Mary S. Reveley and Jeffrey L. Briggs

Glenn Research Center, Cleveland, Ohio

Joni K. Evans

ATK Aerospace Systems, Hampton, Virginia

Sharon M. Jones

Langley Research Center, Hampton, Virginia

Tolga Kurtoglu

Mission Critical Technologies, Moffett Field, California

Karen M. Leone and Carl E. Sandifer

Glenn Research Center, Cleveland, Ohio

Causal Factors and Adverse Events of Aviation 

Accidents and Incidents Related to Integrated 

Vehicle Health Management

NASA/TM—2011-216967

March 2011
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Mary S. Reveley and Jeffrey L. Briggs

Glenn Research Center, Cleveland, Ohio

Joni K. Evans

ATK Aerospace Systems, Hampton, Virginia

Sharon M. Jones

Langley Research Center, Hampton, Virginia

Tolga Kurtoglu

Mission Critical Technologies, Moffett Field, California

Karen M. Leone and Carl E. Sandifer

Glenn Research Center, Cleveland, Ohio

Causal Factors and Adverse Events of Aviation 

Accidents and Incidents Related to Integrated 

Vehicle Health Management

NASA/TM—2011-216967

March 2011

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135
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NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

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Trade names and trademarks are used in this report for identifi cation 

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Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2011-216967 iii

Executive Summary

The causal factors of accidents from the National Transportation Safety Board (NTSB) database and 

incidents from the Federal Aviation Administration (FAA) database associated with failures and 

malfunctions of the various systems and components of commercial aircraft were examined for the years 

1988 to 2003 for three types of flight operations: Federal Aviation Regulation Part 121, Scheduled Part 

135, and Non-Scheduled Part 135. The aircraft systems were divided into the most frequently cited 

groups of failure or malfunction: engine or fuel system, flight control or structure, and landing gear or 

hydraulics. The remaining systems and components were grouped into the “other” category. Most 

accidents in the NTSB database have more than one causal factor cited by accident and incident 

investigators. The total number of accidents found in the NTSB database with a system/component 

failure/malfunction (SCFM) was 370, while the total number of incidents found in the FAA database 

was 7732. 

Maintenance error was a cause in 38 percent of the 179 commercial accidents with an engine or fuel 

SCFM. Some part of the engine or fuel system was said to have failed in 35 percent of the accidents, and 

component fatigue was noted in 23 percent of the accidents. 

Flight control or structural SCFM was involved in 54 of the accidents. Of these, 46 percent were 

related to maintenance errors. Manufacturing or design elements were a causal factor in 40 percent of 

the Part 121 flight control or structural malfunction accidents. A component was said to have failed in 

29 percent of the accidents, a component separated in 23 percent of the accidents, and a component 

jammed in 20 percent of the accidents. 

Of the 115 accidents with landing gear or hydraulic system malfunctions in commercial aircraft, 

28 percent were related to maintenance errors. A landing gear or hydraulic system component was said to 

have failed in 48 percent of the accidents.

The Aviation Safety Reporting System (ASRS) incident database was examined for two types of 

flight operation: Part 121 and Part 135, from January 1993 to March 2008. Equipment problems were the 

cause of 93 percent of the aircraft primary problem events found in ASRS. The most frequent component 

failures were turbine engine, pressurization system, hydraulic main system, flight management 

system/computer, and engine. The data was further categorized in aircraft systems. The monitoring and 

management system accounted for 14.1 percent of all failures, the propulsion system accounted for

13.7 percent, the control surfaces accounted for 9.1 percent, the environmental control system accounted 

for 8.8 percent, and the landing gear system accounted for 7.8 percent of the total equipment failures. 

An adverse events table was updated to provide focus to the direction of the Integrated Vehicle 

Health Management Project. The table contains five types of adverse faults: incipient, slow progression, 

intermittent, cascading, and fast progression. Seventeen different example damage conditions were 

gleaned from ASRS and the NTSB databases as well as from failure modes and effects analyses abstracts.

The severity and frequency of the damage conditions are also provided. 

NASA/TM—2011-216967 1 

Causal Factors and Adverse Events of Aviation Accidents and 

Incidents Related to Integrated Vehicle Health Management

Mary S. Reveley and Jeffrey L. Briggs

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135 

Joni K. Evans

ATK Aerospace Systems

Hampton, Virginia 23681 

Sharon M. Jones

National Aeronautics and Space Administration

Langley Research Center

Hampton, Virginia 23681–2199 

Tolga Kurtoglu

Mission Critical Technologies

Moffett Field, California 94035 

Karen M. Leone and Carl E. Sandifer 

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135 

Summary

Causal factors in aviation accidents and incidents related to system/component failure/malfunction 

(SCFM) were examined for Federal Aviation Regulation Parts 121 and 135 operations to establish future 

requirements for the NASA Aviation Safety Program’s Integrated Vehicle Health Management (IVHM) 

Project. Data analyzed includes National Transportation Safety Board (NSTB) accident data (1988 to 

2003), Federal Aviation Administration (FAA) incident data (1988 to 2003), and Aviation Safety 

Reporting System (ASRS) incident data (1993 to 2008). Failure modes and effects analyses were 

examined to identify possible modes of SCFM. A table of potential adverse conditions was developed to 

help evaluate IVHM research technologies. Tables present details of specific SCFM for the incidents and 

accidents. Of the 370 NTSB accidents affected by SCFM, 48 percent involved the engine or fuel system

and 31 percent involved landing gear or hydraulic failure and malfunctions. A total of 35 percent of all 

SCFM accidents were caused by improper maintenance. Of the 7732 FAA database incidents affected by 

SCFM, 33 percent involved landing gear or hydraulics, and 33 percent involved the engine and fuel 

system. The most frequent SCFMs found in ASRS were turbine engine, pressurization system, hydraulic 

main system, flight management system and flight management computer, and engine. Because the 

IVHM Project does not address maintenance issues, and landing gear and hydraulic systems accidents are 

usually not fatal, the focus of research should be those SCFMs that occur in the engine and fuel and flight 

control and structures systems, as well as power systems. 
NASA/TM—2011-216967 2 

Introduction

Purpose of Study

NASA’s Integrated Vehicle Health Management (IVHM) Project is one of four projects within the 

Agency’s Aviation Safety Program (AvSafe) in the Aeronautics Research Mission Directorate. The 

IVHM Project, which was updated August 14, 2008, conducts research to develop validated tools and

technologies for automated detection, diagnosis, and prognosis that enable mitigation of adverse events 

during flight. Adverse events include those that arise from system, subsystem, or component faults or 

failures due to damage, degradation, or environmental hazards that occur during flight (Ref. 1). 

The purpose of this study is to review statistical data and literature from academia, industry, and other 

Government agencies to interpret and extract information about causal factors in current aircraft safety 

incidents and accidents and failure modes and effects analyses (FMEAs) that are related to the key 

research areas in IVHM. From this information, a list of potential adverse conditions was established 

against which IVHM technologies can be evaluated. This study is considered a waypoint to establish 

future requirements for the project with the following expected outcomes (Ref. 1):

(1) Report and document causal factors gleaned from the analyses of the incidents and accidents 

related to IVHM utilizing the most current statistical and prognostic data available from the 

Aviation Safety Information Analysis and Sharing (ASIAS) Project. 

