the popular theory was that the F104 got caught in the wing vortex of the XB-70
Data from North American and independent calculations made by NASA to determine the energy of the wake vortex flow around the XB-70 wingtip revealed similar results. They indicated that within about eight feet of the XB-70 wingtip, the vortex energy was such that it would equal the F-104's full roll control at the same airspeed. Once the horizontal tail of the F-104 came up under the wingtip of the XB-70, it became pinned by the wingtip vortex from the XB-70. The F-104 lost its trim and pitched up violently, rolling inverted across the top of the XB-70. The accident board concluded that the swirling wake vortex only became a contributory factor in the accident after the F-104's tail was so close to the XB-70 that a collision was imminent.
After searching for F-104 wreckage in the desert (especially for the upper surface of the left tip of the horizontal stabilizer) in the days after the accident, this part of the horizontal stabilizer was found. A careful study of this stabilizer fragment was made. On the top outer edge was an imprint of the XB-70's right wingtip position light.
Thankyou Green-dot and tdracer for putting things straight.
In a better world, with better planning, briefing, training, and authority gradient,
perhaps the F104 pilot would have said: "No! this is too dangerous. I'm backing off."
Possibly before takeoff.
Thanks and well said . . . . in hind sight. But on the day of this accident, the pilot flying chase in the F-104 was the Chief test pilot for NASA and was slated to start flying the XB-70 himself on June 10th '66 (accident date was June 8th '66). The USAF XB-70 program was coming to an end with all the goals set out for the aircraft accomplished. NASA was about to get more involved in the program for further SST research and the aircraft had already been modified with additional instrumentation for this program. Therefore, the F-104 chase pilot had a good reason to be in the air as he was close to flying the XB-70 himself.
The accident XB-70 (A/V-2) was best suited for the NASA program as it was an improved version compared to the first prototype (A/V-1) which was restricted to M 2.6 due to skin panel separation as a result of a steep learning curve during construction and poor quality control. This issue and many others were corrected during construction of A/V-2.