Investigation Summary
The accident occurred in the airspace managed by Skyguide, a private Swiss air traffic control company. On the night of the accident, only one controller, Peter Nielsen, was manning two workstations. Crucial safety systems, including the main radar image processing system and the Short Term Conflict Alert (STCA), were offline for maintenance. When Nielsen realized the two aircraft were on a collision course, he instructed the Bashkirian crew to descend. Simultaneously, the TCAS on both aircraft triggered: it commanded the DHL crew to descend and the Bashkirian crew to climb. The Bashkirian crew, conditioned to prioritize controller instructions over automated systems, continued their descent. The DHL crew followed their TCAS and also descended. The aircraft collided at a near right angle, with the Boeing 757's vertical stabilizer slicing through the Tupolev's fuselage.
Final Conclusions
The German Federal Bureau of Aircraft Accident Investigation (BFU) identified the primary causes as the air traffic controller's late instruction to descend and the Bashkirian crew's decision to follow the controller instead of the TCAS 'climb' advisory. Contributing factors included the maintenance-related disabling of ground-based warning systems and the inadequate staffing at Skyguide during the night shift.
Video Analysis
Two Planes, One Disaster! | Mayday Air Disaster — A detailed investigation into the mid-air collision over Überlingen between DHL Flight 611 and Bashkirian Airlines Flight 2937.
Watch on YouTube ↗If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
TCAS II
Traffic Collision Avoidance System designed to provide Resolution Advisories to pilots to prevent mid-air collisions.
STCA
Short Term Conflict Alert, a ground-based safety system that warns controllers of impending collisions.
Secondary Surveillance Radar
The radar system used by ATC, which was operating in a fallback mode during the accident.
Interesting Facts
- 01All 69 people on the Bashkirian flight (including 45 children) and both DHL pilots were killed.
- 02The collision occurred in German airspace but was under Swiss air traffic control (Skyguide).
- 03The Short Term Conflict Alert (STCA) system was in a degraded mode due to maintenance.
- 04The air traffic controller was working two frequencies simultaneously due to a colleague taking a break.
- 05The DHL Boeing 757's tail fin sliced the Tupolev Tu-154 in half.
Safety Actions & Advisories
TCAS Priority Standardization
ATC Staffing Regulations
Known Controversies & Unanswered Questions
Assassination of Peter Nielsen
Reference ↗In 2004, the air traffic controller on duty, Peter Nielsen, was stabbed to death at his home by Vitaly Kaloyev, a Russian man who lost his wife and two children in the crash.