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Helios Flight 522 crashed when the crew unknowingly suffered hypoxia. Although the masks in the passenger cabin deployed, the crew were unaware of this and didn't realise the extent of the problem.

If I was a passenger on a plane at cruise altitude and the oxygen masks deployed, I know that there is only about 10 minutes oxygen available. I would expect the plane to immediately descend to a lower altitude.

If I don't notice any change in attitude and there is no passenger announcement after a few minutes, would it help to alert a flight attendant to check that the pilots are aware of the issue? Or would it be best to assume that 'they know what they are doing' and just keep quiet?

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    $\begingroup$ Well, the purser was more knowledgeable than a passenger would and he failed to save the plane… $\endgroup$
    – Jan Hudec
    Commented Mar 29, 2017 at 18:16

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It's never bad to inform a crew member about anything you think may be abnormal.

In this special situation, as you know that the oxygen masks deploy automatically if the cabin altitude raises to high, you expect the aircraft to descend in order to allow the pax to breathe normally again. If this doesn't happen it would be possible that the crew deployed the masks manually for no reason or the automatism faulty detected a low cabin pressure. In both cases I would expect an announcement that the oxygen masks are not needed and can be put down safely.

If neither of those options happens something is definitely wrong. Either the pilots already suffered hypoxia or they didn't notice the passenger masks drop at all. In my opinion the cabin crew should be trained to know what's normal procedure if masks drop, but I would definitely tell a flight attendant about my concerns if nothing happens after two minutes or so.

You always have to remember: In high altitudes you become unconscious after less than 30 secs without the mask, and as the masks can only produce a limited amount of oxygen it's a really time critical issue to reach the flight-deck and initiate a descend if the pilots are already out of service!

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    $\begingroup$ I believe the cabin crew has mobile oxygen tanks with masks which would allow people to move around whilst still be able to breathe. $\endgroup$
    – ROIMaison
    Commented Mar 28, 2017 at 11:28
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    $\begingroup$ You don't die! Not that fast, really. You become unusably dizzy and incapable of thinking. You become unable to realize that you should put on the mask. But you really don't die that fast. $\endgroup$
    – Vladimir F Героям слава
    Commented Mar 28, 2017 at 11:38
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    $\begingroup$ Can you actually do anything about it these days though? I thought that since the reinforced doors you can't get into the pilots cabin unless they let you in so if they are both out of commission you're SOL? $\endgroup$
    – DRF
    Commented Mar 28, 2017 at 11:51
  • $\begingroup$ What I was trying to say is that they didn't notice that the pax oxygen masks dropped (automatically or faulty) and therefor do not react via an announcement $\endgroup$
    – pcfreakxx
    Commented Mar 28, 2017 at 13:14
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    $\begingroup$ @njzk2 - you cannot hold your breath. You need to exhale. Pressure outside of your body is so low that your lungs might be damaged [citation needed]. $\endgroup$
    – Peter M. - stands for Monica
    Commented Mar 28, 2017 at 14:19
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First and foremost you should read the accident report which you can find in full here. I will pull some excerpts from that below.

Helios Flight 522 crashed when the crew unknowingly suffered hypoxia. Although the masks in the passenger cabin deployed, the crew were unaware of this and didn't realize the extent of the problem.

This is the one of the debated/interesting aspects of the accident. The crew would have been alerted by alarms to the depressurization event

...Non-identification of the warnings and the reasons for the activation of the warnings (Cabin Altitude Warning Horn, Passenger Oxygen Masks Deployment indication, Master Caution).

Many might say they did in fact know there was a problem but for some unknown reason they did nothing about it. Generally speaking "Don Oxygen Masks" is the first item on the emergency checklist following the mishap of the South Dakota LearJet crash in 1999. One can conclude from the report that its possible the pilots assumed the cabin pressure system was in the proper place (auto) when in fact it was set to manual (MAN) and subsequently were confused by the alarm or thought it was faulty.

