‘Taste 14—Medical certificate status of accident involved
pilots—1974 general aviation accidents

Wedical Certificate Status Frequency

Glass 1 medical, no limitations 384
Glass 1 medical, with limitations 131
Class 2 medical, no limitations 1,386
Class 2 medical, vith limitations 710
Class 3 medical, no limitations 1,079
Clase 3 medical, with limitations 721
Not medically certified 3
Unknown 15

Total 4,491

Note: Of 4,491 accident airmen, 1,562 -- or 34.8 per 100
Limited medical certificates. Of 758,243 act:

298,296 =» or 39.3 per 100 in the population
medical certificates,

Observed = 8S

Expected Rate = 39/3 = 0-88

tion accidents. Other descriptive characteristics
of accident-involved airmen are also presented.

Occupation has been studied under assump-
tions of similar exposure, total cumulative ex-
posure by occupation, and recent exposure by
occupation with the outcome under at least two
methods of analysis being the identification of
physicians, lawyers, sales representatives, farm-
ers, and housewives as having high accident
experience,

This study also considered the relationship of
occupation and age with respect to accident ex-
perience. The anticipated outcome of increased
accident experience with age was observed for
the total group and most of the major occupation
categories.

Percent
100 -
sob
sor | 75% Had Exams
| Within | Yr.
40F |
! |
| 42% Had Exams
cok Within Past 6 Mo.
| |
o Maerthiiitiitiiiiriitiiiis

1 5 10 15 20
Time Elapsed (Months)

25 or>

Figure 10.—Cumulative percent time elapsed since last
medical examination—1974 general aviation accidents

When accident experience was examined by
major occupational category and either cumula-
tive or recent exposure, the outcome was one of
increased risk with increased exposure, regardless
of type.

Taste 15.—Time elapsed since last medical by injury category of accident—1974 general aviation accidents

Time Elapsed Desree of Iniur Gunulative
Qonths) Wone Yinor Serious Fatal Daknown Total Percentage

rT 352 70 42 50 - 514 1b
2 220 45 32 29 - 326 18.7
3 185 30 26 53 - 294 25.2
4 160 37 20 42 - 259 31.0
5 176 al a1 34 1 273 a7
6 170 36 18 25 - 249 42.6
7 133 25 23 28 - 209 50.7
8 130 29 22 35 - 216 52.1
9 147 39 18 3 - 237 57.4
10 149 35 22 34 - 240 62.7
i 159 3 19 34 1 246 68.2
2 181 30 23 51 - 285 78.5
B 83 a 8 22 - 124 77.3
1 39 n 10 20 - 100 79.5
15 48 10 2 v7 - 7 81.2
16 42 16 6 2 - 76 82.9
7 37 10 4 4 - 85 84.8
18 33 2 5 10 - 60 86.2
19 50 7 3 2 - 78 87.9
20 42 10 5 B - 70 89.5
21 39 5 8 a - 63 90.1
22 39 10 2 8 - 69 92.4
23 46 R 9 18 - 85 94.3
2% 48 B 7 a - 85 96.2
25 and up St u 2 32 - 106 98.5
Invalid or Unknown 27 6 8 1s 9 65 100.0

Total 2,826 594 391 669 i 4,491 100.0



Tanre 4.—General aviation accident rates by major occupational category and recent flight experience—1974

Recent Flight Time (Hours)
Major Occupational Category 0-10 11-50 51-100 101-200 201-Plus Total

Professional and Technical 2.3 8.2 15.6 20.7 14.4
Managers and Administrators,

°
&

Except Farm 2.6 6.3 14.3 18.6 18.9 5.7
Sales Workers 2.0 6.6 22.3 26.6 66.1 5.6
Clerical Workers 1.7 6.5 8.9 24.8 - 3.6
Craftsmen La 6.9 14.1 35.2 12. 3.5
Operatives 2.4 8.3 20.7 15.5 - 5.2
Laborers, Except Farm 2.4 4.5 12.4 33.1 49.4 4.4
Farmers and Farm Managers 5.3 11.2 16.4 37.3 98.8 9.9
Farm Laborers and Foremen - - - - - 12.4
Service Workers 2.3 8.4 41.4 21.3 16.0 6.3
Government Employees (nec) 1.4 5.5 6.2 - 12.3 3.6
Housewives 2.3 6.2 18.6 - - 3.7
Student (Academic) 1.4 7.4 9.9 29.0 62.1 3.2
Retired, None or Unknown 3.3 6.4 12.0 20.3 12.8 5.6

TOTAL 2.2 7.3 15.0 21.9 15.0 5.9
*Last six months flight time.
'Tasie 5.—General aviation accidents by cumulative experience and age—1974
‘Gunuiative Experience (Hours)
AGE GROUP 0-10 11-50 31-200 201-1000 Tooi-2000 OOF TOTAL
Less than 20 years
‘Accidents cu 35 27 2 4 16
Won-accidents 31,395 6,006 1,181 : 187 45,633,
Subtotal 31,612 6,041 1,208 - 161 455749
Rate/1000 0.5 3.8 22.3 - 26.8 2.5
20-29
Accidents 67 255 332 192 213 1,207
Non-aceidents 93 606 56,435 32,691 6,976 8,325 228,827
Subtotal 93,673 323943 543690 33,023 7,168 8,538 230,034
Rate/1000 0.7 4.5 4.7 fo.0 26.8 3a.9 3.2
30-39
‘Accidents 65 98 285 362 us 372 1,357
Woneaceidents 51,805 19,555 52,874 53,925 10,215 26,288 214,663
‘Subtotal 513870 19,653 53,159 543287 10,390 26,660 216,020
Rate/1000 1.2 5.0 364 6.7 16.8 Tao 6.3
40-49
‘Accidents 58 60 162 346 ue 31s 1,059
Won-aceidents 30,872 7,108 28,351 55,713 10,917 25,781 158,761
Subtotal 30,929 73168 28,513 56,059 11,035 26,096 159,800
Rate/1000 1.9 a. 5.7 6.2 10.7 6.6
5059 ~~
Accidents 19 22 C) 163 78 263 592
Non-accidents 10,854 3,119 13,142 27,786 10,071 24,887 89,859
Subtotal 10,873 33141 13,209 273949 10,169 255130 90,451
Rate/1000 1? 7.0 pst 5.8 7.7 9.7 65
1-69
‘Accidents 2 4 2 27 10 68 123
Non-aceidonte 1,206 399 ns 4,483 2,086 5,268 14,133
‘Subtotal 1,208 403 ns 43510 25094. 53316 14,256
Rate/1000 1.6 9.9 16.6 6.0 4.8 ie 8.6
70 and above
‘Accidents : 2 4 4 2 8 20
Won-accidents 202 : n 479 159 959 4,913
Subtotal 242 - a1 483 16L 967 13933
Rate/1000 - - 49.7 8.3 12.6 8.3 10.3
Unknown Age Accidents 2 1 2 1 L - uv
Total
‘Accidente 240 366 922 1,262 578 1,223 4,491
Non-aceidents 219,968 69,869 155,595 176,257 40,419 91,64 753,752
Subtotal 8 70,235 156,417 177,519 40,997 92,867 758,243
Rate/1000 La 22 562 7A Tea 13.2 3.9

NOTE: Row and column totals may not equal the sun of cell values due to rounding.

12


7 ce a ak a

This study compares accident experience for
yarious major occupational groups, ages, and ex-
posure categories to appraise differences in acci-

dent experience. Population data necessary for
comparison were obtained by sampling tech-
niques. An important by-product of the stucly
has been the establishinent of a current, descrip-
tive, epidemiologic data base that will be used
in future studies.

The conclusions and descriptive findings of
this study will provide the basis for further
hypothesis formulation and _ intensification of
educational efforts.

