Although sudden incapacitation has received limited scientific attention, its implicationsare often cited in discussions of the Age 60 Rule. Bennett (1992) indicated that, whilenearly a third of air carrier pilots had experienced a level of physical discomfort sufficientto require another crew member to assume their duties, only about three percent werejudged to pose an actual threat to safety. At the time of publication, Bennett (1992)reported that, over a 20 year period only 3 accidents in air carrier operations includedmedically-related causal factors. One involved severe coronary artery disease on the partof the captain, a second involved the crash of a cargo flight that was attributed in part toalcohol consumption, and the third involved a captain with a known psychiatric conditionwho flew his aircraft into the waters of Tokyo Bay in 1982.
Several of the important studies related to incapacitation were completed prior to 1990.For example, Chapman (1984), gathered older data (1965-1981) from 40 InternationalAir Transport Association carriers regarding the frequency of in-flight incapacitations.During the 17-year time span of the study, a total of 277 incidents was reported for agroup of 540,816 pilots. While detailed information regarding the number of accidentsassociated with these incidents was not provided, the author indicates that there was noaccident during the17 years for which the primary cause was cardiac incapacitation.
Using 1 accident in every 400 incapacitations as the basis for a risk assessment, Chapman(1984) indicated that an accident would occur every 8,307,082,800 flying hours(approximately 10-10). According to Chapman (1984), this derived value is better thanthe risk associated with the airworthiness of components of the aircraft. Moreover, thereare several assumptions associated with his calculation that suggest that the estimate maybe conservative.In referencing National Transportation Safety Board (NTSB) data, the OTA (1990)reported that no certified route air carrier accident during 1968-77 was due to acuteincapacitation of the pilot. In general aviation, 1.3 percent of the 1965-75 accidents wereattributed to pilot impairment or incapacitation (OTA, 1990).
A sizeable percentage(60%) was associated with alcohol. In reviewing the NTSB data from 1975 through1982, Booze (1989) reported that approximately 3 in 1,000 (.3%) general aviationaccidents were attributable to some forms of incapacitation. In a case by case review ofsudden in-flight incapacitation in Air France pilots and engineers, Martin-Saint-Laurent,Lavernhe, Casano, and Simkoff (1990) reported that none of the 10 incidents resulted inan accident. Of the 10 incidents, 70% occurred during cruise. The incidents associatedwith gastrointestinal or neurological disorders were reportedly more serious than thosewith a cardiovascular genesis.
While older data revealed that medical disqualificationsassociated with coronary artery disease increased with age, a majority (58%) of theincapacitation incidents in air carriers were associated with gastrointestinal problems(James & Green, 1991).In discussing pilot sudden incapacitation, Froom (1994) indicated that there is no currentdefinition of “acceptable risk,” although some analysts support the one- percent rule (asingle incapacitation case during the course of a year – 864,000 hours). Further, the risk of an accident being caused by human error is much higher than the risk ofincapacitation. The reports by Bennett (1990, 1992) and Simmons et al. (1996) suggestthat the European medical community was in general agreement that, given existingmedical certification procedures, the overall safety target could be maintained even if theage limit were increased to 65. Along these lines, Chapman (1984) described the outcomes of recurrent simulator training where subtle incapacitation of the handling pilotis depicted during a critical stage of flight. Occasionally, the incapacitation coincidedwith other failures.
Of 500 exercises there were 15 occasions during which a hazard tothe aircraft was present, with eight (1.6%) resulting in a crash. In a second series wherethe subtle incapacitation occurred in isolation during a critical stage of flight, a hazard toflight was identified in only ten out of 800 cases (1.2%). Of those ten, only 2 involvedcrashes (0.25% of the 800 cases). The incapacitation data appear to support twoconclusions: first, incapacitations do not pose a significant risk, given present medical certification guidelines; second, incapacitations may not pose a significant increase inrisks (Bennett, 1990, 1992), even if age is extended to 65.
