I was reading reports [1,2,3,4] about a recent Air China flight where one of the pilots was allegedly smoking and, in an effort to prevent the smoke circulating to the cabin, accidentally de-pressurised the aircraft. The passenger oxygen masks were deployed and the crew performed an emergency descent. Eventually the problem was rectified and, after the cabin re-pressurised, the plane climbed again and completed the flight.

The bolded parts of this story are what I'm asking about. If the oxygen masks have been deployed and the plane returns to cruising altitude, then there is no supplementary oxygen available for passengers in the event of a second de-pressurisation incident. This seems unsafe. (I recall reading that the oxygen supply only lasts 12 minutes and is intended only to last for the duration of an emergency descent.)

What are the rules around this situation? Can an aircraft safely/legally climb again after passenger oxygen masks have been deployed?

  • $\begingroup$ There is no definite answer that I can find as the entire topic is debatable $\endgroup$
    – Super
    Jul 14, 2018 at 0:43
  • 2
    $\begingroup$ Why the downvote? @FallenUser given how procedure-oriented commercial aviation is, I would be surprised if there is no answer to this question. $\endgroup$
    – Thomas
    Jul 14, 2018 at 1:43
  • $\begingroup$ Well, guess what! There are 2 answers right now! $\endgroup$
    – Super
    Jul 14, 2018 at 14:42

2 Answers 2


Once the masks have deployed and any of them have been activated, you no longer have an emergency oxygen supply for all the passengers. Not having that, going above FL250 (may vary in jurisdictions besides the FAA) is not allowed. Up to 250, emergency O2 isn't required for the passengers, since you could descend quickly enough to a safe altitude in the event of a depressurization. Above that, though, having the masks available (and no, hanging down doesn't quite count) is required, both for legality and for safety.

To climb back up to a cruise altitude in the 30's is a pretty significant misjudgement, given the facts as they've been presented to date (which may have significant mistakes in the reporting). Up there with depressurizing the aircraft when you meant to turn off the Recirc fan. Or vaping in the cockpit. Or allowing vaping in the cockpit. Or not turning the packs back on immediately when your FO has incorrectly turned them off.

Sometimes you just have a bad day. And then there are some people who need to switch career paths, because they aren't cut out for the one they're in. We all have our own opinions about what the case is here...


No you wouldn't be able to legally climb above 10000ft once the masks have deployed, not even in China. There are a bit behind on Crew Resource Management theory and occasionally, wild and crazy things can happen there, although the CAAC is doing its best to crack down as the article shows.

One problem however is that in the zeal of the authorities to achieve western standards, they have an extremely punitive enforcement regime, both on the pilot and maintenance side, which creates very powerful incentives to hide mistakes. Similar problem in Russia.

  • 3
    $\begingroup$ can you please provide sources for the first statement? $\endgroup$
    – Federico
    Jul 13, 2018 at 21:11
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    $\begingroup$ Hmmm.. what if there was insufficient fuel for nearest-runway diversion at 10000? Could that be an issue on ocean flights? $\endgroup$ Jul 13, 2018 at 21:12
  • $\begingroup$ @Federico Check out the website onemileatatime.boardingarea.com/2018/07/13/…. You might have missed what it said $\endgroup$
    – Super
    Jul 13, 2018 at 22:16
  • $\begingroup$ @MartinJames Fuel planning regulations are in place to cover this case for ETOPS flights (i.e. long overwater/“over-uninhabited-area” flights) - if the normal trip fuel is not enough for diversion after cabin decompression, additional “decompression fuel” is carried. $\endgroup$ Jul 13, 2018 at 22:24
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    $\begingroup$ @FallenUser The "10,000 feet" statement is sourced in the cited article as coming from "a reader's comment" and it's arguably wrong. Up to 24,000' without an emergency O2 source for the passengers is okay. (Not that it's a great plan with the masks all hanging like that.) $\endgroup$
    – Ralph J
    Jul 14, 2018 at 3:54

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