May 2013 

NASA/CR–2013-217989 

An Examination of Aviation Accidents 

Associated with Turbulence, Wind Shear and 

Thunderstorm 

Joni K. Evans 

Analytical Mechanics Associates, Inc., Hampton, Virginia 
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0D\2013 

NASA/CR–2013-217989 

An Examination of Aviation Accidents 

Associated with Turbulence, Wind Shear and 

Thunderstorm 

Joni K. Evans 

Analytical Mechanics Associates, Inc., Hampton, Virginia 
Available from: 

NASA Center for AeroSpace Information 

7115 Standard Drive 

Hanover, MD 21076-1320 

443-757-5802 

The use of trademarks or names of manufacturers in this report is for accurate reporting and does not 

constitute an official endorsement, either expressed or implied, of such products or manufacturers by the 

National Aeronautics and Space Administration. 
1 

Introduction 

One of the technical challenges within the Atmospheric Environment Safety Technologies 

(AEST) Project is to “improve and expand remote sensing and mitigation of hazardous 

atmospheric environments and phenomena”1. Although numerous statistical studies of aviation 

accident and incident data have been conducted in the past regarding the accident categories of 

Turbulence and Windshear/Thunderstorm 234, AEST Project Management desired additional 

information regarding distinct subgroups of atmospheric hazards within those categories, in order 

to better focus their research portfolio toward the most common types of atmospheric hazards. 

The focal point of this study was the definition and examination of turbulence, wind shear and 

thunderstorm in relation to aviation accidents. Several literature sources were examined and 

influenced the study parameters. These include: 

 Characterizing the Severe Turbulence Environments Associated with Commercial Aviation 

Accidents5

, 

 A Federal Aviation Administration (FAA) Review of Aviation Accidents Involving Weather 

Turbulence in the United States 1992-20016, 

 Aviation Occurrence Categories: Definitions and Usage Notes, Advisory Circular: 

Thunderstorms7

, 

 A National Transportation Safety Board (NTSB) Study of Risk Factors Associated with 

Weather-Related General Aviation Accidents4. 

The paper by Michael Kaplan and several others5

 described the results of 44 case study analyses 

that defined the atmospheric structure prior to the development of accident-producing turbulence. 

His work resulted in the definition of a set of turbulence categories. Analyses by the FAA6, 

NTSB4

 and others have similarly attempted to categorize turbulence and thunderstorms. Many of 

these have substantial overlap in their categories, but none are identical. For this study, we 

developed an atmospheric hazard taxonomy which draws on all of these papers, with the 

following categories: 

 

1

 Atmospheric Environment Safety Technologies (AEST) Project Plan. October 1, 2010 (Updated on October 21, 

2011)

2

 Evans, J.K., “An Examination of Aviation Accidents and Incidents During the years 1989-2008 Associated with 

Technical Challenges within the Atmospheric Environment Safety Technologies (AEST) Project.” Internal NASA 

Report; March 2012.

3

 Evans, J.K., “Frequency of Specific Categories of Aviation Accidents and Incidents During 2001-2010.” Internal 

NASA Report; August 2012. 

4

 National Transportation Safety Board. 2005. Risk Factors Associated with Weather-Related General Aviation 

Accidents Safety Study. 

5

 Kaplan, M.L., Huffman, A.W., Lux, K.M., Charney, J.J., Riordan, A.J., Lin, Y.-L., “Characterizing the severe 

turbulence environments associated with commercial aviation accidents,” Meteorology and Atmospheric Physics, 

Vol 88, 2005, pp. 129-152. 

6

 National Aviation Safety Data Analysis Center (NASDAC) FAA Office of System Safety. 2004. Review of 

Aviation Accidents Involving Weather Turbulence in the United States 1992-2001. URL: 

http://www.asias.faa.gov/aviation_studies/turbulence_study/ turbulence_study _new.pdf. 7

 Federal Aviation Administration. 1983. Advisory Circular: Thunderstorms. URL: 

http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/list/AC%2000-24A/$FILE/ac00-

24b.pdf 
2

1. Wake Turbulence (WAKE): Wake turbulence is a by-product of lift and is present behind 

every aircraft in flight. Once the aircraft is airborne, two counter rotating cylindrical vortices 

are created, which are hazardous to any trailing aircraft. This is particularly true during takeoff, initial climb, final approach and landing, when the high angle of attack at which the 

aircraft operates maximizes the formation of strong vortices. 

2. Mountain Wave Turbulence (MTN): Mountain wave turbulence occurs when air flows are 

forced to rise up the windward side of a mountain barrier, then as a result of certain 

atmospheric conditions, sink down the leeward side. This perturbation develops into a series 

of waves which may extend for hundreds of miles. 

3. Clear Air Turbulence (CAT): Clear air turbulence typically occurs in cloud-free regions at 

higher altitude, widely separated from mountains, and often is associated with wind shear, 

particularly between the core of a jet stream and the surrounding air. 

4. Cloud Turbulence (CLD): This turbulence phenomenon occurs in cloud covered regions 

without the requirements of convection or precipitation reaching the ground. 

5. Convective Turbulence (CONV): An air mass which absorbs heat from the earth’s surface 

will rise. As the air rises, it cools, and eventually the cooler air mass descends. This cycle of 

rising and falling air is known as convection. Convective turbulence occurs within, or in 

close proximity to, convective storms, particularly thunderstorms, which result in strong 

updrafts and downdrafts. 

6. Thunderstorm, with no turbulence (TRW): This hazard category is restricted to 

thunderstorms, with or without microbursts or wind shear, but with no mention of turbulence. 

7. Low Altitude Wind Shear, Microburst or Turbulence (LAWMT): This category consists of 

wind shear, microbursts or turbulence occurring at low altitude, with no mention of 

thunderstorms. 

