You're not thinking of the RAF Phantom on approach to Alconbury are you? I think it was on a PD when the radar nose cone unlatched and swung open. The pilot wasn't able to control it (not unsurprisingly) and both crew safely ejected. What is so memorable about this one is that a 'spotter' sat in the undershoot, with a motor wind camera, caught everything on film. From this comes that unbelievable series of shots of the Phantom disintegrating bit by bit as it impacts mother earth.