Only the crew of 757 involved in Ueberlingen collision avoids criticism as Tupolev pilots and ATC come under fire
Swiss air traffic services provider Skyguide is the most widely criticised party cited in the final report into the 1 July 2002 mid-air collision over Ueberlingen, southern Germany. The organisation has accepted the accusation that its controller training and safety management systems (SMS) were not being operated properly.
Other concerns highlighted by German accident investigation agency BFU included ambiguity in International Civil Aviation Organisation regulations on pilot procedures for reacting to airborne collision avoidance system (ACAS) advisories, leading to disparities in national regulators' and equipment manufacturers' interpretations of the required procedures.
The collision occurred after a DHL Boeing 757-200 freighter and a Bashkirian Airlines Tupolev Tu-154M approached each other at right angles at the same flight level, despite both pilots receiving resolution advisories (RA) from their ACAS systems, which were traffic collision avoidance system (TCAS) 2 Version 7, the highest ACAS specification. Both pilots on the 757 and all nine crew and 60 passengers on the Tu-154 were killed. The report gives the "immediate causes" as the fact that "imminent separation infringement was not noticed by ATC in time", and that the "Tu-154 crew followed ATC instructions to descend and continued to do so even after TCAS advised them to climb".
The only totally uncriticised party was the 757 crew who followed their "descend descend" RA and notified Zurich area control centre (ACC) of their manoeuvre, while the Tu-154 crew ignored their "climb climb" RA and instead carried out the late instruction of the controller to descend to flight level 350 (35,000ft) without advising the ACC of their RA. Eurocontrol says that RAs take precedence over all other considerations except fundamentals like collision with terrain.
Eurocontrol director of air traffic management (ATM) programmes George Paulson, commenting on the BFU report, says that its findings emphasise the need for commonly enforced European regulation on ACAS, on incident reporting, and on the implementation and practice by ATM service providers of an SMS. The European Commission has completed the first drafts of what will become European Community law on ATM standards, says Paulson, based on Eurocontrol's ESARRs (Eurocontrol safety regulatory requirements), and he believes they may be ready for the parliamentary and government process by the end of the year.
One of the main BFU technical recommendations is that controllers should receive downlinked RA alert data. Eurocontrol confirms it is working on the technology for this, but there is some way to go yet in proving the technology, which would use the Mode S surveillance datalink.
The BFU report criticises Skyguide rather than the controller, whose competence and record is not questioned. The most basic of the problems the controller faced was that he was alone carrying out a job that needed at least two people to perform it safely, and for which Skyguide now uses three controllers. Also the short-term conflict alert system that warns of potential conflict was down for maintenance, and resectorisation of the Zurich ACC's upper airspace was planned for that night.
DAVID LEARMOUNT / LONDON
Source: Flight International
