TWA Flight 841 (1979)
TWA Flight 841 was a domestic, scheduled passenger flight from John F. Kennedy International Airport in New York City, en route to Minneapolis-Saint Paul International Airport in Minneapolis, Minnesota. On April 4, 1979, at or around 9:48 p.m. Eastern Standard Time (01:48 UTC), while flying over Saginaw, Michigan, the Boeing 727-31 airliner began a sharp, uncommanded roll to the right, and subsequently went into a spiral dive. The pilots were able to regain control of the aircraft and made a successful emergency landing at Detroit Metropolitan Airport. Incident. At 8:25p.m. EST, TWA Flight 841  departed JFK International after a 45-minute delay due to traffic congestion. After traveling nearly , while cruising at near the city of Saginaw, Michigan, Captain Harvey "Hoot" Gibson says the aircraft was operating with the autopilot on "Altitude Hold" mode when it began a steep roll to the right. The crew immediately disconnected the autopilot and tried to bring the aircraft back to a wings-level attitude. Despite the best efforts of the flight crew, the aircraft spiraled out of control, diving about in just 63 seconds. During the course of the dive, the plane rolled through 360 degrees twice  and exceeded the Mach limit for the 727 airframe. Control was regained at about after the pilots extended the landing gear in an attempt to slow the aircraft. The plane suffered substantial structural damage, but made an emergency landing at Detroit Metropolitan Airport in Michigan at 10:31 p.m. EST without further trouble. No fatalities occurred among the 82 passengers and 7 crew members. Eight passengers reported minor injuries related to high g-forces. Investigation. The National Transportation Safety Board (NTSB) investigated the accident, conducting what was at the time the lengthiest accident investigation in NTSB history. In its final report , published in June 1981, the NTSB concluded the probable cause of the accident was a mechanical failure of a slat under inappropriate manipulation and the captain's untimely action. Among the damage discovered after the accident, investigators found the #7 slat missing from the leading edge of the right wing. NTSB investigators requested the aircraft manufacturer, Boeing, inspect the remainder of the slat assembly, including a portion of the slat actuator cylinder (the motor that moves the slat and holds it in position). Boeing determined that the #7 slat had failed because the slats had been extended while the aircraft  was flying at cruising speed. They also determined that it was "impossible" for the flaps to extend without manipulating the controls. After eliminating all individual and combined sources of mechanical failure, the NTSB ruled that the extension of the slats was due to the flight crew manipulating the flap/slat controls in an inappropriate manner. Investigators believed that 727 pilots (in general, and this flight specifically) were setting the trailing edge flaps to two degrees during high altitude cruise, while at the same time pulling the circuit breaker for the slats so that they would not activate. This configuration was  rumored to result in increased lift with no increase in drag, thus allowing more speed, higher elevation, or decreased fuel consumption. Flaps and slats were intended to only be deployed at low speeds during take-off or landing. The crew, Capt. Harvey Glenn "Hoot" Gibson, first officer Jess Scott Kennedy, and flight engineer Gary Nelson Banks, denied that their actions had been the cause of the flaps' extension: The crew suggested instead that an actuator on the #7 slat had failed, causing its inadvertent deployment. The NTSB rejected this as improbable and attributed the extension of the flaps to the  deliberate actions of the crew. The crew claimed that such failures had happened on other 727s prior and subsequent to this incident. The NTSB report noted that between 1970 and 1973, seven separate cases involving a single leading edge slat extension and separation were reported, but none of these reports indicated whether or not the slat extension was due to flight crew involvement. Records after 1974 did include this information, and (other than Flight 174) only two slat extension problems were reported between 1974 and the close of the NTSB's investigation in 1981, one of which was inadvertently caused  by the flight crew. The flight crew testified that they had not engaged the flaps, and the NTSB concluded that "if the flightcrew's recollections are accurate," the slat extension must have been caused by a mechanical failure or defect. However, the NTSB ultimately concluded that the flight crew was probably attempting to use 2º of flaps at cruising speed: When retraction of the flaps was ordered, the Number 7 leading edge slat failed to retract, causing the uncommanded roll to the right. Captain Gibson appealed the NTSB's findings, first to the NTSB itself, and then to the U.S.  Ninth Circuit Court of Appeals. Both petitions were rejected: the former for lack of new evidence, and the latter for lack of jurisdiction due to the NTSB's "unreviewable discretion". The aircraft was repaired and returned to service in May 1979. Cockpit voice recorder. The aircraft was equipped with a Fairchild Industries Model A-100 cockpit voice recorder (CVR). However, 21 minutes of the 30-minute tape were blank. Tests of the CVR in the aircraft revealed no discrepancies in the CVR's electrical and recording systems.The CVR tape can be erased by means of the bulk-erase feature on  the CVR control panel located in the cockpit. This feature can be activated only after the aircraft is on the ground with its parking brake engaged. In a deposition taken by the Safety Board, the captain stated that he usually activates the bulk-erase feature on the CVR at the conclusion of each flight to preclude inappropriate use of recorded conversations. However, in this instance, he could not recall having done so. The NTSB made the following statement in the accident report: In media. This incident was the subject of a 44-minute CBS News Special titled "The Plane That  Fell From The Sky". The special won a Peabody Award in 1983. The incident was featured in the 22nd season of the show "Mayday", titled "Terror over Michigan". Criticism of investigation. In the book "Emergency: Crisis In the Cockpit", Stanley Stewart, a professional pilot, has raised questions about the NTSB findings: