The destructive pressure test has been completed and we hit our engineering numbers almost perfectly.
This test was testing for the worst possible conditions expected in flight. 2000 pounds of lead were loaded onto the seats to simulate the weight of the pilots multiplied by 6 Gs of acceleration. Then the pressure was increased to the maximum expected in flight: the fuselage held the strain. Then the pressure was increased to the safety blowoff-valve pressure: it still held.
So we know it is going to be safe to fly but do we know if it’s over-engineered? We need to keep weight to an absolute minimum so we shouldn’t have any more carbon fibre than we actually need for safety. So we keep increasing the pressure…
The design goal was 25.5 psi. In the end, the pressure bulkhead failed at 25.0 psi. This is almost three times the maximum pressure that could ever occur in flight, even with multiple failures of the pressurisation system and the failure of the pilots to notice that something was wrong. The force on the hatches trying to eject them from the cockpit was more than 9000 pounds on each hatch. That means that each hatch can hold more than four times the weight of the fully-loaded aircraft.