This report examines the historical aviation accidents, using the National Transportation Safety 

Board (NTSB) Aviation Accident and Incident Data System (restricted to 1987-2008). All USbased accidents with a cause or factor of turbulence, thunderstorm, wind shear or microburst 

were assigned to only one of the seven categories defined above, and this report summarizes the 

differences between the categories in terms of factors such as flight operations category, aircraft 

engine type, the accident’s geographic location and time of year, degree of injury to aircraft 

occupants, aircraft damage, age and certification of the pilot and the phase of flight at the time 

the flight encountered severe weather. All percentages shown in tables or charts are based on the 

totals for the particular category listed above. Twelve accidents for which the accident report did 

not provide sufficient detail to classify the type of turbulence with confidence were eliminated 

from the analysis. 
3

Methods 

The National Transportation Safety Board is an independent Federal agency that investigates 

every civil aviation accident in the United States and significant accidents in the other modes of 

transportation, conducts special investigations and safety studies, and issues safety 

recommendations to prevent future accidents. The information the NTSB investigators collect 

during their investigations of these aviation events resides in the NTSB Aviation Accident and 

Incident Data System. A copy of this database in Microsoft Access format was obtained from the 

Aviation Safety Information Analysis and Sharing (ASIAS) department of the FAA’s Office of 

Aviation Safety8

 in March 2010. At that point in time, the NTSB investigation was not complete 

for a substantial number of 2009 accidents, particularly those which occurred toward the end of 

the year. For this reason, all work on the database was restricted to 1987-2008, which was 

primarily an update of two years beyond the previous working version of the data. The update 

process requires several months of cross-checking various data elements and attempting to fill in 

any missing data, followed by the assignment of occurrence categories to each accident. 

The NTSB database includes events involving a wide variety of aircraft (airplanes, helicopters, 

hot air balloons, gliders, ultralight, etc.) with operations conducted under various Federal 

Aviation Regulations (Part 91: General Aviation, Part 121: Commercial Air Carriers, Part 129: 

Foreign Air Carriers, Part 135: Commuters and On-Demand Air Taxis, Part 137: Agricultural 

Operations, etc.). 

The NTSB considers each event to be either an accident or an incident, under the following 

definitions:9

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 

Any injury or aircraft damage which occurs when there was no intent for flight (high speed taxi 

tests, movement of the aircraft around the airfield, maintenance run-ups, etc) is, by definition, an 

incident. 

All recorded accidents involving commercially built fixed-wing airplanes operating under FAR 

Part 121, Part 135 or Part 91 were included in these working datasets, regardless of whether the 

investigation is in a preliminary stage or finalized, and whether or not the event occurred within 

the United States. Amateur built or experimental aircraft were excluded, as were helicopters, 

ultra light aircraft, gliders and balloons. 

 

8

 http://www.asias.faa.gov/portal/page/portal/asias_pages/asias_home/ 

9

 National Transportation Safety Board, “Government Information Locator Service (GILS): Aviation Accident 

Synopses”’ http://ntsb.gov/Info/gils/gilssyn.htm
4

For every accident, the NTSB records a series of occurrence codes (e.g., In Flight Encounter 

with Weather, Loss of Control – In Flight, Hard Landing, etc.) and the associated phase of flight. 

They also record causes, factors and findings associated with each occurrence. Causes are 

actions or events that lead directly to the accident, while factors are actions or events that 

contributed to the accident. Each accident can have multiple causes and multiple factors10. 

Findings are actions or events that occurred in conjunction with the accident, but no 

determination was made that they contributed to the accident. For example, the aircraft might 

have flown in the area of a thunderstorm with lightning, but the lightning had no impact on the 

flight or the accident, so lightning is recorded as a finding. Similarly, the pre-flight weather 

briefing might have included turbulence, icing and low ceiling, but if there was no indication that 

the flight actually encountered turbulence, it would be considered only a finding. 

Accidents were selected for inclusion in this study if turbulence, thunderstorm, wind shear or 

microburst was considered either a cause or a factor (but not a finding) in the accident report. 

The main interest in this analysis with regards to thunderstorms is the effect of turbulence and 

other types of wind. Five accidents in which the primary occurrence was a lightning strike or hail 

damage were excluded, despite the obvious connection to thunderstorm activity. These would be 

considered part of a separate category, based on the taxonomy described above. Similarly, 

accidents resulting from jet blast and propeller/rotor wash have been excluded, despite being 

included in the definition for wake turbulence from the Aeronautical Information Manual 

(AIM)11: "A phenomena resulting from the passage of an aircraft through the atmosphere. The 

term includes vortices, thrust stream turbulence, jet blast, jet wash, propeller wash, and rotor 

wash both on the ground and in the air." This study is interested in the more focused definition of 

“off the ground” wake turbulence that was provided in the introduction. 

In order to describe the types of aircraft which were involved in these accidents, the specific 

aircraft make and model (and in many cases, aircraft series) was determined for each accident. 

For the vast majority of events, this information could be easily found in the data record. For 

some events it was necessary to consult the FAA’s aircraft registry database, and to assume that 

the correct aircraft registration number was recorded in the data system. All aircraft in the data 

system for the chosen time period (1987-2008) were divided into groups based on some 

combination of engine type, aircraft use, aircraft size and aircraft complexity. The aircraft 

categories are as follows, and a list of the particular aircraft models (sometimes including series 

information) within each category can be found in Appendix A. 

 Wide Body Jet Airliners 

 Narrow Body Jet Airliners 

 Regional Jets 

 Medium Sized Business Jets 

 Small Business Jets (maximum takeoff weight <= 12,500 lbs) 

 

10 https://asafe.larc.nasa.gov/DOC/definitions.html 

11 http://www.faa.gov/air_traffic/publications/ATpubs/AIM/aim.pdf; page PCG-W1. 
5

 Large Turbo-props (maximum takeoff weight >= 32,000 lbs and more than 30 seats) 

 Medium Turbo-props (12,500< maximum takeoff weight <32,000 lbs or 15-30 seats)

 Small Turbo-props (maximum takeoff weight <12,500 lbs and less than 15 seats) 

 Heavier multiple reciprocating engines (maximum takeoff weight >15,000 lbs) 

 Lighter multiple reciprocating engines (maximum takeoff weight < 15,000 lbs) 

 Single reciprocating engine, retractable landing gear 

 Single reciprocating engine, fixed landing gear 

 Light Sport Aircraft (Rotax Engines) 
6

Results and Discussion 

Eight hundred sixty-four accidents were considered in this analysis; these were all affected by 

some sort of turbulence, thunderstorm, wind shear or microburst, or a combination thereof. In 

this report, these weather conditions will be referred to collectively as “Atmospheric Hazards.” 

Each accident was assigned to only one hazard category. Sixty-nine of these flights (8.0%) 

encountered wake turbulence, sixty-eight (7.9%) were affected by mountain wave turbulence, 

one hundred thirteen (13.1%) encountered clear air turbulence, eighty-nine (10.3%) were 

affected by turbulence in clouds, one hundred fifty-six (18.1%) were classified as convective 

turbulence, one hundred seventy-seven (20.5%) encountered thunderstorms with no mention of 

turbulence, and one hundred ninety-two (22.2%) were affected by low altitude wind shear, 

turbulence or microburst with no mention of thunderstorm. 