(2) Report and document causal factors gleaned from FMEAs available from relevant literature.

(3) Develop a list of potential adverse conditions against which IVHM technologies can be evaluated.

Overview of Study Contents 

The expected outcomes for this study are addressed in sequential order. Outcome 1 is addressed in the 

NASA Analyses of NTSB and FAA Accident and Incident Data section and the NASA Analysis of ASRS 

Incident Data section; these analyses have been conducted by NASA researchers for this Key Decision 

Point. Outcome 2 is the focus of Failure Modes and Effects Analysis section, while outcome 3 is 

addressed by the Adverse Events Table. Finally, discussion and the conclusions that have been drawn are 

provided. 

The first expected outcome of this study is the results of an examination of the most recent statistical

and prognostic incident and accident data that is available to determine the causal factors of system or 

component failures and/or malfunctions in U.S. commercial aviation accidents and incidents. The next 

two sections contain the results of two separate statistical analyses that have been conducted by NASA to 

address this expected outcome. The first statistical analysis examined publicly available National 

Transportation Safety Board (NTSB) and Federal Aviation Administration (FAA) accident and incident 

data. A second statistical analysis was conducted with the Aviation Safety Reporting System (ASRS) 

reports as the data source. All of these data sources can be accessed using ASIAS (Ref. 2)

NASA Analyses of National Transportation Safety Board and 

Federal Aviation Administration Accident and Incident Data

A statistical analysis was conducted to determine the causal factors of accidents and incidents 

associated with failures or malfunctions of the various systems or components of commercial aircraft 

from 1988 to 2003. A causal factor is described as why the accident or incident happened. In determining 

the causes, the NTSB considers all facts, conditions, and circumstances associated with the accident. 

Often several causes explain why an accident occurred. For this reason, a single accident report can 

include multiple causes (Ref. 3). The safety risk is based on both accidents and incidents, which are 

defined as follows (Ref. 4):
NASA/TM—2011-216967 3 

Accident An occurrence associated with the operation of an aircraft, which takes place between the 

time any person boards the aircraft with the intention of flight and all such persons have 

disembarked, and in which any person suffers death or serious injury, or in which the 

aircraft receives substantial damage. 

Incident An occurrence other than an accident, associated with the operation of an aircraft, which 

affects or could affect the safety of operations. 

In this analysis, “commercial” is defined as Part 121, Scheduled Part 135, and Non-Scheduled Part 

135 flights. Part 121 operations applies to major airlines and cargo carriers that fly large transportcategory aircraft, and Part 135 applies to commercial aircraft air carriers commonly referred to as 

commuter airlines. Prior to March 1997, Part 121 operations included aircraft with 30 or more seats. In 

March 1997, the definition of Part 121 operations changed and now includes those aircraft with 10 or 

more seats. Scheduled operation refers to “any common carriage passenger-carrying operation for 

compensation or hire conducted by an air carrier or commercial operator for which the certificate holder 

or its representative offers in advance of the departure location, departure time, and arrival location.” A 

non-scheduled operation refers to “any operation for compensation or hire in which the departure time, 

departure location, and arrival location are specifically negotiated with the customer” (Ref. 5). 

The source for accident data is the NTSB Aviation Accident and Incident Data System, while the 

source for incident data is the FAA’s Accident/Incident Data System. Although both databases contain 

both accident and incident data, the FAA has primary investigative responsibility for incidents and the 

NTSB is the authority for accident investigation. 

For each accident and incident, the system affected by the system/component failure/malfunction 

(SCFM) was determined (see Tables 1 and 2). In some events, multiple systems were affected, and in 

these cases the first system affected was selected. For example, if an electrical malfunction preceded an 

engine fire, that event was categorized under electrical. 

The NTSB database includes causal factors for each accident that occurs within the United States. 

The aircraft systems identified in Table 1 were divided into four system groups: engine or fuel system; 

flight control or structure; landing gear or hydraulic; and instrumentation/communication/navigation, 

electrical, other, unknown. The first three groups account for the most frequent SCFM-related events. 

TABLE 1.—FREQUENCY OF SYSTEM/COMPONENT FAILURE/MALFUNCTION

ACCIDENTS GROUPED BY SYSTEM AFFECTED AND BY OPERATION CATEGORY

System Operation category

Part 121 Scheduled 

Part 135

Non-Scheduled

Part 135

Parts 121 and 135 

combined

Engine 36 (33%) 12 (36%) 111 (49%) 159 (43%)

Landing gear 23 (21%) 10 (30%) 64 (28%) 97 (26%)

Flight control 10 (9%) 3 (9%) 9 (4%) 22 (6%)

Electrical 8 (7%) 1 (3%) 12 (5%) 21 (6%)

Fuel 4 (4%) 3 (9%) 13 (6%) 20 (5%)

Hydraulic 9 (8%) 2 (6%) 7 (3%) 18 (5%)

Structure 5 (5%) 1 (3%) 7 (3%) 13 (4%)

Other 8 (7%) 1 (3%) 4 (2%) 13 (4%)

Instrumentation/

communication/

navigation

5 (5%) 0 (0%) 0 (0%) 5 (1%)

Unknown 1 (1%) 0 (0%) 1 (0%) 2 (1%)

Total accidents 109 33 228 370
NASA/TM—2011-216967 4 

TABLE 2.—FREQUENCY OF SYSTEM/COMPONENT FAILURE/MALFUNCTION INCIDENTS 

GROUPED BY SYSTEM AFFECTED AND BY OPERATION CATEGORY

System Operation category

Part 121 Scheduled 

Part 135

Non-Scheduled

Part 135

Parts 121 and 

135 combined

Engine 1384 (28%) 486 (31%) 349 (29%) 2219 (29%)

Landing gear 990 (20%) 509 (33%) 558 (46%) 2057 (27%)

Other 615 (12%) 135 (9%) 47 (4%) 797 (10%)

Flight control 431 (9%) 43 (3%) 28 (2%) 502 (6%)

Hydraulic 414 (8%) 57 (4%) 45 (4%) 516 (7%)

Fuel 215 (4%) 80 (5%) 54 (4%) 349 (5%)

Structure 214 (4%) 80 (5%) 49 (4%) 343 (4%)

Comfort systems 246 (5%) 54 (4%) 20 (2%) 320 (41%)

Electrical 191 (4%) 64 (4%) 47 (4%) 302 (4%)

Pressurization 174 (4%) 15 (1%) 8 (1%) 197 (3%)

Instrumentation/communication/navigation 83 (2%) 34 (2%) 13 (1%) 130 (2%)

Total incidents 4957 1557 1218 7732

TABLE 3.—FREQUENCY OF SYSTEM/COMPONENT FAILURE/MALFUNCTION ACCIDENT 

CHARACTERISTIC BY SYSTEM GROUP AND BY OPERATION CATEGORY

System group Accident 

characteristics

Operation category

Part 121 Scheduled 

Part 135

Non-Scheduled

Part 135

Parts 121 and 

135 combined

Engine or fuel system

Total accidents 40 15 124 179

Fatal accidents 4 (10%) 3 (20%) 37 (30%) 44 (25%)

Total fatalities 151 33 92 276

Flight control or 

structure 

Total accidents 15 4 16 35

Fatal accidents 7 (47%) 1 (25%) 4 (25%) 12 (34%)

Total fatalities 279 14 4 297

Landing gear or 

hydraulic

Total accidents 32 12 71 115

Fatal accidents 0 (0%) 1 (8%) 0 (0%) 1 (1%)

Total fatalities 0 5 0 5 

Instrument/ 

communication/ 

navigation, electrical, 

other, unknown

Total accidents 22 2 17 41

Fatal accidents 5 (23%) 0 6 (35%) 11 (27%)

Total fatalities 347 0 13 360
NASA/TM—2011-216967 5 

Further analysis of the SCFM accidents compared the severity of the four system categories. Table 3 

compares the four system groups’ fatal accidents and fatality rates. Although the landing gear or hydraulic 

system category has 115 total accidents, only one was a fatal accident with five fatalities. In contrast, 

within the engine or fuel system category, 25 percent of the total accidents were fatal with 276 fatalities.

