I've been looking at a lot of photographs of the crash site, and it appears to me that the B-17 was mostly airborne when it hit the de-icing facility ground storage tank. Looking at the photo below, note the "box" of the box truck closest to the crash site. There appears to be a gash just below the roof of the "box", yet the truck cab is unscathed. The right side of the "box" is gone, and the rear is displaced aft at its right side. Other photos show a lack of skid marks on the taxi way immediately in front of the crash site. As shown in previous photos posted in this thread, one of the plane's engines went into a building some distance from the crash site itself. This was a high energy impact.
It would be interesting to see an aerial photo of the initial touchdown point (reportedly 1,000 ft. short of Rwy 06) and the tire marks through the grass, to determine, if at some point, the tire marks disappear, indicating the aircraft had become airborne at that point. If the pilots were attempting to bring the aircraft to a stop, I would think that the impact would have been much less violent than it was. Wild-guessing at a touchdown speed of around 80-85 kt., significant speed should have been bled in the approximately 2,000 ft. (straight line distance) between the point of touchdown and the point of impact.
That's just my theory, and probably incorrect at that.
Regards,
Grog