Flight Operations Category 

Table 1 and Figure 1 show how these events were distributed among flight operations. Although 

wake turbulence is caused primarily by large jets12, its effects are felt most among Part 91 flights 

(83%). Similarly, Part 91 flights account for nearly all accidents attributed to mountain wave 

turbulence (90%), thunderstorms with no turbulence (91%) and low altitude wind shear, 

turbulence or microburst (92%). Clear air turbulence primarily affects Part 121 (75%), while 

both cloud and convective turbulence are split more evenly between Part 121 and Part 91. Part 

135 accidents accounted for between two and ten percent of the atmospheric hazards which were 

examined here (5% overall), and roughly five percent of all accidents in this time frame. 

 

12 Nelson, R.C., “The Trailing Vortex Wake Hazard: Beyond the Takeoff and Landing Corridors.” American 

Institute of Aeronautics and Astronautics. 2004-5171. 
7

Table 1. Flight operations among each type of atmospheric hazard (1987-2008) 

Atmospheric Hazard Part 121 Part 135 Part 91 Total 

Wake Turbulence 5 ( 7.2%) 7 (10.1%) 57 (82.6%) 69 (100%) 

Mountain Wave 

Turbulence 4 ( 5.9%) 3 ( 4.4%) 61 (89.7%) 68 (100%) 

Clear Air Turbulence 85 (75.2%) 3 ( 2.7%) 25 (22.1%) 113 (100%) 

Cloud Turbulence 36 (40.4%) 6 ( 6.7%) 47 (52.8%) 89 (100%) 

Convective 

Turbulence 61 (39.1%) 3 ( 1.9%) 92 (59.0%) 156 (100%) 

Thunderstorm (no 

turbulence) 6 ( 3.4%) 10 ( 5.6%) 161 (91.0%) 177 (100%) 

Low Altitude Wind 

Shear, Microburst or 

Turbulence 

 4 ( 2.1%) 11 ( 5.7%) 177 (92.2%) 192 (100%) 

Figure 1. Flight operations among each type of atmospheric hazard (1987-2008). 

Pilot Certification 

Table 2 and Figure 2 show the distribution of pilot certification among each atmospheric hazard 

category. Eighty-four percent of those accidents which encountered clear air turbulence had an 
8

airline transport certificated pilot at the helm, along with fifty-two percent of the accidents 

affected by turbulence in clouds. Sixty-three percent of the pilots encountering thunderstorms 

had only a private license. Fourteen of the wake turbulence accidents had a student pilot in the 

aircraft. Five of the remaining “Other/Unknown” certifications were also student pilots, and three 

pilots had no license. 

Table 2. Pilot certification among each type of atmospheric hazard (1987-2008) 

Atmospheric 

Hazard 

Airline 

Transport Commercial Private Other / Unknown Total 

Wake Turbulence 19 (27.5%) 18 (26.1%) 18 (26.1%) 14 (20.3%) 69 (100%) 

Mountain Wave 

Turbulence 15 (22.1%) 18 (26.5%) 32 (47.1%) 3 ( 4.4%) 68 (100%) 

Clear Air 

Turbulence 95 (84.1%) 6 ( 5.3%) 10 ( 8.8%) 2 ( 1.8%) 113 (100%) 

Cloud Turbulence 46 (51.7%) 17 (19.1%) 25 (28.1%) 1 ( 1.1%) 89 (100%) 

Convective 

Turbulence 68 (43.6%) 33 (21.2%) 53 (34.0%) 2 ( 1.3%) 156 (100%) 

Thunderstorm 

(no turbulence) 24 (13.6%) 39 (22.0%) 112 (63.3%) 2 ( 1.1%) 177 (100%) 

Low Altitude Wind 

Shear, Microburst 

or Turbulence 

 32 (16.7%) 76 (39.6%) 83 (43.2%) 1 ( 0.5%) 192 (100%) 

Figure 2. Pilot Certification among each type of atmospheric hazard (1987-2008). 
9

Pilot Age 

Figure 3 shows the percentage of accidents in each hazard category for ten groupings of pilot 

age. Not surprisingly, most of the pilots in accidents encountering clear air turbulence, 

turbulence in clouds and convective turbulence tend to be between forty-five and sixty years. 

According to the FAA, most active pilots are between the ages of 40 and 60. For every weather 

category except thunderstorm and low altitude wind shear, microburst or turbulence, the top 

three age groups were somewhere between forty and sixty years. However, fifteen percent of the 

accidents encountering thunderstorms were piloted by someone aged sixty-five or older; this was 

the largest percentage associated with any age grouping for that hazard. The age distribution 

among low altitude wind shear, microburst or turbulence was nearly uniform (with every age 

grouping representing 6-13%). 

Figure 3. Pilot Age among each type of atmospheric hazard (1987-2008). 
10

Time of Year 

Figure 4 shows the monthly trend for each type of atmospheric hazard. Thunderstorms and 

convective turbulence follow the same general pattern, peaking in July. Turbulence in clouds 

shows a lack of pattern, with peaks in April, July and September. Mountain wave turbulence 

peaks in December, January, May and September. Wake turbulence has a substantial peak in 

September and a big dip in April. Clear air turbulence peaks in April, and is lowest in August 

and October. Low altitude wind shear, microburst and turbulence tends to follow a similar 

pattern to thunderstorm, but the difference between the low months (December and January) and 

high months (May and July) is not as great. 

Figure 4. Month of Accident among each type of atmospheric hazard (1987-2008). 
11

Aircraft Engine Type and Size 

Aircraft engine types correlate strongly (although not perfectly) with flight operations categories, 

so it is not surprising that the distribution of atmospheric hazard by engine type (Table 3 and 

Figure 5) is very similar to that observed in Table 1 and Figure 1. 

