Compressor stall, I first did UPRT in the 90's and it was going through the industry. It was in response to the two 737 rudder hardovers. The theory being that airline pilots were not trained to deal with sudden unexpected changes in attitude and needed to be more aggressive in their handling of the aircraft. The pilots on the FBW aircraft in the fleet did not have to do this training as it was assumed that the protections on that aircraft would prevent it from ever requiring the pilots to undergo UPRT. So now we have gone full circle. EBT and UPRT does not prepare you for an aircraft that has a design flaw and requires the reflexes and the thought processes of a test pilot to recover from its software malfunctions.