While there are numerous physiological changes that accompany aging, many that exertsome influence on performance are considered under the perceptual-motor skills area.The existing sleep literature provides ample documentation of changes in sleeparchitecture associated with age, from infancy to older adulthood. Gander, DeNguyen,Rosekind, and Connell (1993) provided information concerning the interaction betweenage and sleep loss for pilots involved in long-haul operations, across four age groupsfrom 20-30 years of age to 50-60 years of age.
Amount of sleep loss generally increasedwith age. These findings have important implications for the establishment of dutyschedules and the development of fatigue countermeasures in aviation. Changes inoperator alertness associated with fatigue are a significant problem across all modes oftransportation (U. S. Department of Transportation, 1999). The Department ofTransportation has initiated a coordinated ONEDOT program to reduce fatigue-relatedconcerns in all modes of commerical transportation.
Hardy and Parasuraman (1997) provided the most extensive review of age-related studieson pilot age and cognitive skills to date. Their findings are consistent with those ofTsang (1992) and Morrow and Leirer (1997). Age-related declines in performance weremost evident in perceptual-motor and memory tasks. Lesser effects were noted in attention and problem solving/decision-making. There was little evidence, except fortime-sharing tasks, that pilot expertise reduced the age-related declines in performance.Where appropriate, additional findings have been incorporated in this review. Hardy andParasuraman (1997) described the effects of age on pilot cognition under four categories:perceptual-motor skills, memory, attention, and problem solving/decision making. Anarea not addressed involves general changes in physiology that can influenceperformance.
Perceptual Motor Skills.
Pilots experience many of the same general declines in perception (visual and auditory)that are found in non-pilots. In a review of perceptual and motor functions (IOM, 1981),information is provided regarding the manner in which age-related changes influence theability of pilots to respond to glare and to rapid changes in illumination, to detect finedetails under lowered levels of illumination, and to detect moving targets. Documentedchanges in accommodation associated with age are often reported, although bifocal lensesserve to reduce the potential effects on visual performance. In their overview of theperceptual-motor skills area Hardy and Parasuraman (1997) report that age-relatedchanges in perceptual-motor skills are evident for a variety of pilot types. The findingsappear to be stronger for GA pilots than for commercial or other (e. g. military) pilotgroups. Differences between groups may be attributed in part, to the more restricted agerange for military and commercial pilots.
Studies of pilot performance on memory tasks reveal significant age-related changes formost working memory tasks. Morrow, et al. (1992) found that pilots and non-pilotsexhibited similar age-related declines in the recall of aviation-related materials. In asecond study (Morrow, et al. 1994), had pilots readback routine Air Traffic control(ATC) communications. While expertise eliminated age differences for repeatingheading commands presented visually, it reduced but did not eliminate differences fromspoken messages. Age related declines were equivalent for the two groups on lessdomain-relevant tasks.
However, in a more recent study (Morrow, Menard, & Stine-Morrow, 1999a), the effectsof expertise were not apparent in the recall of ATC messages of a route through aparticular airspace. Differences with earlier studies were attributed to the fact that thetask in the more recent study may have been less domain-relevant. Using the same task,but allowing pilots and non-pilots to make notes of the communications, Morrow,Menard, and Stine-Morrow (1999b) found that age-related declines in readback accuracywere eliminated by expertise. Their earlier findings, when subjects were not allowed towrite down the communications were attributed to age-related declines in storagecapacity.