Table 3. Engine type among each type of atmospheric hazard (1987-2008) 

Atmospheric Hazard Jet Turbo-Prop Reciprocating Total 

Wake Turbulence 7 (10.1%) 3 ( 4.3%) 59 (85.5%) 69 (100%) 

Mountain Wave 

Turbulence 4 ( 5.9%) 4 ( 5.9%) 60 (88.2%) 68 (100%) 

Clear Air Turbulence 81 (71.7%) 11 ( 9.7%) 21 (18.6%) 113 (100%) 

Cloud Turbulence 33 (37.1%) 12 (13.5%) 44 (49.4%) 89 (100%) 

Convective 

Turbulence 60 (38.5%) 13 ( 8.3%) 83 (53.2%) 156 (100%) 

Thunderstorm (no 

turbulence) 7 ( 4.0%) 8 ( 4.5%) 162 (91.5%) 177 (100%) 

Low Altitude Wind 

Shear, Microburst or 

Turbulence 

10 ( 5.2%) 9 ( 4.7%) 173 (90.1%) 192 (100%) 

Figure 5. Engine type among each type of atmospheric hazard (1987-2008). 
12

Among jet aircraft (Table 4), seventy percent of the low altitude events involved business jets, 

and seventy-five percent of mountain wave events involved narrow-body jets. In all other 

categories of atmospheric hazard accidents, between fifty-seven and sixty-seven percent of the 

jet aircraft were narrow-body jets. 

Table 4. Aircraft Size (jet engines) among each type of atmospheric hazard (1987-2008) 

Atmospheric 

Hazard Wide-Body Narrow-Body Regional Business Total 

Wake Turbulence 0 ( 0.0%) 4 (57.1%) 0 ( 0.0%) 3 (42.9%) 7 (100%) 

Mountain Wave 

Turbulence 0 ( 0.0%) 3 (75.0%) 0 ( 0.0%) 1 (25.0%) 4 (100%) 

Clear Air 

Turbulence 22 (27.2%) 48 (59.3%) 8 ( 9.9%) 3 ( 3.7%) 81 (100%) 

Cloud Turbulence 8 (24.2%) 21 (63.6%) 2 ( 6.1%) 2 ( 6.1%) 33 (100%) 

Convective 

Turbulence 14 (23.3%) 40 (66.7%) 3 ( 5.0%) 3 ( 5.0%) 60 (100%) 

Thunderstorm (no 

turbulence) 2 (28.6%) 4 (57.1%) 0 ( 0.0%) 1 (14.3%) 7 (100%) 

Low Altitude 

Wind Shear, 

Microburst or 

Turbulence 

 0 ( 0.0%) 3 (30.0%) 0 ( 0.0%) 7 (70.0%) 10 (100%) 

Among turbo-props (Table 5), seventy-three percent of the CAT accidents were in large aircraft 

(maximum takeoff weight >= 32,000 lbs and more than 30 seats). For every other category of 

atmospheric hazard, at least half of the turbo-prop accidents involved small aircraft (maximum 

takeoff weight <12,500 lbs and less than 15 seats). 
13

Table 5. Aircraft Size (turbo-prop engines) among each type of atmospheric hazard 

 (1987-2008) 

Atmospheric Hazard Large Medium Small Total 

Wake Turbulence 1 (33.3%) 0 ( 0.0%) 2 (66.7%) 3 (100%) 

Mountain Wave 

Turbulence 1 (25.0%) 1 (25.0%) 2 (50.0%) 4 (100%) 

Clear Air Turbulence 8 (72.7%) 0 ( 0.0%) 3 (27.3%) 11 (100%) 

Cloud Turbulence 5 (41.7%) 0 ( 0.0%) 7 (58.3%) 12 (100%) 

Convective 

Turbulence 4 (30.8%) 1 ( 7.7%) 8 (61.5%) 13 (100%) 

Thunderstorm (no 

turbulence) 0 ( 0.0%) 1 (12.5%) 7 (87.5%) 8 (100%) 

Low Altitude Wind 

Shear, Microburst or 

Turbulence 

0 ( 0.0%) 3 (33.3%) 6 (66.7%) 9 (100%) 

Table 6. Aircraft Size (reciprocating engines) among each type of atmospheric hazard 

(1987-2008) 

Atmospheric Hazard Single Engine, 

Fixed Gear 

Single Engine, 

Retractable 

Gear 

Multiple 

Engine Total 

Wake Turbulence 42 (71.2%) 7 (11.9%) 10 (16.9%) 59 (100%) 

Mountain Wave 

Turbulence 26 (43.3%) 24 (40.0%) 10 (16.7%) 60 (100%) 

Clear Air Turbulence 8 (38.1%) 9 (42.9%) 4 (19.0%) 21 (100%) 

Cloud Turbulence 14 (30.8%) 20 (45.5%) 10 (22.7%) 44 (100%) 

Convective 

Turbulence 27 (32.5%) 39 (47.0%) 17 (20.5%) 83 (100%) 

Thunderstorm (no 

turbulence) 65 (40.1%) 55 (34.0%) 42 (25.9%) 162 (100%) 

Low Altitude Wind 

Shear, Microburst or 

Turbulence 

112 (64.7%) 44 (25.4%) 17 ( 9.8%) 173 (100%) 
14

Single-engine, retractable gear aircraft comprise the largest percentage (43%-47%) of pistonengine aircraft in clear air, cloud and convective turbulence (Table 6). In all other categories, the 

largest group was single-engine fixed gear aircraft. 

Figure 6 shows the distribution of all engine-size combinations for each type of atmospheric 

hazard. 

Figure 6. Aircraft engine/size grouping for each type of atmospheric hazard (1987-2008). 
15

Phase of Flight 

Figure 7 shows the phase of flight at the time the aircraft encountered each type of atmospheric 

hazard. All types except wake turbulence and low altitude wind shear, turbulence or microburst 

are most likely to occur during cruise flight. Wake turbulence is most likely during approach or 

landing, and by definition, low altitude wind shear, turbulence or microburst is most likely 

during approach, landing or takeoff. 

Figure 7. Phase of flight at time of each type of atmospheric hazard (1987-2008). 
16

Degree of Injury 

Table 7 describes the highest level of injury sustained among the accidents in each category. 

Seventy-two percent of accidents in which thunderstorms were a factor included at least one 

fatality. Sixty-six percent of accidents in which the flight was caught in mountain wave activity 

were fatal, compared with only seven percent of accidents encountering clear air turbulence. 

However, roughly eighty-five percent of the clear air, cloud and convective turbulence categories 

included either a fatal or serious injury (81% for mountain wave, 75% for thunderstorm). 

Surprisingly, forty-two percent of the accidents affected by wake turbulence and fifty-two 

percent of those affected by low altitude wind shear, microburst or turbulence resulted in no 

injuries whatsoever. 

