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If the pilots, crew and passengers had all passed out from an unexplained result of gradual de-pressurization, and ground personnel were somehow aware of this scenario, would there have been anything that could of been done to save the plane and people before the fuel ran out?

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No. If the crew and passengers have all passed out due to lack of oxygen and the plane has not been commanded for a descent, they will never wake up. This has happened before, e.g. the Payne Stewart fatal accident. In cruise flight an autopilot is only commanded to perform lateral navigation and absent instructions from the crew to initiate a descent it will fly to its last fix and then maintain its current heading, all the while maintaining altitude. When fuel is exhausted it will maintain altitude at the expense of airspeed until the stick shaker activates, disconnecting the autopilot. Absent the pilots input, the stick pusher should next activate to forcefully prevent a stall. You'll probably get some oscillations in pitch but ultimately a steep descent that even if the (literally) brain dead crew could somehow wake would not give them time to act.

While ground crews can get data from the airplane and can attempt to contact the crew, they cannot remotely control the airplane so the best they could do, if aware, is watch. They could perhaps get a fighter scrambles to intercept and visually inspect the cockpit, but that still would not allow them to alter the outcome (just verify the scenario).

Note that this scenario is much more likely to happen in an extreme depressurization event in which the crew is unable to don O2 masks in time. A slow gradual depressurization will give plenty of warning as the cabin begins to climb and automated sensors start complaining. In the EMB-145 you'll start getting aural warnings when the cabin exceeds 10,000 ft pressure altitude and somewhere shortly above that you'll get master caution alarms and automatic pax 02 deployment. These altitudes should give the crew ample warning before becoming hypoxic (you can reach these altitudes for limited time with no supplemental O2 in a Cessna 172 for example). Even at cruise, it only takes a few minutes to get the plane back down to 10,000 ft and as such a slow gradual depressurization should not pose a threat unless multiple warning systems are malfunctioning.

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    $\begingroup$ You beat me to the Payne Stewart example by three minutes. $\endgroup$ – Steve V. Mar 25 '14 at 1:38
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    $\begingroup$ I'd be more worried about a slow depressurization event than a fast one. If the roof of the airplane rips off or something, your blood is still fully oxygenated and you know what to do with the mask hanging in front of you. With a slow depressurization, your blood will be deoxygenated to the 12000-foot level, your thinking will be foggy around the edges, and there's a risk you'll be fixated on a task and ignore your mask for too long. $\endgroup$ – Mark Mar 25 '14 at 5:07
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    $\begingroup$ Another example is Helios 522 a 737 with incorrect pressurization settings that flew for several hours with an unconscious crew before crashing. A flight attendant eventually gained access to the cockpit just as fuel ran out. $\endgroup$ – RedGrittyBrick Mar 25 '14 at 11:44
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    $\begingroup$ @Mark I still don't buy it. An extreme depressurization may start off with oxygenated blood but you may only have 30 seconds to react. With a slow depressurization you have to listen to audible warnings, master warnings, ignore EICAS information for however long it takes to become hypoxic before it is too late. The plane I'm familiar with will start yelling at you at 10000 ft cabin altitude. You have a much longer window of opportunity to act in the slow leak case. $\endgroup$ – casey Mar 25 '14 at 15:10
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    $\begingroup$ @casey: Just go and look up report of the Helios 522. They had warning, didn't recognize it, even called dispatch, but by the time maintenance realized what the warning was, the pilots were too confused to carry out the instructions. $\endgroup$ – Jan Hudec Mar 25 '14 at 22:15

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