That unauthorised procedure nearly caused the demise of a 727 back in 1979 (TWA Flight 841), when the crew allegedly tried to extend the trailing edge flaps 2° independently of the slats while cruising at FL390. The crew never admitted it, but the investigators believed the slats were inadvertently extended and one of the slat segments remained extended when the crew tried to retract them. The aircraft suffered an uncommanded roll, entered a spiral dive and lost 34,000ft in a little over a minute. It rolled through 360° twice during the dive and suffered significant structural damage.
