As Paul Harvey says "Now for the rest of the Story"
George J. Hansen, Advanced HQ, 8th AF in Brussels sent a crew out to investigate the mysterious aircraft. On checking the plane's serial number , he learned that it had come from the 91st Bombardment Group and that the crew was already save in England.
What had happened was that the plane, on a mission to Merseburg oil targets, developed trouble just before reaching the target area. The plane was not able to climb with the rest of the group and , in addition, was plagued with a malfunction of the bomb racks. Then a direct hit knocked out No 3 engine and another filled the center of the plane with a tremendous flash. "We had been hit in the bomb bay", pilot Harold DeBolt reported later "and I'll be darned if I know why the bombs didnt explode."
With one propeller windmilling and the weather closing in, Debolt headed for England and the changed his mind, for the plane was obviously not going to make it back to East Anglia. He then pointed the B-17 towards Brussels and ordered all loose equipment jettisoned to lighten the load. It was then that two engines quit. Setting the B-17 on autopilot, DeBolt ordered the crew to bail out, leaving the plane last.
All landed safely - and so did their stricken B-17. What had undoubtedly happened was that after the crew jumped, with justification as far as they could discern, the trouble in the engines cleared up and the beautifully designed, stable B-17 flew itself. Its malfunctioning engines, however would not keep it up and it simply came down as described by John Crisp. To his uneducated eye the plane appeared undamaged and what he thought were the crew's parachutes were probably extra chute packs.
Throughout the war there were other reports of B-17s which continued to fly though pilotless, but the Phantom Fortress was the only one that succeeded in landing more or less intact.
(remember this was written before 1965)