DHL Boeing 757-23APF plane crash

The aircraft, on a cargo flight from Bergamo to Brussels, collided with a Bashkirian Airlines Tupolev TU-154 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 a few 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. Both crew members were killed in the DHL plane, and all 69 passengers and crew members died in the Bashkirian plane.

This accident raised the problem of the crew decision when both the TCAS and the air traffic controller give opposite orders.