I made a falling pianos mod. It's quite horrible, actually, but it provides you with a model and some ideas for how to make them fall from the sky.
No collision model on the scenery object, just a model.
It would be really cool if you could swap a vehicle's model with the piano model and swap a weapon's projectile with the vehicle, then set the coordinates for the spawn point offset to x = 4, z = 4.
If you just switch the model of the vehicle, the map will crash. Any ideas on how to swap a vehicle's model without nulling the collision or physics? Apparently, I don't remember how to do this...
So eh, right now, try firing the AR and pistol. That is all.

Also, I could use a looping sound of some piano music or whatnot... the explosion effect should have a sound of a breaking/falling piano, and perhaps the falling sound could use that falling PDA satellite missile sound.
Download Falling Pianos