If you are a flightcrew member for an air carrier operating under 14 C.F.R. Part 121 you know that 14 C.F.R. Part 117 contains flight, duty, and rest regulations that apply to all Part 121 passenger operations. One specific regulation, Section 117.5(d), requires a flightcrew member to “affirmatively state that he or she is fit for duty prior to commencing flight.” Section 117.3 defines “fit for duty” as “physiologically and mentally prepared and capable of performing assigned duties at the highest degree of safety.” What does that mean?
Unfortunately, no objective science-based standard currently exists for measuring fatigue levels. As a result, Section 117.5 doesn’t say just how fatigued a flightcrew member must be in order for him or her to be “unfit for duty.” Rather, the regulation simply states that an individual flightcrew member is “fit for duty” if he or she is capable of safely performing his or her assigned duties. According to the FAA, this determination must be made by each individual flightcrew member based upon a variety of factors, such as the length and difficulty of the flight duty assignment, time of day, and the flightcrew member's self-knowledge of how he or she deals with different levels of fatigue.
Which means flightcrew members’ fit for duty determinations are subjective. But, according to the FAA, this subjectivity “is mitigated by the fact that flightcrew members will undergo fatigue education and awareness training, which will increase each flightcrew member's ability to self-assess his or her fatigue levels.”
So, how does this apply in specific situations? For example, what if the flightcrew member is slightly fatigued at the end of a flight duty period (“FDP”)? Does that mean the flightcrew member should not have accepted the flight assignment? The FAA says “no.” Given the various individual factors that go into a fitness for duty determination, the FAA will not categorically say that a slight amount of fatigue that appears at the end of an FDP would always render a flightcrew member unfit for duty. As long as the flightcrew member is able to affirmatively state at the beginning of the FDP that he or she is fit for duty, then the flightcrew member may accept the assigned flight duty.
What about when the flightcrew member has been awake for 16, 18 or even 24 continuous hours prior to accepting the assigned flight duty? If the flightcrew member certifies that he or she is fit for duty in that situation is that a violation of the regulation? Here again, the FAA says “not necessarily.” Although it is significantly more likely that a person who has been awake for such an extended period of time will not be fit for duty, the regulations do not necessarily preclude the flightcrew member from accepting an assigned flight duty under those circumstances. The flightcrew member must still make an individualized determination and consider, as one factor along with others, the amount of time that the flightcrew member has been continuously awake.
Another common situation arises when an FDP involves more than one flight segment. If the flightcrew member is fit for duty at the beginning of the first flight segment but later determines he or she is not fit for duty before starting a subsequent flight segment during that FDP, then what? Since Section 117.5(d) requires a flightcrew member to reassess whether he or she is fit for duty prior to each flight segment, in that situation the flightcrew member would not be permitted to fly the subsequent flight segment. Similarly, if a flightcrew member reports for an FDP and is fit for duty at that time but that FDP is later extended, the flightcrew member must then reassess whether he or she can continue to serve on the extended FDP.
Thus, in order to be “fit for duty”, flightcrew members must decide, both at the beginning of an FDP and during that FDP that they are mentally and physically prepared and capable of safely performing their assigned duties and then take any necessary steps to comply with the rule. Flightcrew members should use their best judgment to make that determination and then act accordingly.