation is itself a fairly risky

maneuver. Thus, a balance must be struck between the risks of autorotation practice and the

benefits of improved pilot performance.

Several key questions remain to be answered before the rotorcraft industry improves its

autorotation experience; several examples follow:

1 Given the risk and cost of aircraft-based autorotation training, is it really necessary?

2. Will the development and availability of low-cost, medium-fidelity small computerbased simulators permit initial and recurrent training, which will improve pilot performance?

3. Can currently available low-cost simulation systems provide the necessary fidelity for

realistic training?

4. Are there other possible methods of improving pilot performance during forced

landings?

5. Can low-cost advanced pilot cueing systems be developed and fielded to improve

RPM awareness and correction of low RPM conditions?

6. Can the pilot be provided “flare now” cues?

7. Can the pilot be provided cues to indicate that the aircraft is nearing or is inside the

“avoid” areas of the height-velocity diagram?

It is not the purpose of this report to suggest specific systems. However, the hope is that by

presenting the reduced and analyzed autorotation data, the rotorcraft industry will have

information that is necessary to develop and implement the systematic changes required to

reduce accidents.
 256

Figure C-1. Autorotation-related accidents by year.

0

908070605040302010

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Number

of

 accidents

Total autorotation accidentsPiston autorotation accidentsSingle-turbine autorotation accidentsTwin-turbine autorotation accidents

Year ending
 257

Figure C-2. Autorotation-related accidents per 1,000 airframes

86420

1210

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Autorotation accident rate/1000 Airframes: allAutorotation accident rate/1000 airframes: pistonAutorotation accident rate/1000 airframes: single-turbineAutorotation accident rate/1000 airframes: twin-turbine

Year ending

Accidents

per

1,000

airframes
 258

Figure C-3. Autorotation-related accident/total accident ratio.

0.60.50.40.30.20.10.0

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Autorotation accidents/total: allAutorotation accidents/all: pistonAutorotation accidents/all: single-turbineAutorotation accidents/all: twin-turbine

Year ending

Ratio
 259

Figure C-4. Autorotation-to-total autorotation and fatal accidents-to-total accident ratios.

0.250.200.150.100.050.00

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

Fatal autorotation/total autorotationTotal fatal/total accidents

Year ending

Ratio
 260

Figure C-5. Reasons for autorotation.

0.6%0.6%

0.4%

0.3%0.3%0.3%0.3%

1.5%

1.3%

2.0%

3.2%

5.6%

8.6%

9.8%

21.2%

44.2%

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50%

Airframe Failure/Fire 

FOD

Main Rotor Hit Tail

Midair Collision 

Flight Control Failure 

Loss of Control

Not Reported

Demonstration 

Test

Precautionary Landing 

Collided with Obstacles

Loss of Directional Control 

Rotor Drive System Failure 

Fuel Exhaustion 

Practice 

Engine Failure or Malfunction
 261

Figure C-6. Reasons for autorotation (problems during practice distributed to reasons).

0.6%

0.4%

0.3%0.3%0.3%0.3%

0.7%

1.3%

1.1%

2.1%

3.4%

5.9%

8.6%

9.8%

17.7%

47.4%

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50%

Airframe Failure/Fire

FOD

Main Rotor Hit Tail

Midair Collision

Flight Control Failure

Loss of Control

Not Reported 

Test

Demonstration

Precautionary Landing 

Collided with Obstacles

Loss of Directional Control 

Rotor Drive System Failure

Fuel Exhaustion 

Practice

Engine Failure or Malfunction
 262

Figure C-7. Engine problems involved in autorotation accidents.

0.5%

0.2%0.2%0.2%0.2%

1.5%

2.2%

4.2%

5.6%

6.1%

17.2%

25.0%

36.8%

0.3%

0.1%0.1%0.1%0.1%

0.8%

1.3%

2.4%

3.5%

3.2%

9.8%

14.3%

21.0%

0% 5% 10% 15% 20% 25% 30% 35% 40%

Environmental

Fire

Fuel System

Water in Intake

Wrong Fuel

Erroneous Instrument Indications

Improper Operation of Controls

Icing

Fuel Starvation

Fuel Contamination

Fuel Exhaustion

Undetermined

Mechanical

Percentage of totalPercentage of engine-related
 263

Figure C-8. Results of autorotative accident landings.

0.6%

0.4%

0.3%

0.1%0.1%

1.5%1.5%

1.4%

1.3%

3.5%

10.1%

14.0%

20.9%

44.2%

0% 5% 10% 15% 20% 25% 30% 35% 40% 45% 50%

Ground Resonance 

Non Autorotative Landing

Tail Boom Failure

Dragged Tail

Gear Collapsed

Nose Over

Successful Autorotative Landing 

Main Rotor Hit Tail

Not Reported

Ditched

Roll Over 

Collided with Obstacles

Collided with Terrain/Water

Hard Landing
 264

Figure C-9. Identified problems in autorotation mishaps.

9

10

11

14

24

27

33

55

66

106

0 20 40 60 80 100 120

Wind Conditions

Poor Visual References

Autorotation Delayed/Not

Performed

Altitude Awareness 

Outside Autorotation Envelope

Improperly Performed

Autorotation

Improper Use of ControlsUnspecified

No Suitable Landing Area

Flare Problems

Rotor RPM Not Maintained 
265

Appendix D

OTHER STATISTICAL DATA TABLES

In preparing this report, the master data file was sorted into a number of data tables. Some of the

most useful tables (tables D-1 through D-31) are included in this appendix. Most of figures 1

through 109 were created from these tables.
266

THIS PAGE INTENTIONALLY BLANK
TABLE D-1. NTSB ACCIDENT COUNT BY YEAR AND TYPE

Count Cum Commercially manufactured helicopters All other rotorcraft types

Year per year count Single Piston Single Turbine Twin Turbine Auto. man. Amateur hel. Amateur auto. Unknown

end all types all types Per yr Cum Per yr Cum Per yr Cum Per yr Cum Per yr Cum Per yr Cum Per yr Cum

1963 4 4 0 0 2 2 2 2 0 0 0 0 0 0 0 01964 260 264 241 241 5 7 3 5 0 0 0 0 9 9 2 21965 243 507 223 464 5 12 1 6 8 8 0 0 4 13 2 41966 300 807 285 749 8 20 5 11 0 8 0 0 1 14 1 51967 239 1,046 221 970 15 35 2 13 0 8 0 0 0 14 1 61968 230 1,276 200 1,170 26 61 2 15 0 8 0 0 1 15 1 71969 264 1,540 217 1,387 45 106 2 17 0 8 0 0 0 15 0 71970 244 1,784 194 1,581 45 151 3 20 0 8 0 0 0 15 2 91971 220 2,004 183 1,764 31 182 2 22 0 8 3 3 0 15 1 101972 248 2,252 157 1,921 62 244 5 27 7 15 2 5 14 29 1 111973 287 2,539 195 2,116 61 305 5 32 2 17 4 9 17 46 3 141974 287 2,826 204 2,320 52 357 4 36 4 21 2 11 18 64 3 171975 315 3,141 220 2,540 72 429 5 41 0 21 3 14 11 75 4 211976 277 3,418 196 2,736 58 487 5 46 4 25 4 18 8 83 2 231977 282 3,700 187 2,923 72 559 11 57 1 26 2 20 9 92 0 231978 328 4,028 216 3,139 77 636 15 72 1 27 3 23 13 105 3 261979 296 4,324 181 3,320 90 726 6 78 0 27 6 29 12 117 1 271980 327 4,651 171 3,491 117 843 12 90 1 28 7 36 17 134 2 291981 319 4,970 168 3,659 122 965 8 98 2 30 5 41 13 147 1 301982 303 5,273 148 3,807 119 1,084 10 108 1 31 9 50 14 161 2 321983 273 5,546 134 3,941 105 1,189 18 126 1 32 2 52 10 171 3 351984 280 5,826 127 4,068 119 1,308 20 146 1 33 5 57 7 178 1 361985 238 6,064 110 4,178 98 1,406 13 159 2 35 3 60 8 186 4 401986 222 6,286 112 4,290 81 1,487 18 177 2 37 1 61 6 192 2 421987 196 6,482 101 4,391 62 1,549 12 189 2 39 7 68 11 203 1 431988 207 6,689 108 4,499 68 1,617 14 203 1 40 3 71 9 212 4 471989 213 6,902 106 4,605 72 1,689 18 221 4 44 6 77 5 217 2 491990 226 7,128 123 4,728 77 1,766 7 228 2 46 6 83 10 227 1 501991 192 7,320 120 4,848 51 1,817 10 238 1 47 3 86 6 233 1 511992 199 7,519 106 4,954 61 1,878 10 248 0 47 12 98 9 242 1 521993 181 7,700 94 5,048 65 1,943 7 255 1 48 3 101 6 248 5 571994 211 7,911 97 5,145 83 2,026 12 267 2 50 7 108 3 251 7 641995 165 8,076 83 5,228 61 2,087 13 280 0 50 5 113 2 253 1 651996 185 8,261 70 5,298 87 2,174 12 292 0 50 11 124 4 257 1 661997 175 8,436 73 5,371 73 2,247 10 302 0 50 13 137 4 261 2 68

267
TABLE D-2. CAA/FAA ROTORCRAFT CENSUS

Commercially manufactured helicopters Amateur/

Census Total Total experimental

Year all Single Twin Single Twin helicopter autogyro total all

end types piston piston turbine turbine mfg. mfg. types

1952 150 150 0 0 0 150 0 0

1953 171 171 0 0 0 171 0 0

1954 192 192 0 0 0 192 0 0

1955 306 306 0 0 0 306 0 0

1956 413 413 0 0 0 413 0 0

1957 540 463 0 0 0 463 0 77

1958 700 576 0 14 1 591 0 108

1959 882 713 1 20 1 735 9 139

1960 1,096 817 1 88 2 908 9 180

1961 1,331 1,006 0 87 10 1,103 9 219

1962 1,606 1,211 2 83 18 1,314 9 283

1963 1,915 1,501 2 52 25 1,580 8 327

1964 2,196 1,717 0 59 29 1,805 17 374

1965 2,390 1,830 0 66 29 1,925 54 411

1966 2,740 2,003 0 88 30 2,121 87 532

1967 3,175 2,141 0 193 31 2,365 88 722

1968 3,755 2,313 0 351 43 2,707 88 960

1969 4,256 2,426 0 558 43 3,027 88 1,141

1970 3,476 2,116 0 498 28 2,642 36 798

1971 3,892 2,328 1 621 33 2,983 36 873

1972 4,265 2,385 3 858 34 3,280 34 951

1973 4,723 2,633 3 993 57 3,686 32 1,005

1974 5,395 2,959 4 1,266 93 4,322 32 1,041

1975 6,011 3,260 5 1,498 148 4,911 32 1,068

1976 6,391 3,411 5 1,710 145 5,271 30 1,090

1977 6,855 3,558 5 1,976 145 5,684 28 1,143

1978 7,688 3,763 47 2,377 172 6,359 26 1,303

1979 8,380 3,942 47 2,701 205 6,895 28 1,457

1980 9,012 4,041 47 3,111 261 7,460 29 1,523

1981 9,522 4,036 47 3,494 424 8,001 27 1,494

1982 9,733 3,897 47 3,745 562 8,251 28 1,454

1983 10,047 3,960 47 3,829 646 8,482 27 1,538

1984 10,416 3,980 47 3,975 773 8,775 27 1,614

1985 10,539 4,000 47 3,965 844 8,856 28 1,645

1986 10,530 3,983 47 3,856 914 8,800 27 1,703

1987 10,374 3,909 46 3,688 932 8,575 27 1,772

1988 10,153 3,840 46 3,518 872 8,276 28 1,849

1989 10,445 3,920 46 3,574 942 8,482 27 1,936

1990 10,646 3,993 46 3,590 965 8,594 26 2,026

1991 10,834 4,037 45 3,676 1,051 8,809 31 1,994

1992 10,952 4,061 45 3,681 1,078 8,865 33 2,054

1993 11,144 4,061 45 3,676 988 8,770 29 2,345

1994 11,459 4,114 45 3,888 1,061 9,109 29 2,322

1995 11,785 4,110 45 4,114 1,051 9,322 35 2,430

1996 12,354 4,172 45 4,410 1,091 9,720 35 2,601

1997 12,911 4,220 45 4,722 1,108 10,097 34 2,782

* 1995, 1996, and 1997 are preliminary

268
Table D-3. FATALITIES, INJURIES AND AIRCRAFT DAMAGE (CUMULATIVE)

Cum People affected Rotorcraft damage (S = substantial, D = destroyed)