The flight control or structural systems category has 40 accidents, yet 12 were fatal accidents, or 

30 percent with 297 fatalities. Even though flight control/structural SCFM accidents were less frequent 

than landing gear/hydraulic SCFMs, the outcomes were far worse. 

The next four tables list the causal factors that are linked to the SCFMs for the four system groups 

identified in Table 3. Some of the causal factors specify the problem with the component (corroded, 

fractured, separated, etc.), and others address errors by individuals (maintenance personnel) or groups of 

people (the manufacturer, the company, or operator) or regulatory deficiencies (the FAA). As stated 

earlier, most events have more than one causal factor.

Each table includes the number of accidents within the particular group of systems; the percentages 

given are based on the number of accidents, not on the number of causal factors. Most accidents contain 

more than one causal factor. For those events for which “unknown” is listed in the table as a causal factor, 

no other causal factors appear in the table for that event. In other words, for those 21 accidents, the cause 

of the failure or malfunction in completely unknown. 

In Table 4, 39 percent of engine or fuel SCFMs in commercial aircraft were related to maintenance 

errors; 42 percent were in Part 121 operations, 20 percent in Scheduled Part 135 and 40 percent in NonScheduled Part 135. Some part of the engine or fuel system failed in 35 percent of 

the accidents, and fatigue was noted in 23 percent of the accidents. A component separated from its 

normal position in 14 percent of the accidents. Manufacturing or design issues were cited much more 

frequently in Part 121 or Scheduled Part 135 than in Non-Scheduled Part 135 accidents. 

Flight control or structural SCFM causal factors are shown in Table 5. Maintenance errors were a 

causal factor in 46 percent of the accidents; Part 121 accounted for 53 percent of these, 50 percent in 

Scheduled Part 135, and 38 percent in Non-Scheduled Part 135. Manufacturing or design elements were 

named as a cause in 40 percent of the Part 121 flight control or structural SCFM accidents. A component 

failed in 29 percent of the accidents, a component separated in 23 percent of the accidents, and a 

component jammed in 20 percent of the accidents.

Landing gear or hydraulic SCFMs are shown in Table 6. Maintenance errors were a causal factor in 

28 percent of the accidents; Part 121 accounted for 25 percent of these, 33 percent in Scheduled Part 135, 

and 28 percent in Non-Scheduled Part 135. A component failed in 48 percent of the accidents, component 

fatigue occurred in 18 percent of the accidents, and there was a loss of hydraulic fluid in 15 percent of the 

accidents. In 33 percent of Scheduled Part 135 accidents a component was inoperative. Manufacturing or 

design issues were cited more frequently in Part 121 or Scheduled Part 135 than in Non-Scheduled Part 

135 accidents. 

The remaining SCFMs are shown in Table 7. Maintenance errors were a causal factor in 32 percent of 

the accidents; Part 121 accounted for 41 percent of these, 50 percent in Scheduled Part 135, and 17 percent

in Non-Scheduled Part 135. There was an electrical failure in 17 percent of the accidents, wire chafed/arcing 

in 15 percent of the accidents, and an electrical short in 12 percent of the accidents. 
NASA/TM—2011-216967 6 

TABLE 4.—FREQUENCY OF CAUSAL FACTORS OF ENGINE OR FUEL SYSTEM/COMPONENT FAILURE/ 

MALFUNCTION (SCFM) ACCIDENTS BY OPERATION CATEGORY

Causal factors of engine or fuel SCFM Operation category

Part 121 Scheduled 

Part 135

Non-Scheduled 

Part 135

Parts 121 and

135 combined

Total engine or fuel SCFM accidents 40 15 124 179

Maintenance related 17 (42%) 3 (20%) 49 (40%) 69 (39%)

Component failure 18 (45%) 5 (33%) 39 (31%) 62 (35%)

Component fatigue 8 (20%) 3 (20%) 30 (24%) 41 (23%)

Component separated 6 (15%) 3 (20%) 16 (13%) 25 (14%)

Manufacturing/design 9 (22%) 3 (20%) 8 (6%) 20 (11%)

Component fractured 3 (8%) 1 (7%) 16 (13%) 20 (11%)

Component disconnected 3 (6%) 1 (7%) 15 (12%) 19 (11%)

Oil deprivation 1 (2%) 1 (7%) 13 (10%) 15 (8%)

Component worn 2 (5%) 1 (7%) 8 (6%) 11 (6%)

Unknown 3 (8%) 0 (0%) 7 (6%) 10 (6%)

Ignition erratic 1 (2%) 1 (7%) 0 (0%) 8 (4%)

Incorrect, improper, or inadequate component 0 (0%) 1 (7%) 7 (6%) 8 (4%)

Component loose 0 (0%) 1 (7%) 6 (5%) 7 (4%)

Company/operator error 2 (5%) 0 (0%) 5 (4%) 7 (4%)

Component corroded 1 (2%) 1 (7%) 5 (4%) 7 (4%)

Component deteriorated 1 (2%) 0 (0%) 6 (5%) 7 (4%)

Fuel leak 2 (5%) 1 (7%) 3 (2%) 6 (3%)

Overspeed/overtemperature 1 (2%) 1 (7%) 3 (2%) 5 (3%)

Overtorque/undertorque 0 (0%) 0 (0%) 5 (4%) 5 (3%)

Federal Aviation Administration 1 (2%) 2 (13%) 1 (1%) 4 (2%)

Component malfunction 1 (2%) 0 (0%) 3 (2%) 4 (2%)

Component ruptured/severed 2 (5%) 0 (0%) 2 (2%) 4 (2%)

Loss of oil pressure 1 (2%) 0 (0%) 3 (2%) 4 (2%)

Component inoperative 1 (2%) 0 (0%) 2 (2%) 3 (2%)

Component bent 1 (2%) 0 (0%) 1 (1%) 2 (1%)

Component movement restricted 1 (2%) 0 (0%) 1 (1%) 2 (1%)

Bolt not secured 1 (2%) 0 (0%) 1 (1%) 2 (1%)

Burned piston 0 (0%) 1 (7%) 1 (1%) 2 (1%)

Mechanical binding of component 1 (2%) 0 (0%) 1 (1%) 2 (1%)

Wiring chafed/arcing 1 (2%) 0 (0%) 1 (1%) 2 (1%)

Fouled spark plug 0 (0%) 0 (0%) 1 (1%) 1 (1%)

Magneto jammed 0 (0%) 0 (0%) 1 (1%) 1 (1%)

Seal not installed 0 (0%) 0 (0%) 1 (1%) 1 (1%)
NASA/TM—2011-216967 7 

Flight control or structural SCFM causal factors are shown in Table 5. Maintenance errors were a 

causal factor in 46 percent of the accidents; Part 121 accounted for 53 percent of these, 50 percent in 

Scheduled Part 135, and 38 percent in Non-Scheduled Part 135. Manufacturing or design elements were 

named as a cause in 40 percent of the Part 121 flight control or structural SCFM accidents. A component 

failed in 29 percent of the accidents, a component separated in 23 percent of the accidents, and a 

component jammed in 20 percent of the accidents.