Il. Historical Background

Occupation has been, and continues to be, a
factor of considerable importance in understand-
ing the etiology of various infectious and pre-
sumably noninfectious diseases that afflict modern
man.

The literature provides numerous examples
indicating the importance of occupation as a
direct cause of disease in man. Most of the more
classic examples are related to the noninfectious
diseases. Early research efforts indicated the in-
creased incidence of scrotal cancer among chim-
ney sweeps. Radiologists were found to
experience more leukemia than other physicians,
suggesting the effects of exposure to x-ray."
Workers who applied radium paint to watch
dials were observed to develop bone cancer. The
high frequency of urinary bladder cancer among
aniline dye workers and of lung cancer in miners
of radioactive ores are additional examples of
findings relating occupation to noninfectious dis-
ease.» © More recently, the association of various
cancers with polyvinyl chloride production and
use has been examined.’

Tuberculosis and silicosis were frequently ob-
served among miners exposed to dusts with high
silica content.2 Jess well known are the findings
associating clinical laboratory personnel and
other hospital personnel who must handle blood
with increased risk of Type B hepatatis.°

Less obvious in terms of cause and effect is the
association between “stress” experienced in many
occupations and the development of various non-
infectious and psychosomatic cliseases. Air traf-
fic control is considered a stressful occupation,
and air traffic controllers have been found to
experience higher-than-expected prevalence rates

for hypertension, peptic ulcer, and diabetes in
comparison to other airman categories."

Studies done on accountants during the stress-
ful income tax season have shown increased levels
of cholesterol during this stressful period.”

Other studies have considered the relationship
of stress presumed to result from certain occu-
pations and the occurrence of heart clisease.
Available evidence suggests that occupation has
considerable impact on an individual, both
physiologically and psychologically.

Historical information relating occupation to
accident occurrence is obvious in some cases but
probably less well known to the medical com-
iInunity. Various occupational and industrial
safety programs have recognized the greater
risks associated with certain occupations involv-
ing the use of powerful and complex machinery,
the handling of chemical agents, and prolonged
exposure to a specific environment, such as
driving.

The epidemiology of accidents is becoming in-
creasingly important in the identification of
factors that Increase one’s accident proneness.
This area of investigation represents a specialty
for the field of epidemiology much the same as
infectious and noninfectious diseases and mental
health have represented areas of specialization.
Public health planners suggest that much greater
attention will be devoted to this area in coming
years.**

It is apparent that many of the previously
mentioned oceupation/morbidity/mortality rela-
tionships are more direct than others, The cause-
effect, relationship is easier to visualize and deal
with in terms of programs for intervention for
radiologists, aniline dye workers, and uranium
miners, for example, than it is for noninfectious
and so-called psychosomatic diseases presumect to
be induced by such vague factors as “stress.”

This study provides an interesting combination
of direct and indirect relationships. [Exposure
in terms of hours flown is an obvious, rather
(livect’ factor that one can observe in terms of
general aviation accident rates. However, with
few exceptions, such as agricultural pilots, occu-
pation is less obvious with regard to the exact
mechanisms that might contribute to differences
in accident rates. This is not the usual relation-
ship of occupational exposure to some toxic sub-
stance that results in disease or occupational
stress resulting in disease. THowever, personality


In several previous studies, age has repeatedly
been shown to be associated with increased risk
of general aviation accidents. The exception,
Mohler’s 1967 study of accident experience by
age,® concluded that the accident experience of
older airmen was comparable to, and in some
cases better than, that of their younger counter-
parts, However, a most important observation.
was made when exposure and age were jointly
considered in this study.

Whether cumulative or recent exposure is con-
sidered, high exposure is associated ‘with the
highest risk, when considered separately and
when combined with the younger ages. High
exposure, in combination with or within any
other comparison category, results in increased
risk, Risk analyses, based on high age alone
or in any combination not also associated with
high exposure, inconclusive.
Whether cumulative or recent experience is con-
sidered, the importance of increased exposure is
apparent. In addition, recent exposure appears
to be more important as a risk factor.

"The frequently observed relationships of
greater risk of accident at higher ages is seen
to result from a dilution of younger age rates

are somewhat

19

by a large number in this age group with little
or no exposure.

Exact mechanisms for the high risk associated
with selected occupations and high-exposure
younger age categories are subject to hypothetical
conjecture. Certainly these areas deserve further
study. Education, however, has proved to be a
powerful tool in past health and safety efforts
and should be utilized again, even in the absence
of clearly established mechanisms.

Other descriptive findings for the accident-
involved group are as follows: Females experi-
enced significantly fewer accidents than expected.
The months of April through September are
peak accident. months. Alaska, Arkansas, Idaho,
Nevada, New Mexico, West Virginia, and
Wyoming all had at least. double the accident
experience expected. Eighty-five percent of all
accidents occurred between 9 o'clock in the morn-
ing and 9 o’clock in the evening. More than half
of all accidents occurred within 1 hour after
takeoff (55 percent). Sixty percent of accident
flights were originated for pleasure purposes.
Fewer-than-expected accident-involved airmen
had medical limitations, and 75 percent had un-
dergone medical examinations within a year
prior to the accident.



Tasre 10.—State of accident occurrence by injury category of accident—1974

general aviation accidents

Tearee of Taian

state ime Hino eclaue Faecal Total Bepected oft patio
Miabaas a2 5 7 ie ee Sh7 i
Ake Pre a u % 207 30:3 an
Aelzona ‘° i B te tos 33 Ue
Aekensas 3 3 % a 3 2
Caitrornta oa a % sar ones oe
Colorado 72 % > 33 26 a8 te
Connectseut 2 ‘ 5 4 36 ae oe
Delaware a : : t : a wos ri
District of Colmbta 1 i : . : 3 33 or
Floriéa 1st n Py a i Pa 255.3 o8
Georets rn 2 io re : us 100.8 ri
aval a 1 ° ‘ : 0 reat ui
Tako a ; 3 a : 6 Ee 23
Titlnote ° re “ a : a abe oe
Tedtona 3 5 ° iu : “ ioe: oe
Tow cH 3 H i : ey m8 o8
Eansea 3 a 2 e : & as Xo

atu FA “ 2 é : a ea ra
Toutetena 56 i é , : ry seca i
aise ie 10 5 é : 2 isa i
tasylend FA * 3 ? : % 2.0 a6
Massachusetts a u 5 ‘ : a a5 o8
freee ra u ? 6 : ue 1668 o8
Minnesota 3 3 H 0 : 2 sta De
Hicsteeipnt 6 re i 3 : 56 38.2 1a
Missourd ts $ u B : % 1036 os
Hoocane & $ é 4 : ey 30:0 i
Meorecta a 3 3 3 : & Bio 3
tosses 3 B 2 A : a3 2
Mow Hanpabire iu 2 a a : o 213 a8
New Jersey us re é 5 : 0 ube oe
New Mexico ord a ‘ “ : re Et a3
New York %6 % u 3 : us 209.6 on
North carolina a u 3 2% : tor 9518 13
North Dakota 2 3 t 5 : 2 2's 3
ohis % % : a : ia 813 oF
Skisnons 35 n & u : re 20.6 oe
Oregon i to 7 a : 2 9 ri)
Penneylvanta 109 5 7 6 : ug as.8 ey
Bhove Tetend 7 i H t : ‘a 8 re
South Caroline n 6 6 6 : 8 9313 ta
South Dakota 20 A H 5 : 2 Ba Ue
Tennessee G $ é 3 : 8 8 os
Teas 202 % n 3 : au 20:3 Yo
Seah a > ‘ 9 : 3 20.3 ut
ersont é 2 i i : io be Ko
Virginia a A 5 u : % ne
asbington 38 re a u : 188 Ri)
fest Werginsa 8 3 2 3 : 33 tne
Mieconsts 22 8 H b : a ye.
tying B ? 5 3 : se io
Teeaitl seate codes or nino 54 3 ro fy ‘ 0

Toaat 2.826 598 oa 68 a west

The purpose of the flight resulting in the ac-
cident is recorded in Table 18. Approximately
40 percent of all accident flights were originated
for business purposes and the remainder for
pleasure.

