117.3 Definitions
We propose the following additions and clarifications to the Definition section.
Acclimated – means a condition in which a crewmember has been in a new
theater for the first 72 hours since arriving and has been given at least 36
consecutive hours free from duty during the 72 hour period.
Rationale: The established science, as we demonstrate below, is that 3
consecutive local nights rest is required to become acclimated. CAP 371 recognizes this
science and requires 3 consecutive local nights rest to be acclimated.
As the rule currently is written, it would allow carriers to provide 36 hours of
uninterrupted rest at the layover location and then be considered “acclimated” to the local
time zone. Such an assumption is incorrect for the following reasons:
1) For typical flights from the U.S. to Europe or Pacific destinations, the number
of time zones crews would transit would be in excess of 5 or more. The general agreed
upon acclimation rate is about 1 time zone or one hour difference per day.1 Some expert
1 It takes about one day for every time zone crossed to recover from jet lag. When circadian
disruption and sleep loss occur together, the adverse effects of each are compounded.
Battelle Memorial Institute. March 1998. A Review of Issues Concerning Duty Period
Limitations, Flight Time Limitations, and Rest Requirements as stated in the FAA’s Notice of
Proposed Rulemaking 95-18, 60 Fed. Reg. 244 (Proposed Dec. 20, 1995).
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researchers have published data showing even longer periods to become acclimated to the
local time zone.2 Conclusion: The crew would not be acclimated after 36 hours of
layover rest.
2) While 3 consecutive physiological nights may start approaching a reasonable
compromise for the purpose of entering the FDP tables, a 36 hour rest by itself clearly
would not. In order for the rules to approach parity, the implication is that a night of
normal sleep would be approximately 8-9 hours of sleep. Three nights of consecutive
sleep would be 24-27 hours of sleep. The 36 hour rule suggests that crews would remain
asleep for nearly the entire layover period. This is not physiologically plausible for
healthy aircrews.
3) Further, when crews are put into a rest period, it is critical for any fatigue
safety regulation to assess where they are in their own circadian cycle – as that will
determine when in the following rest periods, crews would be able and likely to sleep
from a physiological perspective. To be sure, being put into a rest cycle does not mean
that the crew will be able to sleep according to a desired clock position. The crews’
circadian phase will be the key-determining factor as to when and how long crews will
subsequently sleep. In a 36 hour rest situation, crews could have only one full sleep
cycle in their physiological nadir and if that falls early in the layover rest period, they
2 For example: Gander, et al. (1989) showed that it took several days for the acrophase of the
temperature rhythm to come within one standard error of complete resynchronization after a 9h
westward transition, and that the adaptation in an eastward direction took even longer. Paper
presented at the RTO HFM Lecture Series on “Sleep/Wakefulness Management in Continuous/
Sustained Operations,” held in Fort Rucker, Alabama, United States, 17-18 June 2002; Warsaw,
Poland, 24-25 June 2002; Paris, France, 27-28 June 2002, and published in RTO-EN-016,
Gander PH, Myhre G, Graeber RC, Andersen HT, Lauber JK (1989) Aviat Space Environ Med
61: 733-743.
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would initially sleep, then be awake for an extended period before reporting for duty. At
that point, the pilots, through no fault of their own, would be significantly fatigued after
being awake for 12 to 15 hours prior to starting their duty period.
We believe that the regulation should require 3 local nights rest. However, during
the first 72 hours in theater, measured from the time of first arrival, a 36 hour rest within
the 72 hours may allow a flight crewmember to become acclimated. Merely being in
theater for a 72 hour period without at least 36 consecutive hours rest during that time
would not allow a person to become acclimated. It is necessary to have both time in
theater and adequate rest to become acclimated. The preamble to the proposed regulation
states that the tables selected from the ARC were in part based on being the most
conservative approach. The wide range of available research on the topic of acclimation,
combined with operational experience, clearly supports a more conservative approach of
72 hours in theatre with 36 hours free of duty to consider the crew acclimated.
Acclimated Local Time - means the local time at the location where the pilot
last had greater than 36 hours free from duty in the first 72 hours in theater.
Rationale: This definition provides an unambiguous time for applying the
definition of Nighttime Duty Period and for entering the FDP and Flight Time limit
tables. The original NPRM wording of “acclimated or home base” time left many
questions of interpretation. For example, a USA based pilot who acclimates in Europe
and then subsequently flies to Japan would, under the current wording, enter the tables at
Home Base time instead of Europe time. Similarly, the exact location of acclimation
must be known to determine future loss of acclimation. For example, a pilot flies to Paris
and has 37 hours off, but at the end of his 72 hours in theater happens to be 3 more hours
east at Tel Aviv. He is now acclimated, but where? Would a further flight two more
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hours east to Dubai cause him to be unacclimated? It depends whether you define the
point of acclimation as being tied to the 36 hour rest or to the 72 hours in theater
condition. The above proposed definition removes such doubts about the location of
acclimation and the use of regulatory tables, allowing practical and reliable computer
programming of scheduling. Under this proposal, both the tables and the definition of
Nighttime Flight Duty Period would then use the new term, “Acclimated Local Time”.
Consecutive night duty period - means two or more night flight duty periods
that are not separated by at least a Part 117.25 rest between the duty periods
that encompasses a physiological night’s sleep (1:00 am to 7:00 am at home
base or acclimated local time).
Rationale: Part 117.27 limits consecutive nighttime flight duty periods to three
periods. The term consecutive night duty period is not defined, and to avoid confusion in
applying 117.27 we believe it should be defined.