Risk Factors for Pilot Fatalities in General Aviation Airplane Crash Landings FREE

CIVIL (nonmilitary) flights are classified as either general aviation or air carrier operations. Air carrier operations include passenger or cargo transports for hire. General aviation comprises recreational flying, flight instruction, agricultural operations, sightseeing, and business travel flown in a variety of aircraft of all sizes and types, including airplanes, helicopters, balloons, and gliders. The majority of civil aviation crashes, deaths, and injuries are attributed to general aviation operations.

Although general aviation airplane crashes typically generate much media coverage, they are infrequent occurrences. In 1992 there were 39.6 million flight departures and 2075 crashes.¹ In 78% of the crashes there were no deaths and in 68% there were no injuries.² Airplanes are designed with features that can dissipate the kinetic energy of the occupants and minimize injury in the event of a crash landing. If a crash landing is necessary, pilots are taught to keep the plane under control, to land in an upright position at the slowest possible speed, and to avoid obstacles as much as possible.

We examined data from a large number of general aviation airplane crash landings to identify pilot, airplane, environmental, and crash factors associated with pilot fatalities and to estimate the relative risk (RR) of a pilot fatality associated with these factors after adjusting for potential confounders.

We analyzed data from computer tapes containing the standardized findings of National Transportation Safety Board investigations of airplane accidents and incidents. These tapes included data on crashes only if they had occurred during landing or takeoff and involved loss of engine power, which we defined as crash landings. Such events often involve an attempt at a controlled landing. Thus, we attempted to eliminate crashes where the airplane hit a mountain, was torn apart in a thunderstorm, or where aerobatics or low-altitude cruise flight may have occurred.

Crash landings in this study occurred during 1983 through 1992 and were severe enough to result in serious injury or death within 30 days of the crash landing to a pilot or passenger or caused substantial damage to the airplane. Damage to the wings, fuselage, rudder, elevators, or cockpit that adversely affected the ability of a crashed airplane to fly and would usually require repair or replacement is defined as substantial by the National Transportation Safety Board regulations.³ In contrast, damage to an airplane's propeller, landing gear, or wing tips, dents or small holes in the plane's skin, or engine failure are considered minor.

A serious injury is defined as one that results in a hospitalization of more than 48 hours' duration; fractures (except simple ones of the fingers, toes, or nose); internal organ damage; severe nerve, tendon, or muscle damage or bleeding; or a significant second- or third-degree burn. Only airplanes with 10 seats or fewer (98.8% of all the airplane crashes) were selected because they represent most general aviation activity and have different characteristics from other types of aircraft, ie, helicopters, gliders, balloons, or larger airplanes.

Cases were defined as crash landings in which the pilot died, while controls were defined as crash landings in which the pilot survived. Pilot, airplane, environment, and crash variables related to the event were categorized according to Federal Aviation Administration regulations,⁴ National Transportation Safety Board regulations,⁵ or to the standardized reporting categories of National Transportation Safety Board accident and incident investigations.⁶

Exposure to flying was defined as pilot flight hours, ie, the total time a pilot had flown any aircraft. The biennial flight review is a Federal Aviation Administration requirement that all pilots receive theoretical and practical flight training with an instructor at least every 2 years.⁷

Whether or not an instrument flight rules flight plan was filed was used to indicate a potentially high-risk flight condition. An instrument flight rules flight plan is required whenever the flight is under instrument control, takes place 5400 m (18000 ft) or more above mean sea level, or when instrument flight rules are to be followed, which may be due to weather conditions or pilot preference.

Logistic regression was used to adjust for the effects of potential confounders.⁸ Only variables for which the data were at least 90% complete and might be logically related to pilot death were examined. Adjustments were made only for variables that altered the risk estimates by at least 10%. Odds ratios, estimated by the maximum-likelihood method, were used to approximate RRs and were adjusted for pilot age, pilot flight time, airplane landing gear category, and the filing of an instrument flight plan. Other variables examined, but not adjusted for, included pilot characteristics of sex, principal profession, certification, airplane rating, and medical certificate; airplane characteristics of certificated maximum gross weight, engine horsepower greater than 200, airplane hours of use, and whether or not the airplane was owned by the pilot; and environmental and crash characteristics of instrument meteorological conditions, night time, number of occupants, and flight purpose.

There were 8411 eligible crash landings during 1983 through 1992; the number of crash landings decreased from 1235 in 1983 to 681 in 1992. One third of the crash landings occurred in the summer, one quarter in the spring, one fifth in the fall, and one fifth in the winter. Most crash landings occurred in daylight (85.1%), with no restriction of visibility (88.7%) and no weather precipitation (94.2%). A pilot fatality occurred in 437 (5.2%) of the crash landings. In 69.1% of the crash landings there was no pilot injury reported, a minor injury in 17.2%, and a serious injury in 8.3%. The airplane was destroyed in 15.2% of the crash landings, suffered substantial damage in 84.6%, minor damage in 0.1%, and no damage in 0.1%.