Class of medical certificate and whether it con-
tained any limitations of usage are presented
in Table 14 for the accident-involved airmen.

Slightly fewer-than-expected accident-involved
airmen had limitations.

Within the agency, much interest has centered
on frequency of examination and implied re-
cency as a factor in reducing accident risk likely
to result from medical factors. Table 15 and
Figure 10 provide a breakdown of recency of
medical examination among accident-involved

Tasie 11.—Time of accident occurrence by injury category of accident—197+4 general aviation accidents

Time of Degree of Injury
Accident None Minor Serious Fatal Unknown Total Percent
0001-0300 37 1 5 20 1 74 1.6
0301-0600 31 10 8 10 1 60 1.3
0601-0900 214 42 39 61 - 356 7.9
0901-1200 611 109 79 108 - 907 20.2
1201-1500 719 146 98 133 - 1,096 24.4
1501-1800 728 161 100 140 1 1,130 25.2
1801-2100 400 91 51 120 - 662 14.7
2101-2400 78 24 11 52 - 165 3.7
Invalid or
Unknowa 8 - - 25 8 4. 0.9
Total 2,826 594 391 669 aL 4,491 100.0

16


(Rates per 100,000 Hours

5.0r
Cumulative Flight Time)
4.0F 3.7
—
3.2
-
3.0F
2.0b 1.8 1.8
1.5 1.5
2 1.3
Ll Il :
Lor 0.7 0.7
0.5
POPULATION
RATE 0.5 iy 0.2 [|] []
fo) m
> ee) lhlUm!UlUelUMwehUDUlUlUMlUMUO Oy ee
§ $ § &S$ € 55 2 5. 8, 5 Sy EZ 53 &
© 2 3 £ 2. oS & wf ok E c¥ Se =Z F
oS o Bo ] of Se cs 2SE ue ¢& e= SF vx o
2 S $$ S&S $s SB .§ EE ve & EY BF BS §
a E fF s2 Se of ge BE ge 4H £2 3
a go ge 22 6 Eg 23 S50C«<S
22 og = < ee &

Ficure 3.—General aviation accident rates—1974, selected occupations, cumulative flight time

tives, and physicians experienced the highest
rates for specific occupational classifications
based on cumulative experience, their rates being
three and one-half to seven times higher than the
experience of the total population.

Rates per 100,000 hours of recent exposure
were highest for the major occupational cate-
gories of operatives, housewives, farmers and
farm managers, clerical, and general laborers.
The professional category had the lowest rate
of any major category based on recent exposure
(influenced largely by the professional pilot
group). When specific occupations are con-
sidered, sales representatives, farmers, house-
wives, lawyers, and physicians had rates approxi-
mately three times the rate for the total
population.

Regardless of the hypothesis concerning ex-
posure (ie. held constant, based on total ex-

perience, or based on recent experience) the
major occupational categories of general laborers,
farmers and farm managers, service workers, and
housewives were identified as having higher rates
under two of three measures of accident experi-
ence.

With respect to specific occupational classifi-
cations, physicians were identified by all three
measures. Lawyers, sales representatives, farm-
ers, and housewives were identified on two of
the three measures as having high accident ex-
perience.

The persons involved in these occupations are,
in general, likely to share some rather important
personality and other traits. All are likely to
be aggressive, busy, independent, and self-suf-
ficient, accustomed to making important and
weighty decisions, and also accustomed to de-
pending on others to perform more mundane
chores (such as preflight inspection).


while housewives and teachers were found to ex-
perience fewer accidents than expected. Wick
suggests that certain occupations are economic-
ally more capable of flying than other groups
and that this is an important. consideration be-
cause of the greater exposure alone.?? In a later
study dealing with physician pilots, Wick docu-
ments a considerably greater exposure factor for
physicians versus other general aviation pilots
based on a sample.%*

A recognized difficulty in all the studies cited
has been the availability of appropriate and ac-
curate denominator data for rate computation.
Numerator data are easy to acquire from existing
accident files. Occupation and professions listed
on accident reports are, of course, subject to
similar bias type errors normally associated with
such studies; ie., the tendency to upgrade one’s
occupation for reporting purposes.

Exposure also represents an area of difficulty
in regard to availability of population data.
What is the relevant measure of exposure?
Should it be hours flown, number of takeoffs
and landings, type of aircraft, or some other
indicator? Difficulties exist with each measure.

This study represents an effort to bring to-
gether occupation, age, exposure, and other de-
scriptive data on a scale of analysis never before
available in order to appraise the relationships.

III. Methodology

A. General Description of the Research De-
sign. This analytic, epidemiologic study involved
a census of general aviation accidents for the
year 1974 to obtain relevant occupation, expo-
sure, and other epidemiologic profile information
of a descriptive nature. Population comparison
data for occupation and exposure were obtained
from available current records under multi-
nomial sampling techniques and subsequent
extrapolation to the total population. The
approach was retrospective in that accident and
population information were researched for per-
tinent information after the outcome had been
realized; ie., given the outcome, the research
involved categorizing accident-involved airmen
by occupational and exposure groups as opposed
to the prospective approach wherein the occupa-
tion groups are identified and followed to see
what the accident experience was over a certain
period of time. A hypothesis of “no difference”
was tested for accident experience among various
occupation/exposure categories.

Certain other epidemiologic information was
obtained primarily for descriptive purposes and
to provide current profile information in antici-
pation of the formulation of other hypothesis
for testing based on current data.

B. Population Studied. The 1974 general
aviation medical accident files maintained by the
FAA represented the “cases” studied. The
number of such cases was 4,491. A sample of
9,414 was taken from the active airman popula-
tion medical tape files as of December 31, 1974,
for purposes of estimating the population oc-
cupation and exposure characteristics. There
were 762,604 airmen currently medically certified
at that time (having been medically certified
within the 2 preceding years as prescribed by
yvegulations).

The population sampling problem in this study
amounted to an estimation of population param-
eters for 15 major occupation groups. These
occupation groups are based on Bureau of the
Census classifications with some modification and
additions. Sample design and size assure a use-
able error for the smaller proportions expected
for some groups.

Accident files are arranged in numeric se-
quence by date of receipt. No bias was antici-
pated because a census of accident records was
performed. Population records are maintained
by alphabetic sequence, and a sample was drawn
from these records for estimation purposes, The
alphabetic sequence is not expected to introduce
bias among the sample for variables being
analyzed.

Rate computations and extrapolations to the
population from sample results were based on
the December 31, 1978, population of 758,243
active airmen; ie, those airmen medically cer-
tified within the preceding 24 calendar months.
The December 1973 population was used because
it approximates the midpoint of the accident
group. Individuals having accidents in 1974
would have received medical certification after
January 1972 if they were currently certified
at the time of the accident. The population
midpoint. likewise encompasses a group certified
after January 1972.

A midpoint population is desirable for rate
computations. The airman population is grow-
ing, and use of a population total at either time
extreme would bias results somewhat. Numer-



traits, stress of commitments, and other factors
common to certain occupations may very well
result in precipitous action that results in an
accident. An earlier study speculates that occu-
pation (ie., economic ability) simply allows for
greater exposure, which in turn accounts for
higher accident. rates among certain occupation
groups.* Exposure to the environment is a
necessary ingredient of general aviation acci-
dents. However, it is the extent of exposure and
the interaction with other variables that are
being examined here.

