It wasn't the wing sweep rate as such which caused the mishap, as far as I could tell, it was a mis-setting of the CG control and frequent nuisance spurious Master Caution alerts for CG out of limit which were the prime factors. Also a stability augmentation system was trying to compensate until the departure, masking the unusual handling.
The CG had been manually set to a commanded value for the previous test point, but the system hadn't been returned to automatic before the subsequent test point. So the CG control was pumping fuel aft to maintain the previously commanded value when the wings were swept forward. When the Master Caution alerted them to the CG limit error, the LHS pilot would have difficulty in seeing the annunciator and perhaps assumed that it was another transient caution alert; the RHS pilot would have had even more difficulty in seeing it.
If they'd been much, much higher and had sufficient time to raise the landing gear, retract the flaps and slats and sweep the wings aft to a value for which the commanded CG was safe, things might have turned out differently perhaps. But the airspeed was very low by then and the AoA was very high; even with 4 x 30000 lb of thrust available recovery was unlikely to be achievable.
An excellent lecture and something which anyone involved in flight test work should view. I know of one fatal accident in an airliner where a maintenance test pilot tried to rush an acceptance test and didn't stick to the required height, speed and config. points and another serious accident where the fin and tailplane were nearly lost after a test pilot decided to combine 2 test points to save time....
Last edited by BEagle; 2nd Feb 2021 at 23:09.