Sec. 135.89 Pilot requirements: Use of Oxygen.
(a) Unpressurized aircraft. Each pilot of an unpressurized aircraft shall use oxygen
continuously when flying—
(1) At altitudes above 10,000 feet through 12,000 feet MSL for that part of the flight at
those altitudes that is of more than 30 minutes duration; and
(2) Above 12,000 feet MSL.

(b) Pressurized aircraft. (1) Whenever a pressurized aircraft is operated with the cabin
pressure altitude more than 10,000 feet MSL, each pilot shall comply with paragraph (a) of

this section.
(2) Whenever a pressurized aircraft is operated at altitudes above 25,000 feet through 35,000
feet MSL, unless each pilot has an approved quick-donning type oxygen mask–
(i) At least one pilot at the controls shall wear, secured and sealed, an oxygen mask that
either supplies oxygen at all times or automatically supplies oxygen whenever the cabin

pressure altitude exceeds 12,000 feet MSL; and
(ii) During that flight, each other pilot on flight deck duty shall have an oxygen mask,
connected to an oxygen supply, located so as to allow immediate placing of the mask on the

pilot’s face sealed and secured for use.
(3) Whenever a pressurized aircraft is operated at altitudes above 35,000 feet MSL, at
least one pilot at the controls shall wear, secured and sealed, an oxygen mask required by

paragraph(b)(2)(i) of this section.
(4) If one pilot leaves a pilot duty station of an aircraft when operating at altitudes above
25,000 feet MSL, the remaining pilot at the controls shall put on and use an approved

oxygen mask until the other pilot returns to the pilot duty station of the aircraft.

§91.211 Supplemental oxygen.
(a) General. No person may operate a civil aircraft of U.S. registry—

1) At cabin pressure altitudes above 12,500 feet (MSL) up to and including 14,000 feet
(MSL) unless the required minimum flight crew is provided with and uses supplemental

oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration;
(2) At cabin pressure altitudes above 14,000 feet (MSL) unless the required minimum flight
crew is provided with and uses supplemental oxygen during the entire flight time at those

altitudes; and
(3) At cabin pressure altitudes above 15,000 feet (MSL) unless each occupant of the aircraft
is provided with supplemental oxygen.
(b) Pressurized cabin aircraft. (1) No person may operate a civil aircraft of U.S. registry with
a pressurized cabin—
(i) At flight altitudes above flight level 250 unless at least a 10-minute supply of
supplemental oxygen, in addition to any oxygen required to satisfy paragraph (a) of this

section, is available for each occupant of the aircraft for use in the event that a descent is

necessitated by loss of cabin pressurization; and
(ii) At flight altitudes above flight level 350 unless one pilot at the controls of the airplane
is wearing and using an oxygen mask that is secured and sealed and that either supplies

oxygen at all times or automatically supplies oxygen whenever the cabin pressure altitude of

the airplane exceeds 14,000 feet (MSL), except that the one pilot need not wear and use an

oxygen mask while at or below flight level 410 if there are two pilots at the controls and each

pilot has a quick-donning type of oxygen mask that can be placed on the face with one hand

from the ready position within 5 seconds, supplying oxygen and properly secured and sealed.
(2) Notwithstanding paragraph (b)(1)(ii) of this section, if for any reason at any time it is

necessary for one pilot to leave the controls of the aircraft when operating at flight altitudes

above flight level 350, the remaining pilot at the controls shall put on and use an oxygen

mask until the other pilot has returned to that crewmember’s station.