Landing gear or hydraulic SCFMs are shown in Table 6. Maintenance errors were a causal factor in 

28 percent of the accidents; Part 121 accounted for 25 percent of these, 33 percent in Scheduled Part 135 

and 28 percent in Non-Scheduled Part 135. A component failed in 48 percent of the accidents, component 

fatigue occurred in 18 percent of the accidents, and there was a loss of hydraulic fluid in 15 percent of the 

accidents. In 33 percent of Scheduled Part 135 accidents a component was inoperative. Manufacturing or 

design issues were cited more frequently in Part 121 or Scheduled Part 135 than in Non-Scheduled Part 

135 accidents. 

The remaining SCFMs are shown in Table 7. Maintenance errors were a causal factor in 32 percent of 

the accidents; Part 121 accounted for 41 percent of these, 50 percent in Scheduled Part 135, and 17 percent

in Non-Scheduled Part 135. There was an electrical failure in 17 percent of the accidents, wire chafed/arcing 

in 15 percent of the accidents, and electrical short in 12 percent of the accidents. 

TABLE 5.—FREQUENCY OF CAUSAL FACTORS OF FLIGHT CONTROL OR STRUCTURAL SYSTEM/ 

COMPONENT FAILURE/MALFUNCTION (SCFM) ACCIDENTS BY OPERATION CATEGORY

Causal factors of flight control 

or structural SCFM

Operation category

Part 121 Scheduled 

Part 135

Non-Scheduled

Part 135

Parts 121 and 

135 combined

Total flight control or structural SCFM accidents 15 4 16 35

Maintenance related 8 (53%) 2 (50%) 6 (38%) 16 (46%)

Component failure 3 (20%) 2 (50%) 5 (31%) 10 (29%)

Component separated 4 (27%) 1 (25.0%) 3 (19%) 8 (23%)

Manufacturing/design 6 (40%) 0 (0%) 1 (6%) 7 (20%)

Component jammed 2 (13%) 1 (25%) 4 (25%) 7 (20%)

Component inoperative 2 (13%) 0 (0%) 3 (19%) 5 (14%)

Federal Aviation Administration 3 (20%) 1 (25%) 0 (0%) 4 (11%)

Company/operator error 2 (13%) 1 (25%) 0 (0%) 3 (9%)

Component corroded 2 (13%) 0 (0%) 1 (6%) 3 (9%)

Component fatigue 1 (7%) 0 (0%) 2 (12%) 3 (9%)

Unknown 3 (20%) 0 (0%) 0 (0%) 3 (9%)

Screws/bolts not secured 1 (7%) 1 (25%) 0 (0%) 2 (6%)

Component fractured 1 (7%) 0 (0%) 1 (6%) 2 (6%)

Elevator control movement restricted 1 (7%) 0 (0%) 1 (6%) 2 (6%)

Elevator trim/tab control disconnected 1 (7%) 0 (0%) 1 (6%) 2 (6%)

False indication 1 (7%) 0 (0%) 0 (0%) 1 (3%)

Inadequate lubrication 1 (7%) 0 (0%) 0 (0%) 1 (3%)

Jackscrew assembly worn 1 (7%) 0 (0%) 0 (0%) 1 (3%)
NASA/TM—2011-216967 8 

TABLE 6.—FREQUENCY OF CAUSAL FACTORS OF LANDING GEAR OR HYDRAULIC SYSTEM/COMPONENT 

FAILURE/MALFUNCTION (SCFM) ACCIDENTS BY OPERATION CATEGORY

Causal factors of landing gear 

or hydraulic SCFM

Operation category

Part 121 Scheduled 

Part 135

Non-Scheduled

Part 135

Parts 121 and

135 combined

Total landing gear or hydraulic SCFM accidents 32 12 71 115

Component failure 18 (56%) 3 (25%) 34 (48%) 55 (48%)

Maintenance related 8 (25%) 4 (33%) 20 (28%) 32 (28%)

Component fatigue 7 (22%) 2 (17%) 12 (17%) 21 (18%)

Hydraulic fluid loss 8 (25%) 3 (25%) 6 (8%) 17 (15%)

Component fractured 4 (12%) 1 (8%) 8 (11%) 13 (11%)

Manufacturing/design 6 (19%) 2 (17%) 4 (6%) 12 (10%)

Component inoperative 3 (9%) 4 (33%) 3 (4%) 10 (9%)

Component overload 1 (3%) 1 (8%) 4 (6%) 6 (5%)

Component collapsed 0 (0%) 1 (8%) 4 (6%) 5 (4%)

Component frozen 0 (0%) 1 (8%) 4 (6%) 5 (4%)

Component separated 1 (3%) 1 (8%) 3 (4%) 5 (4%)

Federal Aviation Administration 1 (3%) 0 (0%) 3 (4%) 4 (3%)

False indication 1 (3%) 0 (0%) 3 (4%) 4 (3%)

Unknown 1 (3%) 0 (0%) 3 (4%) 4 (3%)

Component corroded 0 (0%) 0 (0%) 3 (4%) 3 (3%)

Component jammed 0 (0%) 1 (8%) 2 (3%) 3 (3%)

Component malfunction 0 (0%) 0 (0%) 3 (4%) 3 (3%)

Gear switch movement restricted 1 (3%) 0 (0%) 1 (1%) 2 (2%)

Component disconnected 0 (0%) 0 (0%) 2 (3%) 2 (2%)

Component vibration 1 (3%) 0 (0%) 1 (1%) 2 (2%)

Mechanical binding of component 0 (0%) 1 (8%) 1 (1%) 2 (2%)

Company/operator surveillance 1 (3%) 0 (0%) 0 (0%) 1 (1%)

Bolt sheared 0 (0%) 0 (0%) 1 (1%) 1 (1%)

Brakes overheated 1 (3%) 0 (0%) 0 (0%) 1 (1%)

Gear strut washer worn 0 0 (0%) 1 (1%) 1 (1%)

Nose gear strut underinflated 1 (3%) 0 (0%) 0 (0%) 1 (1%)

Tires underinflated 0 (0%) 0 (0%) 1 (1%) 1 (1%)

Wiring chafed/arcing 0 (0%) 0 (0%) 1 (1%) 1 (1%)
NASA/TM—2011-216967 9 

TABLE 7.—FREQUENCY OF CAUSAL FACTORS OF OTHERa SYSTEM/COMPONENT FAILURE/ 

MALFUNCTION (SCFM) ACCIDENTS BY OPERATION CATEGORY

Cause of other SCFM Operation category

Part 121 Scheduled 

Part 135

Non-Scheduled

Part 135

Parts 121 and 

135 combined

Total other SCFM accidents 22 2 17 41

Maintenance related 9 (41%) 1 (50%) 3 (17%) 13 (32%)

