"Gearbox failure due to overtorque"
Zantop had a gearbox failure on an Electra in the cruise due to fatigue. The Prop and most of the gearbox came off and ended up in a tree in upstate New York. The only airframe damage was a slight nick on the stab. Lucky guys.
This may be related to over torque events.
Just after this event I was training on the Electra with Zantop and we were doing circuits at Lincoln Nebraska. The temp was about 10 degrees F (-12C). Doing a 3 engine GA the PF fire walled the power levers and and kept his hand on them preventing me from pulling them back to limit the HP to 4000. I saw about 4500HP. I don't think this was written up in the log.
There were several other gearbox events on this type of engine over the years.
When the Electra was put on the UK register the CAA required new gearbox casings to be fitted as there was no record of the number of cycles they had done as they were zeroed lifed at each overhaul.