2002 Überlingen mid-air collision

On 1 July 2002, BAL Bashkirian Airlines Flight 2937, a Tupolev Tu-154 passenger jet, and DHL International Aviation ME Flight 611, a Boeing 757 cargo jet, collided in mid-air over Überlingen, a southern German town on Lake Constance, near the German-Swiss border. All of the passengers and crew aboard both planes were killed, resulting in a total death toll of 71 including 52 children.

The official investigation by the German Federal Bureau of Aircraft Accident Investigation (Bundesstelle für Flugunfalluntersuchung; BFU) identified the main cause of the collision to be a number of shortcomings on the part of the Swiss air traffic control (ATC) service in charge of the sector involved, as well as ambiguities in the procedures regarding the use of the traffic collision avoidance system (TCAS) on board.

On 24 February 2004, Peter Nielsen, the air traffic controller on duty at the time of the collision, was murdered in an apparent act of revenge by Vitaly Kaloyev, a Russian architect whose wife and two children died in the accident.

Accident

The airspace was controlled from Zürich, Switzerland, by the Swiss federal airspace control Skyguide. Air traffic controller Peter Nielsen, the only controller handling the airspace, was burdened with working two workstations at the same time.

At 23:21 CEST (21:21 UTC), DHL Flight 611 reported to the area control center responsible for southern German airspace. Nielsen then instructed Flight 611 to climb from flight level 260 (26000 ft) to flight level 320 (32000 ft). Flight 611 requested permission to continue the climb to flight level 360 (36000 ft) to save fuel. Nielsen permitted Flight 611 to climb after about four to five minutes, after which Flight 611 reached the desired altitude at 23:29. Meanwhile, Flight 2937 contacted Nielsen at 23:30, which also reported to be at flight level 360. Nielsen acknowledged the flight, but did not assign a different altitude to either aircraft. That meant that both were now at the same altitude and on a collision course.

At 23:34:49 CEST (21:34:49 UTC), about a minute before the collision, Flight 2937's TCAS instructed them to climb; seconds later, Nielsen, realizing the oncoming danger, contacted Flight 2937 and instructed the pilot to descend to flight level 350 (1000 ft lower) to avoid collision with crossing traffic (Flight 611). The crew of Flight 2937 disengaged the autopilot and initiated their descent at 23:35, obeying the controller instead of the TCAS. At about the same time, the TCAS on Flight 611 instructed the crew of that aircraft to descend. The collision would thus not have occurred if both the aircraft's crews had obeyed the TCAS's instructions.

Flight 611's pilots followed their TCAS instructions and initiated a descent, but could not immediately inform Nielsen as he was dealing with Flight 2937. The crew of Flight 2937, however, descended as instructed by Nielsen, contrary to the TCAS's instructions which advised the crew to climb. Both planes were now descending.

Unaware of the TCAS-issued alerts, Nielsen repeated his instruction to Flight 2937 to descend, giving the crew incorrect information as to the position of the DHL plane, telling them that the plane was to the right (2 o'clock position) when it was in fact to the left (10 o'clock position). About eight seconds before the collision, Flight 611's descent rate was about 2400 ft/min, not quite as rapid as the 2500 to 3000 ft/min range advised by the TCAS.

Flight 611, responding to the developing situation, increased its descent rate. Eight seconds before the collision, Flight 2937's crew became aware of the situation when they gained visual sight of Flight 611 incoming from the left, and, two seconds before the collision, obeyed their TCAS instruction and attempted to put the aircraft into a climb. Unfortunately, the collision had by then become inevitable. The two aircraft collided at 23:35:32 CEST (21:35:32 UTC), at almost a right angle, at an altitude of 34890 ft, with Flight 611's vertical stabilizer slicing completely through Flight 2937's fuselage just ahead of the wings. Flight 2937 broke into several pieces, scattering wreckage into the Brachenreute neighborhood over a wide area. The nose section of the aircraft fell vertically, while the tail section with the engines continued, stalled, and fell. Many of the children's bodies fell in the field just southeast of the memorial.

Flight 611, now with 80% of its vertical stabilizer lost, entered a flat spin dive, and continued for a further 7 km for two minutes, before crashing into a wooded area close to the village of Taisersdorf at a 70° downward angle. Each engine ended up several hundred meters away from the main wreckage after being torn from the plane due to airframe stress, causing the black boxes to stop before the plane hit the ground, and the tail section was torn from the fuselage by trees just before impact. All 69 people on board Flight 2937 and the two crew members on board Flight 611 died.