Year accident Serious Minor/ Single piston Single turbine Twin turbine Auto. man. Amateur hel. Amateur auto. Unknown

end count Cum Killed injury none S D S D S D S D S D S D S D

1963 4 22 6 0 16 002011000000001964 264 471 33 44 394 187 52 6141000063201965 507 886 56 84 746 361 100 8451620094311966 807 1,462 102 146 1,214 575 169 14 6 10 1620095411967 1,046 1,904 144 187 1,573 745 220 25 10 12 1620095421968 1,276 2,389 224 220 1,945 892 272 43 17 12 3620096521969 1,540 2,897 273 254 2,370 1,057 323 74 31 13 4620096521970 1,784 3,376 298 278 2,800 1,205 366 110 37 15 5620096631971 2,004 3,768 322 311 3,135 1,334 418 136 42 16 6623096731972 2,252 4,306 386 351 3,569 1,447 459 176 59 20 7 12 3 4 1 18 10 8 31973 2,539 4,881 433 404 4,044 1,597 504 217 77 22 7 14 3 7 2 29 16 8 61974 2,826 5,410 500 451 4,459 1,728 575 251 94 24 8 17 4 9 2 41 22 10 71975 3,141 6,019 550 503 4,966 1,892 630 308 108 26 10 17 4 12 2 49 25 13 81976 3,418 6,552 614 581 5,357 2,026 692 350 124 31 10 20 5 15 3 53 29 15 81977 3,700 7,083 671 630 5,782 2,164 741 397 143 38 14 21 5 16 4 58 33 15 81978 4,028 7,713 749 698 6,266 2,313 805 443 172 47 19 22 5 18 5 64 40 17 91979 4,324 8,259 840 750 6,669 2,446 848 507 197 53 19 22 5 23 6 71 45 18 91980 4,651 8,927 942 813 7,172 2,568 897 584 232 57 24 22 6 30 6 82 51 20 91981 4,970 9,548 1,013 874 7,661 2,685 948 659 271 59 27 23 7 34 7 88 58 21 91982 5,273 10,167 1,101 952 8,114 2,797 984 730 316 62 32 23 8 38 12 96 64 21 111983 5,546 10,768 1,166 1,013 8,589 2,901 1,014 799 347 70 38 24 8 39 13 101 69 22 131984 5,826 11,382 1,246 1,088 9,048 2,988 1,050 880 379 80 46 25 8 40 17 104 73 22 141985 6,064 11,896 1,313 1,162 9,421 3,074 1,071 933 421 87 52 27 8 43 17 109 76 23 171986 6,286 12,435 1,414 1,218 9,803 3,154 1,101 975 456 99 57 27 10 43 18 110 81 23 191987 6,482 12,832 1,483 1,259 10,090 3,229 1,125 1,016 477 102 63 29 10 47 21 118 84 24 191988 6,689 13,255 1,527 1,320 10,408 3,312 1,148 1,061 497 107 68 30 10 48 23 122 89 25 221989 6,902 13,681 1,591 1,376 10,714 3,388 1,177 1,108 520 116 77 33 11 51 26 124 92 26 231990 7,128 14,147 1,640 1,427 11,080 3,481 1,206 1,157 541 120 79 35 11 57 26 128 97 27 231991 7,320 14,558 1,710 1,480 11,368 3,572 1,235 1,190 559 124 84 36 11 59 27 131 100 27 241992 7,519 14,951 1,793 1,527 11,631 3,653 1,260 1,230 579 128 88 36 11 69 29 136 104 27 251993 7,700 15,321 1,866 1,573 11,882 3,719 1,285 1,271 601 130 91 37 11 71 30 138 108 30 271994 7,911 15,763 1,951 1,623 12,189 3,792 1,309 1,320 633 135 98 38 12 75 33 138 111 36 281995 8,076 16,080 1,997 1,657 12,426 3,857 1,326 1,363 651 141 103 38 12 80 33 140 111 37 281996 8,261 16,437 2,063 1,692 12,682 3,910 1,343 1,430 669 147 108 38 12 87 37 142 112 38 281997 8,436 16,825 2,135 1,760 12930 3,971 1,354 1,468 702 152 112 38 12 95 42 145 113 40 28

 269
TABLE D-4. ALL ROTORCRAFT ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY

NTSB first event category 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

Loss of engine power 2 58 56 79 64 57 74 72 72 65 86 77 104 86 86 96 80 98 107 99 90 82 85In flight collision with object 0 50 52 70 47 38 45 53 47 61 51 58 58 51 42 56 56 52 38 33 26 36 34Loss of control 0 21 17 16 22 29 42 26 26 23 38 33 26 22 26 20 17 23 22 48 45 52 38Airframe/component/system failure/malfunction 1 22 24 29 30 31 29 17 19 27 31 39 36 42 39 53 53 56 45 41 47 30 20Hard landing 0 42 31 22 15 27 21 29 24 22 28 22 27 26 28 24 30 33 31 12 11 9 10In flight collision with terrain/water 0 19 21 27 20 13 13 18 17 12 22 19 29 13 27 39 30 23 38 25 19 22 13Rollover/noseover 0 15 13 10 12 15 26 15 5 15 8 24 28 32 15 23 20 21 29 9 10 10 3Weather 0 0 0 4 2 3 0 0 1 1 1 0 0 0 0 0 2 1 1 17 8 18 11Miscellaneous/other 0 12 9 3 4 1 0 1 0 2 2 0 4 1 2 4 2 0 1 8 4 7 9Propeller/rotor contact to person 0212233547251 0 141523243Stall/settling with power 0 9 10 20 11 6 5 1 1 5 4 0 0 1 2 2 1 1 0 0 0 0 0Midair collision 0014002200241 0 202522124On ground/water collision with object 0345602032410 0 230003030Fire/explosion 0211110213221 3 310620322Abrupt maneuver 0001200000200 0 000011302Gear collapsed 1123011102110 0 201100201Undershoot/overshoot 0314030001120 0 210002000Dragged wing, rotor, pod, float or tail/skid 0000000000000 0 000000101Undetermined 0100121100200 0 221200010On ground/water encounter with terrain/water 0000000000000 0 000000122Missing 0000000100000 0 100000000

Total by year 4 260 243 300 239 230 264 244 220 248 287 287 315 277 282 328 296 327 319 303 273 280 238

270
TABLE D-4. ALL ROTORCRAFT ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY (CONCLUDED)

NTSB First Event Category 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Cum

Loss of engine power 65 55 60 56 62 46 55 43 61 38 43 49 2,408In flight collision with object 26 21 18 31 26 12 22 25 24 24 19 20 1,322Loss of control 35 43 49 40 48 43 31 41 42 32 32 46 1,114Airframe/component/system failure/malfunction 32 26 32 30 26 29 23 20 22 28 32 22 1,083Hard landing 8 13 10 12 7 16 12 7 16 11 10 10 656In flight collision with terrain/water 11 10 8 16 14 23 22 19 16 10 10 4 642Rollover/noseover 3 4 8 3 13 4 9 6 6 5 10 4 433Weather 18 9 9 6 9 4 8 7 5 6 3 5 159Miscellaneous/other 744376723384 134Propeller/rotor contact to person 402140111012 79Stall/settling with power 000000000022 83Midair collision 221352014032 61On ground/water collision with object 000501052020 56Fire/explosion 320010311000 50Abrupt maneuver 353212102010 32Gear collapsed 110100100110 27Undershoot/overshoot 110010000010 24Dragged wing, rotor, pod, float or tail/skid 303323210311 24Undetermined 000000113034 28On ground/water encounter with terrain/water 000101113430 19Missing 000000000000 2

Total by year 222 196 207 213 226 192 199 181 211 165 185 175 8,436

271
TABLE D-5. MANUFACTURER SINGLE-PISTON ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

NTSB first event category

Loss of engine power 0 53 53 74 60 50 59 53 59 45 61 56 81 62 63 66 42 53 48 51 49 39 45In flight collision with object 0 46 50 69 42 36 41 47 41 43 40 48 42 40 32 37 38 32 22 19 13 18 11Loss of control 0 20 14 16 20 26 34 22 20 10 22 20 13 13 15 10 7 8 6 20 20 19 16Airframe/component/system failure/malfunction 0 21 22 28 30 27 24 15 16 15 21 26 25 27 26 31 34 32 29 17 19 13 8Hard landing 0 38 30 20 13 23 18 23 21 16 19 12 19 18 19 22 20 21 22 8 8 4 7In flight collision with terrain/water 0 19 18 27 20 12 8 17 15 6 15 14 20 11 17 30 21 11 21 17 11 13 9Rollover/noseover 0 13 12 10 11 13 22 9 4 12 6 15 17 21 7 14 13 10 16 7 7 5 3Weather 0004220 010100 0 001116252Miscellaneous/other 0 11 9 2 4 1 0 001102 0 111003164Propeller/rotor contact to person 0212211 133130 0 021010021Stall/settling with power 0 8 7 19 11 6 5 1 0 1 3 0 0 1 2 1 0 1 0 0 0 0 0Midair collision 0013002 200040 0 001000000On ground/water collision with object 0335301 020210 0 000000010Fire/explosion 0211100 113221 3 010210211Abrupt maneuver 0001200 000000 0 000010100Gear collapsed 0121001 102010 0 101000001Undershoot/overshoot 0303030 000020 0 200000000Dragged wing, rotor, pod, float or tail/skid 0000000 000000 0 000000101Undetermined 0100001 100100 0 211000000On ground/water encounter with terrain/water 0000000 000000 0 000000011Missing 0000000 100000 0 000000000

Total by year 0 241 223 285 221 200 217 194 183 157 195 204 220 196 187 216 181 171 168 148 134 127 110

Registered fleet size 1501 1717 1830 2003 2141 2313 2426 2116 2328 2385 2633 2959 3260 3411 3558 3763 3942 4041 4036 3897 3960 3980 4000

Accidents per 1,000 aircraft 140 122 142 103 86 89 92 79 66 74 69 67 57 53 57 46 42 42 38 34 32 28