Much of the research on pilot age and simulator performance has been conducted at theStanford University Laboratory of Dr. Jerome Yesavage. Leirer, Yesavage, and Morrow(1989) had reported that the performance of older pilots compared to that of youngerpilots, exhibited greater deviation from a prescribed flight path. Older pilots alsoexhibited greater impairment in simulator performance following alcohol consumption.However, follow-on studies did not support the age differences in overall flight performance found in this initial study (Morrow, Leirer, & Yesavage, 1990; Morrow,Yesavage, Leirer, Tinklenberg (1993), Morrow, Yesavage et al. (1993); Taylor, Dohlert,Morrow, Friedman, & Yesavage (1994); and Yesavage, Dohlert, and Taylor (1994).Differences in outcomes could not be clearly attributed to the age categories used sinceseveral of the more recent studies involved a greater age difference. Variability in the effects of age on performance and the small number of subjects (N=7) in the 1989 studymay have been significant factors. However, there were other conditions under whichage-related differences in performance were found, including handling malfunctions andresponding to ATC communications (Morrow, Leirer, & Yesavage, 1990; Morrow,Yesavage, Leirer, & Tinklenberg 1993; Morrow, Yesavage, Leirer, Dolhart, Taylor &Tinklenberg 1993; Taylor, et al., 1994a; and Taylor, et al. 1994b.
Age and Expertise
An issue that is often brought up in discussions or reviews of the literature regarding theeffects of age on performance concerns the benefits of experience and expertise.Researchers and the general public are typically of the opinion that experience willreduce the magnitude of the age differences in cognitive functioning. As Salthouse(1990) points out, despite the general acceptance of this concept, the scientific evidenceis less clear cut. Salthouse provides a review of the literature regarding the effects ofincreased age on familiar and novel tasks, whether increased experience reduces themagnitude of overt manifestations of age-related differences in performance, and finally,whether age-effects are attenuated when the tasks are overlearned and in continuous use,as one would expect with respect to various occupational activities. The latter aspect isparticularly pertinent with regard to age, pilot experience, and flight performance.
Salthouse, in reviewing a number of studies, including those involving air trafficcontrollers and pilots, tentatively concluded that age-related declines in performance arestill evident in measures of occupationally relevant activities. Salthouse (1994), indiscussing the relationship among age, experience, cognitive processes, and occupationalperformance theorizes that the accumulation of occupation-specific knowledge associatedwith age may explain how older employees maintain job performance. The declines incognitive performance evident in pilots and non-pilots are often attributed to the effectsof age on fluid intelligence (Hardy & Parasuraman, 1997). Fluid intelligence refers to theability of the individual to rapidly take in and process information. In contrast,crystallized intelligence, which is based on the store of information or knowledge anindividual builds up through experience, is less susceptible to aging. The benefits offlight experience should be reflected by an increase in the domain-specific knowledgebase.
SUMMARY AND CONCLUSIONS
While sudden incapacitation is often cited as a major concern in efforts to remove the agerestriction for air carrier pilots, data presented (Froom 1994; Froom, et al. 1988;Simmons, et al., 1996, OTA, 1990; and Bennet, 1990, 1992) concerning the frequencyand extent to which incapacitation events posed a threat to flight safety suggest thatincapacitation does not pose a significant risk in light of the influence of other humanfactors, e.g. judgment, decision making, and communication. In fact, OTA (1990) statedthat even more rigorous medical examinations were not likely to significantly alteraccident rates since no sudden physical impairment had been associated with an aircarrier accident.
This conclusion appears to be at odds with Bennet (1992) who cites aninstance where severe coronary artery disease was involved in an accident. Estimates ofthe relatively low risk associated with sudden incapacitation appear to have been a factorin the decision by the JAA to allow European contries to adopt 65 as the upper age limitfor multi-crew operations. While less concerned about sudden incapacitation, OTA(1990) was concerned about the effects of subtle age-related changes in cognitive abilitiesthat could have a significant influence on pilot performance.
Recent research is consistent with Hardy and Parasuraman’s (1997) conclusion that older pilots exhibit many of the age-related differences in cognitive abilities, when comparedwith their younger colleagues in the general population. The influence is observed mostclearly on tasks involving memory and rapid processing of information. With thepossible exception of selected time-shared tasks, flight experience does not appear toreduce the extent to which age-related declines in performance are detected.Furthermore, many of the authors reported that performance variability increased withage. The precise influence of these age-related changes in cognitive performance onperformance in the simulator and in the operational flight environment is less clear.
