Coasting out from Cap Gris Nez (in a PA28 with roof windows) having come up from Le Touquet. The other aircraft, going in the opposite direction, was close enough for me to feel, hear and see it flashing just over my head. I didn't see it coming and afterwards, I couldn't see a trace of where it had gone. I was just left with immense shock and a memory that is is still with me, crystal clear, thirty years later.