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 57 passengers – mostly children – and twelve 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 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 controlsystem supervising the flights at the time of the accident and by ambiguities in the use of TCAS, the on-board aircraft collision avoidance system.
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.
Bashkirian Airlines Flight 2937 [RA-85816], on a flight from Moscow, Russia to Barcelona, collided with DHL FLight 611 [A9C-DHL] at FL390 near Ueberlingen on the northern shore of Lake Constance, which borders Switzerland and Austria, around 11:43pm local time. Both aircraft were level at FL360, under Swiss air traffic control (Zurich). Approximately 50 seconds before the collision, Swiss ATC instructed the Russian Tupolev to descend from FL360 to FL350 to avoid a conflict with the DHL Boeing 757. No response was registered by the Russian crew. A second descent instruction was made by Swiss controllers seconds later, and the Tupolev crew acknowledged the instruction. The TU-154 initiated its descent about 25 seconds before the collision. At nearly the same instant, the Boeing 757′s TCAS (Traffic Collision Avoidance System) issued a Resolution Advisory (RA) in response to the threat of a collision with the TU-154, and the pilots began a descent in an attempt to avoid the Russian aircraft. The aircraft collided at FL354, broke apart and crashed, with debris scattered over an area nearly 40km wide.