Electrical failure 1 (4%) 0 (0%) 6 (35%) 7 (17%)

Wiring chafed/arcing 3 (14%) 1 (50%) 2 (12%) 6 (15%)

Manufacturing/design 4 (18%) 1 (50%) 0 (0%) 5 (12%)

Component failure 3 (14%) 0 (0%) 2 (12%) 5 (12%)

Electrical short 4 (18%) 0 (0%) 1 (6%) 5 (12%)

Company/operator error 2 (9%) 1 (50%) 1 (6%) 4 (10%)

Unknown 2 (9%) 0 (0%) 2 (12%) 4 (10%)

Federal Aviation Administration 1 (4%) 1 (50%) 0 (0%) 2 (5%)

Battery discharged 0 (0%) 0 (0%) 2 (12%) 2 (5%)

Hazardous material 2 (9%) 0 (0%) 0 (0%) 2 (5%)

Alternator belt disconnected 0 (0%) 0 (0%) 1 (6%) 1 (2%)

Alternator wiring disconnected 0 (0%) 0 (0%) 1 (6%) 1 (2%)

Alternator inoperative 0 (0%) 0 (0%) 1 (6%) 1 (2%)

Anti-ice system inoperative 0 (0%) 0 (0%) 1 (6%) 1 (2%)

Auxiliary power unit (APU)

combustor cap drain line clogged 1 (4%) 0 (0%) 0 (0%) 1 (2%)

APU malfunction 1 (4%) 0 (0%) 0 (0%) 1 (2%)

Attitude indicator malfunctioned 1 (4%) 0 (0%) 0 (0%) 1 (2%)

Autopilot servo frozen 1 (4%) 0 (0%) 0 (0%) 1 (2%)

Galley elevator drive shaft 

fatigue/failure 1 (4%) 0 (0%) 0 (0%) 1 (2%)

Heater over temperature 0 (0%) 0 (0%) 1 (6%) 1 (2%)

Hydraulic fluid loss 1 (4%) 0 (0%) 0 (0%) 1 (2%)

Oxygen leak 1 (4%) 0 (0%) 0 (0%) 1 (2%)

Wiring not secured 0 (0%) 1 (50%) 0 (0%) 1 (2%)

a

Other includes electrical, instrumentation/communication/navigation, anti-ice/deice system, APU, cargo fire, galley, 

heating, oxygen, pressurization, warning systems, vacuum pump, and unknown.

NASA Analysis of Aviation Safety Reporting System Incident Data 

This section examines the composition of SCFM incidents as reported in the Aviation Safety 

Reporting System (ASRS). ASRS is a voluntary, nonpunitive, self-reporting system administered by 

NASA Ames Research Center that includes incident reports submitted by members of the flightcrew and 

other people working in the aviation industry (Ref. 2). The ASRS reports do not represent an unbiased 

sample of aviation incidents, and the results presented here should not be considered statistically 

representative, but rather informational in nature. 

Data used in this analysis are from the years January 1993 through March 2008. While the ASRS 

online database includes incidents starting in 1988, information on which Federal Aviation Regulation 

(FAR) flight operation the incident occurred during is available only beginning in 1993. Because other 
NASA/TM—2011-216967 10

flight operations, such as Part 91 (general aviation), may have substantially different data compared with 

Parts 121 and 135, it was decided to use only those years for which FAR part was known (1993 to 2008). 

During this time period, there were 60 380 incident reports for Part 121 operation and 6151 incident 

reports for Part 135 operation. Each ASRS incident report lists the primary problem (or causal factor), 

and, if applicable, the component involved. While this categorization is performed by the experts at 

ASRS, the component data was further categorized into groups based on aircraft subsystems. 

To obtain information relevant to SCFM, the ASRS Web tool was used to query the database. The

initial selection criterion was incidents in which the primary problem was “aircraft.” The Web tool allows 

the user to export the results to an Excel file, and relevant information such as the FAR Part and Primary 

Problem were kept. Because the Web tool’s data export function only includes those fields that can be 

queried using the tool, component information was later obtained through permission of the ASRS team 

at NASA Ames Research Center. These data were provided in a spreadsheet with only the component and 

incident report number (ACN), and were matched to the exported data using the ACN. After combining 

the data in one file, the aircraft system categorization was added, and SAS software was used to perform 

the analysis. 

Primary Problems of Incidents

ASRS identifies the most significant factor of the incident and includes it under the category Primary 

problem. Table 8 shows the frequency of different primary problems or causal factors of incidents from 

January 1993 to March 2008 for both Part 121 and Part 135 operations. It must be noted that not every 

incident report has an identified primary problem. Therefore, the number of incidents shown in Table 8

are less than the total of 66 531 incidents contained in the database for the given time period. 

TABLE 8.—FREQUENCIES OF PRIMARY PROBLEM BY FLIGHT OPERATION CATEGORY

Primary problem Operation category

Part 121 Part 135 Parts 121 and

135 combined

Flight crew human performance 20378 (37%) 3181 (56%) 23559 (39%)

Aircraft 12179 (22%) 1211 (21%) 13390 (22%)

Air traffic control (ATC) human performance 7811 571 8382

Maintenance human performance 4500 102 4602

Company 2947 80 3027

Weather 1865 221 2086

Passenger human performance 1349 2 1351

Airport 1132 136 1268

Chart or publication 888 40 928

Environmental factor 513 35 548

Federal Aviation Administration 375 38 413

Navigational facility 350 28 378

Airspace structure 247 25 272

Cabin crew human performance 230 0 230

ATC facility 108 9 117

Total 54872 (100%) 5679 (100%) 605551 (100%)
NASA/TM—2011-216967 11

The aircraft primary problem category is the second most frequent primary problem (causal factor) in 

both Parts 121 and 135 incidents containing 22 percent of all primary problems. It occurs more frequently 

than all other primary problems combined excluding the flight crew human performance category. Of 

interest to the IVHM Project is the aircraft category because it contains incident causal factors related to 

SCFM. ASRS reports include more specific descriptions of the type of problem in the aircraft category. 

Table 9 shows a further breakdown of the aircraft primary problem category into different types of 

subcategories. The most frequent subcategory cited is the equipment problem subcategory. 

The numbers reflected in Table 9 are the number of ASRS incident reports citing each of these 

problem subcategories. For example, there were 12 395 reports that listed the primary problem as being 

aircraft and the type of aircraft problem being equipment problem for the combined Parts 121 and 135. 

During some incidents, multiple components failed in succession. Later in this study, the tables will 

reflect higher numbers because of multiple component failures in a single report. Separately and

combined, equipment problems account for approximately 93 percent of incidents whose primary factor 

was aircraft for both FAR Parts 121 and 135. A closer look at the equipment problem subcategory is 

presented next. 