Table 7. Degree of injury among each type of atmospheric hazard (1987-2008) 

Atmospheric 

Hazard Fatal Serious Minor None Total 

Wake Turbulence 11 (15.9%) 15 (21.7%) 14 (20.3%) 29 (42.0%) 69 (100%) 

Mountain Wave 

Turbulence 45 (66.2%) 10 (14.7%) 5 ( 7.3%) 8 (11.8%) 68 (100%) 

Clear Air 

Turbulence 8 ( 7.1%) 89 (78.8%) 1 ( 0.9%) 15 (13.3%) 113 (100%) 

Cloud Turbulence 36 (40.4%) 41 (46.1%) 5 ( 5.6%) 7 ( 7.9%) 89 (100%) 

Convective 

Turbulence 66 (42.3%) 65 (41.7%) 7 ( 4.5%) 18 (11.5%) 156 (100%) 

Thunderstorm 

(no turbulence) 128 (72.3%) 5 ( 2.8%) 10 ( 5.6%) 34 (19.2%) 177 (100%) 

Low Altitude 

Wind Shear, 

Microburst or 

Turbulence 

 27 (14.1%) 33 (17.2%) 33 (17.2%) 99 (51.6%) 192 (100%) 

Degree of Aircraft Damage 

As shown in Table 8, nearly seventy-two percent of accidents encountering clear air turbulence 

suffered no damage to the aircraft. In more than ninety-two percent of accidents affected by 

wake turbulence, mountain wave turbulence, thunderstorm, or low altitude wind shear, 

microburst or turbulence, the aircraft was either destroyed or suffered substantial damage. In the 

categories of turbulence in clouds and convective turbulence, nearly equal numbers of aircraft 

suffered no damage as were destroyed. 
17

Table 8. Aircraft damage among each type of atmospheric hazard (1987-2008) 

Atmospheric 

Hazard Destroyed Substantial Damage 

Minor 

Damage No Damage Total 

Wake Turbulence 20 (29.0%) 45 (65.2%) 1 ( 1.4%) 3 ( 4.3%) 69 (100%) 

Mountain Wave 

Turbulence 45 (66.2%) 18 (26.5%) 0 ( 0.0%) 5 ( 7.3%) 68 (100%) 

Clear Air 

Turbulence 8 ( 7.1%) 16 (14.2%) 8 ( 7.1%) 81 (71.7%) 113 (100%) 

Cloud Turbulence 35 (39.3%) 15 (16.9%) 0 ( 0.0%) 39 (43.8%) 89 (100%) 

Convective 

Turbulence 67 (42.9%) 28 (17.9%) 6 ( 3.8%) 55 (35.3%) 156 (100%) 

Thunderstorm 

(no turbulence) 121 (68.4%) 55 (31.1%) 0 ( 0.0%) 1 ( 0.6%) 177 (100%) 

Low Altitude 

Wind Shear, 

Microburst or 

Turbulence 

 43 (22.4%) 149 (77.6%) 0 ( 0.0%) 0 ( 0.0%) 192 (100%) 

Geographic Location 

In order to examine the areas of the country more prone to specific types of atmospheric hazards, 

the author created regions based on the location of the aircraft at the time of the accident. These 

regions were defined as follows: 

 Northeast: Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, Connecticut, 

New York, New Jersey, Pennsylvania, Delaware, Maryland and the District of Columbia 

 Southeast: North Carolina, South Carolina, Georgia, Florida, Alabama, Mississippi, 

Louisiana, Tennessee, Kentucky, Virginia and West Virginia 

 Great Lakes: Ohio, Indiana, Illinois, Michigan, Wisconsin and Minnesota 

 Plains: Iowa, Missouri, Arkansas, Oklahoma, Kansas, Nebraska, South Dakota and North 

Dakota 

 Northwest: Montana, Wyoming, Idaho, Oregon and Washington 

 Southwest: California, Utah, Nevada, Arizona, Colorado, New Mexico and Texas 

 Alaska: Alaska 
18

 Pacific Ocean: Generally flights to or from the US, Asia, Australia and New Zealand, 

including Guam and Hawaii 

 Other: Generally flights in or near South America, the Caribbean and Europe 

Figure 8. Geographic region at time of each type of atmospheric hazard (1987-2008). 

Thunderstorms, convective turbulence and turbulence in clouds most often occur in the southeast 

United States (US), followed by the southwest US (see Figure 8). All other types of atmospheric 

hazards, particularly mountain wave activity, are most likely to occur in the southwest US. 

Mountain wave activity is rarely involved in accidents outside of Alaska and the Southwest. Low 

altitude wind shear, microburst or turbulence occurs most often in the southwest, but is just as 

likely in the northeast or great lakes regions as in Alaska. Thunderstorms and convective 

turbulence are least often involved in accidents in the northwest US, Alaska and the Pacific 
19

Ocean. Forty percent of wake turbulence occurs in the southwest, compared with less than 20% 

in the southeast. 

In order to further examine the location of accidents with a cause or factor of some type of 

atmospheric hazard, Figure 9 shows the percentage of each type of atmospheric hazard in the 

states which were defined as part of the southwest and southeast regions. In general, the states 

with the most events are California, Colorado, Texas and Florida. The most wake turbulence is in 

California, the most mountain wave activity is in California, Colorado and New Mexico, and the 

most low altitude wind shear, microburst or turbulence in California and Colorado. Clear air 

turbulence was felt most often in Colorado and Florida, turbulence in clouds was most often 

encountered in Florida and California, convective turbulence in Florida and thunderstorms in 

Florida and Texas. 

Figure 9. State nearest occurrence of each type of atmospheric hazard (1987-2008). 
20

Summary 

The purpose of this analysis was to compare the characteristics of accidents associated with 

seven categories of atmospheric hazard (mostly turbulence, thunderstorm and windshear). Eight 

hundred sixty-four accidents from 1987-2008 were selected from the NTSB accident database. 

All are considered US-based accidents, and were operating under FAR Part 121, 135 or 91 flight 

rules at the time. 

