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2.15 2003 Crash of Air Midwest/U.S. Airways Express Beech 1900D (shortcutting of required maintenance procedures)
During a routine maintenance job at night, a third-party subcontracted maintenance trainee was tasked to check the tensioning of control cables. The paperwork called for an apparently complex procedure to access and retension cables, including removing seats and other parts. Some cables appeared to need retensioning, in particular the elevator cables. The trainee and his supervisor discussed the task and decided that the procedure was more complex than necessary and in any case was probably for a different-model aircraft. They decided the cables could be tensioned in a simpler manner and shortcut many of the recommended maintenance procedures for tensioning them (and in the process shortening them).
The first flight following the tensioning maintenance had a full load of 19 passengers and a larger than normal batch of luggage. Immediately upon takeoff, after the wheels came up, the captain noticed that it was hard for the nose to go down: full forward yoke reached a limit that was not enough, and the nose stayed up. When the nose pointed 68 degrees upward and the aircraft had slowed to 31 knots (kts), the aircraft stalled. Still over the runway, it rolled, fell, and crashed, killing all aboard.
Three factors contributed to the accident. First, the aircraft was unusually tail-heavy with passengers and luggage. Second, an error was made in computing the excess weight of passengers and luggage (the conventions used in the computations for passengers and luggage were too light). Finally, the combination required full forward yoke, but the cable hit-stop and elevator nose-down had been adjusted 2 inches short of full forward nose down position as part of the improvised maintenance shortcut (Casey, 2006).
John Denver, an experienced pilot and popular singer, bought a Burt Rutan, designed and “homebuilt” Long EZ experimental aircraft (pusher propeller, canard). To simplify fuel piping, in contrast to the original Rutan design the fuel valve (to switch fuel tanks) had been placed in the rear passenger compartment, reachable only by releasing the control stick, turning around, and using a short pole to operate the valve in an awkward direction. The float-ball indicator of available fuel was also nonlinear, showing one-third full when the tank was actually almost empty.
Denver trusted his maintenance technician who, not aware of this nonlinearity, said there was quite enough fuel for a few touch-and-goes that Denver wanted to practice at the Monterey Peninsula Airport in California. When the engine surprised him by running out of fuel, Denver apparently tried to turn and operate the fuel valve but inadvertently activated a pedal (rudder control). This stalled the aircraft, which rolled and crashed into Monterey Bay (Casey, 2006).
2.17 U.S. Soldier in Afghanistan Inadvertently Calls for Air Strike on Own Position (ignorance of reset operation)
In December 2001, a U.S. soldier in Afghanistan needed to call in an air strike using a handheld GPS /communication device. After entering the coordinates for the strike into the device, he noticed that it indicated a need for battery replacement. Having a spare battery available and thinking that he had better do that quickly, he replaced the battery. What the soldier did not realize was that when the battery was replaced the system reset to the present (his own) coordinates. The air strike came down on his position, killing two-dozen people (Casey, 2006).
2.18 Loss of Black Hawk Helicopters to Friendly Fire (ill-defined procedures and traffic management responsibilities)
A major factor in the loss of the Black Hawk helicopters to friendly fire over northern Iraq is that they normally flew only in the boundary areas of the No Fly Zone, and procedures for handling aircraft in those areas were ill-defined (Leveson, Allen, and Storey, 2002). An Army base controlled the flights of the Black Hawks while an Air Force base controlled all other airspace activity. A common control level was higher in the control management structure than the level at which the decisions were made in this accident. Communication problems existed between the Army and Air Force bases at the intermediate control levels. The aircraft surveillance officer (ASO) thought she was responsible only for identifying and tracking aircraft south of the 36th parallel. The air traffic controller for the area north of the 36th parallel thought the ASO was also tracking and identifying aircraft in his area and accordingly took no action (Leveson, 2004).
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