That only happens with Mi-48 Kajman.
Mods: Midrange Terrain Texture Replacement; CBA; HRP.
One time it happened when I was inside (pilot) and closed my map (engine was off) (I was pressing "Shift" while in map)
One time it happened when I landed the Kajman on Airstation Mike and repaired the engine, then started the engine and it crashed. (at EUTW server)
*In all these situations there was no rocks under landing gear, only thing there could be is the soldiers (I'm not sure about)
Not sure - sometimes or random
Maybe it can happen in the editor.