I vaguely remember a story I read about an Italian (?) Military jet aerobatic team doing a show in very poor vis. One of the solo's saw a flash and the next millisecond second he is being blasted upwards in his ejection seat. His helmet had a slight groove which was later determined to be from the bottom of the tail skid of the other aircraft involved in the head on mid-air. The skid went through the canopy, creased his helmet and then pulled out the ejection handles at the top of the seat. The pilot reported he never saw the other aircraft and had the hit been a half inch lower it would have ended very badly for the him.