Überlingen mid air collision

Flights involved

Bashkirian Airlines Flight 2937 was a chartered flight from Moscow, Russia, to Barcelona, Spain, carrying sixty passengers and nine crew. Forty-five of the passengers were Russian schoolchildren from the city of Ufa in Bashkortostan on a school trip organized by the local UNESCO committee to the Costa Dorada area of Spain. 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 Tupolev Tu-154M registered as RA-85816, was piloted by an experienced Russian crew: 52-year-old Captain Alexander Mihailovich 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 to his credit. Grigoriev, the chief pilot of Bashkirian Airlines, had 8,500 hours of flying experience and his task was to evaluate Captain Gross's performance throughout the flight. 41-year-old Murat Ahatovich Itkulov (Мурат Ахатович Иткулов), a seasoned pilot with close to 7,900 flight hours who was normally the first officer, did not officially serve on duty due to the captain's assessment. 50-year-old Sergei Gennadyevich Kharlov (Сергей Геннадьевич Харлов), a flight navigator with approximately 13,000 flight hours, and 37-year-old Flight Engineer Oleg Irikovich Valeev (Олег Ирикович Валеев), who had almost 4,200 flight hours, joined the three pilots in the cockpit.

DHL Flight 611, a Boeing 757-23APF cargo aircraft 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 – the captain had logged close to 12,000 flight hours and the first officer had accumulated more than 6,600 flight hours. 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 (36,000 feet, 10,973 m) 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. He did not realize the problem in time and thus failed to keep the aircraft at a safe distance from each other. Only less than a minute before the accident did he realize the danger and contacted Flight 2937, instructing the pilot to descend by a thousand feet to avoid collision with crossing traffic (Flight 611). Seconds after the Russian crew initiated the descent, however, 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 2,400 feet per minute (12 m/s), not as rapid as the 2,500 to 3,000 ft/min (13 to 15 m/s) range advised by TCAS. Having already commenced his descent, as instructed by the controller, the pilot on the Tupolev disregarded the TCAS instruction to climb, 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).

The aircraft collided at 23:35:32, at almost a right angle at an altitude of 34,890 feet (10,630 m), with the Boeing's vertical stabilizer 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 stabilizer lost, struggled for a further seven kilometres (four miles) 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 two on board the Boeing, died.

Other factors in the crash

Only one air traffic controller, Peter Nielsen of ACC Zurich, was controlling the airspace through which the aircraft were flying. The other controller on duty was resting in another room for the night. This was against the regulations, but had been a common practice for years and was known and tolerated by management. Maintenance work was being carried out on the main radar image processing system, which meant that the controllers were forced to use a fallback system. The ground-based optical collision warning system, which would have alerted the controller to the pending collision approximately 2½ minutes before it happened, had been switched off for maintenance; Nielsen was unaware of this. There still was an aural STCA warning system, which released a warning addressed to workstation RE SUED at 23:35:00 (32 seconds before the collision); this warning was not heard by anyone present at that time, although no error in this system could be found in a subsequent technical audit; whether this audible warning is turned on or not, is not logged technically. Even if Nielsen had heard this warning, at that time finding a useful resolution order by the air traffic controller is impossible.

Deviating statements in the official report

All countries involved could add additional "deviating" statements to the official report. The Kingdom of Bahrain, Switzerland, and the Russian Federation did submit positions that were published with the official report. The U.S. did not submit deviating positions. The deviating statements were published verbatim as an appendix to the report by the German federal investigators.

The statement by the Kingdom of Bahrain, the home country of the DHL plane, mostly agrees with the findings of the report. It says that the report should have put less emphasis on the actions of individuals and more on the faults within Skyguide's organisation and management. Bahrain's statement also mentions the lack of crew resource management in the Tupolev's cockpit as a factor in the crash.

The Russian Federation states that the Russian pilots were unable to obey the TCAS advisory to climb; the advisory was given when they were already at 35,500 feet (10,800 m) while the controller wrongly stated there was conflicting traffic above them at 36,000 feet (11,000 m). Also, the controller gave the wrong position of the DHL plane (2 o'clock instead of the actual 10 o'clock). Russia asserts that the DHL crew had a "real possibility" to avoid a collision since they were able to hear the conversation between the Russian crew and the controller.

Switzerland notes that the Tupolev was about 33 metres (108 ft) below the flight level ordered by the Swiss controller, and still descending at 1,900 feet per metre (180 m/ft). The Swiss say that this was also a cause of the accident. Switzerland also requested that the BFU make a formal finding that the TCAS advisories would have been useful if obeyed immediately; the BFU declined to do so.

Aftermath

Nielsen needed medical attention due to traumatic stress caused by the accident. At Skyguide, his former colleagues maintained a vase with a white rose over Nielsen's former workstation. Skyguide, after initially having blamed the Russian pilot for the accident, accepted full responsibility and asked relatives of the victims for forgiveness.

On 27 July 2006, a court in Konstanz decided that the Federal Republic of Germany should pay compensation to Bashkirian Airlines. The court found that Germany was legally responsible for the actions of Skyguide. The government appealed the ruling; however, in the autumn of 2013 Bashkirian Airlines and the Federal Republic of Germany reached a tacit agreement, ending the court case before a decision on the legal issues was reached.

