Early reports of the plane being flown to 40K feet suggested everyone in the plane OTHER THAN possibly the captain (who has a better system of reserve air tanks to breath) would have been rendered unconscious and likely died within 5 minutes.
That would leave the captain to do as he pleased. Likely he sent the copilot out of the cabin and locked the door when he did this.
It is possible according to this that when power was cut to go dark the oxygen to the passengers/crew was cut at the same time. Those 7 minutes between 18:22 and 18:29 might be when everyone but the pilot succumbed to hypoxia.
Careful. Simply flying the plane to the upper limit of its service ceiling would not incapacitate anyone. Unless of course the cabin was deliberately depressurized, and the plane flown at altitude for long enough to deplete the oxygen generators for the cabin masks; then death follows shortly thereafter for those outside the cockpit.
The cockpit masks - the “rubber jungle” - are full face masks, not just nose cups, and are pressurized to PUSH air into the pilots’ lungs.
In the general cabin, the O2 generators just try hard to increase the O2 PPM to the point where you just MIGHT get enough 02 into your lungs to survive the emergency descent.
Thing is, at altitudes above 30-35,000 feet, the atmosphere is sooo thin, that even though the masks expel 02, there is little pressure to fill your lungs when your diaphragm tightens (ie you try to inhale). In a ‘normal’ depressurization in flight emergency, the pilot MUST descend to an altitude where there is enough ambient air pressure to fill your lungs. If indeed the cabin depressurized at 40K feet or so, hypoxia and suffocation would take less than 3 minutes once the cabin pressure dropped below about .5 atmospheres.
SO ... a sole pilot (or two pilots) could kill everyone but themselves via this method.
But sadly(?), the OCCAM’S RAZOR model points to a fire that screwed up a lot of systems serially.
Every advanced aircraft I've flown in the last 5 years (747's,777s,A380s,A330s) have had "sky phones" on them.In a scenario like the one you describe *someone* would have been able to call a relative...call *someone*...telling them what was happening.