While considerable research effort has been
devoted to the areas of commercial and general
aviation safety, most has been directed to im-
provement of the environment in terms of equip-
ment. and facilities. Very limited information
exists concerning the more classical epidemiologic

variables in an attempt to better understand the

etiology of aircraft accidents. Zeller and his col-
leagues have done substantial work in a military
environment on the epidemiology of accidents.
In a 1953 study by Zeller and Mosely, young
anc inexperienced pilots were found to contribute
to a disproportionately large number of military
jet aircraft accidents, Results of a similar study
by Zeller in 1956 suggested improved accident
experience for younger ages, but overall younger
age groups continued to experience higher acci-
dent rates.* However, as previously mentioned,
the equipment, age distribution, and medical eri-
teria for Air Force pilots make comparisons with
general aviation accident data difficult, if not
inappropriate.

Medical factors have long been recognized as
Important in the epidemiology of both military
and civilian aircraft accidents. For this reason,
the FAA devotes considerable effort to screening

prospective airmen for pathology likely to result
in sudden incapacitation.

Dougherty et al. found the relative risk of
accident to be 2.24 for airmen with any physica]
defect; the relative risk of fatal accident was
2.41, with increasing risk for multiple defects,
Rohde and Ross, in a 1970 contract study, con-
sidered 25 medical variables and found 7 to be

associated with increased risk of accident.’

Lhe contribution of suicide to general aviation
accident morbidity and mortality is recognized

and has been studied in a limited way because
of the small number of observations,?® 1°

Alcohol and drugs have been implicated in air-
craft accidents to an alarming degree.2"* This
sxperience would certainly parallel auto accident
experience. In the past, alcohol has been present
in up to 85 percent of fatal general aviation
accidents, and a causal role has been established
in about 7 percent.**

several studies have dealt with accident risk
related to age. Costin found an increased tisk
of accident with age in 1959.27 These results
were verified by Harper in 1963, Lategola et al.
in 1970, and Rohde and Ross in 1970.28 2%
Mohler et al. found the higher age groups to
experience no greater risk of accident than
younger airmen. in a 1967 studcy.%

Occupation and risk of accident has been a
subject of continuing interest to the FAA and
its prececessors, as well as the aviation commu-
nity. Since the days of the barnstormers, wing-
walkers, and daredevil stunt pilots of the early
1900’s, certain very definite risks have been
realized and dealt with in terms of regulations
to protect the population as well as the individual
pilot. Agricultural pilots have long been recog-
nized as a group subject to increased risk of
aircraft accident. Substantial improvement in
morbidity and mortality among this group has
been realized in recent years because, of improve-
ments In equipment. Ryan and Dougherty
(1969) found that age and experience were un-
related to agricultural accidents by type of
equipment.*t. Their findings involved extensive
analysis of differences in morbidity and mortality
by types of equipment utilized and environmental
factors.

Attention has been focused on selected occu-
pations and professions in recent years with re-
spect to their accident experience. Mohler et al.
in a nuch publicized 1966 report indicated that
physicians have four times the accident rate of
other general aviation pilots.®

Wick has done considerable work in analyzing
the relationship of aircraft accidents to occupa-
tions. In his 1966 study, he makes some perti-
nent observations concerning this relationship.
Wick considers exposure and personality traits
reflected by some professions and occupation
groups to be important in the etiology of aircraft
accidents, with the greater emphasis on exposure.
Physicians, executives, salesmen, farmers, and
ranchers were found to have higher accident ex-
perience, both fatal and nonfatal, than expected

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TaBiy 12.—Flight time in the 24 hours preceding accident occurrence by injury category of accident—1974 general
aviation accidents

Flight Time Degree of Injury

Last 24 Hours Wone Viner, Serious Fatai Taknowm Total Cumulative Percent

Tess than .5 hours 777 162 Tir 390 Tr 1,457 32.4
y 669 141 89 129 - 1,028 55.3
2 435 75 51 33 - 614 69.0
3 234 65 26 30 - 355 76.9
4 190 42 35 2 - 201 83.4
3 151 33 2 2 - 218 88.2
6 138 28 2 8 : 196 92.6
7 56 2 10 u - 87 94.5
8 n B u 3 - 99 96.7
9 20 7 - 2 - 29 97.4
10 3 9 4 4 - 60 98.7
uw n 2 - L - rs 99.0
2 15 - 1 1 : uv 99.4
B 3 2 - : - 3 99.5
9 6 2 : - - 7 99.7
15 3 1 3 - - 7 99.8
16 3 - : : - 3 99.9
uv - - : : - : 99.9
18 2 : - - - 2 99.9
19 : - - : : 99.9
20 or more - 1 - 1 - 2 100.0

Total 2,826 594, 301 669 un 4,491

airmen. It may be seen from Figure 10 that
42 percent of all accident-involved airmen had
undergone medical examinations within 6 months
prior to their accidents and 75 percent had un-
dergone examinations within a year prior to
their accidents. These data are difficult to in-
terpret other than to observe that most: accident-
involved airmen had undergone fairly recent
medical examinations. However, had the reverse
situation been true, a stronger basis for hypothe-
sizing medical factors causation would have
existed.

Taste 13.—Vurpose of flight resulting in accident by
injury category of accident—1974 general aviation
accidents

Purpose of Degree “of Tajur:

Fligne Yone”Wivor ‘Serious Fatal —Unkeowa___tocat
Business 1,191 22300 17s? 1 1,825
Pleasure 1,635 ah 218 432 102,666
Total 2,826 594 301669 4,491
V. Conclusion and Summary
General aviation accidents obviously result

from multiple causes. However, in applying the
methods of epidemiology to this area, the as-
sumption is not one of single causation but
rather to search for a factor (or factors) with
respect to the agent (aircraft), the host (pilot),
or the environment, that can be controlled or
mitigated to favorably influence accident inci-
dent or outcome.

Cockpit design has improved in recent years
to increase the likelihood of accident survival.

17

Agricultural accidents and resulting equipment
are a prime example. Air traffic control and
navigational equipment is constantly being scru-
tinized to improve the interface of the pilot with
the environment.

Some other studies have been made to identify
host-related factors that may have significant
influence. Alcohol, drugs, medical factors, ex-
perience, and age are some variables that have
been considered. Occupation, age, exposure, and.
their interrelationships have received consider-
able attention in this study in an attempt to
better understand the etiology of general avia-

Percent
100 Fr

80
60
40

20-

[a ee ee
65) 2 34 867 B10! 2/314! 16! "1g '9 2007
Flight Time Last 24 Hours

Fieve 9.—Cumulative percent flight time last 24 hours—
1974 general aviation accidents



While estimates were made for all occupa-
tional classifications within the major occupa-
tion categories, some results were numerically
so small that further analysis was considered
inappropriate. Analysis was performed in all
instances where an occupational classification
contained approximately 1 percent of the acci-
dent group. This criteria identified 11 specific
occupations in addition to the major occupa-
tional categories. These 11 occupations plus
the students and retired, none, or unknown cate-
gories accounted for 72 percent of all accidents.

Among the professional and technical occupa-
tions, the accident experience of lawyers,
physicians, and professional pilots was signifi-
cantly greater than expected. Engineers and
teachers had significantly fewer accidents than
expected.

The accident experience of sales representa-
tives and farmers was significantly greater than
expected. Consistent with expectations was the

accident experience of managers and adminis-
trators, mechanics and repairmen, and policemen
and detectives, Current and former members,
of the armed forces had significantly fewer
accidents than expected.

B. Accident Experience by Occupation and
Eeposure. The preceding discussion considered
accident experience based solely on proportional
expectations and holds exposure constant, or
assumes similar exposure, for the several cate-
gories. Empirically, this is not a realistic
assumption.