272
TABLE D-5. MANUFACTURER SINGLE-PISTON ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY (CONCLUDED)

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Cum

NTSB first event category

Loss of engine power 36 28 35 26 33 30 31 22 33 15 19 24 1,554In flight collision with object 14 13 11 17 15 9 11 17 12 12 3 12 953Loss of control 20 19 28 21 26 29 17 20 19 21 15 19 625Airframe/component/system failure/malfunction 15 11 14 13 18 12 9 7 8 12 9 5 639Hard landing 5 9 4 8 4 10 8 5 11 8 5 5 483In flight collision with terrain/water 6 5 6 11 8 17 12 11 3 5 5 2 443Rollover/noseover 1341946 42342 290Weather 6521313 41120 57Miscellaneous/other 3322333 12121 74Propeller/rotor contact to person 2001101 10000 33Stall/settling with power 0000000 00001 67Midair collision 0100100 10010 17On ground/water collision with object 0002010 01010 26Fire/explosion 0000001 01000 28Abrupt maneuver 0300110 02000 12Gear collapsed 1000001 00110 16Undershoot/overshoot 1100000 00010 16Dragged wing, rotor, pod, float or tail/skid 2023131 10311 20Undetermined 0000001 01011 12On ground/water encounter with terrain/water 0000001 01100 5Missing 0000000 00000 1

Total by year 112 101 108 106 123 120 106 94 97 83 70 73 5,371

Registered fleet size 3983 3909 3840 3920 3993 4037 4061 4061 4114 4110 4172 4220

Accidents per 1,000 aircraft 28 26 28 27 31 30 26 23 24 20 17 17

273
TABLE D-6. MANUFACTURER SINGLE-TURBINE ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

NTSB first event category

Loss of engine power 2 3 3 4 3 7 15 18 11 15 18 17 19 19 15 21 34 39 49 42 36 37 33In flight collision with object 0 0 1 0 5 2 4 6 6 15 10 7 14 9 9 14 15 17 13 12 10 14 21Loss of control 0 0 0 0 2 3 8 3 3 6 8 5 4 7 5 5 7 9 12 14 17 19 15Airframe/component/system failure/malfunction 0 0 0 1 0 1 3 0 3 6 6 6 9 8 9 14 9 17 11 18 16 13 8Hard landing 0 2 0 1 2 3 3 6 3 6 7 3 7 5 9 2 10 10 7 3 2 4 2In flight collision with terrain/water 0 0 0 0 0 1 5 1 2 4 3 4 7 1 9 7 7 8 14 6 5 8 4Rollover/noseover 0 0 0 0 1 2 4 6 1 3 2 9 9 9 7 6 6 6 12 2 3 5 0Weather 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0 11 6 10 7Miscellaneous/other 0000000101101 0 120015213Propeller/rotor contact to person 0000022414011 0 120411221Stall/settling with power 0000000000000 0 000000000Midair collision 0001000000201 0 201512123On ground/water collision with object 0010101011200 0 130002010Fire/explosion 0000010000000 0 300110111Abrupt maneuver 0000000000000 0 000000200Gear collapsed 0001010000000 0 000000100Undershoot/overshoot 0000000001100 0 000001000Dragged wing, rotor, pod, float or tail/skid 0000000000000 0 000000000Undetermined 0000120000100 0 010100010On ground/water encounter with terrain/water 0000000000000 0 000000110Missing 0000000000000 0 100000000

Total by year 2 5 5 8 15 26 45 45 31 62 61 52 72 58 72 77 90 117 122 119 105 119 98

Registered fleet size 52 59 66 88 193 351 558 498 621 858 993 1266 1498 1710 1976 2377 2701 3111 3494 3745 3829 3975 3965

Accidents per 1,000 aircraft 85 76 91 78 74 81 90 50 72 61 41 48 34 36 32 33 38 35 32 27 30 25

274
TABLE D-6. MANUFACTURER SINGLE-TURBINE ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY (CONCLUDED)

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Cum

NTSB first event category

Loss of engine power 24 22 23 27 26 15 17 16 22 17 19 16 704In flight collision with object 8 5 6 10 8 2 8 7 9 11 15 5 298Loss of control 12 15 13 7 11 8 4 12 14 6 12 18 284Airframe/component/system failure/malfunction 13 8 10 12 5 10 9 10 9 11 15 12 282Hard landing 145326425245 140In flight collision with terrain/water 2 3 0 2 4 4 8 5 10 4 4 1 143Rollover/noseover 112240324052 119Weather 11 1 5 3 5 3 4 3 3 5 1 5 85Miscellaneous/other 101142311243 42Propeller/rotor contact to person 101020001001 35Stall/settling with power 000000000011 2Midair collision 211241001022 37On ground/water collision with object 000000040000 18Fire/explosion 220010010000 15Abrupt maneuver 201200000010 8Gear collapsed 000000000000 3Undershoot/overshoot 000010000000 4Dragged wing, rotor, pod, float or tail/skid 100000100000 2Undetermined 000000012012 13On ground/water encounter with terrain/water 000100012330 12Missing 000000000000 1

Total by year 81 62 68 72 77 51 61 65 83 61 87 73 2,247

Registered fleet size 3856 3688 3518 3574 3590 3676 3681 3676 3888 4114 4410 4722

Accidents per 1,000 aircraft 21 17 19 20 21 14 17 18 21 15 20 15

275
TABLE D-7. MANUFACTURER TWIN TURBINE ACCIDENT COUNT BY YEAR END AND BY FIRST EVENT CATEGORY

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

NTSB first event category

Loss of engine power 00010001110000520120155In flight collision with object 02010000021110151110241Loss of control 00100000100011110103252Airframe/component/system failure/malfunction 10000221011113154535932Hard landing 01010000000100000010100In flight collision with terrain/water 00000000001010100000200Rollover/noseover 00000000000001001100000Weather 00000000000000000000022Miscellaneous/other 00010000000010010000000Propeller/rotor contact to person 00000000001100000102000Stall/settling with power 00000000000000000000000Midair collision 00000000000000000010001On ground/water collision with object 00002000010000100000010Fire/explosion 00000001000000000200000Abrupt maneuver 00000000000000000000000Gear collapsed 10010000001000100000100Undershoot/overshoot 00000000000000010000000Dragged wing, rotor, pod, float or tail/skid 00000000000000000000000Undetermined 00000000000000000000000On ground/water encounter with terrain/water 00000000000000000000000Missing 00000000000000000000000

Total by year 2 3 1 5 2 2 2 3 2 5 5 4 5 5 11 15 6 12 8 10 18 20 13

Registered fleet size 25 29 29 30 31 43 43 28 33 34 57 93 148 145 145 172 205 261 424 562 646 773 844

Accidents per 1,000 aircraft 103 34.5 167 64.5 46.5 46.5 107 60.6 147 87.7 43 33.8 34.5 75.9 87.2 29.3 46 18.9 17.8 27.9 25.9 15.4

276
TABLE D-7. MANUFACTURER TWIN TURBINE ACCIDENT COUNT BY YEAR END AND BY FIRST EVENT CATEGORY (CONCLUDED)

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Cum

NTSB first event category

Loss of engine power 210011212211 39In flight collision with object 221331112111 43Loss of control 202412011404 40Airframe/component/system failure/malfunction 366314411532 89Hard landing 200000000010 8In flight collision with terrain/water 100201122110 16Rollover/noseover 001000000000 4Weather 111210101000 12Miscellaneous/other 310000000020 9Propeller/rotor contact to person 101000000001 8Stall/settling with power 000000000010 1Midair collision 000101002000 6On ground/water collision with object 000200011010 10Fire/explosion 100000100000 5Abrupt maneuver 011000000000 2Gear collapsed 000100000000 6Undershoot/overshoot 000000000000 1Dragged wing, rotor, pod, float or tail/skid 001000000000 1Undetermined 000000000011 2On ground/water encounter with terrain/water 000000000000 0Missing 000000000000 0

Total by year 18 12 14 18 7 10 10 7 12 13 12 10 302

Registered fleet size 914 932 872 942 965 1051 1078 988 1061 1163 1203 1220

Accidents per 1,000 aircraft 19.7 12.9 16.1 19.1 7.25 9.51 9.28 7.09 11.3 11.2 9.98 8.2

277
TABLE D-8. MANUFACTURER AUTOGYRO ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

NTSB First Event Category

Loss of engine power 00000000010101010010000In flight collision with object 00100000000001000000000Loss of control 00200000020100000101000Airframe/component/system failure/malfunction 00100000010101100000000Hard landing 00000000001101000010000In flight collision with terrain/water 00100000011000000000000Rollover/noseover 00100000000000000000000Weather 00000000010000000000010Miscellaneous/other 00000000000000000000100Propeller/rotor contact to person 00000000000000000000001Stall/settling with power 00100000010000000000000Midair collision 00000000000000000000000On ground/water collision with object 00000000000000000000000Fire/explosion 00000000000000000000000Abrupt maneuver 00000000000000000000001Gear collapsed 00000000000000000000000Undershoot/overshoot 00100000000000000000000Dragged wing, rotor, pod, float or tail/skid 00000000000000000000000Undetermined 00000000000000000000000On ground/water encounter with terrain/water 00000000000000000000000Missing 00000000000000000000000

Total by year 00800000072404110121112

278
TABLE D-8. MANUFACTURER AUTOGYRO ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY (CONCLUDED)

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Cum

NTSB First Event Category

Loss of engine power 000000001000 6In flight collision with object 100000000000 3Loss of control 011210011000 14Airframe/component/system failure/malfunction 000101000000 7Hard landing 000100000000 5In flight collision with terrain/water 100010000000 5Rollover/noseover 000000000000 1Weather 000000000000 2Miscellaneous/other 000000000000 1Propeller/rotor contact to person 000000000000 1Stall/settling with power 000000000000 2Midair collision 000000000000 0On ground/water collision with object 000000000000 0Fire/explosion 000000000000 0Abrupt maneuver 000000000000 1Gear collapsed 010000000000 1Undershoot/overshoot 000000000000 1Dragged wing, rotor, pod, float or tail/skid 000000000000 0Undetermined 000000000000 0On ground/water encounter with terrain/water 000000000000 0Missing 000000000000 0

Total by year 2 2 1 4 2 1 0 1 2 0 0 0 50

279
TABLE D-9. AMATEUR HELICOPTER ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

NTSB first event category

Loss of engine power 00000000102100112123100In flight collision with object 00000000000000000000000Loss of control 00000000212010102124141Airframe/component/system failure/malfunction 00000000010002002000000Hard landing 00000000000100000100010In flight collision with terrain/water 00000000000011000102000Rollover/noseover 00000000000011010310000Weather 00000000000000000000000Miscellaneous/other 00000000000000000000002Propeller/rotor contact to person 00000000000000000000000Stall/settling with power 00000000000000010000000Midair collision 00000000000000000000000On ground/water collision with object 00000000000000000000000Fire/explosion 00000000000000000000000Abrupt maneuver 00000000000000000000000Gear collapsed 00000000000000000000000Undershoot/overshoot 00000000000000000000000Dragged wing, rotor, pod, float or tail/skid 00000000000000000000000Undetermined 00000000000000000000000On ground/water encounter with terrain/water 00000000000000000000000Missing 00000000000000000000000