Wake turbulence accounted for eight percent of the accidents selected. Although most wake 

turbulence is initiated by large jet aircraft, the resulting accidents are suffered mostly by singleengine, fixed gear aircraft (61%) operating under FAR Part 91 (83%). The pilots’ certifications 

vary widely, with twenty-eight percent airline transport rated pilots, twenty-six percent 

commercial, twenty-six percent private and twenty percent student pilots. The pilot ages also 

vary, with twenty-five percent under age 40, fifty-four percent between 40 and 55, and the 

remaining twenty-two percent over 55. Forty-three percent of wake turbulence occurred in July, 

September or November, and all other months accounted for between three and nine percent of 

the events. Seventy-four percent of wake turbulence accidents occur during approach or landing, 

which in part explains why forty-two percent of the accidents result in no injury, even though 

ninety-four percent result in at least substantial damage to the aircraft. Twenty-six percent of 

wake turbulence accidents happen in California, and nine percent in Florida. 

Sixty-two percent of accidents related to mountain wave turbulence occurred in California 

(38%), Colorado or New Mexico. Thirty-eight percent of the accidents occurred during 

December, January or May. Seventy-four percent of these accidents involved single pistonengine aircraft and ninety percent of the aircraft were operating under Part 91 rules. Forty-seven 

percent of the pilots had only a private license, and sixty percent of the pilots were between the 

ages of 40 and 60. Seventy percent of the accidents occurred during either cruise or maneuvering 

flight. Sixty-six percent of the mountain wave accidents resulted in a fatality and sixty-six 

percent resulted in destruction of the aircraft. Eight percent of the accidents selected for this 

report were affected by mountain wave turbulence. 

Clear air turbulence represented thirteen percent of the atmospheric hazards in this analysis. 

Seventy-five percent of these flights were Part 121 flights, eighty-four percent of the pilots were 

licensed for airline transport flight, and seventy-two percent of the aircraft were jets (mostly 

narrow-body airliners). Seventy-two percent of the pilots were between 40 and 60 years of age. 

Thirteen percent of the accidents took place in April, and all other months accounted for between 

five and eleven percent of the accidents. Eighty-six percent of the encounters occurred during 

cruise or descent. Eighty-six percent of the accidents resulted in at least a serious injury but in 

seventy-two percent of the accidents there was no damage to the aircraft. Less than three percent 

of the clear air turbulence was encountered over the Plains states, compared with thirty-five 

percent in the southwest US. 

Ten percent of the selected accidents involved turbulence in clouds. Forty-eight percent of that 

turbulence was encountered in the southwest or southeast United States. Nine percent of the 

flights were in the northwest US, which was the highest percentage in that region of any type of 

atmospheric hazard except wake turbulence. Fifty-three percent of the flights were Part 91 and 
21

forty-nine percent of the aircraft had reciprocating engines. Forty-four percent of the aircraft 

received no damage, but either a serious or fatal injury was recorded in eighty-six percent of the 

accidents. Fifty-two percent of the pilots had airline transport licenses, and two thirds of them 

were between 40 and 60 years of age. Seventy-five percent of the turbulence encounters were 

during cruise or descent. Less than three percent of these accidents occurred in December, with 

fifteen percent each in April and September. 

One hundred fifty-six accidents (18%) were caused in part by convective turbulence. Nearly 

sixty percent of those flights were operating under Part 91 regulations and forty-two percent of 

the aircraft had a single reciprocating engine. Forty-four percent of the aircraft were destroyed, 

and a serious or fatal injury occurred in eighty-four percent of the accidents. Forty-four percent 

of the pilots were rated for airline transport, and fifty-eight percent were between 45 and 60 

years old. Seventy-six percent of the accidents occurred from April through September and 

eighty percent occurred during cruise or descent. Thirty-six percent of the convective turbulence 

was encountered in the southeast US, with thirteen percent in Florida. 

Roughly twenty percent of the accidents selected for this analysis encountered a thunderstorm 

but no mention of turbulence was made in the accident report. One might expect these accidents 

to be similar to those encountering convective turbulence, but the greatest similarities are in 

geography and time of the year. Thirty-six percent occurred in the southeast (14% in Florida) 

and, as with convective turbulence, only six percent of these accidents were outside the 

contiguous US. Sixty-three percent of the accidents occurred in June through August, and fiftythree percent occurred during cruise flight. Ninety-one percent of these were in Part 91 flights 

(versus 60% for convective turbulence), and ninety-two percent (versus 54%) of the aircraft had 

reciprocating engines. Sixty-three percent of the pilots had only a private license, and one-third 

of them were aged 45-60. Seventy-two percent of the accidents included at least one fatality 

(versus 43%), and the aircraft was destroyed sixty-eight percent of the time (versus 44%). 

The largest category of atmospheric hazards was low altitude wind shear, microburst or 

turbulence (with no mention of thunderstorm) at twenty-two percent of the total. By a slight 

margin it had the largest percentage of Part 91 flights (92%), and was second to thunderstorms in 

the percentage of aircraft with reciprocating engines (90%). Fifty-two percent of these accidents 

resulted in no injury (the largest percentage of all types), but all resulted in at least substantial 

damage to the aircraft. Only seventeen percent of the pilots were rated for airline transport. This 

category also shows the most uniformity in the distribution of age (percentages in the ten 

groupings range from 6.3% to 12.6%). Twenty-nine percent of these accidents occurred in May 

or July, and more than one-quarter (26.5%) occurred in either California or Colorado. Eightynine percent of the accidents occurred during takeoff, approach or landing. 

Each of these seven categories of atmospheric hazards has some characteristics in common with 

other categories, and some characteristics that separate them. The category of atmospheric 

hazards with the largest number of accidents was low altitude wind shear, microburst or 

turbulence (with no mention of thunderstorm). Clear air turbulence is the most frequent category 

among both Part 121 and jet aircraft, followed by cloud turbulence and convective turbulence. 

