If you have an emergency that requires immediate descent and you are over a large expanse of water with the nearest airport directly in front of you, why do you say the general rule is to first make a 90 degree right turn that takes you further away from land and the nearest airport?
I'm not a pilot, but if my radio was out and I knew I was on someone's radar screen, I might turn just to get someone's attention. Kind of a non-verbal distress call?
Of course, if the plane came apart in mid-air, pieces of it might fly off in any and all direction...
BBC had a aviation expert on, who said if your priority was to get rapid descent (losing cabin pressure), you’d make the 90-degree turn....which is exactly what the Egypt radar guys say they did. Because they never did radio contact....I think they lost full functionality on comms when this whole thing started up.