http://www.finkelaviationlaw.com/art7.html
Weather, ATC and mechanical delays often compromise rest requirements. To these, an FAA attorney has given this interpretation:
"The FAA has consistently interpreted delays due to weather, ATC, and mechanical delays as examples of circumstances beyond the control of the certificate holder under FAR 135.263(d). A correct interpretation of the flight time limitations under FAR 135.265, together with the flexibility of FAR 135.263(d), results in a requirement to add a flight crewmember's actual flight time accumulated in the previous days to the flight time scheduled to be flown for the particular day that is under review. If the total flight time, actual plus scheduled, is not in excess of the limitations under FAR 135.265, then the flight crewmember may complete all flight segments for that day."
However, as a caveat, the interpretation makes clear the FAA's ultimate position:
"Lastly, we point out that in the course of a day's scheduled events, delays due to adverse weather conditions, ATC, or unscheduled maintenance, may cause a flight crewmember to become significantly fatigued. If the state of fatigue would endanger or potentially endanger the life or property of other persons, then the certificate holder should relieve the flight crewmember from further duty aloft. In this respect, note the provisions of FAR 91.13 entitled 'Careless or Reckless Operation.'"
If the FAA believes careless or reckless operation was involved, certificate action will probably occur. Otherwise, rest period violations often involve civil penalties, where the losing pilot ends up with a hefty fine.
One such case resulted in a $10,000 civil penalty assessed against a charter operator,
and $2,000 each against the two Lear Jet pilots. The pilots were held to have had
less than the required 10 consecutive hours of required rest. They argued that
delay of delivery of freight to an airport constituted a circumstance beyond their control. But the Administrative Law Judge was quick to point out that the pilots were aware when they accepted the assignment that the freight would be late in delivery.
The lesson to be learned from this decision is that pilots must formulate a planned completion time. They must make certain in advance that duty times will not be excessive, and rest periods complied with. ...
Part 121 and 135 operators and pilots must be thoroughly aware of duty/rest period requirements. Inspectors and attorneys are under considerable pressure to police the industry. One aftermath of the ValueJet crash into the Florida Everglades was increased scrutiny into commercial operations. The public demands that the FAA make certain commercial operators are safe. That means inspectors will be paying more and more attention to records. As long as operators and pilots follow the rules and make certain their record keeping is precise, the flying public can feel more secure about their safety, and pilots more secure about their future.
§ 121.471 Flight time limitations and rest requirements: All flight crewmembers.