I am unable to reproduce the issue offline using the editor however it does occur online because I guess desync issues are what causing players to glitch outside the helicopter.
1. Go to an online server
1a. Leave the server running until server fps degrades towards unplayability; this is indicated by AI starting to lag (moonwalking, warping)
2. Get into any transport helicopter
3. Load up a few player passengers (I have had it occur with a minimum of 2 passengers)
4. Start up the helicopter
5. If any of the passengers are glitching and appear to be outside the chopper while actually sitting inside they will collide with the main rotor and destroy it. The player themselves will be unhurt from the collision (but will probably die from the chopper crash)