What regulation governs the flight time limitations for crew members?

The regulation that governs the flight time limitations for crew members is FAR Part 117. This part specifically addresses flight and duty time limitations and rest requirements for flight crew members operating under 14 CFR. It was designed to enhance the safety of flight operations by promoting adequate rest for pilots, which is vital for combating fatigue.

FAR Part 117 outlines the maximum flight time a crew member can accumulate in various timeframes, along with the required rest periods between duty periods. This regulation is particularly stringent for operations that involve airline transport, reflecting the critical nature of maintaining alertness and performance in commercial aviation.

While the other parts listed have their regulations — Part 91 focuses on general aviation operations and does not set specific rules for airline transport crews, Part 121 applies to air carrier operations but has its own guidelines that are less comprehensive regarding rest and duty times than those in Part 117, and Part 135 covers commuter and on-demand operations but also does not provide the same detailed requirements — it is FAR Part 117 that is explicitly concerned with the flight time limitations and rest requirements that the question addresses.