In another case before the court in Konstanz, Skyguide's liability insurance is suing Bashkirian Airlines for 2.5 million euro in damages. The case was opened in March 2008; the legal questions are expected to be difficult, as the airline has filed for bankruptcy under Russian law.

A criminal investigation of Skyguide began in May 2004. On 7 August 2006, a Swiss prosecutor filed manslaughter charges against eight employees of Skyguide. The prosecutor called for prison terms of up to 15 months if found guilty. The verdict was announced in September 2007. Three of the four managers convicted were given suspended prison terms and the fourth was ordered to pay a fine. Another four employees of the Skyguide firm were cleared of any wrongdoing.

Murder of Peter Nielsen

Devastated by the loss of his wife and two children aboard flight 2937, Vitaly Kaloyev, a Russian architect, held Peter Nielsen responsible for their deaths. He tracked down and stabbed Nielsen to death at his home in Kloten, near Zürich, on 24 February 2004. The Swiss police arrested Kaloyev at a local motel shortly after, and he was sentenced to prison for the murder in 2005. He was released in November 2007 because his mental condition was not sufficiently considered in the initial sentence. After his release, Kaloyev was dubbed a hero in North Ossetia. In January 2008, he was appointed deputy construction minister of North Ossetia.

TCAS and conflicting orders

The accident raised questions on how pilots must react when they receive conflicting orders from the TCAS and from air traffic control (ATC). TCAS was a relatively new technology at the time of the accident, having been mandatory in Europe since 2000. When the TCAS issues a resolution advisory (RA), the pilot flying should respond immediately by direct attention to RA displays and maneuver as indicated, unless doing so would jeopardize the safe operation of the flight, or unless the flight crew can assure separation with the help of definitive visual acquisition of the aircraft causing the RA. In responding to a TCAS RA that directs a deviation from assigned altitude, the flight crew should communicate with ATC as soon as practicable after responding to the RA. When the RA is removed, the flight crew should advise ATC that they are returning to their previously assigned clearance or should acknowledge any amended clearance issued.

Whilst the TCAS is programmed to assume that both crews will promptly follow the system's instructions, the operations manual did not clearly state that TCAS should always take precedence over any ATC commands. The manual described TCAS as "a backup to the ATC system", which could be wrongly interpreted to mean that ATC instructions have higher priority. This ambiguity was replicated in the Tu-154 Flight Operations Manual, which contained contradictory sections. On the one hand, chapter 8.18.3.4 emphasized the role of the ATC and describes the TCAS as an "additional aid", whilst chapter 8.18.3.2 forbade manoeuvers contrary to the TCAS. The BFU recommended that this ambiguity should be resolved in favor of obeying TCAS advisories even when these were in conflict with ATC instructions.

Prior incident

Seventeen months before the Bashkirian Airlines-DHL collision there had already been another incident involving confusion between conflicting TCAS and ATC commands. In 2001 two Japanese airliners nearly collided with each other in Japanese skies. One of the aircraft had received conflicting orders from the TCAS and ATC; one pilot followed the instructions of the TCAS while the other did not. A collision was only averted because one of the pilots made evasive maneuvers based on a visual judgement. The aircraft missed each other by about 135 metres (443 ft), and the abrupt maneuver necessary to avert disaster left 100 occupants injured on one aircraft, some seriously. In its report, published eleven days after the Überlingen accident, Japan called on the International Civil Aviation Organization (ICAO) to make it clear that TCAS advisories should always take precedence over ATC instructions. ICAO accepted this recommendation and amended its regulations in November 2003.

Technical solutions

Before this accident a change proposal (CP 112) for the TCAS II system had been issued. This proposal would have created a "reversal" of the original warning – asking the DHL plane to climb and the Tupolev crew to descend. According to an analysis by Eurocontrol this would have avoided the collision if the DHL crew had followed the new instructions and the Tupolev had continued to descend. All TCAS II equipped aircraft have been upgraded to support RA reversal.

Additionally, an automatic downlink for the TCAS – which would have alerted the controller that a TCAS advisory had been issued to the aircraft under his control, and notified him of the nature of that advisory – had not been deployed worldwide at the time of the accident.

Recommendations after the accident

The investigation report contains a number of recommendations concerning TCAS, calling for upgrades and for better training and clearer instructions to the pilots.

Notable passengers on Flight 2937

Fourteen-year-old Kirill Degtyarev created paintings from age 4 to his death and had held two public exhibitions. After his death, Ufa hosted one exhibition and Überlingen hosted another.

Dramatization

The Discovery Channel Canada documentary series Mayday featured this accident in the episode titled Deadly Crossroads, which was released in 2004. The same episode is also known by Air Crash Investigation titled Mid-air collision.

The National Geographic Channel documentary series Seconds From Disaster featured this mid-air collision in the episode entitled Collision at 35,000 feet released on 26 September 2011.

"Flug in die Nacht – Das Unglück von Überlingen" (2009), ("Flight into the night – the accident at Überlingen") produced by German and Swiss TV stations SWR and SF, is a motion picture based on the crash and the subsequent killing of the air traffic controller.

The Smithsonian Channel's "Air Disasters" documentary series, featured this accident in the second season's third episode titled "System Breakdown", released in 2011. Available on Netflix as of Oct. 2015.

The upcoming American film Aftermath is based on the aftermath of the disaster with Arnold Schwarzenegger portraying a character largely based on Vitaly Kaloyev.