[Cap'n Wannabe]

I am very curious as to whether Mr Quartermain was suffering a medical event during the takeoff. Medical events are not necessarily flick the switch and the lights go out - they can sneak up on you very gradually. So gradually that you don't notice. Or your girlfriend doesn't notice.
When you suffer an emergency in an aircraft, there are certain drill you follow, depending on the nature of the emergency, and when it occurs. If Mr Quatermain was suffering say a neurological episode, those drills could well have flown out the window.
IMO, it could explain the panicked Mayday calls..