2002 Überlingen mid-air collision

On the night of 1 July 2002, Bashkirian Airlines Flight 2937, a Tupolev Tu-154 passenger jet, and DHL Flight 611, a Boeing 757 cargo jet, collided in mid-air over Überlingen, a southern German town on Lake Constance, near the Swiss border. All 69 passengers and crew aboard the Tupolev and both crew members of the Boeing were killed.

The official investigation by the German Federal Bureau of Aircraft Accident Investigation (German: Bundesstelle für Flugunfalluntersuchung, (BFU)) identified as the main cause of the collision a number of shortcomings on the part of the Swiss Air Traffic Controller (ATC) service in charge of the sector involved as well as ambiguities in the procedures regarding the use of Traffic Collision Avoidance System (TCAS), the on-board aircraft collision avoidance system. A year and a half after the crash, 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 citizen whose wife and two children had been killed in the accident.

Aircraft involved
Bashkirian Airlines Flight 2937 was a chartered flight from Moscow, Russia, to Barcelona, Spain, carrying 60 passengers and nine crew. Forty-five of the passengers were Russian schoolchildren from the city of Ufa, in Bashkortostan, on a school trip organised by the local UNESCO committee to the Costa Daurada beach area of Catalonia. Most of the parents of the children were high-ranking officials in Bashkortostan. One of the fathers was the head of the local UNESCO committee.

The aircraft, a 1995-built Tupolev Tu-154M registered as RA-85816, was piloted by an experienced Russian crew: 52-year-old Captain Alexander Mikhailovich Gross (Александр Михайлович Гросс) and 40-year-old First Officer Oleg Pavlovich Grigoriev (Олег Павлович Григорьев). The captain had more than 12,000 flight hours (including 4,918 hours on the Tu-154) to his credit. Grigoriev, the chief pilot of Bashkirian Airlines, had 8,500 hours of flying experience (with 4,317 hours on the Tu-154) and his task was to evaluate Captain Gross's performance throughout the flight.

41-year-old Murat Akhatovich Itkulov (Мурат Ахатович Иткулов), a seasoned pilot with close to 7,900 flight hours (with 4,181 of them on the Tu-154), who was normally the first officer, did not officially serve on duty, because this was the captain's assessment flight. 50-year-old Sergei Gennadyevich Kharlov (Сергей Геннадьевич Харлов), a flight navigator with approximately 13,000 flight hours (including 6,421 hours on the Tu-154), and 37-year-old Flight Engineer Oleg Irikovich Valeev (Олег Ирикович Валеев), who had almost 4,200 flight hours (all of which were on the Tu-154), joined the three pilots in the cockpit.

DHL Flight 611, a Boeing 757-23APF cargo aircraft built in 1990 and registered as A9C-DHL, had originated in Bahrain and was being flown by two Bahrain-based pilots, 47-year-old British Captain Paul Phillips and 34-year-old Canadian First Officer Brant Campioni. Both pilots were very experienced — Phillips had logged close to 12,000 flight hours (including 4,145 hours on the Boeing 757) and Campioni had accumulated more than 6,600 flight hours, with 176 of them on the Boeing 757. At the time of the accident, the aircraft was en route from Bergamo, Italy, to Brussels, Belgium.

Accident
The two aircraft were flying at flight level 360 (11,000 metres (36,000 ft)) on a collision course. Despite being just inside the German border, the airspace was controlled from Zürich, Switzerland, by the private Swiss airspace control company Skyguide. The only air traffic controller handling the airspace, Peter Nielsen, was working two workstations at the same time. Partly because of the added workload, and partly because of delayed radar data, he did not realize the problem in time and thus failed to keep the aircraft at a safe distance from each other.

Less than a minute before the accident, he realized the danger and contacted Flight 2937, instructing the pilot to descend to flight level 350 to avoid collision with crossing traffic (Flight 611). Seconds after the Russian crew initiated the descent, their traffic collision avoidance system (TCAS) instructed them to climb, while at about the same time the TCAS on Flight 611 instructed the pilots of that aircraft to descend. Had both aircraft followed those automated instructions, the collision would not have occurred.

Flight 611's pilots on the Boeing jet followed the TCAS instructions and initiated a descent, but could not immediately inform Nielsen because the controller was dealing with Flight 2937. About eight seconds before the collision, Flight 611's descent rate was about 12 metres per second (2,400 ft/min), not quite as rapid as the 13 to 15 m/s (2,500 to 3,000 ft/min) range advised by that jet's TCAS; as for the Tupolev, the pilot disregarded his jet's TCAS instruction to climb, having already commenced his descent as instructed by the controller. Thus, both planes were now descending.

Unaware of the TCAS-issued alerts, Nielsen repeated his instruction to Flight 2937 to descend, giving the Tupolev crew incorrect information as to the position of the DHL plane (telling them that the Boeing was to the right of the Tupolev when it was in fact to the left).

Eight seconds before the collision, Flight 2937's crew finally realised their actual position when they gained visual sight of Flight 611 incoming from the left. Flight 611, in response, increased its descent rate. Two seconds before the collision, Flight 2937's pilots finally obeyed the jet's TCAS instruction to climb and attempted to put the aircraft into a climb, but the collision was now inevitable. The aircraft collided at 23:35:32 local time (21:35 UTC), at almost a right angle at an altitude of 10,630 metres (34,890 ft), with the Boeing's vertical stabiliser slicing completely through Flight 2937's fuselage just ahead of the Tupolev's wings. The Tupolev broke into several pieces, scattering wreckage over a wide area.

The nose section of the aircraft fell vertically, while the tail section with the engines continued, stalled, and fell. The crippled Boeing, now with 80% of its vertical stabiliser lost, struggled for a further 7 kilometres (4.3 mi; 3.8 nmi) before crashing into a wooded area close to the village of Taisersdorf at a 70-degree downward angle. Each engine ended up several hundred metres away from the main wreckage, and the tail section was torn from the fuselage by trees just before impact. All 69 people on the Tupolev, and the 2 on board the Boeing, died.