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2.11 2002 Midair Collision Over Uerberlingen, Germany (pilot decision to follow ATM advice rather than TCAS resolution advisory)
On the night of July 1, 2002, a DHL B757 collided with a Bashkirian Airlines Tupolev-154 over Lake Constance in Germany, resulting in 71 fatalities. After contacting the 757, a Swiss controller (Zurich Center, by agreement with the German government) issued two successive clearances to climb. There was no further contact with either aircraft until the TCAS gave both pilots a traffic advisory. At that point the controller instructed the T154 to descend. The TCAS then instructed the T154 to climb and the 757 to descend. The T154 pilot chose to obey the controller rather than TCAS and descended, while the 757 did as instructed by TCAS and also descended. They collided at FL 350.
A number of factors contributed to the accident. First, the pilot of the Tupolev, whose command of English was questionable, was apparently slow in responding to the controller’s descent instructions before the TCAS issued the contrary resolution (which had seemed warranted due to low expected traffic). Second, even though the controller was also at fault for not detecting the conflict earlier, there was only a single controller working, and he was monitoring two different radars. Third, the radar had been downgraded as the main radar system was out for maintenance and a backup was in use. Fourth, German controllers working the Karlsruhe sector had noticed the unfolding situation and had tried to contact the Swiss controller on the telephone, but the telephone was non-functional due to lack of maintenance and the German controllers could not get through. Finally, the TCAS communicates only with the pilot; it does not communicate its resolution instructions to the controller, and the Swiss controller had no
way of knowing the TCAS was giving instructions that were in conflict with his own. As a result, the controller did not anticipate a conflict.
This accident is an example of Reason’s (1990) “Swiss cheese” model, i.e., when multiple risk factors come together accidents are likely to happen. To add to the original tragedy, the controller was later murdered by a man whose wife and children died in the crash, and eight employees of the Swiss Skyguide navigation service were charged with manslaughter for “organizational shortcomings” (Nunes and Laursen, 2004).
On a flight from Australia to Malaysia, the aircraft suddenly climbed 3,000 ft. The pilot immediately disconnected the autopilot and pointed the nose down. The plane then jerked into a steep dive. The pilot throttled back and tried to slow the aircraft, but it again raced into another climb. The pilot finally regained control.
An investigation revealed a defective software program that provided incorrect speed and acceleration data. This confused the flight computers and ignored some of the pilot’s commands. Boeing mandated a software fix. While no crash has yet been attributed to serious software errors, there are concerns that it surely will happen (Michaels and Pasztor, 2006).
2.13 October 2005 British Airways A319 Electronics Failure (unanticipated and unreplicated software problem)
On a night flight from London to Budapest, nearly all cockpit lights and electronic displays, along with radios and autopilot systems, went dark for 90 seconds. Efforts to replicate the failure failed. (Allegedly, British Airways had already discovered four similar cases on Airbus jets) (Michaels and Pasztor, 2006).
2.14 Embraer Test Flight: One-Minute Blackout of Computer Displays (presumably due to a software glitch)
During an Empresa Brasileira de Aeronautica SA test flight of a new jetliner, the cockpit displays went dark for one minute, then came back on. Embraer says it has fixed the problem. FAA has since ordered programming changes to the plane (Michaels and Pasztor, 2006).
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