DHL flight DHL611 and Baskirian flight V92937 collided near Ueberlingen (Switzerland on 1 July 2002 at 21:35:32 hrs.
A mid-air collision between a Tupolev TU154M, which was on a flight from Moscow/ Russia to Barcelona/ Spain, and a Boeing B757-200, on a flight from Bergamo/Italy to Brussels/ Belgium, occurred north of the city of Ueberlingen (Lake of Constance). Both aircraft flew according to IFR (Instrument Flight Rules) and were under control of ACC Zurich. After the collision both aircraft crashed into an area north of Ueberlingen. There were a total of 71 people on board of the two airplanes, none of which survived the crash.
The following immediate causes have been identified:
• The imminent separation infringement was not noticed by ATC in time. The instruction for the TU154M to descend was given at a time when the prescribed separation to the B757-200 could not be ensured anymore.
• The TU154M crew followed the ATC instruction to descend and continued to do so even after TCAS advised them to climb. This manoeuvre was performed contrary to the generated TCAS RA.
..TCAS generated an RA (“climb, climb“). At 21:34:59 hrs, the CVR recorded the voice of the copilot stating: “It (TCAS) says (говорит): ‘climb’ “. The PIC replied: “He (ATC) is guiding us down“. The copilot’s enquiring response: “descend?“
The following systemic causes have been identified:
• The integration of ACAS/TCAS II into the system aviation was insufficient and did not correspond in all points with the system philosophy. The regulations concerning ACAS/TCAS published by ICAO and as a result the regulations of na-tional aviation authorities, operations and procedural instructions of the TCAS manufacturer and the operators were not standardised, incomplete and partially contradictory.
• Management and quality assurance of the air navigation service company did not ensure that during the night all open workstations were continuously staffed by controllers.
• Management and quality assurance of the air navigation service company tolerated for years that during times of low traffic flow at night only one controller worked and the other one retired to rest.