One in service "test flight" that went badly was a 727 flown about 35 years ago by a fellow named Hoot Gibson. Hoot decided that he could deploy a litte flaps at cruise to achieve a higher altitude. The 27's did have locks on the leading edge devices, but guess what? Hoot just unlocked them! The result was much the same as the 37 real test flight. Hoot took a 30,000 foot spiral dive. Initial press reports extolled his hero flying skills, but when the facts were known he was unemployed.
This incident involved TWA Flight 841, a 727-100 on April 4 1979. The number seven leading edge slat extended in flight at altitude. The crew was accused of "cracking" the flaps - following an "urban myth" on increasing performance at altitude. This was denied by the entire crew, under oath. No crew could ever be found to have actually attempted the procedure, and when tested it was shown that performance immediately and markedly deteriorated (as you would expect, or Boeing would sell the aircraft with drooping flaps!).
While the slat is held shut by hydraulic pressure, and a mechanical lock, fracture of the actuating piston could cause a separation, however the suspect parts were never recovered. Boeing issued an AD strengthening the area in 1973, prior to this there were fifteen instances of uncommanded slat deployment. After the AD, and up to the accident there were a further two slat deployments, one from a failure of the slat actuator support fitting.
The CVR on the aircraft was found to be erased after the aircraft landed, however it was proven that this was impossible to achieve from the cockpit, as the landing gear squat switches were damaged in the event, and CVR erasure requires a safe gear indication (i.e. three greens, and the aircraft landed with three reds).
On balance, Captain Gibson most probably
was a hero, and regardless it
was his excellent flying skills which managed to save his aircraft and passengers.