When a commercial passenger airliner suffers a rapid decompression, it is critical that everybody on board gets oxygen quickly. In the passenger rows, oxygen masks connected to chemical oxygen masks will drop. In the cabin, the flight crew will pull out their oxygen masks, which are connected to pressurized oxygen canisters. The chemical generators will last for 10-15 minutes, but apparently the flight crew's oxygen supply will last for a couple of hours.

Why would the flight crew's supply last for so much longer? If the plane isn't at a breathable altitude after 30 minutes, it seems like it'd probably be unrecoverable, and the passengers will be in irreversible comas anyway.

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    $\begingroup$ Basically, if the passengers all pass out, it's not a huge deal. They will likely recover. If the pilots pass out, the plane is likely to crash - which is exactly what is thought to have happened with Helios Airways Flight 522. $\endgroup$
    – Keegan
    Oct 12, 2014 at 23:30
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    $\begingroup$ @KeeganMcCarthy as I mentioned in my post, the passengers can only recover up to a point. After about 30 minutes at cruising altitude, most will be in an irreversible coma. If the Helios 522 pilots had put their masks on, they would have had ample time to descend to a breathable altitude. $\endgroup$ Oct 12, 2014 at 23:34
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    $\begingroup$ I know that there was a lot more to Helios 522, but I was just giving an example of what can happen if a pilot doesn't have O2, vs passengers not having it. Has a plane ever been at cruising altitude for more than 30min without O2? I'm sure it CAN happen, but it is very unlikely. $\endgroup$
    – Keegan
    Oct 12, 2014 at 23:55
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    $\begingroup$ Helios 522, the pilots mistook a depressurization warning for a takeoff configuration warning. The master warning/caution went off (not sure which) after the oxygen masks dropped, but they thought it was for overheating systems. The pressurization was on manual after a test instead of auto and the pilots didn't know. $\endgroup$
    – ptgflyer
    Dec 25, 2014 at 16:54
  • $\begingroup$ @ptgflyer: Master caution. 737s don't have a master warning. $\endgroup$
    – Vikki
    Apr 2, 2023 at 23:07

2 Answers 2


The pilots also need to use oxygen in case of smoke, fumes, or fire in the aircraft. Thus, they need enough oxygen to be able to get down and land in a fire scenario, which is much more than a decompression!

Fire procedures have the crew on 100% oxygen at positive pressure to prevent them from breathing in smoke and fumes, while in a decompression, their masks mix oxygen with cabin air, in much the same way the cabin masks do. This is also why the cabin masks are not used in smoke/fumes scenarios.

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    $\begingroup$ In a fume event, the pilots may need to keep using oxygen until landing. There are routes with points almost 6 hours from nearest usable airport, so the aircraft that fly them have to have corresponding amount of oxygen for the flight crew. $\endgroup$
    – Jan Hudec
    Oct 12, 2014 at 10:05

Limited space and weight come into play. As well as the fact that sufficient air to keep one alive is not enough for peak performance. The masks for passengers are enough to keep the passengers alive during the descent to a survivable air pressure. Once there, the pilots will still want more oxygen so they can better deal with the emergency (and landing preparations).

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    $\begingroup$ Also ... AFAIK Pilots are required to wear an oxygen mask when alone in the cockpit (e.g. when co-pilot steps out of the cockpit for a moment) - So they probably use up oxygen routinely. Also the plane can survive passengers being woozy and unable to concentrate, by contrast, the plane is in jeopardy if pilots are anoxic. $\endgroup$ Oct 11, 2014 at 22:04
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    $\begingroup$ Also, during the cockpit preflight, the cockpit crew dons their oxygen mask to check for oxygen flow, which uses a little of the supply each time. In addition, some use oxygen as a "pick me up". When I saw that happening, I usually remarked, "Hard night last night?" $\endgroup$
    – Terry
    Oct 11, 2014 at 22:15
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    $\begingroup$ @RedGrittyBrick Isn't the requirement for that situation just that the mask automatically turns on flow in the event of a decompression? I don't think the mask actually has to be drawing from supplemental oxygen unless cabin pressure actually drops below a certain level. $\endgroup$
    – cpast
    Oct 12, 2014 at 1:37

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