TABLE 9.—SUBCATEGORY FREQUENCIES OF THE PRIMARY PROBLEM: 

AIRCRAFT BY FLIGHT OPERATION CATEGORY

Subcategory Operation category

Part 121 Part 135 Parts 121 and 

135 combined

Equipment problem 11268 (93%) 1127 (93%) 12395 (93%)

Nonadherence 164 31 195 

Airspace violation 5 0 5 

Altitude deviation 203 11 214 

Cabin event 44 1 45 

Conflict 77 10 87 

Excursion 2 1 3 

Ground encounter 4 0 4 

Incursion 2 1 3 

Inflight encounter 62 9 71

Maintenance problem 15 0 15 

Other anomaly 325 20 345

Other spatial deviation 8 0 8 

Total 12179 (100%) 1211 (100%) 13390 (100%)
NASA/TM—2011-216967 12

Aircraft SCFM Analysis

Most ASRS incident reports include a list of which components failed during the occurrence. 

Unfortunately, because ASRS is voluntarily reported, not all reports included the same amount of detail. 

A small number of those reports listing the primary problem as aircraft were excluded because they did 

not state which components were affected. For the remainder of this section, all results are based only on 

reports that list the primary problem as aircraft and include specific component failures. The data 

presented shows FAR Parts 121 and 135 combined. 

The top 20 most frequent individual component failures can be seen in Table 10. The components are 

labeled as they were listed in ASRS and any acronyms can be found in the appendix of this document. 

One difficulty with this study was the lack of clarity in the reports concerning engine failures. Although 

many pilots and ASRS officials were very specific in noting exactly which component of the engine 

failed, others just listed “engine” or “turbine engine” as having failed without providing any more detail. 

The top 10 failures in Table 10 account for 22 percent of all of the equipment failures in the ASRS 

incident reports. In the incident reports, 463 different component failures were cited. 

TABLE 10.—MOST FREQUENT COMPONENT FAILURES OR MALFUNCTIONS

Component Frequency of failure 

or malfunction

Turbine engine 752

Pressurization system 351

Hydraulic main system 274

Flight management system/flight management computer 267

Engine 259

Autopilot 241

Air conditioning and pressurization 192

Flap/slat control system 175

Gear extend/retract mechanism 174

Trailing edge flap control 170

Main gear tire 165

Pressurization control system 162

Indicating and warning-landing gear 142

Air conditioning distribution system 130

Nose gear 128

Cockpit window 128

Hydraulic system 127

Trailing edge flap 124

Ground proximity warning system (GPWS) 120

Aircraft logbook 105
NASA/TM—2011-216967 13

Aircraft System Category Failures

To provide an alternative look at the incident data, the component failures were later grouped by 

aircraft system. Then the systems were ranked in order of frequency within the new subcategories. Shown 

in Table 11, the top five systems cause 54 percent of all aircraft equipment failures during incidents. 

Those systems are monitoring and management, propulsion, control surfaces, environmental control, and 

landing gear. Some ASRS incident reports included multiple failures, and that is why 12 772 component 

failures came from 10 121 reports.

TABLE 11.—FREQUENCIES OF COMPONENT FAILURES/MALFUNCTIONS GROUPED BY SYSTEM

Aircraft system System description SCFM 

frequency

Monitoring and 

management

Any component or system that monitors the aircraft status and functions and 

relays them to the pilots; centralized control of complex systems including health 

monitoring

1801

Propulsion Propulsion system components 1754

Control surfaces Moving surface used for attitude, lift, and drag control 1166

Environmental control Provides air supply, thermal control cabin pressurization, avionics cooling, 

smoke detection, and fire suppression

1127

Landing gear Components that provide support on the ground and allow taxiing, takeoff and 

landing

1003

Navigation Determination of the position on or above the surface of the Earth; also collision 

avoidance including navigation around other aircraft and avoidance of terrain

988

Electrical/power Includes power generation, distribution protection, and storage 933

Hydraulics/pneumatics Any systems using a fluid or gas to transmit force; includes actuators 671

Automated flight control Automated means of flight control 543

Structures The fuselage, empennage, wings; the control surfaces and landing gear have been 

subcategorized

543

Fuel Any portion of the fuel system 414

Miscellaneous Anything that does fit into any of the other categories 404

Communication Connects the flight deck to the ground and the flight deck to the passengers 362

Oil Oil lubrication and components 337

Brakes Landing gear braking system 287

Furnishings and

equipment

Aircraft seats, cargo, entertainment, etc. 263

Icing Anti-icing or deicing systems 140

Weather Weather radar/information and lightning detectors 36
NASA/TM—2011-216967 14

Monitoring and Management 

The monitoring and management category is of particular importance to the IVHM Project because of 

its focus on the health management of aircraft components and systems. This category includes any 

component or system that monitors the aircraft status and functions and relays them to the pilots as well as 

centralized control of complex systems including health monitoring. While hardware features have 

extensive background research and testing of failures, monitoring and management failures may be harder 

to predict and test. Information given by United Airlines in reference to Boeing 777 aircraft indicates that 

health monitoring significantly reduces mechanical problems, but increases software problems (Ref. 6). 

More research is needed to ensure that mechanical problems are not replaced by software problems (Ref. 6). 

Included in Table 12 are the top 20 most frequent specific component failures of the monitoring and 

management system. This category contains 75 different types of component failure. These failures 

account for 64 percent of all monitoring and management system failures.

TABLE 12.—TOP 20 MOST FREQUENT SYSTEM/COMPONENT FAILURE/ 

MALFUNCTIONS (SCFMs) OF MONITORING AND MANAGEMENT 

SYSTEM COMPONENTS

Component SCFM frequency 

Landing gear indicating and warning 142

Landing gear indicating system 98

Fire/overheat warning 95

Cargo compartment fire/overheat warning 86

Door warning system 83

Fuel quantity pressure indication 81

Powerplant fire/overheat warning 77

Oil pressure indication 65

Air data computer 57

Altimeter 52

Airspeed indicator 39

Flight and navigation systems indicating and warning 39

Pneumatic system indicating and warning 39

Fuel system indicating and warning 37

Primary flight display 29

Oil contents indication 28

Attitude indicator 26

Engine pressure ratio indication 26

APU fire/overheat warning 25

Engine indications 25
NASA/TM—2011-216967 15

Propulsion 

The propulsion system category contains SCFMs of 82 different components and systems. Shown in 

Table 13 are the top 20 most frequent specific component failures of the propulsion system. These 

failures account for 88 percent of all propulsion SCFMs. The turbine engine and engine components 

account for 58 percent of all the cited propulsion SCFMs. Again, these components skew the results 

because of lack of detail in the reports. The rest of the propulsion SCFMs were actually remarkably 

specific and diverse. Without engine and turbine engine, most of the propulsion components do not fail a 

significant amount of the times. 

TABLE 13.—TOP 20 MOST FREQUENT SYSTEM/

COMPONENT FAILURE/MALFUNCTIONS (SCFMs) 

OF PROPULSION SYSTEM COMPONENTS

Component SCFM frequency 

Turbine engine 752

Engine 259

Compressor 73

Throttle/power level 69

Cowling 50

Turbine assembly 48

Turbine engine thrust reverser 31

Engine air starter 27

Compressor bearing 26

Reciprocating engine assembly 24

Thrust reverser control 24

Fan blade 23

Turbine assembly blade 23

Engine air 22

Engine-driven pump 22

Reverser actuator 16

Compressor blade 15

Propeller autofeather system 15

Fan reverser 12

Propeller blade 11
NASA/TM—2011-216967 16

Control Surfaces

The control surface system category contains SCFMs of 33 different components and systems. Shown 

in Table 14 are the top 20 most frequent specific component failures of the control surface system. These 

failures account for 94 percent of all control surface SCFMs. The flap/slat control system, trailing edge 

flap control, and trailing edge flap components account for 40 percent of all the cited control surface 

SCFMs. 

