Have a mission with an empty MH-9 (also tested with a UH-80)
Ensure Advanced Flight Model is active
Get in as copilot
Take controls
Engine on
Release controls
Take controls
The game now runs at a very low framerate and sometimes the helicopter explodes while still on the ground.
Turning the engine off after these steps seems to have a higher chance of exploding the helicopter.
You can also reproduce it by changing the later steps:
Get in as copilot
Take controls
Engine on
Release controls
Get out
Get in as pilot