Total By Year 00000000324234236759253

280
TABLE D-9. AMATEUR HELICOPTER ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY (CONCLUDED)

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Cum

NTSB first event category

Loss of engine power 031100412328 40In flight collision with object 010000200001 4Loss of control 020421322042 44Airframe/component/system failure/malfunction 000121103042 19Hard landing 000010000000 4In flight collision with terrain/water 010001100000 8Rollover/noseover 100000000210 11Weather 001000000000 1Miscellaneous/other 000000000000 2Propeller/rotor contact to person 000000000000 0Stall/settling with power 000000000000 1Midair collision 000000000000 0On ground/water collision with object 000000000000 0Fire/explosion 000000100000 1Abrupt maneuver 001000000000 1Gear collapsed 000000000000 0Undershoot/overshoot 000000000000 0Dragged wing, rotor, pod, float or tail/skid 000010000000 1Undetermined 000000000000 0On ground/water encounter with terrain/water 000000000000 0Missing 000000000000 0

Total by year 1 7 3 6 6 3 12 3 7 5 11 13 137

281
TABLE D-10. AMATEUR AUTOGYRO ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

NTSB first event category

Loss of engine power 02000000035233251453312In flight collision with object 00000000010211002221100Loss of control 01000000045551441325343Airframe/component/system failure/malfunction 01000100022511214221211Hard landing 01100000001301000101001In flight collision with terrain/water 00200000012100012320110Rollover/noseover 02000000000010120000000Weather 00000000000000000000000Miscellaneous/other 01000000000001001000000Propeller/rotor contact to person 00000000000000000000000Stall/settling with power 01110000031000001000000Midair collision 00000000000000000000000On ground/water collision with object 00000000000000000001000Fire/explosion 00000000000000000000000Abrupt maneuver 00000000001000000001000Gear collapsed 00000000000000000100000Undershoot/overshoot 00000000000000000001000Dragged wing, rotor, pod, float or tail/skid 00000000000000000000000Undetermined 00000000000000000100000On ground/water encounter with terrain/water 00000000000000000000001Missing 00000000000000000000000

Total by year 0 9 4 1 0 1 0 0 0 14 17 18 11 8 9 13 12 17 13 14 10 7 8

282
TABLE D-10. AMATEUR AUTOGYRO ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY (CONCLUDED)

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Cum

NTSB first event category

Loss of engine power 111110110010 52In flight collision with object 100100001000 16Loss of control 164273631113 88Airframe/component/system failure/malfunction 102001020010 36Hard landing 001000000100 12In flight collision with terrain/water 111110001001 23Rollover/noseover 000000000000 6Weather 020000000000 2Miscellaneous/other 000001100000 5Propeller/rotor contact to person 000010000010 2Stall/settling with power 000000000000 8Midair collision 000000000000 0On ground/water collision with object 000000000000 1Fire/explosion 000000000000 0Abrupt maneuver 110001100000 6Gear collapsed 000000000000 1Undershoot/overshoot 000000000000 1Dragged wing, rotor, pod, float or tail/skid 000000000000 0Undetermined 000000000000 1On ground/water encounter with terrain/water 000000000000 1Missing 000000000000 0

Total by year 6 11 9 5 10 6 9 6 3 2 4 4 261

283
TABLE D-11. UNKNOWN CONFIGURATION ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

NTSB first event category

Loss of engine power 00001000000011001000000In flight collision with object 02000000000000000001001Loss of control 00000001001220000001211Airframe/component/system failure/malfunction 00100001011000020000101Hard landing 00000100000111000000000In flight collision with terrain/water 00000000000000010010000Rollover/noseover 00000000000000000100000Weather 00000000000000000000000Miscellaneous/other 00000000000000000000000Propeller/rotor contact to person 00000000000000000000000Stall/settling with power 00100000100000000000000Midair collision 00000000000000000000000On ground/water collision with object 00000000000000000000000Fire/explosion 00000000000000000100000Abrupt maneuver 00000000001000000000001Gear collapsed 00000000000000000000000Undershoot/overshoot 00010000000000000000000Dragged wing, rotor, pod, float or tail/skid 00000000000000000000000Undetermined 00000000000000000000000On ground/water encounter with terrain/water 00000000000000000000000Missing 00000000000000000000000

Total by year 02211102113342031212314

284
TABLE D-11. UNKNOWN CONFIGURATION ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY (CONCLUDED)

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Cum

NTSB first event category

Loss of engine power 200110021110 13In flight collision with object 000000000001 5Loss of control 001000124000 19Airframe/component/system failure/malfunction 010000001001 11Hard landing 000000000000 4In flight collision with terrain/water 001000010000 4Rollover/noseover 001000000000 2Weather 000000000000 0Miscellaneous/other 001000000000 1Propeller/rotor contact to person 000000000000 0Stall/settling with power 000000000000 2Midair collision 000000001000 1On ground/water collision with object 000100000000 1Fire/explosion 000000000000 1Abrupt maneuver 000000000000 2Gear collapsed 000000000000 0Undershoot/overshoot 000000000000 1Dragged wing, rotor, pod, float or tail/skid 000000000000 0Undetermined 000000000000 0On ground/water encounter with terrain/water 000001000000 1Missing 000000000000 0

Total by year 2 1 4 2 1 1 1 5 7 1 1 2 68

285
TABLE D-12. LOSS OF ENGINE POWER BY TYPE AND SUBCATEGORY

 Single piston Single turbine Twin turbine All other types Totals

Loss of engine power 1,554 704 39 111 2408

 Mech failure/malf 413 293 22 53 781 Non-mechanical 735 227 11 35 1008 Undetermined 406 184 6 23 619

Sub - Category Classification

Engine structure 263 189 15 28 495Fuel / Air Mixture Related 686 299 17 40 1042 Fuel exhaustion 326 82 1 8 417 Fuel contamination 97 43 1 4 145 Fuel starvation 72 26 5 4 107 Carburetor heat 70 0 0 6 76 Fuel system 67 92 3 10 172 Fuel control 42 27 3 7 79 Fuel improper 6 3 0 1 10 Induction air system 6 26 4 0 36Other Systems 101 17 1 16 135 Ignition system 69 0 0 13 82 Lubricating system 24 15 1 3 43 Accessory drive assy 8 2 0 0 10Rotor Drive System 53 7 0 2 62 Clutch assembly 33 1 0 1 35 Transmission to main rotor 14 1 0 0 15 Engine to transmission driv

e 4 40 1 9

 Freewheeling unit 2 1 0 0 3Other Sub-categories 54 11 0 0 65 Simulated power failure 36 8 0 0 44 Rotor rpm not maintained 18 3 0 0 21Undetermined/Other 397 181 6 25 609

286
TABLE D-13. AIRFRAME/COMPONENT/SYSTEM FAILURE/MALFUNCTION BY TYPE AND SUBCATEGORY

Single piston Single turbine Twin turbine All other types Totals

Cnt. % Cnt. % Cnt. % Cnt. % Cnt. %

Drive train-main 129 20.2 44 15.6 13 14.6 7 9.6 193 17.8Drive train-tail 111 17.4 55 19.5 18 20.2 6 8.2 190 17.5Main rotor 54 8.5 25 8.9 15 16.9 18 24.7 112 10.3Tail rotor 113 17.7 19 6.7 8 9.0 2 2.7 142 13.1Control system-main 64 10.0 31 11.0 11 12.4 11 15.1 117 10.8Control system-tail 35 5.5 19 6.7 8 9.0 0 0.0 62 5.7Airframe 50 7.8 36 12.8 14 15.7 7 9.6 107 9.9Landing gear 23 3.6 2 0.7 1 1.1 3 4.1 29 2.7Other 60 9.4 51 18.1 1 1.1 19 26.0 131 12.1

Totals 639 282 89 73 1083

287
TABLE D-14. LOS OF CONTROL BY TYPE AND SUBCATEGORY

Single piston Single turbine Twin turbine All other types Totals

Cnt. % Cnt. % Cnt. % Cnt. % Cnt. %

Improper operation of controls 209 33.4 82 28.9 8 20.0 70 42.4 369 33.1Low rotor RPM 105 16.8 8 2.8 1 2.5 13 7.9 127 11.4Winds 72 11.5 28 9.9 5 12.5 8 4.8 113 10.1Undetermined 44 7.0 32 11.3 4 10.0 20 12.1 100 9.0Attached/snagged to grd. equip. 38 6.1 30 10.6 3 7.5 0 0.0 71 6.4Flight control failure/deficiency 33 5.3 14 4.9 6 15.0 11 6.7 64 5.7Weight/CG 29 4.6 14 4.9 0 0.0 2 1.2 45 4.0Loss of visual ref./spatial disorient. 21 3.4 36 12.7 7 17.5 0 0.0 64 5.7Unqualified operator 20 3.2 6 2.1 0 0.0 29 17.6 55 4.9Airframe/comp./sys. fail. or malf. 13 2.1 7 2.5 1 2.5 6 3.6 27 2.4Inadequate preflight planning 12 1.9 5 1.8 0 0.0 1 0.6 18 1.6Other 9 1.4 8 2.8 1 2.5 0 0.0 18 1.6FOD 8 1.3 7 2.5 2 5.0 1 0.6 18 1.6Aircraft performance 6 1.0 3 1.1 0 0.0 0 0.0 9 0.8Passenger interference 4 0.6 1 0.4 1 2.5 0 0.0 6 0.5Pilot impairment/incapacitation 2 0.3 3 1.1 1 2.5 4 2.4 10 0.9

Totals 625 284 40 165 1114

288
TABLE D-15. IN FLIGHT COLLISION WITH OBJECT BY TYPE AND SUBCATEGORY

Single piston Single turbine Twin turbine All other types Totals

Cnt. % Cnt. % Cnt. % Cnt. % Cnt. %

Wire 310 32.5 108 36.2 13 30.2 10 35.7 441 33.4Wire/pole 197 20.7 24 8.1 0 0.0 5 17.9 226 17.1Tree(s) 148 15.5 50 16.8 7 16.3 6 21.4 211 16.0Pole/pipe 47 4.9 19 6.4 2 4.7 0 0.0 68 5.1Crop 35 3.7 1 0.3 0 0.0 0 0.0 36 2.7Vehicle 35 3.7 4 1.3 0 0.0 0 0.0 39 3.0Airport/helipad facility 32 3.4 20 6.7 12 27.9 0 0.0 64 4.8Rock/brush/terrain 30 3.1 11 3.7 1 2.3 1 3.6 43 3.3Building 27 2.8 5 1.7 1 2.3 1 3.6 34 2.6Fence/fence post 26 2.7 20 6.7 2 4.7 0 0.0 48 3.6FOD 19 2.0 13 4.4 1 2.3 2 7.1 35 2.6Aircraft 14 1.5 4 1.3 2 4.7 1 3.6 21 1.6Unspecified object 10 1.0 2 0.7 0 0.0 1 3.6 13 1.0Electronic tower 8 0.8 9 3.0 2 4.7 0 0.0 19 1.4Miscellaneous 8 0.8 1 0.3 0 0.0 0 0.0 9 0.7Bird strike 7 0.7 7 2.3 0 0.0 1 3.6 15 1.1