When rates were computed on the basis of
total hours flown (as recorded by the airman ‘on
his most recent medical examination), the major
occupational categories of academic students,

housewives, and service workers experienced the -

highest rates per 100,000 hours of total cumula-
tive exposure, their rates being four to seven
times greater than the total population experi-
ence, Students, housewives, policemen and detec-

25-7
(Rates per 1,000 Airmen)
20r
15.9
15h
1.0
10.1
lor 8.7 9.0
6.9 6.6
POPULATION 4.7 eo 5.6
RATE 5.9 > - 4.2 3.7
3.2
~ [] []
° o e a o 3 uy 3: - o 9 ee ec 2.
¢ 8 5 & § 58 Z 5. $, S Sy EE SF $
&£ F 2 8 go gf 2 22 $§ E se 83 28 3
2 5S $ $8 $s $8 5 EE 2 & ES 8% BE 8
w a oF $F ge 33 2a 26 ge a 3. 2
ao 3s ge oF S
" 22 33 2 < a «*

Fioure 2.—General aviation accident rates—1974, selected occupations, cumulative flight time

7



TECHNICAL REPORT STANDARD TITLE PAGE
T. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

FAA-AM-77- 10

4. Title and Subtitle 5. Report Date

AN EPIDEMIOLOGIC INVESTIGATION OF OCCUPATION, APRIL 1977

AGE, AND EXPOSURE IN GENERAL AVIATION 6. Performing Organization Code
ACCIDENTS

7. Author(s) 8. Performing Organization Report No.
Charles F. Booze, Jr., Ph.D. FAA-AM-77-10

9. Performing Organization Name and Address 10. Work Unit No.

FAA Civil Aeromedical Institute

P.O. Box 25082 TT. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

T2. Sponsoring Agency Name and Address

Office of Aviation Medicine
Federal Aviation Administration
800 Independence Avenue, S.W. 14. Sponsoring Agency Code
Washington, D.C. 20591 FAA

15. Supplementary Notes

16. AbsoctThis study involved a census of 4,491 general aviation accident-|
involved airmen records for the year 1974 to obtain relevant occupa-
tion, age, exposure, and other epidemiologic profile information ofa
descriptive nature. Population comparison data for occupation, age,
and exposure were obtained from a sample of 9,414 currently certified
airmen medical records as of December 1974. Occupation was studied
under assumptions of similar exposure, total cumulative exposure by
occupation, and recent exposure by occupation with the outcome under at
least two methods of analysis being the identification of physicians,
lawyers, sales representatives, farmers, and housewives as having high
accident experience. Whether considering cumulative or recent exposure
high exposure is associated with the highest risk when considered

separately and when combined with the younger ages. Recent exposure
appears to be more important as a risk factor. The months of April
through September are peak accident months. Alaska, /rkansas, Idaho,

Nevada, New Mexico, West Virginia, and Wyoming all had at least double
the accident experience expected. Eighty-five percent of all accidents
occurred between 9 o'clock in the morning and 9 o'clock in the evening.
More than half (55 percent) of all accidents occurred within 1 hour
after takeoff. Sixty percent of accident flights were originated for
pleasure purposes. Fewer than expected accident~involved airmen had
limitations and 75 percent had a medical examination within a year
prior to the accident

17, Key Words 18, Distribution Statement
Accidents, General Aviation, Document is available to the public
Statistic, Airman through the National Technical

Information Service,
Springfield, Virginia 22151

19. Security Classif. (of this report) 20. Security Classif, (of this page) Ti. No. of Pages | 22. Price

Unclassified Unclassified

Form DOT F 1700.7 (8-69)



‘Tare 2.—General aviation accident rates by major occupational category and age—1974

Age Interval

Major Occupational Category Tess than

20 years

20-29

30-39 40-49 50-59 60-69 __70-Plus

Professional and Technical 6.6 9.

Managers and Administrators,
Except Farm

Sales Workers

Clerical Workers

Craftsmen

Operatives

Laborers, Except Farm

Farmers and Farm Managers
Farm Laborers and Foremen
Service Workers

Government Employees (nec)

Housewives

Students (Academic)

Retired, None or Unknown

Wor rUonnuie@as

ees
URENURLESL

.
NR AANOOHRN

Leb ebaraarro

BS
er

TOTAL 2.5

2

7.9 7.6 7.4 14.7 49.4 8.2

ME aeuan
Cian aourore

_

NR BLURS EOLAU
1orHoHaso
-

49.4

Rao
'
'

who wUbE Er vebwuUs

o

a
o
o
o
&
©
o

Rates were highest for the professional and
technical and farmers and farm managers cate-
gories in all age intervals. Since these rates do
not consider exposure, the influence of the pro-
fessional pilot experience in the professional and
technical major occupational category is appar-
ent (Table 1 indicates a low “per unit of ex-
posure” accident experience for professional
pilots, but even low rates produced high absolute
numeric experience when a high group exposure
existed). The experience of the farmers and
farm managers category was consistent with pre-
vious findings.

Rate Per
1,000 Airmen
10
8
6
4
2
rn 1 L L 1 1.4

Lessthan 20- 30- 40- 50-  60-. 708
20 yrs, 29 39,49 59 69 Above

Fioure 5—General aviation accident rates by age—1974

10

D. Accident Experience by Major Occupa-
tional Category and Cumulative Flight Time.
Requirements for the various airman ratings
stipulate certain levels of cumulative flight ex-
perience, under various conditions, for minimum
qualification. Thus, one assumes that a beneficial
effect accrues with greater cumulative experi-
ence. However, at some point, cumulative flight
experience ceases to be an asset and becomes a
risk factor. As seen in the 1974 general aviation
accident data presented in Table 3 and Figure 6,
accident rates increase with cumulative exposure
for all but the highest exposure category, where
the drop is slight. Overconfidence and lack of
vigilance by high-time pilots have been cited as
possible contributors to this situation. Airline
pilots, on the other hand, have the highest cumu-
lative experience of any group but continue to
have low accident rates. Airline pilots, as a
rule, use more sophisticated equipment, both air-
craft and navigational, and have professional
help in performance of the flight task. Preflight
planning and the flight routine are also likely
to be more disciplined.

General aviation accident rates increase with
an increase in cumulative flight experience with-
in all major occupational categories and for the
total population (an increase of 13-14 times from
low to high cumulative categories). Highest
rates are consistently in the greatest. cumulative
flight time intervals (see Table 8). Farmers and
farm managers have among the highest rates re-
gardless of exposure category. No other cate-


(Rates per 100,000 Hours

of Recent Flight Time)

50r
40.7
407 36.6 ere 37.6
33.1
30k r 28.5 25.0
20 + 18.9 19.2 ise 16.9
13.3 a. 13.8
POPULATION
RATE 12.6
10 F 6.3
Ove 2 # # 3 Bf 2 2 ¢ 2 8¢ 2 8
rn ry 5 5 § sf 2 5. 8 © Sw Ef SE =
2 2 so £ 2) oF 5 gS se £ cf SB 22 =F
< & 3s 8 es $5 = $F "8 § #2 BS vE 2
2 3 5 8 #8 of § EL uv 2 £€3 85 35 8
& © €2 Se oS Ss BE oO ’> 3
a a ca ge 22 §2 FS 85 * g. 2
oa 32 58 g& < go e°
oe

Figure 4.—General aviation accident rates—1974, selected occupations, recent flight time

Leisure time is probably at a premium among
these individuals, and pressing business commit-
ments are a frequent occurence in an already
overcrowded schedule. When these factors are
combined with the personality traits previously
mentioned, it is easy to imagine the mechanisms
for increased accident proneness.