TABLE 14.—TOP 20 MOST FREQUENT SYSTEM/

COMPONENT FAILURE/MALFUNCTIONS (SCFMs) 

OF CONTROL SURFACES SYSTEM COMPONENTS

Component SCFM frequency 

Flap/slat control system 175

Trailing edge flap control 170

Trailing edge flap 124

Rudder control system 82

Leading edge slat 77

Horizontal stabilizer trim 73

Aileron control system 50

Elevator control system 49

Elevator trim system 43

Speedbrake/spoiler 42

Spoiler system 41

Leading edge flap 32

Horizontal stabilizer control 26

Rudder 22

Rudder trim system 19

Elevator 18

Elevator feel system 15

Aileron trim system 14

Aileron 13

Horizontal stabilizer 10
NASA/TM—2011-216967 17

Environmental Controls 

The environmental control system had the fourth highest impact on the incidents reported from 1993 

to 2008. The environmental control system category contains SCFMs of 16 different components and 

systems shown in Table 15. The pressurization system, air conditioning and pressurization, pressurization 

control system, and air conditioning distribution system components account for 74 percent of all the 

cited environmental controls SCFMs. 

TABLE 15.—SYSTEM/COMPONENT FAILURE/MALFUNCTION 

(SCFM) OF ENVIRONMENTAL CONTROLS SYSTEM 

COMPONENTS 

Component SCFM frequency

Pressurization system 351

Air conditioning and pressurization 192

Pressurization control system 162

Air conditioning distribution system 130

Aircraft cooling system 76

Oxygen system/crew 52

Pressurization outflow valve 49

Air conditioning compressor 40

Oxygen system/passenger 19

Aircraft heating system 17

Fire extinguishing indication system 14

Fire protection system 10

Aircraft auto temperature system 6 

Oxygen system/portable 5 

Oxygen system/general 3 

Other fire extinguishing system 1 
NASA/TM—2011-216967 18

Landing Gear 

The landing gear system also contributed to a significant number of failures. The landing gear system 

category contains SCFMs of 23 different components and systems. Shown in Table 16 are the top 20 

most frequent specific component failures of the landing gear system. The gear extend/retract mechanism, 

main gear tire, and nose gear components account for 47 percent of all the cited landing gear SCFMs . 

TABLE 16.—TOP 20 MOST FREQUENT SYSTEM/

COMPONENT FAILURE/MALFUNCTIONS (SCFMs) 

OF LANDING GEAR SYSTEM COMPONENTS 

Component Frequency of 

failure/malfunction

Gear extend/retract mechanism 174

Main gear tire 165

Nose gear 128

Nose wheel steering 90

Main gear 68

Main gear door 58

Landing gear 44

Nose gear tire 37

Gear down lock 34

Nose gear door 33

Wheels/tires/brakes 26

Gear up lock 24

Tires 23

Main gear wheel 22

Gear lever/selector 19

Emergency extension system 18

Nose gear wheel 16

Supplemental landing gear 12

Wheel assemblies 5 

Gear ski 2 
NASA/TM—2011-216967 19

Failure Modes and Effects Analysis

FMEA is a method that systematically examines individual system components to assess risk and 

reliability. It is a bottom-up approach and follows an inductive logic to determine critical component 

failures and their consequences. The FMEA starts with decomposition of the system into subsystems and 

finally into individual components. Ways in which each component can potentially fail, called failure 

modes, are then recorded and evaluated separately to determine what effect they have at the component 

level and the system level. 

As part of the system analysis task, FMEA data from literature has been examined to identify and 

document failure modes of aerospace components/subsystems as they relate to the adverse conditions 

documented in the adverse events table. In most cases, the actual FMEA data and quantitative values regarding 

criticality were not included in the reviewed literature documents due to the sensitivity of the information. 

However, we have captured critical failure modes regarding a number of aerospace components and 

subsystems. Examples include component failure mechanisms in wiring components such as wire chafing, 

stalling in turbomachinery, solder or joint problems for electronic components, and spalling of engine bearings. 

Where appropriate, this information is incorporated into the adverse events table (Table 17). 

Adverse Events Table

The purpose of the adverse event type table is to provide focus to the direction of the IVHM Project. As 

the IVHM Project matures and future technologies and trends become clear, this initial set of adverse event 

types and candidate examples will change. These adverse event types are categorized into five classes based 

on the overall remaining useful life of the affected system, subsystem, or component: incipient failures, 

slow-progression failures, intermittent faults, cascading faults, and fast-progression failures. 

The systems analysis team has updated the initial adverse events table by collecting data gleaned from 

findings within the ASRS and NTSB databases, in addition to FMEA abstracts. The intent was to call 

attention to damage conditions that occur frequently while providing insight on their severity and 

detectability. Depending on the nature of the damage condition, there are scenarios in which they may 

apply to more than one adverse event type. For example, a software fault could lead to a fast-progression 

fault as in the case of a stack overflow, or a slow-progression fault, as in the case of a memory leak. In 

addition, improper maintenance is a key issue that was omitted from the table but is applicable within all 

event types. Primarily, the majority of the accidents were derived from the NTSB database, and the 

incidents were extracted from the ASRS database.

Because the IVHM Project does not address maintenance issues, and Landing Gear and Hydraulic 

systems accidents are usually not fatal, the focus of research should be those SCFMs that occur in the 

engine/fuel and flight control/structures systems as well as power systems. Some examples of damage 

conditions for these systems can be found in the Adverse Events Table (Table 17). Of particular interest are

• Icing conditions in propulsion systems 

• Turbine engine bearings failures

• Fatigue cracks on metallic airframe structures

• Delamination in composites

• Ball-jam in electromechanical actuator (EMA) 

• Aileron, rudder or control surface faults 

• Fuel system faults

• Engine stall/faults in turbomachinery

• Power electronics/power system faults
NASA/TM—2011-216967 20

TABLE 17.—ADVERSE EVENTS AND EXAMPLE DAMAGE CONDITIONS WITH SEVERITY AND FREQUENCY

Adverse event type Example damage condition Severity (frequency)

Incipient Fault: 

Hard to detect and differentiate due 

to extremely slow degradation in 

performance

1. Icing conditions in propulsion system 1. Accident (6)

2. Fault of power electronics

• Power drivers

• Power supplies

• Switching transistors

• Electronics packaging

• Electronic circuit boards

2. Accident (11)

Incident (417)

3. Turbine engine bearings

• Fatigue spallation 

3. Accident (4) 

Slow Progression Fault: 

Very hard to detect and gradual 

degradation in performance

4. Fatigue cracks on metallic airframe structure 4. Accident (13)

Incident (343)

5. Delamination in composites 5. Accident (2) 

6. Ball-jam in EMA

• Hydraulic actuator failures

6. Accident (18)

Incident (516)

