Originally Posted by The_Jazz

And I think that point has been discredited above. Also, anything dropped from a plane would most likely be lethal if it hit you, unless that plane was flying into a severe headwind. Given the absense of wind, anything that qualifiies as a "plane" (i.e. not an ultralite) is going to be moving at a groundspeed of at least 110 mph (for a single engine in level flight). If a bullet (or more likely a nut from a screw) fell off of a plane and struck you on a windless day, the horizontal velocity would be enough to kill you if it struck your head. Clearly, wind will have a great effect on the object, but if the plane is flying with the wind, that effect will increase.