C. Accident Experience by Major Occupa-
tional Category and Age. Another variable of
interest with respect to general aviation acci-
dents has been age. Several studies have demon-
strated an increase in accident rates with
age.!" 272822 Table 2 provides age/major oc-
cupational category-specific rates. The trend of
the total age-specific rates shows an increase with
age of approximately four times from the
youngest to the oldest age intervals. The ex-
perience within the major occupational categories
is generally supportive of this pattern with some
dropoff in older age groups (where retirement

normally occurs). The highest rates for 9 of 14
major occupational categories occurred in the
age intervals above 49 years of age. Sales
workers and general laborers both experienced
highest: rates in the 30-39 age interval. In both
instances, however, rates did not dropoff appreci-
ably after reaching this peak. Observations for
the farm laborers and foreman category were too
small for meaningful analysis.

Academic students experienced their highest
rate in the 20-29 age interval. However, the
highest student rate was considerably below the
total age-specific rate of 5.2. The retired, none,
or unknown category also experienced a peak in
the 30-39 age interval with a rather erratic pat-
tern afterwards. The age distribution of this
group (from raw data) clearly indicates that
this category predominantly comprises “none” or
“unknown” with a concentration seen in the
younger ages and decreasing in higher ages.



ator data (accident airmen) are constant; there-
fore, higher rates would result if an earlier
population total was used (ie, 1972) because
the denominator would be smaller. The opposite
bias would occur if the 1974 population total
were used.

Occupation was obtained from entries by the
airman on the hard-copy application form and
was later coded according to Bureau of the
Census occupational codes. Traditional prob-
lems associated with overstatement of occupation
were experienced. Problem cases were resolved
by study team decision. Some problems are
recognized with respect to accuracy of flight time
data. Airmen with low flight time are likely
to know and record their flight time more accur-
ately than are airmen with high flight time,
who may tend to round off their responses.
Since there are many more airmen in the lower
categories, the impact on this study is felt to be
minimal. Further, much of the analysis to fol-
low makes use of rather broad intervals for
higher flight time groups where accuracy is ex-
pected to depreciate.

IV.

A. Accident Experience by Occupation. Pro-
fessional and technical occupations, farmers and
farm managers, and service workers (mainly
protective service workers) had the highest
occupation-specific rates among the major occupa-
tional categories (Table 1). These three cate-
gories exceeded the overall crude accident rate
of 5.9 per 1,000 for the population. All other
major occupational categories had rates of Jess
than 5.9 per 1,000 (with the exception of the
farm laborers, whose number was so small as
to make results questionable, and these are thus
eliminated from further discussion). Accident
experience of the professional and technical cate-
gory and the farmers and farm managers cate-
gory significantly exceeded expectations (this
and all subsequent statements of significance are
at the 0.05 level or less) whereas service workers
exceeded expectations only slightly. The accident
experience of all other major occupational cate-
gories was less than expected and significantly
less for clerical workers, craftsmen, general
laborers, housewives, and students.

Results and Discussion

‘Tare 1.—General aviation accident experience by occupation—1974

‘Ubsceved Expected 2 ‘Occupation
Accident Accident Ratio of |x Specific Rate per 100,000 hours Rate per 100,000 hours
Occupation Frequency Frequency __O/E. jest __Rates (per 1,000) _of Total Flight Tine of Recent Flight Time _
ALL PROPESSTONAL AND TEGHNTGAL 2,019 1,658 1s 3. 3.3 302
Engineers 125 156 018 “7 rat 18.9
37 31 Ls ino us 36.6
Physicians 6 52 us 87 U8 33.1
8 43 60 or a2 ma Bs
Professional Pilots 1,302 485 27 15:9 on 623
[ALL MANAGERS AND ADMINISTRATORS 643 669 0.9 Le 5.7 0.7 19.2
Managers and Adninistrators~
General 352 542 1.0 0.2 6.0 0.7 19.2
ALL SALES WORKERS 258 2m 009 La 5.6 0.7 26.5
Sales Representatives 437 90 US 25.6 3.0 2 40.7
[ALL CLERICAL WORKERS 6 102 0.6 (15.7 3.6 13 30.8
‘ALL CRAFTSMEN 460 1% 0.6 155.0 35 ha 24.6
Mechanics and Repaimen=
General os 38 12 La 6.9 Ls 28.5
Members of the Armed Forces M11 as O13 246.4 Le 0.7 15.8
‘ALL OPERATIVES ror us 0.9 Le 5.2 1a 43.9
[ALL LABORERS , EXCEPT FARM 34 n 0.8 46 4h LT 29.6
[ALL FARMERS AND FARM MANAGERS 167 100 17 46.7 9. 13 36.9
Farmers 166 97 v7 asia rot 13 378
ALL FARM LABORERS AND FOREMEN 3 1 3.0 M7 12.4 22 248.3
ALL SERVIGE WORKERS 96 88 La 0.6 6.3 2.0 21.0
Policenen and Detectives 43 43 ma 0.6 66 LB 13.8
GOVERIUENT EMPLOYERS (nec) 2 20 0.6 2.9 3.6 0.6 16.5
HOUSEWIVES 29 47 0.6 68 3 3.2 37.6
STUDENTS (ACADEMIC) 188 348 05 80.4 312 37 25.9
RETIRED, NONE, OR UNKNOW 403 423 0.8 ua 5.6 05 16.9
TOTAL (Crude Rates) 4,491 5.9 0.5 12.6

‘values Less than 3.84 are not significant at probability level 0.05

values
values
values

equal to or greater than 3.84 are significant at probability level 0.05
equal to or greater than 6,64 are significant at probability level 0.01
equal to or greater than 10,83 are significant at probability level 0.001

6


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8. Gardner, L. U.: Inhaled Silica and Its Effects on
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Friedman, M., Rosenman, R. H., and Carroll, V.:

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@

a

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20

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Harper, C. R., and Albers, W. R.: Alcohol and Gen-

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22,

23,

24,

25.

26.

27.

Physical Defects of Civilian Pilots Re-

AEROSPACE MEDI-

30.

31.

32.


TRANSPORTATION ACCIDENTS *
49,502 FATALITIES

IN 1975

MARINE
-——_"——__ GENERAL AVIATION

COMM. RECR. 1,324
380 1,480
RAILROAD AIRCARRIERS
564 124
GRADE CROSSING PIPELINE
910 30

PEDALCYCLES
(Bicycles)
900

Numbers are
Preliminary estimates.

NATIONAL TRANSPORTATION SAFETY BOARD

Figure 1.—Distribution of transportation fatalities

2


times in rates by age has also been discussed.
When the cumulative exposure intervals in Table
5 are considered separately, some increase in
accident experience with age is noted for low
experience intervals. However, for the higher
cumulative exposure intervals, younger ages have
much higher rates. Large numbers of airmen
in lower age groups at lower exposure intervals
tend to weight the total rates and produce low
overall rates for younger ages. Well over one-
half of the airman population has cumulative
experience of 200 hours or less while only one-
third of the accidents were in this interval.

When the age intervals are considered sepa-
rately, a pattern of increasing rates with in-
creased exposure is clear for all age intervals
through 50-59. The trend for age intervals 60
and above is not so clear, with higher rates
occurring at lower exposure intervals.

For purposes of the current analysis, Table 5
has been partitioned into four quadrants, de-
picted by the heavy lines, to indicate distinct
categories of age or exposure as well as various
combinations of the variables. The ratio of
accident rates (relative risk) has been computed
for the several pertinent comparison possibilities.
Results are summarized in Table 6.

