The Überlingen mid-air collision occurred at 23:35 UTC on 1 July 2002 between Bashkirian Airlines Flight 2937 (a Tupolev Tu-154M passenger jet carrying 60 passengers -- mostly children -- and 9 crew) and DHL Flight 611 (a Boeing 757-23APF cargo jet manned by two pilots) over the towns of Überlingen and Owingen in southern Germany. All 71 people on board the two aircraft were killed.
On 24 February 2004, Peter Nielsen, the air traffic controller on duty at the time of the accident, was stabbed to death by Vitaly Kaloyev. Kaloyev, an architect, had lost his wife and two children in the accident. On 19 May 2004, the German Federal Bureau of Aircraft Accidents Investigation (BFU) published its determination that the accident had been caused by shortcomings in the Swiss air traffic control system supervising the flights at the time of the accident and by ambiguities in the use of TCAS, the on-board aircraft collision avoidance system.