1 Epidemic Intelligence Service, Division of Applied Public Health Training, Epidemiology Program Office, Centers for Disease Control and Prevention, Atlanta, GA.
2 Alaska Field Station, Division of Safety Research, National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention, Anchorage, AK.
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ABSTRACT |
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accidents, occupational; aircraft; aviation; occupational health; transportation
Abbreviations: CFIT, controlled flight into terrain; FAA, Federal Aviation Administration; NTSB, National Transportation Safety Board
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INTRODUCTION |
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Covering over 586,000 square miles (937,600 km2), Alaska has more than twice the land area of Texas, and with over 47,000 miles (75,200 km) of coastline, it has more coastline than the remaining 49 US states combined (2). It also has 17 of the 20 highest peaks in the United States, yet only 60 percent of Alaska has radar coverage over 10,000 feet (3,047.6 m) above mean sea level. Radar coverage allows aircraft to be seen and followed on a radar screen by air traffic controllers and allows for flight in low-visibility (poor weather) conditions.
Even though Alaska is very large, it has only 12,200 miles (19,520 km) of public roadsapproximately the same mileage as Vermont. Furthermore, 90 percent of Alaska's communities are not connected to a highway system (3). Because of this, commuter and air taxi flights must serve in lieu of a traditional road system, making aircraft essential for transportation of passengers and delivery of goods, services, and mail to outlying communities.
Between 1990 and 1999, aircraft crashes in Alaska caused 106 occupational deaths among workers classified as civilian pilots. This is equivalent to 410 deaths per 100,000 pilots per yearapproximately 100 times the mortality rate for US workers as a whole (4). The Alaska pilot fatality rate is higher than the fatality rate for any other occupation in Alaska; the two next-highest occupational fatality rates are logging (150/100,000/year) and commercial fishing (125/100,000/year) (5
), and this rate is five times the fatality rate for all US pilots (80/100,000/year) (1
).
Controlled flight into terrain (CFIT) has been found to be a leading cause of aircraft fatalities in Alaska. A CFIT crash refers to any collision with land or water in which there was no detectable mechanical or equipment failure, where the pilot was in control of the aircraft but lost situational awareness and flew into terrain. A recent study by Thomas et al. (6) identified CFIT crashes in Alaska as entailing higher risks for pilot and passenger fatality; however, the study did not analyze survival factors. Understanding the survival factors associated with both CFIT and non-CFIT crashes is paramount in discerning the risk factors associated with overall aircraft crash fatality in Alaska.
Li and Baker (7) studied pilot survival in US commuter and air taxi crashes occurring from 1983 to 1988. They identified four key factors associated with pilot fatality: postcrash fire, an off-airport crash location, poor weather, and nonuse of a shoulder restraint. Although this study was significant in identifying factors that impact survivability, it was conducted using 19831988 crash data, which may not be representative of trends in more recent crashes. Li and Baker also used a national population, which may not be representative of survival factors that appear to be unique to Alaska's flying environment.
Eckert (8) conducted a national descriptive study of fatal commercial air transport crashes occurring between 1924 and 1981. This study provided historical baseline data on aircraft crashes but provided no analysis of variables associated with pilot survival and provided no data beyond 1981. Eckert included national data for all categories of air transportation, which may not be useful for Alaska-specific air taxi and commuter crashes.
Li and Baker (9) also conducted a national study examining the injury patterns of persons who died in aviation crashes during the 1980s (19801990). Their findings indicated that despite a 34 percent reduction in aviation-related fatalities, injury patterns remained constant. These injury patterns demonstrated that blunt injuries resulting from deceleration forces, particularly head injuries, were the most life-threatening to occupants in aviation crashes.
Alaska is widely regarded as having a unique aviation environment for crashes, with different risks than those incurred elsewhere in the United States. Pilot information on necessary flying skills specific to the area is largely passed on by word of mouth or by reading aviation magazines. Articles written on flying in Alaska describe typical conditions as rough terrain, sparse population, and unpredictable weather and emphasize the geographic and climatic impediments to air transportation (1013
). The sheer numbers of commuter and air taxi operations in Alaska, due mostly to the lack of roads, are also seen as being representative of the distinctiveness of the Alaskan flying environment.
In the current study, we sought to determine factors associated with pilot survival in work-related aircraft crashes in Alaska and to determine whether risk factors in Alaska vary from those seen elsewhere in the United States. To accomplish this, we evaluated all work-related aircraft crash fatalities that occurred in Alaska from 1990 through 1999. Through this evaluation, we hoped to find ways to decrease the high pilot fatality rate from occupational aircraft crashes in Alaska.
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MATERIALS AND METHODS |
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An accurate record of commercial pilots operating in Alaska who were not involved in crashes during this period does not exist. Because of the lack of adequate exposure data for all commercial pilots operating in Alaska (i.e., denominator information), a traditional case-control approach was not feasible. Thus, a comparative analysis of fatal crashes versus nonfatal crashes was completed. Crashes in which the pilot in command died were compared with crashes in which the pilot in command survived. Initial analysis included crude models utilizing Wald 2 statistics to test the relations between individual variables and the outcome of interest (pilot fatality). A main-effects logistic regression model was also tested to determine the relation between the dependent and independent variables. Odds ratios were then generated in a final adjusted model. Statistical Analysis System software (SAS Institute, Inc., Cary, North Carolina) was utilized in data analysis.
