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Computer-Related Incidents with Commercial Aircraft

Various aircraft, TCAS chain reaction, over Trasadingen, Switzerland, 13 September 2000

13 September 2000

Synopsis Four aircraft were involved in this incident. One of them filed an airprox (report of a near miss). The lowest aircraft was climbing rapidly to its assigned altitude. The rate of climb triggered a TCAS Resolution Advisory in the next higher, whose climb manoeuvre triggered a TCAS Resolution Advisory (RA) in the next, whose .... etc. Such a "chain reaction" scenario, whereby two aircraft departed radically from their cleared airspace, can cause problems for air traffic control, let alone for the crew and occupants of the aircraft. There was in fact no danger to any aircraft in the original scenario; the behavior of TCAS and the reaction of the crews to the TCAS RAs created the incident. The versions of TCAS involved were more sensitive than current installed versions. Some experts suggest that with the current less-sensitive versions, and with better pilot training, such incidents won't happen again. Think of that what you will. Here is the Report.


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