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I've noticed some strange inconsistencies regarding the documentation of Helios Airways Flight 522.

So first:

Autopsies on the crash victims showed that all were alive at the time of impact

But then:

The emergency oxygen supply in the passenger cabin of this model of Boeing 737 is provided by chemical generators that provide enough oxygen, through breathing masks, to sustain consciousness for about 12 minutes

So, the oxygen masks in the passenger cabin automatically deployed at 18,000 feet, probably around 09:20. The aircraft did not impact until 12:04. 2 hours, 44 minutes later. Obviously the oxygen masks didn't keep them alive for that long, so:

How could they have survived so long?

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    $\begingroup$ I think you are confusing "alive" with "conscious". $\endgroup$
    – Giacomo Catenazzi
    Feb 7, 2018 at 11:19
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    $\begingroup$ "If there is no oxygen": There is oxygen, the same percentage as at sea level, but at lower pressure. This allows to use air from the outside to breath in the cabin, after compressing it. $\endgroup$
    – mins
    Feb 7, 2018 at 13:18
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    $\begingroup$ While the aircraft continued to climb well above 18,000 feet, it is worth mentioning that The Death Zone is above 8km/26k feet. A moderately healthy and fit individual should be able to maintain consciousness below that altitude, and a very fit individual could possibly stay conscious up to the cruise altitude of 34,000 feet as on that flight, given the lack of heavy mountain climbing gear and likely less brutal cold in the cabin. But yes, most people will pass out by then. $\endgroup$
    – user3305
    Feb 7, 2018 at 21:02
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    $\begingroup$ @Snowman I think you are looking at climbing data. These levels are assuming acclimatisation, $\endgroup$
    – RoyC
    Feb 8, 2018 at 11:54
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    $\begingroup$ Hence the advice drummed into pilots during training: get your mask on first, deal with everything else afterwards. At an airline I worked for, every single flight saw the pilots test the mask oxygen flow, and practice putting the mask on quickly. Not sure if this is universally done though. $\endgroup$
    – Pete855217
    Mar 13, 2019 at 15:02

3 Answers 3

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To add to Daniele's answer, from the final report:

The forensic report concluded that the aircraft occupants had heart function during the impact. The report noted that this did not necessarily imply that they were alert. The report further estimated that they were in deep non-reversible coma due to their prolonged exposure (over 2.5 h) to the high hypoxic environment.

So, again, saying that they were alive does not mean that they were well.

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    $\begingroup$ That must've been quite the morbid scene, an entire airliner seated full of comatose or brain-dead, but still alive, individuals. $\endgroup$
    – Nils Guillermin
    Feb 7, 2018 at 21:26
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    $\begingroup$ @NilsGuillermin If it's any consolation at least it means they didn't suffer. $\endgroup$
    – Dai
    Feb 7, 2018 at 23:56
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    $\begingroup$ I wonder how exactly one can determine if someone's was alive at the time of impact? $\endgroup$
    – ebrohman
    Feb 8, 2018 at 2:16
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    $\begingroup$ Physiological reactions prior to death leave different results from postmortem trauma. @ebrohman $\endgroup$
    – Nij
    Feb 8, 2018 at 5:11
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    $\begingroup$ It's science of autopsy. You can tell whether someone was dead then was frozen, or someone was frozen, then died because of the cold. Injuries affect a dead person differently than a live person. $\endgroup$
    – Nelson
    Feb 8, 2018 at 5:54
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Consciousness requires quite a bit more oxygen than merely being alive.

Human beings can last remarkably long with very little oxygen, but not remain conscious. And lack of oxygen will soon enough cause permanent damage.

The passengers may have been alive, even if they were not conscious, but they could have been anything from temporarily incapacitated to on the way to certain death by the oxygen starvation, even if they somehow had been rescued before the crash.

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    $\begingroup$ A body can go ~5 minutes without air before irreversible brain damage occurs. But a damaged brain can still keep the body "alive" - at least alive enough for the autopsy to detect them as such at the time of the crash. And that is total oxygen denial. In high altitude, some oxygen is still present. Not a vacuum. $\endgroup$
    – Mindwin Remember Monica
    Feb 8, 2018 at 17:36
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Here is a list of those people who survived as stowaway in the unpressurized and extremely cold wheel well.

On June 19, 2015 an unidentified male who was 24 years old survived 11(!!) hours in the wheel weel of British Airways Flight 54 from Johannesburg to London. As you also see, this is incredible because as you suggested most of the people simply die.

Another surviving victim without permanent damage was paraglider Ewa Wiśnierska, who survived half an hour long in a thunderstorm cloud at a height of nearly 10 000 m (33 000 feet).

You must also be aware that the passengers breathed pure oxygen allowing the oxygen supply to enter the blood and increase the level in the organs before they passed out, so the permanent effects of hypoxia may be delayed.

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    $\begingroup$ The cold actually lower the oxygen consumptions. Childs have been known to remain UNDER water at frigid temperatures for long periods of time before being revived without any permanent damage. $\endgroup$
    – Antzi
    Feb 8, 2018 at 7:20

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