Final answer:
All flight crew members must be awake during critical phases of flight, including takeoffs and landings, as well as during changes in flight conditions. The FAA has established regulations for controlled rest that include mandatory wakefulness periods before descent.
Step-by-step explanation:
When discussing controlled rest on the flight deck, it is crucial for safety reasons that all flight crew members be awake during critical phases of flight, which include at least all takeoffs and landings. Additionally, they should be awake and able to assess the situation whenever there's a change in flight conditions or when preparing for any procedural actions, such as weather changes, entering busy airspace, or other scenarios that may require immediate action.
Controlled rest is designed to mitigate fatigue during long-haul flights, but it must be used judiciously to ensure that crew members can maintain the highest level of vigilance during crucial moments. The regulations, introduced by the Federal Aviation Administration (FAA), include mandatory wakefulness periods before the descent phase of the flight to allow pilots to regain full situational awareness and operate the aircraft safely.