Totals 953 298 43 28 1322

289
TABLE D-16. HARD LANDING PLUS IN FLIGHT COLLISION WITH TERRAIN/WATER PLUS ROLLOVER/NOSEOVER 

 BY TYPE AND SUBCATEGORY

Single piston Single turbine Twin turbine All other types Total

Cnt. % Cnt. % Cnt. % Cnt. % Cnt. %

Practice/demo autorotation 318 26.2 89 22.1 3 10.7 1 1.2 411 23.7Misjudged altitude/speed/descent rate/distance/flare 231 19.0 98 24.4 8 28.6 25 29.4 362 20.9Improper operation of flight/throttle/power controls 197 16.2 49 12.2 6 21.4 26 30.6 278 16.1Failed to maintain adequate rotor RPM 174 14.3 24 6.0 2 7.1 11 12.9 211 12.2Adverse/unfavorable weather/wind 78 6.4 47 11.7 4 14.3 5 5.9 134 7.7Emergency/precautionary landing 71 5.8 14 3.5 0 0.0 1 1.2 86 5.0Other causes 43 3.5 26 6.5 4 14.3 9 10.6 82 4.7Selected unsuitable terrain 34 2.8 24 6.0 0 0.0 3 3.5 61 3.5Lift-off restricted 35 2.9 20 5.0 0 0.0 2 2.4 57 3.3Improper weight/cg 24 2.0 5 1.2 1 3.6 1 1.2 31 1.8Poorly maintained/Airframe failure 11 0.9 6 1.5 0 0.0 1 1.2 18 1.0

Totals 1216 402 28 85 1731

290
TABLE D-17. ALL OTHER ROTORCRAFT TYPES ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY

1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985

NTSB first event category

Loss of engine power 02001000147445374586412In flight collision with object 02100000010212002222101Loss of control 0 1 2 0 0 0 0 1 2 7 8 8 8 1 5 4 3 5 4 11 6 9 5Airframe/component/system failure/malfunction 01200101053614336221312Hard landing 01100100002613000211011In flight collision with terrain/water 00300000023111022432110Rollover/noseover 02100000000021130410000Weather 00000000010000000000010Miscellaneous/other 01000000000001001000102Propeller/rotor contact to person 00000000000000000000001Stall/settling with power 01310000141000011000000Midair collision 00000000000000000000000On ground/water collision with object 00000000000000000001000Fire/explosion 00000000000000000100000Abrupt maneuver 00000000002000000001002Gear collapsed 00000000000000000100000Undershoot/overshoot 00110000000000000001000Dragged wing, rotor, pod, float or tail/skid 00000000000000000000000Undetermined 00000000000000000100000On ground/water encounter with terrain/water 00000000000000000000001Missing 00000000000000000000000

Total by year 0 11 14 2 1 2 0 2 4 24 26 27 18 18 12 20 19 27 21 26 16 14 17

Registered fleet size 327 374 411 532 722 960 1141 798 873 951 1005 1041 1068 1090 1143 1303 1457 1523 1494 1454 1538 1614 1645

Accidents per 1,000 aircraft 29.4 34.1 3.76 1.39 2.08 0 2.51 4.58 25.2 25.9 25.9 16.9 16.5 10.5 15.3 13 17.7 14.1 17.9 10.4 8.67 10.3

291
TABLE D-17. ALL OTHER ROTORCRAFT TYPES ACCIDENT COUNT BY YEAR AND BY FIRST EVENT CATEGORY (CONCLUDED)

1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 Cum

NTSB first event category

Loss of engine power 342320544448 111In flight collision with object 210100201002 28Loss of control 1 9 6 8 10 4 10 8 8 1 5 5 165Airframe/component/system failure/malfunction 112223124053 73Hard landing 001110000100 25In flight collision with terrain/water 222121111001 40Rollover/noseover 101000000210 20Weather 021000000000 5Miscellaneous/other 001001100000 9Propeller/rotor contact to person 000010000010 3Stall/settling with power 000000000000 13Midair collision 000000001000 1On ground/water collision with object 000100000000 2Fire/explosion 000000100000 2Abrupt maneuver 111001100000 10Gear collapsed 010000000000 2Undershoot/overshoot 000000000000 3Dragged wing, rotor, pod, float or tail/skid 000010000000 1Undetermined 000000000000 1On ground/water encounter with terrain/water 000001000000 2Missing 000000000000 0

Total By Year 11 21 17 17 19 11 22 15 19 8 16 19 516

Registered Fleet Size 1703 1772 1849 1936 2026 1994 2054 2345 2321 2625 2798 2979

Accidents per 1,000 aircraft 6.5 11.9 9.2 8.8 9.4 5.5 10.7 6.4 8.2 3.0 5.7 6.4

292
TABLE D-18. HARD LANDING BY TYPE AND SUBCATEGORY

Single piston Single turbine Twin turbine All other types Total

Cnt. % Cnt. % Cnt. % Cnt. % Cnt. %

Practice/demo autorotation 236 48.9 76 54.3 3 37.5 0 0.0 315 48.0Misjudged altitude/speed/descent rate/distance/flare 54 11.2 18 12.9 0 0.0 11 44.0 83 12.7Failed to maintain adequate rotor RPM 56 11.6 10 7.1 0 0.0 3 12.0 69 10.5Emergency/precautionary landing 48 9.9 12 8.6 0 0.0 0 0.0 60 9.1Adverse/unfavorable weather/wind 32 6.6 11 7.9 2 25.0 2 8.0 47 7.2Improper operation of flight/throttle/power controls 34 7.0 5 3.6 2 25.0 4 16.0 45 6.9Other causes 23 4.8 8 5.7 1 12.5 5 20.0 37 5.6

Totals 483 140 8 25 656

293
TABLE D-19. LOSS OF ENGINE POWER STATISTICS

Loss of All

Single Single Twin All other power accidents

People involved piston turbine turbine types totals totals

Fatal 106 129 16 17 257 2,135

Serious 234 237 26 23 494 1,760

Minor/none 2,281 1,480 99 93 3,879 12,930

Total 2,621 1,846 141 133 4,630 16,825

Aircraft damage

None 0 10 1 0 11 78

Minor 3 9 4 1 17 85

Substantial 1,286 546 21 82 1,935 5,909

Destroyed 265 139 13 28 445 2,363

Unkown 0 0 0 0 0 1

Total 1,554 704 39 111 2,408 8,436

Flight activity

Unknown/not reported 2 3 0 0 5 22

Public/military use 27 16 0 0 43 183

Executive/corporate 26 33 3 0 62 203

Flight/maintenance test 30 26 3 9 68 239

Ferry/reposition 80 53 5 1 139 389

Business use 97 71 4 3 175 581

Instructional/training 173 15 0 14 202 1,198

Passenger service 117 215 11 0 343 1,161

Personal use 231 58 1 80 370 1,351

General utility 277 162 11 3 453 1,457

Aerial application 494 52 1 1 548 1,652

Total 1,554 704 39 111 2,408 8,436

Phase of operation (common nomenclature)

Standing/static 1 2 0 0 3 250

Unknown 3 1 0 1 5 89

Taxi 10 0 0 1 11 238

Other 18 5 0 1 24 108

Climb 35 15 2 4 56 128

Descent 72 24 2 5 103 259

Landing 60 33 2 13 108 1,359

Hover 53 58 8 2 121 757

Approach 87 64 2 14 167 467

Takeoff 280 104 8 26 418 1,405

Maneuvering 328 84 2 8 422 1,519

Cruise 607 314 13 36 970 1,857

Total 1,554 704 39 111 2,408 8,436

294
TABLE D-20. FAA ROTORCRAFT CENSUS AND HOURS FLOWN PER YEAR (REF. TABLES D-21 A, B, C)

Census Census Census Census Census Census

all all all all all all Hours flown per year by active rotorcraft

Year registered active registered active registered active Total All Allend types types pistons pistons turbines turbines fleet piston turbine Reference

1964 2,196 1,325 2,105 1,266 91 59 447,000 ?? ?? FAA Stat. Handbook of Av.,1965, Table 5.11965 2,390 1,525 2,290 1,456 100 69 450,000 ?? ?? FAA Stat. Handbook of Av.,1966, Table 5.11966 2,740 1,652 2,614 1,564 126 88 492,000 ?? ?? FAA Stat. Handbook of Av.,1967, Table 5.21967 3,175 1,925 2,844 1,733 231 192 538,000 ?? ?? FAA Stat. Handbook of Av.,1968, Table 5.21968 3,755 2,373 3,355 2,033 400 340 617,000 ?? ?? FAA Stat. Handbook of Av.,1969, Table 9.71969 4,256 2,584 3,642 2,065 614 519 778,000 ?? ?? Table 30, 19691970 3,476 2,275 2,793 1,669 683 606 844,268 543,062 301,206 GA Activity and Avionics Survey (R. Fox)1971 3,892 2,375 3,095 1,692 797 683 869,400 516,891 352,509 GA Activity and Avionics Survey (R. Fox)1972 4,265 2,787 3,373 1,957 892 830 1,018,523 591,138 427,385 GA Activity and Avionics Survey (R. Fox)1973 4,723 3,143 3,673 2,157 1,050 986 1,169,000 654,000 515,000 Census Table 3.7, 19791974 5,395 3,597 4,036 2,315 1,359 1,282 1,426,000 729,000 697,000 Census Table 3.7, 19791975 6,011 4,054 4,365 2,498 1,646 1,556 1,482,000 686,000 796,000 Census Table 3.7, 19791976 6,391 4,425 4,536 2,701 1,855 1,724 1,703,000 753,000 950,000 Census Table 3.7, 19791977 6,855 4,726 4,734 2,658 2,121 2,067 1,868,000 609,000 1,259,000 Census Table 3.7, 19791978 7,688 5,315 5,139 2,822 2,549 2,492 2,227,651 806,410 1,421,241 Census Table 3.6, 1979, 1983, 1984, 19911979 8,380 5,864 5,474 3,123 2,906 2,740 2,555,000 892,000 1,664,000 Census Table 3.7, 1984 &19911980 9,012 6,001 5,640 2,794 3,372 3,207 2,338,000 736,000 1,603,000 Census Table 3.7, 19891981 9,522 6,974 5,604 3,250 3,918 3,724 2,685,000 930,000 1,754,000 Census Table 3.7, 19911982 9,733 6,169 5,426 2,419 4,307 3,749 2,350,000 579,000 1,771,000 Census Table 3.7, 19911983 10,047 6,540 5,572 2,541 4,475 3,998 2,271,000 572,000 1,700,000 Census Table 3.8, 19931984 10,416 7,096 5,668 2,936 4,748 4,160 2,495,000 592,000 1,903,000 Census Table 3.8, 19931985 10,539 6,000 5,720 2,700 4,809 3,300 1,990,000 521,000 1,468,000 Census Table 3.8, 1993*1986 10,530 6,500 5,760 2,700 4,770 3,800 2,424,000 742,000 1,682,000 Census Table 3.8, 1993*1987 10,374 5,900 5,754 2,600 4,620 3,300 2,108,000 602,000 1,506,000 Census Table 3.8, 1993*1988 10,153 6,000 5,763 2,400 4,390 3,600 2,507,000 533,000 1,974,000 Census Table 3.8, 1993*1989 10,445 7,000 5,929 3,000 4,516 4,000 2,610,000 692,000 1,918,000 Census Table 3.8, 1993*1990 10,646 6,900 6,091 3,200 4,555 3,700 2,209,000 716,000 1,493,000 Census Table 3.8, 1993*1991 10,834 6,292 6,107 2,470 4,727 3,822 2,757,000 585,000 2,172,000 Census Table 3.8, 1993*1992 10,952 5,753 6,193 2,211 4,759 3,542 2,283,000 416,000 1,866,000 Census Table 3.8, 1993*1993 11,144 4,510 6,480 1,646 4,664 2,864 1,832,000 370,000 1,462,000 Census Table 3.8, 19941994 11,459 4,390 6,510 1,381 4,949 3,009 2,006,000 340,000 1,666,000 Census Table 3.8, 19941995 11,785 5,830 6,620 1,863 5,165 3,967 1,961,000 337,000 1,624,000 GA Activity Survey, Table 1.5, 19971996 12,354 6,570 6,853 2,507 5,501 4,063 2,122,000 591,000 1,531,000 GA Activity Survey, Table 1.5, 19971997 12,911 6,786 7,081 2,259 5,830 4,527 2,083,699 343,841 1,739,858 GA Activity Survey, Table 1.4, 1997 

