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"Long Duty Days Lead to Higher Accident Risk, Study Shows"

Tuesday, December 18, 2001

Long Duty Days Lead to Higher Accident Risk, Study Shows
Commuter/Regional Airline News

A tired pilot is two to four times more likely to be involved in an
accident, according to a new study that compares accidents to the number
of hours the pilots involved were on duty. The longer the time on duty,
the greater the proportion of accidents, the study finds.

The study may well provide the "scientific basis" for updated flight
time/duty time rules that have been a matter of much controversy in
recent years. The results of the risk-analysis study are considered
statistically significant.

Highlights of the study appeared in the current issue of an internal
Federal Aviation Administration (FAA) newsletter, Safety Risk Assessment
News. This is a bimonthly publication of the FAA's System Safety
Engineering & Analysis Division.

The article by Dr. Jeffrey Goode, Ph.D., acknowledges the problem with
the current, and widely-regarded as obsolete, regulations: "Current
rules have nothing to say about duty limits per se, and instead focus on
flight limitations and rest requirements." Goode went on to provide
insights into FAA thinking about the form that new rules might take.
They are expected to soon be issued by the FAA for industry comment.
Goode said the FAA believes that "pilots should have the opportunity for
at least 7-8 hours of sleep in a rest period."

"The current regulations do not provide the opportunity for this amount
of sleep in most cases," Goode said. Indeed, the current regulations,
according to the FAA's interpretation of them, limit the pilot's duty
day to 16 hours. Of the remaining eight hours in the day, by the time
movement to and from the place of rest is factored in, pilots often do
not have sufficient time to gain seven to eight hours of actual sleep.

There is a real difference between the airlines and the pilots' unions
about the form updated regulations should take. The airlines have argued
for a maximum duty day of 14 hours, with two hours for delays. The
Allied Pilots Association (APA) and the Air Line Pilots Association
(ALPA) have argued for a 12-hour scheduled duty day, with two hours for
delays. The APA/ALPA position also calls for a maximum of eight hours of
flight time. During the so-called window of circadian low (WOCL), they
have called for a maximum of 10 hours of duty and seven hours of flight

The FAA study relating accidents to duty time adds grist to the debate,
as it shows a sharp increase in the proportion of accidents that occur
when pilots are on duty 13 hours or more.

The study covered all human factors-related accidents over a 20-year
period (1978-1998) where substantial damage to the aircraft or serious
injuries/deaths were involved, and in which a 72-hour pilot history
prior to the accident could be determined. The review focused on Part
121 operations (scheduled carriers) and excluded all turbulence-related

Data on pilot work patterns (schedules) also were compiled. The work
schedules of pilots involved in accidents were compared to the schedule
patterns of pilots not involved in accidents.

The study supports the need to limit pilot duty time. As Goode pointed
out, approximately 10 percent of pilot duty hours are in the 10-12 hour
period, while 20 percent of the accidents occur in this time block.
"Similarly, 4 percent of the accidents occur when a pilot has been on
duty for 13 or more hours, where only 1 percent of the pilot duty hours
occur," he noted.

For pilots with 13 or more hours of duty, the proportion of accident to
non-accident pilots is nearly four times higher.

"Although the empirical analysis ... notes that pilot scheduling was not
a factor in all these accidents, it does point to increased risk of
accidents with increased duty time and cumulative duty time." Therefore,
Goode concluded, establishing hard duty limits for airline pilots "would
reduce risk." ? David Evans, Air Safety Week.

Captain Duty Hours and Accidents by Length of Duty Period

Hours in Duty Period: 1-3

Captains' Hours: 430,136

Exposure Proportion: 0.35

No. of Accidents: 15

Accident-pilot Proportion: 0.28

Accident Proportion Relative to Exposure Proportion : 0.8

Hours in Duty Period: 4-6

Captains' Hours: 405,205

Exposure Proportion: 0.33

No. of Accidents: 15

Accident-pilot Proportion: 0.28

Accident Proportion Relative to Exposure Proportion : 0.85

Hours in Duty Period: 7-9

Captains' Hours: 285,728

Exposure Proportion: 0.23

No. of Accidents: 14

Accident-pilot Proportion: 0.26

Accident Proportion Relative to Exposure Proportion : 1.13

Hours in Duty Period: 10-12

Captains' Hours: 109,820

Exposure Proportion: 0.09

No. of Accidents: 8

Accident-pilot Proportion: 0.15

Accident Proportion Relative to Exposure Proportion : 1.68

Hours in Duty Period: ? 13

Captains' Hours: 12,072

Exposure Proportion: 0.01

No. of Accidents: 2

Accident-pilot Proportion: 0.04

Accident Proportion Relative to Exposure Proportion : 3.81

Hours in Duty Period: Total

Captains' Hours: 1,242,961

Exposure Proportion: 1

No. of Accidents: 54

Accident-pilot Proportion: 1

Accident Proportion Relative to Exposure Proportion : Source: FAA


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