A common gearbox design of the Puma family is that the annular gear is part of the gearbox housing. This breaks, so does the gearbox, leading to the rotor assembly leaving the aircraft as the stabilising struts are not strong enough to retain it.
All gearboxes need to be redesigned so that there is a failure path which would stop at the annular gear. You will lose your drive but you are still alive and have some control over where the aircraft is going.
Should you lose the main drive in the gearbox in a Puma remember NOT to shut down the engines in the autorotation or you will lose your hydraulics and alternators. The electric pump cannot cope with the rotor control.
Last edited by Fareastdriver; 10th Nov 2017 at 12:31.