(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 crew-
member’s station.
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.
PART 135
OPERATING REQUIREMENTS:
Commuter and On Demand Operations and Rules
Governing Persons On Board Such Aircraft