7. Air conditioning and pressurization faults 7. Incident (408)

8. Oil and lubrication system failures 8. Incident (463)

Intermittent Fault: 

Fault does not degrade but instead is 

a recurring hard fault that comes and 

goes, for example, a signal 

conducted via a loose connector 

9. Wire chafing resulting in an electrical short due to an 

unexpected ground path

9. Accident (9) 

Cascading Fault: 

Faults that may have a single root 

cause yet progress to create faults in 

other systems, subsystems, or 

components

10. Power system faults resulting in wide-spread systemic 

issues

• Electrical distribution problems

10. Accident (10)

Incident (738)

11. Aileron, rudder, or control surface (elevator) faults 11. Accident (22)

Incident (620)

12. Instrumentation, communication, and navigation 12. Accident (5)

Incident (1278)

13. Fuel system faults 13. Accident (20)

Incident (349)

Fast Progression Fault: 

Limited precursor signature but 

rapid degradation

14. Engine stall/faults in turbomachinery 14. Accident (52)

Incident (2312)

15. Landing gear faults

• Gear extension/retraction

15. Accident (97)

Incident (2057)

16. Brake/anti-skid system faults 16. Accident (22)

Incident (423)

17. Lightning- and radiation-related avionics faults 17. Accident (1)
NASA/TM—2011-216967 21

Discussion and Conclusion

Of the 370 National Transportation Safety Board (NTSB) accidents affected by system/component 

failure/malfunction (SCFM) in the study period of 1988 to 2003, 48 percent involved the engine or fuel 

system, 31 percent involved landing gear or hydraulic failure and malfunctions, 9 percent involved flight 

control or structural failure and malfunctions, and 11 percent involved all other SCFMs. A total of 

35 percent of all the SCFM accidents were caused by improper maintenance. The leading causes of 

engine or fuel SCFM were maintenance related (39 percent), component failure (35 percent), component 

fatigue (23 percent), component separation (14 percent), manufacturing/design (11 percent), and 

component disconnected (11 percent). For flight control or structural failure events, the leading causes of 

SCFM were maintenance related (46 percent), component failure (29 percent), and manufacturing/design 

(20 percent). The leading causes of landing gear or hydraulic SCFM were component failure (48 percent), 

maintenance related (28 percent), and component fatigue (18 percent), For the “other” category 

(electrical, instrumentation/communication/navigation, anti-ice/deice system, auxiliary power unit (APU), 

cargo fire, galley, heating, oxygen, pressurization, warning systems, vacuum pump, and unknown), the 

leading causes of SCFM were maintenance related (32 percent), electrical failure (17 percent), wire 

chafed/arcing (15 percent), and electrical short (12 percent).

A total of 7732 FAA database incidents were affected by SCFM. Of these, 33 percent involved the 

landing gear or hydraulics, 33 percent involved the engine and fuel system, while 11 percent involved the 

flight control or structural systems. 

Ninety-three percent of the aircraft primary problem incidents found in Aviation Safety Reporting 

System (ASRS) were attributed to equipment problems. The most frequent component failures were 

turbine engine, pressurization system, hydraulic main system, flight management system/flight 

management computer, and engine. The data was further categorized into aircraft systems. The 

monitoring and management system accounted for 14.1 percent of the system failures, the propulsion 

system accounted for 13.7 percent, the control surfaces accounted for 9.1 percent, and the environmental 

control accounted for 8.8 percent. Unfortunately, the propulsion system failures and malfunctions often 

were not clearly defined in the reports. 

NASA/TM—2011-216967 23

Appendix.—Acronyms

ACN incident report number 

APU auxiliary power unit 

ASIAS Aviation Safety Information and Analysis Sharing 

ASRS Aviation Safety Reporting System

ATC air traffic control

AvSafe Aviation Safety Program

EMA electromechanical actuator

FAA Federal Aviation Administration 

FAR Federal Aviation Regulation

FMEA failure modes and effects analysis

GPWS ground proximity warning system

IVHM Integrated Vehicle Health Management

MEA measurement and inspection technologies

NASA National Aeronautics and Space Administration

NTSB National Transportation Safety Board 

SCFM system/component failure/malfunction 
NASA/TM—2011-216967 24

References

1. Integrated Vehicle Health Management. NASA Aviation Safety Program, Technical Plan, version 

2.03, 2009. http://www.aeronautics.nasa.gov/nra_pdf/ivhm_tech_plan_c1.pdf Accessed December 9, 

2010. 

2. Aviation Safety Information Analysis and Sharing (ASIAS) System. Federal Aviation 

Administration, 2010. http://www.asias.faa.gov Accessed December 9, 2010. 

3. Annual Review of Aircraft Accident Data, U.S. Carrier Operations Calendar Year 2005. 

NTSB/ARC–09/01, NTIS PB2009–106372, Notation 7502F, 2009. 

http://www.ntsb.gov/publictn/2009/ARC0901.pdf Accessed December 9, 2010.

4. GILS: Aviation Accident Synopses. National Transportation Safety Board, 2010. 

http://ntsb.gov/Info/gils/gilssyn.htm Accessed December 9, 2010.

5. Annual Review of Aircraft Accident Data U.S. Air Carrier Operations, Calendar Year 1999. 

NTSB/ARC–02/03, PB2002–109241, 2002. http://www.ntsb.gov/publictn/2002/arc0203.pdf

Accessed December 9, 2010.

6. Zuniga, Fanny, et al.: Integrated Systems Health Management for Exploration Systems. AIAA 2005–

2586, 2005. 
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Causal Factors and Adverse Events of Aviation Accidents and Incidents Related to Integrated 

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13. SUPPLEMENTARY NOTES

14. ABSTRACT

Causal factors in aviation accidents and incidents related to system/component failure/malfunction (SCFM) were examined for Federal Aviation Regulation Parts 121 and 135 

operations to establish future requirements for the NASA Aviation Safety Program’s Integrated Vehicle Health Management (IVHM) Project. Data analyzed includes National 

Transportation Safety Board (NSTB) accident data (1988 to 2003), Federal Aviation Administration (FAA) incident data (1988 to 2003), and Aviation Safety Reporting System 

(ASRS) incident data (1993 to 2008). Failure modes and effects analyses were examined to identify possible modes of SCFM. A table of potential adverse conditions was 

developed to help evaluate IVHM research technologies. Tables present details of specific SCFM for the incidents and accidents. Of the 370 NTSB accidents affected by 

SCFM, 48 percent involved the engine or fuel system, and 31 percent involved landing gear or hydraulic failure and malfunctions. A total of 35 percent of all SCFM accidents 

were caused by improper maintenance. Of the 7732 FAA database incidents affected by SCFM, 33 percent involved landing gear or hydraulics, and 33 percent involved the 

engine and fuel system. The most frequent SCFM found in ASRS were turbine engine, pressurization system, hydraulic main system, flight management system/flight 

management computer, and engine. Because the IVHM Project does not address maintenance issues, and landing gear and hydraulic systems accidents are usually not fatal, the 

focus of research should be those SCFMs that occur in the engine/fuel and flight control/structures systems as well as power systems. 

15. SUBJECT TERMS

Flight safety; Aircraft safety 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

32 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

U 

19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. Z39-18