If it was on the ground you could get the distance from the centre of the plane (the position gained by getPos), and the direction the plane is facing, compare the two with some fancy mathmatics which I am absolutely no good at whatsoever, the compare that to the getPos of the nearest man object or defined unit, and if it's close enough run a setdammage and perhaps a little bit of setVelocity for eyecandy.
Would all be in the math.. which ofcourse I'm no good at :p
**edit**
although, again, with a small config edit of the unit you could add a cargo position on the rotor and fill it with a gamelogic (could be done inside the addon automatically so the player can't forget to add them)
I think these kind of faked cargo positions would be a very god idea for future addons, and could add quite a bit of realism to the game. A few times I've had my helo rotors go through an opponent and wished for them to be cut to shreds by them.