...that the following factors could have contributed to the accident: omission of returning the cabin pressurization mode selector to the AUTO position after non-scheduled maintenance on the aircraft;

This is a procedural failure on the implementation end. The report would cite bad procedures for this

...the report also identifies a number of additional safety deficiencies pertaining to: maintenance procedures; pilot training, normal and emergency procedures; organizational issues of the Operator; organizational issues related to safety oversight of maintenance and flight operations by Cyprus DCA, EASA/JAA and ICAO; issues related to the aircraft manufacturer’s documentation for maintenance and flight operations;

If I was a passenger on a plane at cruise altitude and the oxygen masks deployed, I know that there is only about 10 minutes oxygen available. I would expect the plane to immediately descend to a lower altitude.

There are some assumptions here of course first and foremost that the plane is still maneuverable. There are any number of things that could cause a depressurization and some may also cause flight control issues as we saw Aloha Airlines Flight 243 a situation where the crew did not immediately know what was going on. However generally speaking, once the issue has been identified the plane should start a decent if possible.

If I don't notice any change in attitude and there is no passenger announcement after a few minutes, would it help to alert a flight attendant to check that the pilots are aware of the issue? Or would it be best to assume that 'they know what they are doing' and just keep quiet?

This of course brings up another debate. In almost all cases you should alert the crew to anything you feel is strange our out of place. Of course in this instance it may be hard to move about the cabin, and potentially hard to shout or get your message to the crew. In some cases the crew may be working the issue and getting in the way of that can be problematic. Again generally alerting them is a good thing but its a situation by situation basis for sure.

In regards to the comments on other answers you will not die, at least one flight attendant (who was also a pilot) survived the ordeal and made his way into the cockpit as was heard on the CVR

At 08:54:18 h, the following distress was recorded by the CVR “MAYDAY, MAYDAY, MAYDAY, Helios Airways Flight 522 Athens … (unintelligible word)”. A few seconds later, another “MAYDAY, MAYDAY” with a very weak voice was recorded.When the Boeing 737 was at about 7 000 ft, the person in the Captain’s seat for the first time appeared to acknowledge the presence of the F-16s and he made a hand motion.

Could a knowledgeable passenger have saved Helios Flight 522?

Unlikely as these days its hard to get in the cockpit, or even get a message to the pilots. But you should, in any event at least try. This saved some lives on Air Florida 90 when a passenger realized icing on the wings and assumed the crash position and informed the other around him.

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    $\begingroup$ The pilot did not regain conciousness, it was a flight attendant named Andreas Prodromou with a commercial pilots license (not rated for that aircraft) that was sitting in the pilots seat. $\endgroup$
    – Ron Beyer
    Commented Mar 28, 2017 at 19:05
  • $\begingroup$ interesting, ill remove that section. $\endgroup$
    – Dave
    Commented Mar 28, 2017 at 19:06
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It seems from the Wikipedia page that there was indeed an knowledgeable passenger. Not fully qualified, but ...

At 11:49, flight attendant Andreas Prodromou entered the cockpit and sat down in the captain's seat, having remained conscious by using a portable oxygen supply. Prodromou held a UK Commercial Pilot License, but was not qualified to fly the Boeing 737. Crash investigators concluded that Prodromou's experience was insufficient for him to gain control of the aircraft under the circumstances. Prodromou waved at the F16s very briefly, but almost as soon as he entered the cockpit, the left engine flamed out due to fuel exhaustion and the plane left the holding pattern and started to descend. Ten minutes after the loss of power from the left engine, the right engine also flamed out, and just before 12:04 the aircraft crashed into hills near Grammatiko.

So depending on how knowledgeable you're looking for, this seems pretty clear-cut.

https://en.wikipedia.org/wiki/Helios_Airways_Flight_522

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  • $\begingroup$ I agree that he was a pilot, but why did he wait until the fuel was exhausted before entering the cockpit? Maybe he didn't know that he should act quickly? $\endgroup$
    – David Glickman
    Commented Mar 28, 2017 at 16:02
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    $\begingroup$ @David Glickman The CVR only recorded the last 30 min of the flight and the F16 intercept did not arrive until 2 hours after the last contact with the pilots. So we don't know what the cabin crew may have done during that period of time. The FDR does not register the operation of the intercom or the cockpit door. It's quite possible the FA's may have tried to call the pilots or entered the cockpit earlier. They may have tried calling ATC for help. The report says that when the FA tried to call mayday it did not go out over VHF, so he was probably not familiar with how to operate the radio. $\endgroup$
    – TomMcW
    Commented Mar 29, 2017 at 5:43

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