If an unpressurized aircraft is operated above 12,500 feet MSL for a period of 2 hours 20 minutes, how long is the minimum flightcrew required to use supplemental oxygen?

In the context of operating unpressurized aircraft at high altitudes, the regulations regarding supplemental oxygen usage specify that when flying above 12,500 feet MSL, oxygen must be used for crew members based on the duration of the flight and altitude. For altitudes between 12,500 feet and 14,000 feet, supplemental oxygen is required after 30 minutes of flight time at that altitude. Whenever the altitude exceeds 14,000 feet, oxygen is required for the entire flight duration.

Given that the aircraft is being operated at a minimum of 12,500 feet for a flight period of 2 hours and 20 minutes, the regulations dictate that crew members must use supplemental oxygen for the portion of the flight that exceeds the initial 30 minutes necessary at that altitude.

In this case, the crew must use supplemental oxygen for the entire period of 2 hours and 20 minutes, but the regulation indicates that verification of the minimum duration would actually account for only that time exceeding the first 30 minutes at altitude. The calculation becomes:

• Total flight time = 2 hours 20 minutes = 140 minutes.

• The initial 30 minutes does not require supplemental oxygen, leading to 140 - 30 = 110 minutes of