Relative risks were adjusted for pilot age, pilot flight hours, airplane landing gear type, and the filing of an instrument flight plan, except that the estimates for each of these 4 variables were adjusted only for the other 3 variables. Relative risk estimates showed little change with further adjustment for other variables.

A fatal pilot injury was most strongly associated with destruction of the airplane (RR, 42.6) or an airplane fire or explosion on the ground (RR, 20.4) (Table 1). Failure to use both a lap belt and shoulder harness and failure to use a shoulder harness were associated with an increased RR of death compared with use of both a lap belt and shoulder harness (RR, 6.8 and 1.7, respectively). The RR of pilot death was also increased if the crash site was not on an airport or airstrip (RR, 3.2).

The RR of pilot death in an airplane with retractable tricycle landing gear was about twice that in one with fixed tricycle landing gear (RR, 2.2). Multiengine planes were associated with an elevated RR of pilot death (RR, 1.9).

Older pilots were more likely to die; for the 11% of pilots aged 60 years or older, the RR of death was 2.9 (95% confidence interval [CI], 1.7-4.9); for the 19% of pilots aged 50 to 59 years, the RR for death was 1.9 (95% CI, 1.1-3.2), compared with the 6.8% of pilots younger than 25 years. The RR of death was twice as great among pilots without a current biennial flight review, a requirement established to attempt to ensure periodic pilot flight training.

We found that general aviation airplane crash landings were usually survivable, with pilot fatalities occurring in only 5% of the crashes we examined.

The increased risk of fatal injury associated with failure to use restraining belts is consistent with other studies of both motor vehicle and aircraft crashes.^9- 10 Federal Aviation Administration regulations require that restraints be used during takeoff and landing,¹¹ and it is possible that some pilots who survived may falsely claim that they used restraints; restraint use by fatally injured pilots might be less likely to suffer from this bias. If this occurred, it would exaggerate the strength of the association that we found when we compared pilots who used no restraints with those who used both lap belts and shoulder harnesses. However, this should not explain the difference in survival when we compared pilots who used lap belts only with those who used both lap and shoulder belts, since both types of restraints meet the legal requirements.

Our finding that crashes that occurred off an airport or airstrip were more deadly seems plausible, due to the obstructions that would be encountered in many such landings. The increased RR of death associated with destruction of the airplane was expected because of the large amount of kinetic energy that is involved in such a crash. We found that the type of landing gear best controlled for airplane size characteristics of certificated maximum gross weight, engine horsepower, number of engines, and type of landing gear. The presence of multiple engines may increase the risk of death because planes with more than 1 engine have to land at a higher velocity, resulting in the potential for transferring more energy to the occupants during a crash landing. Some of the increase in mortality associated with fire or explosion may reflect more forceful crashes that might have been lethal even without thermal or blast injuries.

The reasons for the association of a pilot death with some of the other factors examined are less apparent. The increased risk of pilot death associated with airplanes that had more than 1 engine or had retractable tricycle landing gear may be related to flight complexity. We adjusted for the filing of an instrument flight plan as a surrogate measure of flight complexity. The filing of an instrument flight rules flight plan, which may be done because of flight conditions or for pilot convenience, does not necessarily describe flight complexity. Other measures of flight complexity, such as total duration of flight or weather conditions during flight, were not available in the data. These measures might be related to pilot fatigue and therefore might affect the ability of a pilot to cope with a crash landing. The lack of a current biennial flight review, associated with a 2-fold risk of pilot death, may indicate pilots lacking the skills needed for a crash landing or pilots prone to risk-taking behavior.

Previous analyses of aviation crashes have examined a number of risk factors for aircraft crashes.¹² A recent investigation of commuter and air taxi aircraft crashes found that the characteristics of multiengine aircraft, off-airport crash site, night flights, instrument meteorological conditions, nonuse of shoulder restraints, and fire or explosion after the crash were associated with a greater risk of pilot fatality, although pilot age, sex, and flight experience were not.¹⁰

Some of the risk factors identified are more amenable to change than others. Certain characteristics associated with fatal pilot injury during crash landings, such as travel in airplanes that land at a high velocity, have multiple engines or retractable tricycle landing gear, or travel in complex flight conditions may be difficult to alter. Stricter enforcement of the Federal Aviation Administration's requirement for a biennial flight review might decrease the likelihood of pilot death in some crash landings. Federal Aviation Administration regulations require that starting in 1978, new aircraft must have shoulder harnesses for pilots as well as seat belts¹³; however, a large proportion of general aviation aircraft were manufactured before that year, as the average date of aircraft manufacture is 1969.¹⁴ Retrofitting restraints is technically a fairly easy process but costs $300 to $800 per seat. Pilots who wish to reduce their risk of death in a crash landing should ensure that their airplanes are equipped with lap and shoulder restraints.