High exposure is seen to produce highest risk
when. considered separately and when combined
with younger ages. For higher ages, increased
cumulative exposure does not appear to be so
important.
with

Tasre 6.—Relative risks associated cumulative

experience and age

Risk Factor (ay Relative Wisk

High age only
High exposure only

High age, high exposure

High age, low exposure

Low age, high exposure 207
Low age, low exposure 0.3
Within low ages - high vs low exposure 3.4
Within high ages - high vs low exposure 1.6
Within high exposure - high va low age 0.8
Within low exposure - high vs low age 1.6

‘Relative risk is the ratio of accident rates among those
with the characteristic to the accident rate of those
without the characteristic,

aceident rate among high age airmen
Relative Risk = Z5G{G¢ne rate anoue all other airmen

18

H. Recent Flight Experience and Age. Recent
flight experience (during the 6 months prior
to the accident or medical application) and age
are considered jointly in Table 7. Rates in-
creased tenfold from the lowest recent exposure
intervals to the higher intervals for total popu-
lation experience. Age relationships are the
same as described previously (fourfold increase
from low to high ages). Holding exposure con-
stant by considering the intervals separately, one
can observe that rates increase with age in the
three lowest exposure intervals. For higher ex-
posure intervals, rates are higher in younger
ages. About 60 percent of the population indi-
cates flight time during the last 6 months in the
0-10 hours interval. This group experiences
about 20 percent. of the accidents. Conversely,
33 percent of all accidents occur among approxi-
mately 11 percent of the population with the
higher recent experience (100 hours or greater).

Table 7 has also been partitioned to allow for
risk comparison within and between some per-
tinent risk categories. Results are presented in
Table 8 along with comparable results for the
cumulative experience analysis. High recent ex-
posure and lower ages are again seen to increase
risk of accident. The only additional conclusion
reached from analysis of recent experience is the
increased importance of recent high exposure
among the higher age groups. Risk magnitudes
are also higher, according to recent. experience
analysis.

Whether one considers total experience or re-
cent experience, the importance of increased
exposure is apparent. Furthermore, recent ex-
perience appears to be more important than
cumulative experience as a risk factor, accord-
ing to the present analysis.

Some accepted relationships of greater accident
experience with age have been shown to be
erroneous when exposure is added to the equa-
tion for risk determination.

Younger ages have been found to experience
higher general aviation accident rates at both
higher cumulative and recent experience levels.
Although younger ages are broadly, defined here,
this finding is consistent with motor vehicle ac-
cident experience; however, an assumed causal
factor in motor vehicle accidents is lack of ex-



TaBLe 9,—Month of accident oecurrence—1974 general
aviation accidents

Wonth of Accident Frequency Wercent
January 313 7.0
February 248 5.5
March 326 72
April 400 8.9
May 452 10.1
June 486 10.8
July 516 iver)
August 507 13
Septenber an 83
october 352 78
Novenber as 5.7
December 258 5.7
Invalid moneh code or unknown 5 on

TOTAL, 4494 100.0

Table 10 shows the geographic distribution of
accidents. While State of occurrence is often
different from State of pilot residence, it is clear
that States with the largest pilot population ex-
perience the highest frequency of accidents; i.e.,
California, Texas, and Florida. However, ac-
cording to proportional expectations, these States
have experience that is about as would be ex-
pected. Alaska has four times the number of
accidents expected. Weather and type of flying
may be part of the reason for Alaska’s increased
accident experience. Arkansas, Idaho, Nevada,
New Mexico, West Virginia, and Wyoming all

Number Of
Accidents

500

Jan = Mar May Jul-Sep
Feb Apr Aug” Oct

Jun
Month

Fieure 7.—Month of accident occurrence—1974 general
aviation accidents

15

have at least double the accident experience ex-
pected, for reasons that are not obvious. States
with substantially less than expected accident
experience (about one-half) include Connecticut,
Illinois, Indiana, Maryland, New Jersey, Ten-
nessee, and the District of Columbia.

The distribution of accidents by time of occur-
rence within the day is what would be expected
(see Table 11 and Figure 8). No important dif-
ferences in the distribution of accidents by time
of day are observed when less serious accidents
are compared with serious or fatal accidents.

Percent
25

20

001-0300 O60I-0900 1201-1500 1801-2100
0301-0600 0901-1200 1801-1800

Time Of Accident

Ficure 8.—Time of accident occurrence—1974 general
aviation accidents

Table 12 and Figure 9 presents some interest-
ing findings with respect to amount of exposure
to the flight environment within the past 24
hours. Fifty-five percent of all accident-involved
pilots had flown less than 1 hour in the past 24
hours. More fatal and serious accidents than less
serious accidents occurred during the first hour
of flight. Furthermore, almost half (48 percent)
of the fatal and serious accidents occurred dur-
ing the first half hour of flight. From these
data, fatigue associated long-duration
flights does not appear to be a significant factor
in the epidemiology of general aviation accidents.

with

2101-2400


AN EPIDEMIOLOGIC INVESTIGATION OF OCCUPATION, AGE,
AND EXPOSURE IN GENERAL AVIATION ACCIDENTS

I, Introduction

Accidents as a cause of disability and death
represent an area of increasing public health
concern, and an area deserving of considerably
more attention in future public health planning.
When all ages are considered, accidents currently
rank fourth as a cause of death, after cardio-
vascular disease, malignancies, and cerebrovascu-
lar disease. Accidents represent the leading
cause of death for younger age groups. Tre-
mendous losses are incurred in terms of perma-
nent disability, disfigurement, and economic
productivity for accident survivors.

Transportation accidents have historically
made a major contribution to overall accident
morbidity and mortality. According to pre-
liminary estimates published by the National
Transportation Safety Board in May 1976, 49,502
fatalities occurred in transportation accidents of
all types during 1975. Highway accidents, which
include automobile, truck, pedestrian, motorcycle,
and bicycle accidents, are, of course, the major
cause of transportation fatalities. Following
highway accidents, in terms of magnitude, are
marine accidents and general aviation accidents.
Grade crossing, railroad, air carrier, and pipeline
accidents comprise the remainder of transporta-
tion accidents" (see Figure 1).

The primary mission of the Federal Aviation
Administration (FAA) is air safety, Conse-
quently, the agency devotes considerable effort to
control of the aviation environment, including
commercial and general aviation equipment test-
ing, inspection, and maintenance; qualifications
of airmen as relates to both competency and
medical aspects; and air traffic control equipment
and manpower. Research and development are
of continuing concern to the FAA in furthering
administration objectives with respect to air
safety in those areas described. Much of this
research effort has been concerned with environ-
mental hardware factors (ie. better equipment

and facilities) or with human factors aspects of
crash survival. Very little attention has been
devoted to classical epidemiologic methods and
variables as an approach to a better understand-
ing of the etiology of aircraft accidents.

Much of the available research has been con-
ducted in a military setting on a group that
might be considered unique with respect to popu-
lation characteristics and equipment.

Interest has been apparent in recent years con-
cerning the possible importance of occupation as
a risk factor in general aviation accidents. The
various rationales for such interest include the
personality traits likely possessed by persons in
certain occupational categories; ¢.g., physicians
and executives are usually characterized as being
aggressive and independent. Another variable
of obvious importance involves amount and type
of exposure to the aviation environment. His-
torically, this has been a rather elusive factor
for a number of reasons, ranging from definition
to accuracy of data. for analysis.

The FAA is continually searching for risk
factors or categories of airmen likely to represent
higher accident proneness. The mechanisms for
airmen education are well established and have
been quite effective in reducing risk of accident
once a factor is realized, documented, and
brought to the attention of the proper authority.

General aviation has experienced substantial
growth during the past decade. Given that oc-
cupation and the economic feasibility of general
aviation as a means of transportation are so ob-
viously related to exposure, these factors appear
to represent important areas to consider in
achieving a better understanding of the epide-
miology of accidents.