Flight into thunderstorms (no turbulence) is the category most likely to result in both fatalities 

and aircraft destruction, but 91% of those accidents were in Part 91 flights. 
22

Appendix A 

List of Specific Aircraft Make and Model within Each Aircraft Group 
23

Wide-Body Jet Airliner Narrow Body Jet Airliner 

Airbus A300 A318 

A310 A319 

A330 A320 

 A321 

Boeing 747 707 

767 717 

777 727 

737 

757 

Lockheed L-1011 TRISTAR 

McDonnell-Douglas DC-8 

DC-9 

DC-10 

MD-11 

MD-80 

MD-90 

HS-BAE Systems BAE-146 

Regional Jet

Bombardier CRJ-100 

CRJ-200 

CRJ-700 

CRJ-900 

CRJ-5000 

Embraer ERJ-135 

ERJ-140 

ERJ-145 

ERJ-170 

ERJ-190 

Fairchild DO-328 (series 300) 

Fokker F-100 

F-28 
24

Medium Business Jet 

Aero Commander Jet Commander 1121 

Aerospatiale Corvette 

Bombardier Challenger 

 DHC-112 (called the venom – military aircraft) 

Cessna CE-560 

Citation II 

Citation III 

Citation Sovereign 

Citation X 

Dassault Falcon 10-100 

Falcon 20-200 

Falcon 50 

Falcon 900 

Falcon 2000 

Douglas A-4 (military) 

Gulfstream GA-1159 

Gulfstream II 

Gulfstream III 

Gulfstream IV 

Gulfstream V 

Hamburger Flugzeugbau 320 

Beech Hawker-800 

HS-BAE Systems 125-HAWKER 

Raytheon 125-HAWKER 

 400 

 Hawker-1000 

Rockwell Sabreliner 

Israel Aircraft Industries Astra 

Westwind 
25

Medium Business Jet (continued) 

Learjet 24 

25 

31 

35 

36 

45 

55 

60 

Lockheed Jetstar 

Mitsubishi 300 

 

 

Small Business Jet 

Cessna Citation I 

CitationJet 

Mustang 

T-37 (military) 

Eclipse 500 

Learjet 23 

Morane Saulnier MS-760 

Raytheon 390 
26

Large Turbo-prop 

ATR 42 

72 

Convair CV-580 

CV-600 

CV-640 

De Havilland Dash 7 

Dash 8 

Fokker F-27 

HS-BAE Systems BAE-ATP 

Lockheed L-188 

L-382 

NAMC YS-11 

Medium Turbo-prop 

Aerospatiale NORD-262 

Air Tractor 602 

802 

Beech/Raytheon BE-100 

BE-200 

BE-300 

99 

1900 

CASA 212 

De Havilland DHC-6 

Douglas DC-3 (Turbo conversion) 
27

Medium Turbo-prop (continued) 

Embraer EMB-110 

EMB-120 

Fairchild DO-228 

 DO-328 (series 100) 

Fairchild-Swearingen SA-226 

SA-227 

Metro 

GAF-ASTA Nomad 

Grumman 73-T 

Gulfstream Gulfstream I 

Jetstream-BAE Systems 31 

41 

Rockwell OV-10 

Saab 340 

Shorts 3-60 

 SC.7 Skyvan 

Small Turbo-prop 

Ayres Turbo Thrush 

Air Tractor AT-400 

AT-402 

AT-503 

Beech/Raytheon BE-18 (conversions) 

BE-45 (T-34C) 

BE-60-T 

BE-90 
28

Small Turbo-prop (continued) 

Cessna CE-208 

CE-425 

CE-441 

De Havilland DHC-2-MKIII 

DHC-3T 

Fairchild-Swearingen SA-26 

Grumman G-164 

Gulfstream GA-164 

GA-680 

GA-681 

GA-690 

GA-695 

McKinnon G-21 

Mitsubishi MU-2B 

SIAI Marchetti SF-260-TP 

Partenavia AP-68-TP 

Piaggio P180 

Pilatus PC-6 

PC-7 

PC-12 

Piper PA-31T 

PA-42 

PA-46-310TP, PA-46-350TP, PA-46-500TP 

Reims F406 

Socata TBM-700 

PZL-Mielec M-18/T-45 
29

Heavier Multi-Engine (Reciprocating) 

Boeing B-17 

B-307 

Convair CV-240 

CV-340 

CV-440 

Curtiss C-46 

De Havilland DHC-4 

Douglas DC-3 

DC-4 

DC-6 

DC-7 

DC-A20 

DC-A26 

Fairchild C-119 

Grumman C-1 

HU-16 

S-2F 

Lockheed L-1049 

L-18 

P-38 

Martin B26 

Lighter Multi-Engine (Reciprocating) 

Beagle 206 

Beech BE-18 

BE-50, BE-55, BE-56, BE-58 

BE-60, BE-65, BE-70, BE-76, BE-95 
30

Lighter Multi-Engine (Reciprocating) (continued) 

Britten-Norman Islander 

Tri-Islander 

Defender 

Stout Bushmaster 2000 

Camair 480 

Cessna CE-303, CE-310, CE-320 

CE-335, CE-336, CE-337, CE-340 

CE-401, CE-402, CE-404 

CE-411, CE-414, CE-421 

T-50 (Military) 

Champion Lancer 

De Havilland DHC-90 

Dornier DO-28 

Grumman 21, 44, 73 

Gulfstream GA-7 

GA-500, GA-520, GA-560 

GA-680, GA-685 

GA-700, GA-720 

Lockheed L-12 

Navion D-16 

Partenavia P-68 

Piper PA-23 

PA-30, PA-30A, PA-30B 

PA-31, PA-34, PA-39 

PA-44, PA-60 

STOL Aircraft Corp UC-1 

Wing Aircraft D-1 
31

Single-Engine (Reciprocating) Retractable Gear 

Beech BE-17 

BE-23 (series codes 24R, A24R, B24R, C24R) 

BE-33, BE-35, BE-36 

BE-45 (except BE-45-T34C) 

Bellanca BL-14, BL-17, BL-260 

Cessna CE-172-RG 

 CE-177-RG 

 CE-182-RG 

 CE-182-TR 

CE-210 

Colonial Aircraft C-1, C-2 

Culver LCA, LFA, V 

Curtiss-Wright P-40 

Douglas A-1 

Globe GC-1 

Grob G-115, G-120 

Grumman Avenger 

Gulfstream GA-112, GA-114 

Lake LA-4 

Meyers Aero Commander 200 

 MAC-145 

Mooney M-18, M-20, M-22 

North American AT-6 

 SNJ-2, SNJ-4, SNJ-5, SNJ-6 

 Harvard 

Navion NAV-1 

 NAV-A, NAV-B, NAV-D 

NAV-G, NAV-H, NAV-L 
32

Single-Engine (Reciprocating) Retractable Gear (continued) 