*Earlier data revised [downward] to correct for nonresponsive bias

 295
TABLE D-21A. FAA ROTORCRAFT CENSUS Hours flown per year by active rotorcraft

All All All All All All Total All All

Year registered active reg. active reg. active active active activeend types types pistons pistons turbines turbines Reference fleet piston turbine Reference

1964 2,196 1,325 2,105 1,266 91 59 Table 1, 1964 447,000 ?? ?? FAA Stat. Handbook of Aviation,1965, Table 5.11965 2,390 1,525 2,290 1,456 100 69 Table 1, 1965 450,000 ?? ?? FAA Stat. Handbook of Aviation,1966, Table 5.11966 2,740 1,652 2,614 1,564 126 88 Table 1, 1966 492,000 ?? ?? FAA Stat. Handbook of Aviation,1967, Table 5.21967 3,175 1,925 2,844 1,733 231 192 Table 1, 1967 538,000 ?? ?? FAA Stat. Handbook of Aviation,1968, Table 5.21968 3,755 2,373 3,355 2,033 400 340 Table 1, 1968 617,000 ?? ?? FAA Stat. Handbook of Aviation,1969, Table 9.71969 4,256 2,584 3,642 2,065 614 519 Table 1, 1969 778,000 573,000 205,000 Table 30, 19691970 3,476 2,275 2,793 1,669 683 606 Table 6, 1970, 1971 867,000 552,000 315,000 Table 29, 1971/19701971 3,892 2,375 3,095 1,692 797 683 Table 6, 1970, 1971 891,000 527,000 364,000 Table 29A, 1971/1970 1972 4,265 2,787 3,373 1,957 892 830 Table 21, 1972 1,018,523 591,138 427,385 Table 29, 19721973 4,723 3,143 3,673 2,157 1,050 986 Table 20,1973 1,169,000 654,000 515,000 Table 3.7, 19791974 5,395 3,623 4,036 2,332 1,359 1,291 Table 6,1974 1,426,000 729,000 697,000 Table 3.7, 19791975 6,011 4,085 4,365 2,502 1,646 1,583 Table 6,1975 1,482,000 686,000 796,000 Table 3.7, 19791976 6,391 4,513 4,536 2,753 1,855 1,760 Table 6,1976 1,703,000 753,000 950,000 Table 3.7, 1979

TABLE D-21B. FAA ROTORCRAFT CENSUS Hours flown per year by active rotorcraft

All All All All All All Total All All

Year registered active reg. active reg. active active active activeend types types pistons pistons turbines turbines Reference fleet piston turbine Reference

1973 4,723 3,115 3,673 2,122 1,050 993 Table 3.5,1979 1,169,000 654,000 515,000 Table 3.7, 19791974 5,395 3,597 4,036 2,315 1,359 1,282 Table 3.5,1979 1,426,000 729,000 697,000 Table 3.7, 19791975 6,011 4,054 4,365 2,498 1,646 1,556 Table 3.5,1979 1,482,000 686,000 796,000 Table 3.7, 19791976 6,391 4,425 4,536 2,701 1,855 1,724 Table 3.5,1979 1,703,000 753,000 950,000 Table 3.7, 19791977 6,855 4,726 4,734 2,658 2,121 2,067 Table 3.5,1979 1,868,000 609,000 1,259,000 Table 3.7, 19791978 7,688 5,315 5,139 2,822 2,549 2,492 Table 3.5, 1979, 1983 2,227,651 806,410 1,421,241 Table 3.6, 1979, 19831979 8,380 5,864 5,474 3,123 2,906 2,740 Table 3.5, 1983, 1984 2,555,000 892,000 1,664,000 Table 3.7, 1983, 1984, 19891980 9,012 6,001 5,640 2,794 3,372 3,207 Table 3.5, 1983, 1984, 1989 2,338,000 736,000 1,603,000 Table 3.7, 1983, 1984, 19891981 9,522 6,974 5,604 3,250 3,918 3,724 Table 3.5, 1983, 1984, 1989, 1991 2,685,000 930,000 1,754,000 Table 3.7, 1983, 1984, 1989, 19911982 9,733 6,169 5,426 2,419 4,307 3,749 Table 3.5, 1983, 1984, 1989, 1991 2,350,000 579,000 1,771,000 Table 3.7, 1983, 1984, 1989, 19911983 10,047 6,540 5,572 2,541 4,475 3,998 Table 3.5, 1984, 1989, 1991 2,271,000 572,000 1,700,000 Table 3.7, 1984, 1989, 19911984 10,416 7,096 5,668 2,936 4,748 4,160 Table 3.5, 1989, 1991 2,495,000 592,000 1,903,000 Table 3.7, 1989, 19911985 10,539 6,418 5,720 2,877 4,809 3,541 Table 3.5, 1989, 1991 2,155,000 564,000 1,590,000 Table 3.7, 1989, 19911986 10,530 6,943 5,760 2,921 4,770 4,022 Table 3.5, 1989, 1991 2,625,000 804,000 1,821,000 Table 3.7, 1989, 19911987 10,374 6,333 5,754 2,813 4,620 3,520 Table 3.5, 1989, 1991 2,283,000 652,000 1,631,000 Table 3.7, 1989, 19911988 10,153 6,406 5,763 2,584 4,390 3,822 Table 3.5, 1989, 1991 2,707,000 576,000 2,131,000 Table 3.7, 1989, 19911989 10,445 7,475 5,929 3,244 4,516 4,232 Table 3.5,1991 2,826,000 749,000 2,077,000 Table 3.7, 19911990 10,646 7,397 6,091 3,459 4,555 3,938 Table 3.5,1991 2,392,000 775,000 1,617,000 Table 3.7, 1991

296
TABLE D-21C. FAA ROTORCRAFT CENSUS Hours flown per year by active rotorcraft

All All All All All All Total All All

Year registered active reg. active reg. active active active activeend types types pistons pistons turbines turbines Reference fleet piston turbine Reference

1985 10,539 6,000 5,720 2,700 4,809 3,300 Table 3.5,1993*, Table 1.7 1994 1,990,000 521,000 1,468,000 Table 3.8, 1993*1986 10,530 6,500 5,760 2,700 4,770 3,800 Table 3.5,1993*, Table 1.7 1994 2,424,000 742,000 1,682,000 Table 3.8, 1993*1987 10,374 5,900 5,754 2,600 4,620 3,300 Table 3.5,1993*, Table 1.7 1994 2,108,000 602,000 1,506,000 Table 3.8, 1993*1988 10,153 6,000 5,763 2,400 4,390 3,600 Table 3.5,1993*, Table 1.7 1994 2,507,000 533,000 1,974,000 Table 3.8, 1993*1989 10,445 7,000 5,929 3,000 4,516 4,000 Table 3.5,1993*, Table 1.7 1994 2,610,000 692,000 1,918,000 Table 3.8, 1993*1990 10,646 6,900 6,091 3,200 4,555 3,700 Table 3.5,1993*, Table 1.7 1994 2,209,000 716,000 1,493,000 Table 3.8, 1993*1991 10,834 6,292 6,107 2,470 4,727 3,822 Table 3.5,1993*, Table 1.7 1994 2,757,000 585,000 2,172,000 Table 3.8, 1993*1992 10,952 5,753 6,193 2,211 4,759 3,542 Table 3.5,1993*, Table 1.7 1994 2,283,000 416,000 1,866,000 Table 3.8, 1993*1993 11,144 4,510 6,480 1,646 4,664 2,864 Table 3.5,1993*, Table 1.7 1994 1,832,306 370,103 1,462,206 Table 3.7, 19941994 11,459 4,390 6,510 1,381 4,949 3,009 Table 3.5,1993*, Table 1.7 1994 2,006,470 340,189 1,666,282 Table 3.7A, 19941995 11,785 5,830 6,620 1,863 5,165 3,967 GA Act. Survey, Table 1.2, 1997 1,961,000 337,000 1,624,000 GA Act. Survey, Table 1.5, 19971996 12,354 6,570 6,853 2,507 5,501 4,063 GA Act. Survey, Table 1.2, 1997 2,122,000 591,000 1,531,000 GA Act. Survey, Table 1.5, 19971997 12,911 6,786 7,081 2,259 5,830 4,527 GA Act. Survey, Table 1.1, 1997 2,083,699 343,841 1,739,858 GA Act. Survey, Table 1.4, 1997

*Earlier data revised [downward] to correct for nonresponse bias 

297
TABLE D-22. GENERAL AVIATION ACTIVITY AND AVIONICS SURVEY SUMMARY FOR SELECTED YEARS

Year Rotorcraft Approximate Sample Postmaster Counted Response Active Fleet Average

end type Census population size returns responses rate* rotorcraft hours hours

1977 Total rotorcraft 6,855 6,845 1,924 na 1,548 80.5 4,725 1,867,644 396.3

Total piston 4,734 4,652 1,486 na 1,189 80.0 2,658 608,603 230.5

Total turbine 2,121 2,193 438 na 359 82.0 2,067 1,259,041 608.3

Single 1,976 na na na na na na na na

Multi 145 na na na na na na na na

1987 Total rotorcraft 10,374 10,034 3,171 na 1,555 49.0 6,333 2,283,000 360.5

Total Piston 5,754 5,555 2,360 na 1,185 50.2 2,813 652,000 231.8

Total Turbine 4,620 4,479 811 na 370 45.6 3,520 1,631,000 463.4

Single 3,688 na na na na na na na na

Multi 932 na na na na na na na na

1988 Total rotorcraft 10,153 9,768 2,965 na 1,417 47.8 6,406 2,706,719 423.3

Total piston 5,763 5,334 2,078 na 979 47.1 2,584 575,955 227.9

Total turbine 4,390 4,434 887 na 438 49.4 3,822 2,130,764 576.7

Single 3,518 na na na na na na na na

Multi 872 na na na na na na na na

1989** Total rotorcraft 10,445 10,469 10,469 1,874 6,725 78.2 7,488 2,828,696 377.8

Manufacturer built

Piston 3,993 3,994 3,994 720 2,488 76.0 2,684 728,125 277.8

Single turbine 3,574 3,616 3,616 648 2,549 85.9 3,248 1,532,270 480.5

Multi-turbine 942 1,069 1,069 184 709 80.1 984 546,471 551.8

Amateur built 1,936 1,790 1,790 322 979 66.7 572 21,830 38.2

* Adjusted for postmaster returns [i. e., 100*counted responses / (sample size – postal returns)]** One time only Rotorcraft Activity Survey of all registered rotorcraft in the United States (Normal GAAAS not conducted for rotorcraft)