All variables, except age, were dichotomized for entry into logistic regression models. Dichotomous variables that were evaluated included use of a shoulder restraint (no = 0, yes = 1), meteorologic conditions (visual flight conditions vs. instrument flight conditionsused as a marker for poor weather) (visual = 0, instrument = 1), light conditions (darkness = 0, daylight = 1), type of aircraft (airplane = 0, helicopter = 1), presence of postcrash fire (no = 0, yes = 1), location of crash (on-airport = 1, off-airport = 0), and pilot's state of residence (Alaska = 0, other = 1). Pilot flight experience was dichotomized by determining the median flight experience of all pilots in the study (4,350 hours) and grouping the data according to that figure (greater than median = 1, less than median = 0). Crude models for each risk factor were modeled with pilot fatalities; then a final model incorporating all variables was completed.
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RESULTS |
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After all of the variables were introduced into the model, most relations remained consistent with those of the crude models. However, pilot's state of residence achieved statistical significance when it was included with the other variables. These results are summarized in table 2. In crashes where the pilot was not an Alaska resident, the odds of fatality were twice as high as when the pilot was an Alaska resident. This relation may be dependent upon the combined effects of the other variables, which may explain why it was not significant in the crude model.
We tested a main-effects model excluding the shoulder restraint variable to determine whether the high level of missing information on this variable substantially changed the results. In this model, fire, instrument weather conditions, and off-airport location remained significant risk factors for fatality, and daylight remained a significant protective factor. However, non-Alaska residence dropped out as a significant risk factor for fatality, while increased flight experience demonstrated a significant relation with survival.
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DISCUSSION |
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Postcrash fire was the strongest predictor of fatality for pilots in this study. Pilots in these types of crashes might benefit from fire-resistant clothing that gives them more time to exit a burning aircraft. In many cases, a pilot is aware that impact is imminent and can take measures that increase survivability, such as assuming a braced position and/or lessening the angle of impact. In addition, fuel systems that could withstand impact forces more effectively and keep from igniting when a crash occurred could lessen the number of postcrash fires, improving survivability.
Flying under instrument conditions was also highly associated with fatality. Few aircraft and facilities allowing for instrument navigation exist in Alaska. Company policies that encourage pilots to return to base if they encounter conditions requiring instrument navigation or that discourage pilots from taking off in marginal weather may aid in decreasing pilot fatality. Additional training of pilots in the use of emergency procedures that should be implemented if instrument conditions are unexpectedly encountered might also decrease this rate.
The high level of missing data for fatal crashes in which shoulder restraint use was unknown was probably due to the severity of those crashes. Some of these crashes were not survivable, while others may have incapacitated the pilot only temporarily. Nevertheless, temporary incapacitation might keep a pilot from exiting the aircraft prior to a fire's breaking out and smoke's consuming the aircraft, causing death. Crash severity often precluded determination of shoulder restraint use because the restraint had been burned away or the aircraft had been destroyed so completely that there was not enough evidence to determine use. In some of these cases, the use of a shoulder restraint would not have affected survival. In the main-effects model excluding shoulder restraint use, the strong relations maintained for fire, weather, location, and light conditions suggest that the missing data had little effect on the results. However, the changing relations for state of residence and flight experience require further investigation.
In an NTSB study of crashes of noncommercial small aircraft occurring between 1972 and 1981, it was shown that most crashes involved circumstances where the crash forces themselves were survivablethat is, within human tolerancewith aircraft cabin areas remaining substantially intact. After studying impact angles, air speeds, and the tolerance of the human body to impact, the NTSB concluded that installation and use of shoulder restraints would provide a 20 percent reduction in fatality and reduce the severity of injury for 88 percent of the seriously injured occupants (15).
Many older aircraft are not equipped with shoulder restraints (15). In 1977, the FAA mandated installation of shoulder restraints in the crew positions of all small aircraft manufactured after July 1978. Thus, any small aircraft manufactured prior to July 1978 would require after-manufacture retrofitting performed by the owner/operator on a voluntary basis. This regulation was supplemented in 1986 to require that all seats in newly produced small aircraft (not just crew seats) be equipped with lap belts and shoulder restraints. Modifications needed in order to retrofit these older aircraft with restraints are relatively inexpensive, costing $800$2,000, on average, depending on the amount of structural reinforcement needed (Dr. Jon Bolles, National Institute for Occupational Safety and Health, personal communication, 2001). Retrofitting commercially used aircraft with shoulder restraints might improve survivability.
Currently, the FAA does not require shoulder restraints to be worn in flight, only for takeoff and landing (14). For crashes in which the initial impact is survivable, having the shoulder restraint fastened could improve outcomes and decrease temporary incapacitation from crash injuries. Therefore, requiring use of a shoulder restraint throughout the flight should be considered as a possible additional measure for reducing fatalities.
The National Institute for Occupational Safety and Health recently undertook a joint initiative with the FAA, the NTSB, and the National Weather Service to reduce work-related aviation injuries and fatalities. To accomplish this, officials will complete detailed analyses of crash data, collaborate with aircraft operators, evaluate new technologies, and obtain an accurate and reliable source of denominator data for pilots operating in Alaska. Combined with results from this study and future work, this information will be useful in implementing interventions aimed at decreasing the number of work-related aircraft crashes and increasing survivability for pilots involved in such crashes.
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ACKNOWLEDGMENTS |
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NOTES |
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REFERENCES |
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