Piper PA-24, PA-28R, PA-28RT 

PA-32S-300 

PA-32R, PA-46 

Raytheon Commander 114 

Reims FR-182 

SIAI Marchetti S-205 

SF-260 

FN-333 

Socata TB-9, TB-10, TB-20 

Spartan 7W 

STOL Aircraft RC-3 

Thurston Teal TSC-1A 

Yakovlev Yak-3 

Single-Engine (Reciprocating) Fixed Gear 

Aero Mercantil Gavilan 358 

Air Tractor AT-301 

 AT-401 

 AT-501 

 AT-502 

AMD Alarus-2000 

American Legend AL-11 

 AL-3 

Avions Robin R-2160 

Arctic S1A, S1B 
33

Single-Engine (Reciprocating) Fixed Gear (continued) 

Aeronca AR-7, BL-7, AR-11, AR-15 

 AR-50, AR-58, AR-65 

 AR-C3, AR-K, AR-L3 

 Bubeck-Irving 

Aviat A-1 

Ayres Thrush 

Bellanca BL-7, BL-8 

 BL-DW1 

Beech BE-19, BE-23, BE-77 

Boeing B-75 

Call Aircraft A-2, A-3, A-9 

Cavalier Mustang 

CASA BU-131 

Centaur Longren 

Cessna CE-120, CE-140, CE-145, CE-150, CE-152 

 CE-170, CE-172, CE-175, CE-177 

CE-180, CE-182, CE-185, CE-188 

CE-190, CE-195, 

CE-205, CE-206, CE-207, CE-305 

Champion Champ-7, Champ-8 

Cirrus SR-20, SR-22 

Columbia XJ-7 

 350 

Commonwealth Skyranger, Sportster 

Convair – General Dynamics BT-13, BT-15, CV-L13 

DeHavilland DHC-1, DHC-2, DHC-3, DHC-82 
34

Single-Engine (Reciprocating) Fixed Gear (continued) 

Diamond DA-20, DA-40, DA-42 

ERCO Alon-415 

 Ercoupe-415 

 Forney-415 

Emigh Trojan 

Extra EA 

Fairchild F-24, M-62 

 PT-19, PT-23, PT-26 

Fieseler Fi-156 

Fleet Model 2, Model 16 

Found FBA-2 

Funk Model B 

Great Lakes 2T1 

Grumman G-164 

Gulfstream GA-AA, GA-AG 

Helio H-250, H-295, H-391, H-395 

 H-700, H-800 

Helton Lark-95 

Howard DGA-15 

Indus Thorp T-211 

Lancair LC-40, LC-41, LC-42 

Liberty XL-2 

Lockheed L-402 

Luscombe LL-8, LL-11 

 Phantom 
35

Single-Engine (Reciprocating) Fixed Gear (continued) 

Maule M-4, M-5, M-6, M-7, M-8 

 MX-7, MT-7, MXT-7 

MBB BO-209 

Meyers OTW 

Monocoupe D-145 

Morane-Saulnier MS-880, MS-894 

Mooney M-10 

Moravan Zlin-242 

Mudry CAP-10 

Naval Aircraft Factory N3N-3 

Noordyun UC-64 

OMF Symphony 

Pilatus PC-6-350 

Piper L-21, L-4 

 PA-11, PA-12, PA-14, PA-15, PA-16, PA-17, PA-18, PA-19 

 PA-20, PA-22, PA-25, PA-28 

PA-32, PA-36, PA-38 

PA-J3, PA-J3C, PA-J3F, PA-J3L, PA-J4, PA-J5 

Pitts S-1, S-2 

Porterfield CP-55, CP-65, FP-65, LP-65 

PZL-Mielec M-18, M-104 

Rawdon T-1 

Reims FA-150, FR-172 

Ryan ST-A, ST-3 
36

Single-Engine (Reciprocating) Fixed Gear (continued) 

Socata MS-Ralleye 

Stinson AT-19, SR-10, SR-V77, SR-JR, SR-L5, SR-108 

Stearman C-3 

Sukhoi SU-26, SU-29 

SZD Koliber-150 

Taylorcraft 15A, 19, 20, 21 

 BC, BF, BL 

 DC, DL 

Tecnam P-2002 

Timm N2T 

Varga 2150A, 2180 

Volaircraft Aero Commander 100 

WACO AGC, AVN, ARE, HRE, SRE, UKS, QCF, UPF, YPF, YMF 

Weatherly 201, 620 

Zenair CH-2000 
37

Light Sport Aircraft (Rotax Engines) 

Aero Ltd. AT-4 

Aeropro Eurofox 

Bush Caddy LSA 

Colyaer Freedom 

Czech Aircraft Works Parrot 

 Sport Cruiser 

Evektor Sportstar 

Fantasy Air Allegro 2000 

Flight Design CT 

Higher Class Aviation Sport Hornet 

Iniziative Sky Arrow 600 

Jihlavan KP-5 

Moravan/Zlin Savage 

 

Tecnam P-92 

Zenair CH-600 
REPORT DOCUMENTATION PAGE Form Approved

OMB No. 0704-0188

2. REPORT TYPE 

Contractor Report

 4. TITLE AND SUBTITLE

An Examination of Aviation Accidents Associated with Turbulence, Wind 

Shear and Thunderstorm 

5a. CONTRACT NUMBER

NNL12AA09C 

 6. AUTHOR(S)

Evans, Joni K.

 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

NASA Langley Research Center 

Hampton, Virginia 23681 

 

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National Aeronautics and Space Administration

Washington, DC 20546-0001

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Langley Technical Monitor: Sharon M. Jones

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14. ABSTRACT

The focal point of the study reported here was the definition and examination of turbulence, wind shear and thunderstorm in relation to aviation accidents. 

NASA project management desired this information regarding distinct subgroups of atmospheric hazards, in order to better focus their research portfolio.

A seven category expansion of Kaplan's turbulence categories was developed, which included wake turbulence, mountain wave turbulence, clear air 

turbulence, cloud turbulence, convective turbulence, thunderstorm without mention of turbulence, and low altitude wind shear, microburst or turbulence (with 

no mention of thunderstorms).More than 800 accidents from flights based in the United States during 1987-2008 were selected from a National Transportation 

Safety Board (NTSB) database. Accidents were selected for inclusion in this study if turbulence, thunderstorm, wind shear or microburst was considered either 

a cause or a factor in the accident report, and each accident was assigned to only one hazard category. This report summarizes the differences between the 

categories in terms of factors such as flight operations category, aircraft engine type, the accident's geographic location and time of year, degree of injury to 

aircraft occupants, aircraft damage, age and certification of the pilot and the phase of flight at the time of the accident. 

15. SUBJECT TERMS

Aircraft accidents; Aircraft safety; Statistical analysis; Thunderstorms; Turbulence

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