On Wednesday, April 1, 2015 at 1:38:13 AM UTC+13, Martin Gregorie wrote:
However, Don's reference to MH370 and one of the causes that has been put
forward for that crash does suggest a more benign reason for the A320's
altitude change: if the pilot became anoxic, realised a bit too late and
lost conciousness while he was lowering the cruise altitude, mis-setting
it as a result.

It would be a big mystery how the young guy in the cockpit was anoxic (and just happened to misset the autopilot AND lock the door), while the older guy in the passenger cabin was perfectly ok and demanding to be let back in.

As for MH370 .. as I recall it turned back, descended, flew low over the mainland, and then climbed back to a normal cruise altitude, while starting to follow a precise route via 3 or 4 standard navigation points (that had NOTHING to do with their route), until it was out of radar range, when it (supposedly) turned to the southern Indian Ocean and oblivion.

That's a heck of a lot of carefully coordinated seemingly purposeful things for a hypoxic pilot to do accidentally. Boggles the mind, it does.