What happened
On July 1, 2002, a mid-air collision occurred near Überlingen, Germany, involving two commercial airliners: a Boeing B757-200 and a Tupolev TU154M. The collision resulted in 71 fatalities, with both aircraft being destroyed upon impact. The accident also caused significant damage to the surrounding fields and forests.
The investigation
The BFU investigation examined the flight paths of both aircraft, the performance of the air traffic control services at ACC Zurich, and the functionality of the onboard collision avoidance systems. The investigation analyzed radar data, cockpit voice recorders, and flight data recorders from both aircraft. Investigators also scrutinized the communication between the pilots and air traffic controllers, as well as the technical status of the Short Term Conflict Alert (STCA) and the Airborne Collision Avoidance System (ACAS/TCAS II) during the sequence of events.
Findings
Technical and operational analysis revealed a complex chain of errors. A critical factor in the collision was the conflicting instructions between air traffic control and the aircraft's automated safety systems. While the air traffic controller issued instructions that were inconsistent with the automated collision avoidance maneuvers, the investigation highlighted significant issues within the air traffic control environment, including the failure of the Short Term Conflict Alert (STCA) to effectively warn the controller of the impending danger. Furthermore, discrepancies in how different crews responded to TCAS Resolution Advisories (RA) contributed to the inability to avoid the conflict.