The fate of 32-year-old Captain Craig Button and his A-10 jet has mystified experts and fascinated the American public ever since it was reported that he appeared to have left his three-aircraft formation deliberately, heading north and east, straight for the Rockie Mountains.
Despite the mobilisation of U2 spy-planes and Awacs reconnaissance aircraft neither the jet nor its pilot, nor any wreckage, has yet been found.
In a detailed briefing, a spokesman for the Pentagon traced the pilot's route, quoting telephone calls made by members of the public, logged according to time and place. These suggested that the pilot had set a direct course until reaching the higher peaks of the Rockies, then effected two zigzags.
Several reports spoke of an explosion heard in the vicinity of Vail, Colorado, around the time the aircraft's fuel would have run out. As the Air Force stepped up its search yesterday, officials said progress was being made, but stressed the difficulties of the search in an area where there has been heavy snowfall.
The disappearance of Capt Button, a career officer whose one ambition is said to have been to become a fighter pilot, has prompted speculation. There has been talk of abduction byaliens. Another theory was that Button might have been trying to deliver the aircraft - and its four bombs - to one of American's fringe militia groups.
A more earthly working hypothesis is that Capt Button was depressed and may have committed suicide. But the pilot's parents and family friends have taken pains to contest this view.
For the Air Force, a worrying fact - described as "highly unusual" - is that a trainee fighter pilot and his aircraft can disappear so totally for so long.