298
TABLE D-22. GENERAL AVIATION ACTIVITY AND AVIONICS SURVEY SUMMARY FOR SELECTED

 YEARS (CONTINUED)

Year Rotorcraft Approximate Sample Postmaster Counted Response Active Fleet Average

end type Census population size returns responses rate* rotorcraft hours hours

1990 Total rotorcraft 10,646 10,422 2,313 na 1,221 52.8 7,394 2,392,066 320.7

Total piston 6,091 5,802 1,505 na 783 52.0 3,456 774,774 216.4

Total turbine 4,555 4,620 808 na 438 54.2 3,938 1,617,292 424.9

Single 3,590 na na na na na na na na

Multi 965 na na na na na na na na

1991 Total rotorcraft 10,834 10,474 2,856 na 1,331 46.6 6,292 2,755,599 451.6

Total piston 6,107 5,848 1,786 na 814 45.6 2,470 583,688 233.7

Total turbine 4,727 4,626 1,070 na 517 48.3 3,822 2,171,911 592.2

Single 3,676 na na na na na na na na

Multi 1,051 na na na na na na na na

1992 Total Rotorcraft 10,952 9,599 3,101 na 1,522 49.1 5,752 2,282,701 381.7

Total piston 6,193 5,209 1,918 na 980 51.1 2,211 416,375 184.6

Total turbine 4,759 4,390 1,183 na 542 45.8 3,541 1,866,326 491.3

Single 3,681 na na na na na na na na

Multi 1,078 na na na na na na na na

1993 Total rotorcraft 11,144 8,220 2,919 155 1,545 52.9 4,508 1,832,305 398.6

Total piston 6,480 4,274 1,741 115 952 58.5 1,645 370,099 218.8

Total turbine 4,664 3,946 1,178 40 593 52.1 2,863 1,462,206 506.0

Single 3,676 3,040 780 32 381 50.9 2,144 1,072,604 501.8

Multi 988 906 398 8 212 54.4 719 389,602 525.5

* Adjusted for postmaster returns [i. e., 100*counted responses / (sample size 

– postal returns)]

299
TABLE D-22. GENERAL AVIATION ACTIVITY AND AVIONICS SURVEY SUMMARY FOR SELECTED

 YEARS (CONCLUDED)

Year Rotorcraft Approximate Sample Postmaster Counted Response Active Fleet Average

end type Census population size returns responses rate* rotorcraft hours hours

1994 Total rotorcraft 11,459 7,866 1,307 148 683 52.3 4,388 2,006,459 458.6

Total piston 6,510 3,485 643 85 345 61.8 1,380 340,183 252.7

Total turbine 4,949 4,381 664 63 338 56.2 3,008 1,666,276 571.4

Single 3,888 3,528 493 48 242 54.4 2,298 1,197,043 526

Multi 1,061 853 171 15 96 61.5 710 469,233 762

1995 Total rotorcraft 11,785 8,217 1,557 121 737 47.3 5,117 2,332,905 439.2

Total piston 6,620 3,428 718 62 333 50.8 1,474 341,241 233.7

Total turbine 5,165 4,789 839 59 404 51.8 3,643 1,991,664 528.1

Single 4,114 3,760 569 38 279 52.5 2,773 1,450,197 504

Multi 1,051 1,029 270 21 125 50.2 870 541,467 637

1996 Total rotorcraft 12,354 8,279 1,397 70 749 56.4 6,390 2,026,000 317.1

Total piston 6,853 3,488 644 32 335 54.7 2,415 574,000 237.7

Total turbine 5,501 4,791 753 38 414 57.9 3,975 1,452,000 365.3

Single 4,410 3,880 542 30 302 59.0 3,329 1,202,000 361.1

Multi 1,091 911 211 8 112 55.2 646 250,000 387.0

1997 Total rotorcraft 12,911 8,455 2,727 170 1,489 58.2 6,785 2,083,699 307.0

Total piston 7,081 3,378 1,130 84 545 52.1 2,259 343,841 152.2

Total turbine 5,830 5,077 1,597 86 944 62.5 4,526 1,739,858 384.3

Single 4,722 4,061 1,178 66 660 59.4 3,762 1,310,878 348.4

Multi 1,108 1,016 419 20 284 71.2 764 428,980 561.0

* Adjusted for postmaster returns [i. e., 100*counted responses / (sample size 

– postal returns)]

300
TABLE D-23. ACCIDENT AND FATALITY COUNT, HOURS FLOWN AND ACCIDENT RATE BY YEAR AND TYPE

 AND TYPE

100,000 hours flown per year Accidents per Fatalities per

Accidents Accidents Accidents Fatalities by active rotorcraft 100,000 hours flown per year 100,000 hrs

Year per year All piston all turbine Per year Total All All Total All All Total

end All types Per year Per year All types fleet piston turbine fleet piston Tturbine fleet

1963 4 0 4 6 ?? ?? ?? ?? ?? ?? ??1964 260 252 8 27 4.47 ?? ?? 58.17 ?? ?? 6.041965 243 237 6 23 4.50 ?? ?? 54.00 ?? ?? 5.111966 300 287 13 46 4.92 ?? ?? 60.98 ?? ?? 9.351967 239 222 17 42 5.38 ?? ?? 44.42 ?? ?? 7.811968 230 202 28 80 6.17 ?? ?? 37.28 ?? ?? 12.971969 264 217 47 49 7.78 5.73 2.05 33.93 37.87 22.93 6.301970 244 196 48 25 8.44 5.43 3.01 28.90 36.09 15.94 2.961971 220 187 33 24 8.69 5.17 3.53 25.30 36.18 9.36 2.761972 248 181 67 64 10.19 5.91 4.27 24.35 30.62 15.68 6.281973 287 221 66 47 11.69 6.54 5.15 24.55 33.79 12.82 4.021974 287 231 56 67 14.26 7.29 6.97 20.13 31.69 8.03 4.701975 315 238 77 50 14.82 6.86 7.96 21.26 34.69 9.67 3.371976 277 214 63 64 17.03 7.53 9.50 16.27 28.42 6.63 3.761977 282 199 83 57 18.68 6.09 12.59 15.10 32.68 6.59 3.051978 328 236 92 78 22.28 8.06 14.21 14.72 29.27 6.47 3.501979 296 200 96 91 25.55 8.92 16.64 11.59 22.42 5.77 3.561980 327 198 129 102 23.38 7.36 16.03 13.99 26.90 8.05 4.361981 319 189 130 71 26.85 9.30 17.54 11.88 20.32 7.41 2.641982 303 174 129 88 23.50 5.79 17.71 12.89 30.05 7.28 3.741983 273 150 123 65 22.71 5.72 17.00 12.02 26.22 7.24 2.861984 280 141 139 80 24.95 5.92 19.03 11.22 23.82 7.30 3.211985 238 127 111 67 19.90 5.21 14.68 11.96 24.38 7.56 3.371986 222 123 99 101 24.24 7.42 16.82 9.16 16.58 5.89 4.171987 196 122 74 69 21.08 6.02 15.06 9.30 20.27 4.91 3.271988 207 125 82 44 25.07 5.33 19.74 8.26 23.45 4.15 1.761989 213 123 90 64 26.10 6.92 19.18 8.16 17.77 4.69 2.451990 226 142 84 49 22.09 7.16 14.93 10.23 19.83 5.63 2.221991 192 131 61 70 27.57 5.85 21.72 6.96 22.39 2.81 2.541992 199 128 71 83 22.83 4.16 18.66 8.72 30.77 3.80 3.641993 181 109 72 73 18.32 3.70 14.62 9.88 29.46 4.92 3.981994 211 116 95 85 20.06 3.40 16.66 10.52 34.12 5.70 4.241995 165 91 74 46 19.61 3.37 16.24 8.41 27.00 4.56 2.351996 185 86 99 66 21.22 5.91 15.31 8.72 14.55 6.47 3.111997 175 92 83 72 20.84 3.44 17.40 8.40 26.76 4.77 3.46

301
TABLE D-24. MANUFACTURER SINGLE-PISTON ACCIDENT SUMMARY

NTSB accident People Aircraft

first event category involved Fatalities Serious Minor/none involved Destroyed Substantial Minor None Unknown

Loss of engine power 2,621 106 234 2,281 1,554 265 1,286 3 0 0In flight collision with object 1,417 166 205 1,046 953 327 620 4 2 0Loss of control 1,048 92 105 851 625 194 428 3 0 0Airframe/component/system failure/malfunction 1,051 153 109 789 639 212 422 3 2 0Hard landing 915 4 35 876 483 51 430 2 0 0In flight collision with terrain/water 708 47 61 600 443 119 323 1 0 0Rollover/noseover 519 8 17 494 290 53 237 0 0 0Weather 97 21 7 69 57 23 34 0 0 0Miscellaneous/other 133 13 8 112 74 20 49 1 4 0Stall/settling with power 120 6 15 99 67 21 46 0 0 0Propeller/rotor contact to person 57 14 9 34 33 2 12 7 12 0Midair collision 43 22 3 18 17 13 3 1 0 0On ground/water collision with object 43 1 2 40 26 0 26 0 0 0Fire/explosion 38 2 5 31 28 22 6 0 0 0Abrupt maneuver 19 5 1 13 12 4 8 0 0 0Undetermined 21 18 1 2 12 11 1 0 0 0Gear collapsed 29 0 0 29 16 4 12 0 0 0Dragged wing, rotor, pod, float or tail/skid 29 2 1 26 20 6 14 0 0 0Undershoot/overshoot 33 2 0 31 16 6 10 0 0 0On ground/water encounter with terrain/water 7 0 0 7 5 1 4 00 0Missing 1 1 0 0 1 0 0 00 1

Total 8,949 683 818 7,448 5,371 1,354 3,971 25 20 1

 302
TABLE D-25. MANUFACTURER SINGLE-TURBINE ACCIDENT SUMMARY

NTSB accident People Aircraft

first event category involved Fatalities Serious Minor/none involved Destroyed Substantial Minor None Unknown

Loss of engine power 1,846 129 237 1,480 704 139 546 9 10 0In flight collision with object 688 140 106 442 298 114 182 0 2 0Loss of control 754 155 123 476 284 125 159 0 0 0Airframe/component/system failure/malfunction 705 157 110 438 282 111 163 4 4 0In flight collision with terrain/water 389 104 52 233 143 68 75 0 0 0Hard landing 359 3 14 342 140 11 128 0 1 0Rollover/noseover 275 13 9 253 119 22 96 1 0 0Weather 246 107 32 107 85 54 30 0 1 0Miscellaneous/other 186 9 15 162 42 7 20 1 14 0Midair collision 195 66 17 112 37 21 9 5 2 0Propeller/rotor contact to person 108 12 13 83 35 0 14 15 6 0On ground/water collision with object 58 0 4 54 18 1 16 1 0 0Fire/explosion 37 5 0 32 15 10 4 1 0 0Undetermined 39 34 4 1 13 11 2 0 0 0On ground/water encounter with terrain/water 23 0 0 23 12 1 11 0 0 0Abrupt maneuver 30 7 7 16 8 3 5 0 0 0Undershoot/overshoot 18 2 0 16 4 3 1 0 0 0Gear collapsed 5 0 0 5 3 0 3 00 0Stall/settling with power 6 5 0 1 2 0 2 00 0Dragged wing, rotor, pod, float or tail/skid 5 0 0 5 2 0 2 00 0Missing 3 3 0 0 1 1 0 00 0