From a public health standpoint as well as
from the FAA mission standpoint, it is appro-
priate to consider these rather obvious factors in
an attempt to identify potential higher risk
groups.



ACKNOWLEDGEMENT

The author expresses gratitude to Dr. Paul S. Anderson, Chairman of
the Department of Biostatistics and Epidemiology, Oklahoma University
Health Sciences Center, for his helpful. assistance during the design and
preparation of this study.

The author also wishes to express appreciation to Mrs. Judy Toberman.
and Mrs. Mary Randall for their assistance in review and preparation of
this study.


gory demonstrates such a pattern. Within the
farmers and farm managers category, the pat-
tern of increased rates with higher cumulative
flight time is present but somewhat more erratic.

E. Accident Experience by Major Occupa-
tional Category and Recent Flight Experience.
FAA regulations also require a minimum amount
and type of recent flight experience for an air-
man to be current. Some minimum recent ex-
perience is thus considered necessary for the
pilot to perform safely in the aviation environ-
ment. One might logically extend this argument
to the conclusion that the greater the amount
of recent experience one has, the safer he or she
is as a pilot.

Rote Per 000 Airmen
25

Recent Exposure

20
15
[nas
10
-—" cumulative Exposure
5 -—- Cw

7
i 1 1 L L 4
Recent Exposure 0-10 _I1-50_51-100 101-200 201 & Above

i 0-10 11-50 51-200 201-1000 1001-2000
Cumulative Exposure {O01 2000

Exposure (Hours)

Fievre 6,—General aviation accident flight

time—1974

rates by’

However, the same patterns that are described
for cumulative flight time emerge for recent
flight time. Greater recent exposure to the gen-
eral aviation flight environment results in higher
risk, as shown in Table 4 and Figure 6. Overall
and for all major occupational categories, rates
increase with increased recent flight time. Over-
all, risk increases approximately 10 times from
the 0-10 interval to the 101-200 interval. When
flight time intervals are considered separately,
farmers and farm managers again experience the
highest rates in all but one interval. Some sug-
gestion of a decrease in risk for the highest flight
time interval is shown in the total rates.

F. Accident Experience by Flight Experience
and Age. From the literature and preceding
discussions, it appears that occupation, age, and
flight experience are important variables with
respect to the epidemiology of general aviation
accidents. Exposure to the environment is ob-
viously necessary to incur risk of accident. This
fact is, and always has been, indisputable. It
is the interrelationships of exposure with other
variables that will provide additional informa-
tion. Occupational and exposure relationships
are presented in Tables 1, 3, and 4. Trends by
occupation and age are apparent from data pre-
sented in Table 2. The relationship of age and
exposure remain to be examined.

G. Cumulative Flight Eaperience and Age.
The approximate fourteenfold increase from low
to high cumulative flight time intervals for the
total population has been previously noted.
Likewise, the increase of approximately four

‘Tape 8.—General aviation accident rates by major occupational category and cumulative flight time—1974

Cumulative Flight Time (Hours)

2001-
Major Occupational Category 0-10 11-50 51-200 201-1000 1001-2000 Plus ‘Total
Professional and Technical 0.9 4.3 4.9 8.7 19.9 14.3 8.2
Managers and Administrators,

Except Farm 1.5 6.8 5.8 5.9 9.2 10.4 5.7
Sales Workers 1.0 6.7 5.5 6.4 8.3 11.2 5.6
Clerical Workers 0.6 8.1 4.2 5.9 10.4 47 3.6
Craftsmen 0.6 2.7 4.2 5.8 12.7 9.9 3.5
Operatives 0.6 6.6 8.1 7.1 14.5 6.9 5.2
Laborers, Except Farm 0.9 4.1 6.0 7.0 5.3 16.5 4.4
Farmers and Farm Managers 2.5 12.4 10.1 9.9 20.1 15.1 9.9
Farm Laborers and Foremen 6.2 - - - - = 12.4
Service Workers Leal 4.5 72 8.9 12.4 40.4 6.3
Government Employees (nec) - 24.7 LL 1.6 12.4 37.3 3.6
Housewives 1.4 10.5 4.7 2.5 - - 3.7
Student (Academic) 0.7 6.3 4.9 8.7 21.7 16.5 3.2
Retired, None or Unknown 2.8 5.9 6.5 5.9 9.0 9.9 5.6

TOTAL La 5.2 5.2 2 14d 13.2 5.9

11



Tare 7—General aviation accidents by recent experience and age—1974

“Recent Experience (Hours)
‘Age Group Pau 1-30, a OIE Total
‘Less than 20 years
Accidents 35 50 u 6 4 116
Non-accidents 37,257 6,474 1,842 75 - 45,633
Subtotal 37,292 6,524 1,853 aL : 45,749
Rate/1000 9 17 3.9 14.5 - 2.5
20-29
‘Accidents 261 299 169 164 4 1,207
Non-accidents 157,042 42,389 10,141 6,118 13,137 228,827
Subtotal 157,303 42,688 10,310 6,282 13,451 230,034
Rate/1000 . 7.0 16.4 26.1 23.3 5.2
30-39
‘Accidents 275 361 207 2u7 287 1,357
Non~accidents 122,716 49,254 14,281 8,160 20,252 214,663
Subtotal 122,991 49,615 14,498 8,377 20,539 216,020
Rate/1000 2.2 7.3 15.0 25.9 14.0 6.3
40-49
‘Accidents 222 335 203 138 161 1,059
Non-aceidents 81,611 43,562 12,765 6,869 13,934 158,741
Subtotal 81,833 43,897 12,968 7,007 14,095, 159,800
Rate/1000 2.7 7.6 15.6 i9.7 114 6.6
50-59
‘Accidents 123 178 125 ca 82 592
Non-accidents 40,552 25,677 8,493 5,796 9,342 89,859
Subtotal 40,675 25,855 8,618 5,880 9,424 90,451
Rate/1000 3.0 6.9 14.5 14.3 8.7 6.5
1-69
‘Accidents 31 39 2 16 15 123
Non-accidents 5,929 5,116 1,669 709 70 14,133,
Subtotal 5,960 5,155 1,691 725 725
Rate/1000 5.2 7.6 13.0 22.1 20.7 8.6
70 and above
‘Accidents 8 7 4 - 1 20
Non-accidents 878 718 157 161 - 1,913
Subtotal 886 725 161 161 : 1,933
Rate/1000 9.0 9.6 26.8 - - 10.3
Unkmown Age Accidents wv - - - - v
Total
‘Accidents 972 1,269 751 625 874 4,491
Non-accidents 445,968 173,190 49,347 27,888 57,359 753,752
Subtotal 446,940 174,459 50,098 28,513 58,233 758,243,
Rate/1000 2.2 7.3 15.0 21.9 15.0 5.9

NOTE: Row and column totals may not equal the sum of cell values due to rounding.

Taste 8.—Relative risks associated
cumulative experience and age

with

recent and

Risk Factor

(test

Relarive i

Experience

(cumulative

Relative ny +
Experience

High age only
High exposure only

igh a

high exposure
High age, low exposure
Low age, high exposure
Low age, low exposure

Withia low age--high vs. low
exposure

Within high age--high vs. low
exposure

Within high exposure--high vs.

low age

Within low exposure--high vs.
age

Lez

low

12

perience. Other factors characteristic of younger
ages must be of importance for general aviation
accidents.

I. Some Characteristics of Accident-Involved
Airmen. Additional data of a descriptive nature
concerning airmen involved in general aviation
accidents during 1974 are as follows:

Females experienced significantly fewer ac-
cidents than expected (103 observed; 215
expected).

From data presented in Table 9 and Figure 7,
the peak months for general aviation accidents
are observed to be April through September, con-
sistent. with an increase in general aviation
activity during these months.

14