In terms of written communication from passengers on the plane to people down below -- e-mail, text messages sent from cell phones, social network posts -- the more the better.

CNN: Cell phones on planes? For texting, not gabbing

The altitude at which the co-pilot handed control of the plane to his colleague was below the minimum altitude considered safe to continue final descent.

CNN: Pilot training blamed for Bali airliner crash

Cypriot Transport Minister Haris Thrassou has denied reports of 48 children being aboard the plane, telling Reuters the number of people below the age of 20 was "between 15 and 20".

BBC: A plane's tail fin after crashing near Athens

Ms Vulovic plummeted 33, 000 feet in the tail section of the plane to the snowy slopes of the Czech Republic below.

BBC: NEWS | UK | Magazine | Can you survive a plane crash?

Harten said he lost radio contact with Flight 1549 and the plane disappeared from his radar screen as it dropped below New York's skyscrapers.

CNN: Controller thought Hudson landing would be 'death sentence'

There are also varying guidelines about how many hours of training pilots must complete, below what altitude they should not hand over control of a plane and when they should abort landings.

BBC: How human error can cause a plane crash