Since the final decision to remove a pilot or first officer from his/her position is likely tobe performance-based, employers will need to develop and validate the necessaryassessment (simulator or flight) procedures for determining whether a pilot can operatethe aircraft at an acceptable level of safety. These test scenarios will need to besufficiently intense to demonstrate that the pilot can operate the aircraft safely underdemanding operational conditions where workload is high and pilot resources andmemory are challenged. Because this procedure involves a retirement decision, it willhave to be sufficiently rigorous to withstand the legal challenges that inevitably will beraised regarding age discrimination. Considerable resources will be required to developand validate these procedures and to administer them periodically to all pilots. Once challenged, this could mean that all pilots might be tested periodically and that somepilots under the age of 60 could be removed from their positions if they did not performat an acceptable level. The economic burden on the FAA and corporations to develop anon-age safety basis for denying pilots continued employment could be significant.
Airline Pilots Association (ALPA) (1959a). Special report: Comments of ALPA to theFAA on pilot age limitations.
The Airline Pilot, 28: October, 16-25 Airline Pilots Association (ALPA) (1959b). Special report: APLA supplementary brief submitted to FAA on pilot age limitation question.
The Airline Pilot, 28: December, 16-20. Airline Pilots Association, International v. Quesada, 276F.2d (2nd Cir. 1960) cert. denied366 U.S. 962 (1961).Baker v.
Federal Aviation Administration, 917 F.2d 318 (7th Cr. 1990). Bennet, G. (1990). Harmonization of age limits for professional pilots. Report of the FCL Sub-Group on Medical Certification. Presented at the European Civil Aviation Conference, Paris, France, September.Bennett, G. (1992).
Medical-cause accidents in commercial aviation. European HeartJournal, 13 (Supplement H), 13-15.Beringer, D.B., & Harris, H.C. (1997). Automation in General Aviation: Two studies of pilot responses to autopilot malfunctions. (Tech. Rep. No. DOT/FAA/AM-97/24).
Washington, DC: Federal Aviation Administration, Office of Aviation Medicine.Beringer, D.B., Harris, H.C., & Joseph, K.M. (1998). Hearing thresholds among pilotsand non-pilots. Implications for auditory warning design.
Proceedings of the Annual Meeting of the Human Factors and Ergonomics Society, pp. 92-6.Biren, J.E., & Fisher, L.M. (1995). Rules and reason in the forced retirement of commercial airline pilots at age 60. Ergonomics, 38, 518-25.Booze, C. (1989).
Sudden inflight incapacitation in general aviation. Aviation, Space, and Environmental Medicine, 60, 332-5.Bruckart, J.E. (1992). Analysis of changes in the pilot population and general aviation accidents. Aviation, Space, and Environmental Medicine, 63, 75-9.Chapman, P.J.C. (1984).
The consequences of in-flight incapacitation in civil aviation.Aviation, Space, and Environmental Medicine, 55, 497-500.Froom, P. (1994).
The risks of piloting with advanced age. Journal of CommunityHealth, 19, 71-2.Froom, P., Benbassat, J., Gross, M., Ribak, J., & Lewis, B.S. (1988).
Air accidents, pilot experience, and disease-related inflight sudden incapacitation. Aviation, Space, andEnvironmental Medicine, 59, 278-81. Gander, P.H., De Nguyen, B.E., Rosekind, M.R., & Connell, L.J. (1993). Age, circadianrhythms, and sleep loss in flight crews. Aviation, Space, and Environmental Medicine,64, 189-95.
Pilot Age and Performance
This bibliography represents an update of the bibliography prepared for the Hilton Age 60 study initiated in 1990 (Hyland, D.T., Kay, E.J., Deimler, J.D., and Gurman, E.B. Age60 Study, Part II: Airline pilot age and performance
A review of the scientific literature.
Technical Report DOT/FAA/AM-94/21, Civil Aeromedical Institute, FAA, Oklahoma City, 1994). While the primary focus is on literature associated with pilot ageand performance, selected documents are included from the broader literature that relate to job performance and age.