High Altitude Cruising

[Hydrant]

A topic of interest is that i find it hard to understand why when cruising at high altitude ie FL 410 and above there isn't a universal requirement for at least one flight deck member to be on oxygen.

Surely give an explosive decompression in a jet transport aircraft at these types of Flight Levels the seconds of expected survival would dictate this requirement.

I believe Military fighters have pressure breathing oxygen above say FL 380 which pressurises the lungs.

Would 100 % oxygen at these levels in a passenger airliner be enough to push the required amount of oxygen across the lungs to prevent a very nasty sceanario ???

[Intruder]

When was the last time you heard of an explosive decompression in a transport aircraft?

In military aircraft, pressure breathing begins around 30,000' CABIN altitude.

[boofhead]

FAR 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.

[PantLoad]

Hydrant,

You are correct, in principle, about oxygen and pressure feed. However, the effect of partial pressure of gasses begins to become evident at cabin altitudes above FL250, begins to become a signficant factor beginning around FL300, and is critical factor at and above FL350.

It is for this reason that today's modern quick don masks automatically begin to pressure feed around FL300...regardless of mask control settings. For example, in the Airbus A-320 series FCOM (1.35.20 Page 7), I quote:

Note: Overpressure supply is automatically started, when the cabin altitude exceeds 30,000 feet.


Boofhead accurately and appropriately states the regulations.


Good question!!!!


Fly safe,

PantLoad

[PA38-Pilot]

(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.

Does anyone actually follow that one?

[Dream Land]

Does anyone actually follow that one?
:ugh:

No, because we are are too busy following this one (USA):} : FAR (3) Notwithstanding paragraph (c)(2) of this section, if for any reason at any time it is necessary for one pilot to leave his station at the controls of the airplane when operating at flight altitudes above flight level 250, the remaining pilot at the controls shall put on and use his oxygen mask until the other pilot has returned to his duty station.
121.33

[PantLoad]

Dreamland is absolutely correct!!!

And, yes, we follow that. Anyone who has gone through the physiological training of the U.S. military will need no coercion.

Fly safe...be careful...

PantLoad