Re the poster who stated that 'aircraft do not drop out of the cruise, with no calls etc. unless a catastrophic failure or something sinister' -
Actually, they sometimes do.
AF 447, Air Asia 8501, and Air Algerie (MD-83) are three recent examples.
The crew was far too busy "Aviating" (or trying to) -- to be bothered with step 3 "Communicate"
Unless a flight crew gets the plane back under control, there isn't much point sending a mayday call. There will be no one to rescue.
(Air professionals all know this, but others reading this thread today may not).