Total 5,975 951 743 4,281 2,247 702 1,468 37 40 0

 303
TABLE D-26. MANUFACTURER TWIN-TURBINE ACCIDENT SUMMARY

NTSB accident People Aircraft

first event category involved Fatalities Serious Minor/none involved Destroyed Substantial Minor None Unknown

Airframe/component/system failure/malfunction 452 148 37 267 89 34 40 8 7 0In flight collision with object 175 35 29 111 43 16 25 2 0 0Loss of control 135 38 14 83 40 17 22 1 0 0Loss of engine power 141 16 26 99 39 13 21 4 1 0In flight collision with terrain/water 52 18 4 30 16 10 6 0 0 0Weather 29 16 3 10 12 9 2 1 0 0On ground/water collision with object 80 18 2 60 10 2 8 0 0 0Miscellaneous/other 30 6 1 23 9 2 4 0 3 0Hard landing 23 0 2 21 8 1 6 1 0 0Propeller/rotor contact to person 48 3 2 43 8 0 1 1 6 0Midair collision 32 13 3 16 6 3 3 0 0 0Gear collapsed 54 4 1 49 6 0 4 2 0 0Fire/explosion 27 0 0 27 5 1 3 1 0 0Rollover/noseover 18 0 0 18 4 1 3 0 0 0Abrupt maneuver 6 2 0 4 2 1 1 00 0Undetermined 5 1 0 4 2 1 1 00 0Stall/settling with power 1 0 0 1 1 0 1 00 0Dragged wing, rotor, pod, float or tail/skid 2 0 0 2 1 0 1 00 0Undershoot/overshoot 6 3 0 3 1 1 0 00 0On ground/water encounter with terrain/water 0 0 0 0 0 0 0 00 0Missing 0 0 0 0 0 0 0 00 0

Total 1,316 321 124 871 302 112 152 21 17 0

 304
TABLE D-27. ALL OTHER ROTORCRAFT TYPES ACCIDENT SUMMARY

NTSB accident People Aircraft

first event category involved Fatalities Serious Minor/none involved Destroyed Substantial Minor None Unknown

Loss of control 175 77 21 77 165 78 87 0 0 0Loss of engine power 133 17 23 93 111 28 82 1 0 0Airframe/component/system failure/malfunction 78 43 6 29 73 40 33 0 0 0In flight collision with terrain/water 45 13 7 25 40 13 27 0 0 0In flight collision with object 35 11 6 18 28 13 15 0 0 0Hard landing 29 0 1 28 25 3 22 0 0 0Rollover/noseover 25 4 2 19 20 3 17 0 0 0Stall/settling with power 13 0 3 10 13 3 10 0 0 0Abrupt maneuver 11 8 1 2 10 8 2 0 0 0Miscellaneous/other 9 1 1 7 9 1 8 00 0Weather 7 0 1 6 5 1 4 00 0Propeller/rotor contact to person 6 1 1 4 3 0 1 11 0Undershoot/overshoot 3 1 0 2 3 0 3 00 0On ground/water collision with object 2 0 0 2 2 1 1 00 0Fire/explosion 5 0 0 5 2 1 1 00 0Gear collapsed 2 0 2 0 2 0 2 00 0On ground/water encounter with terrain/water 3 2 0 1 2 1 1 00 0Midair collision 2 1 0 1 1 0 1 00 0Undetermined 1 1 0 0 1 1 0 00 0Dragged wing, rotor, pod, float or tail/skid 1 0 0 1 1 0 1 00 0Missing 0 0 0 0 0 0 0 00 0

Totals 585 180 75 330 516 195 318 2 1 0

 305
TABLE D-28. ACCIDENT SUMMARY BY TYPE OF ACTIVITY AND PHASE

 OF OPERATION

Single Single Twin All other

Activity piston turbine turbine types Totals

Aerial application 1,494 150 4 4 1,652

General utility 875 520 49 13 1,457

Personal use 787 200 6 358 1,351

Instructional/training 976 127 13 82 1,198

Passenger service 421 642 97 1 1,161

Business use 338 209 23 11 581

Ferry/reposition 205 135 46 3 389

Flight/maintenance test 113 67 16 43 239

Executive/corporate 75 97 31 0 203

Public/military use 78 93 12 0 183

Unknown/not reported 9 7 5 1 22

Total 5,371 2,247 302 516 8,436

Single Single Twin All other

Phase of operation piston turbine turbine types Totals

Cruise 1,047 633 84 93 1,857

Maneuvering 1,149 270 30 70 1,519

Takeoff 889 353 36 127 1,405

Landing 949 301 35 74 1,359

Hover 450 247 32 28 757

Approach 241 146 26 54 467

Descent 168 73 6 12 259

Standing/static 126 97 22 5 250

Taxi 164 40 15 19 238

Climb 64 40 14 10 128

Other 76 24 0 8 108

Unknown 48 23 2 16 89

Totals 5,371 2,247 302 516 8,436

306
TABLE D-29. COLLECTED ACCIDENT SUMMARY BY NUMERICAL COUNT

Commercially manufactured helicopters All other rotorcraft types All

Commercial Commercial Amateur Amateur Amateur other

NTSB accident Single Single Twin helicopter piston piston piston unknown type

first event category piston turbine turbine total autogyro helicopter autogyro type total

Loss of engine power 1,554 704 39 2,297 6 40 52 13 111In flight collision with object 953 298 43 1,294 3 4 16 5 28Loss of control 625 284 40 949 14 44 88 19 165Airframe/component/system failure/malfunction 639 282 89 1,010 7 19 36 11 73Hard landing 483 140 8 631 5 4 12 4 25In flight collision with terrain/water 443 143 16 602 5 8 23 4 40Rollover/noseover 290 119 4 413 1 11 6 2 20Weather 57 85 12 154 2 120

5

Miscellaneous/other 74 42 9 125 1 251

9

Stall/settling with power 67 2 1 70 2 182 13Propeller/rotor contact to person 33 35 8 76 1 020

3

Midair collision 17 37 6 60 0 001 1On ground/water collision with object 26 18 10 54 0 011

2

Fire/explosion 28 15 5 48 0 101

2

Abrupt maneuver 12 8 2 22 1 162 10Undetermined 12 13 2 27 0 010 1Gear collapsed 16 3 6 25 1 010

2

Dragged wing, rotor, pod, float or tail/skid 20 2 1 23 0 100 1Undershoot/overshoot 16 4 1 21 1 011

3

On ground/water encounter with terrain/water 5 12 0 17 0 011

2

Missing 11 0

2 0 000

0

Total 5,371 2,247 302 7,920 50 137 261 68 516

 307
TABLE D-30. COLLECTED ACCIDENT SUMMARY BY PERCENTAGE

Commercially manufactured helicopters All other rotorcraft types All

Commercial Commercial Amateur Amateur Amateur other

NTSB accident Single Single Twin helicopter piston piston piston unknown type

first event category piston turbine turbine total autogyro helicopter autogyro type total

Loss of engine power 28.93 31.33 12.91 29.00 12.00 29.20 19.92 19.12 21.51In flight collision with object 17.74 13.26 14.24 16.34 6.00 2.92 6.13 7.35 5.43Loss of control 11.64 12.64 13.25 11.98 28.00 32.12 33.72 27.94 31.98Airframe/component/system failure/malfunction 11.90 12.55 29.47 12.75 14.00 13.87 13.79 16.18 14.15Hard landing 8.99 6.23 2.65 7.97 10.00 2.92 4.60 5.88 4.84In flight collision with terrain/water 8.25 6.36 5.30 7.60 10.00 5.84 8.81 5.88 7.75Rollover/noseover 5.40 5.30 1.32 5.21 2.00 8.03 2.30 2.94 3.88Weather 1.06 3.78 3.97 1.94 4.00 0.73 0.77 0.00 0.97Miscellaneous/other 1.38 1.87 2.98 1.58 2.00 1.46 1.92 1.47 1.74Stall/settling with power 1.25 0.09 0.33 0.88 4.00 0.73 3.07 2.94 2.52Propeller/rotor contact to person 0.61 1.56 2.65 0.96 2.00 0.00 0.77 0.00 0.58Midair collision 0.32 1.65 1.99 0.76 0.00 0.00 0.00 1.47 0.19On ground/water collision with object 0.48 0.80 3.31 0.68 0.00 0.00 0.38 1.47 0.39Fire/explosion 0.52 0.67 1.66 0.61 0.00 0.73 0.00 1.47 0.39Abrupt maneuver 0.22 0.36 0.66 0.28 2.00 0.73 2.30 2.94 1.94Undetermined 0.22 0.58 0.66 0.34 0.00 0.00 0.38 0.00 0.19Gear collapsed 0.30 0.13 1.99 0.32 2.00 0.00 0.38 0.00 0.39Dragged wing, rotor, pod, float or tail/skid 0.37 0.09 0.33 0.29 0.00 0.73 0.00 0.00 0.19Undershoot/overshoot 0.30 0.18 0.33 0.27 2.00 0.00 0.38 1.47 0.58On ground/water encounter with terrain/water 0.09 0.53 0.00 0.21 0.00 0.00 0.38 1.47 0.39Missing 0.02 0.04 0.00 0.03 0.00 0.00 0.00 0.00 0.00

Total Accident Count For % Basis 5,371 2,247 302 7,920 50 137 261 68 516

 308
TABLE D-31. ALL ROTORCRAFT ACCIDENT SUMMARY

NTSB accident People Aircraft

first event category involved Fatalities Serious Minor/none involved Destroyed Substantial Minor None Unknown

Loss of engine power 4,741 268 520 3,953 2,408 445 1,935 17 11 0In flight collision with object 2,315 352 346 1,617 1,322 470 842 6 4 0Loss of control 2,112 362 263 1,487 1,114 414 696 4 0 0Airframe/component/system failure/malfunction 2,286 501 262 1,523 1,083 397 658 15 13 0Hard landing 1,326 7 52 1,267 656 66 586 3 1 0In flight collision with terrain/water 1,194 182 124 888 642 210 431 1 0 0Rollover/noseover 837 25 28 784 433 79 353 1 0 0Weather 379 144 43 192 159 87 70 1 1 0Miscellaneous/other 358 29 25 304 134 30 81 2 21 0Stall/settling with power 140 11 18 111 83 24 59 0 0 0Propeller/rotor contact to person 219 30 25 164 79 2 28 24 25 0Midair collision 272 102 23 147 61 37 16 6 2 0On ground/water collision with object 183 19 8 156 56 4 51 1 0 0Fire/explosion 107 7 5 95 50 34 14 2 0 0Abrupt maneuver 66 22 9 35 32 16 16 0 0 0Undetermined 66 54 5 7 28 24 4 0 0 0Gear collapsed 90 4 3 83 27 4 21 2 0 0Undershoot/overshoot 60 8 0 52 24 10 14 0 0 0Dragged wing, rotor, pod, float or tail/skid 37 2 1 34 24 6 18 0 0 0On ground/water encounter with terrain/water 33 2 0 31 19 3 16 0 0 0Missing 4 4 0 0 2 1 0 00 1

Total 16,825 2,135 1,760 12,930 8,436 2,363 5,909 85 78 1

 309