B4/2002L TCAS Manoeuvre South of Jyväskylä on 29 October 2002
On Tuesday October 29, 2002, at 14.33 Finnish time a serious incident occurred about 50 km south of Jyväskylä, when a passenger aircraft Airbus 340-600 operated by Virgin Atlantic Airways Ltd, call sign Virgin 901 en route from Tokyo to London and a passenger aircraft MD-83, call sign Finnair 473, operated by Finnair Oyj en route from Kittilä to Helsinki, passed each other at about 11000 m on crossing tracks losing the separation minimum required by the authorities. The aircraft took avoiding action by following instructions from their TCAS (Traffic alert and Collision Avoidance System) - Virgin 901 up and Finnair 473 down. Both aircraft flew above clouds in visual meteorological conditions and saw each other. The Accident Investigation Board, Finland, appointed an investigation commission on October 30, 2002, to investigate the incident. Chief air accident investigator Tero Lybeck was appointed chairman and air traffic controller Martti Lantela, airline pilot Timo Uramaa and Ville Hämäläinen were appointed members of the commission.
Finnair 473 and Virgin 901 flew in accordance with their air traffic control clearances at FL (flight level) 360, Finnair 473 on track Haapajärvi - Jyväskylä - Orimattila and Virgin 901 on track Joensuu - Maarianhamina. Originally Finnair 473 should have flown at FL 340 and Virgin 901 at FL 380. Finnair 473 flew at a flight level higher than normally because the aircraft was light. Virgin 901 flew on a flight level lower than normally because there was other air traffic near to it and in the same ATS (Air Traffic services) route at FL 380. The executive controller (R1) responsible for air traffic and the planning controller (R2) did not notice in any phase that the two aircraft were approaching each other. Slightly before the two aircraft would meet R1 gave to Finnair 473 clearance to descend to a lower altitude, leaving the decision to start the descent to the pilots’ discretion. After this R1 focused on other traffic, for which he was responsible. He became aware of the incident when the separation minima had been lost and Finnair 473 had started to descend.
In passing each other Virgin 901 flew at heading 240 and Finnair 473 at heading 171. The shortest horizontal distance between the two aircraft was about 1610 m (0.87 NM, nautical miles) and the shortest vertical distance was 360 m (1200 ft). The evasive manoeuvres were normal. Finnair 473, however, started descent in accordance with its clearance immediately after TA but prior to RA. Both aircraft reported taking evasive action. When R1 became aware of the conflict and noticed that the aircraft would not collide, he intentionally avoided giving instructions to the aircraft so that they would not be contradictory to the TCAS RAs.
The chain of events resulting in a serious incident begun when R1 and R2 prepared themselves for their work and noted that the westbound traffic from Russia flying over Finland flew at FL 380, whereas the southbound traffic from Northern Finland was at lower flight levels. They noted that there should be no separation problems between the two traffic flows. This initial assumption probably contributed to the fact that neither controller eventually noticed the two aircraft approaching each other at FL 360 which deviated from their original flight levels. Another contributing factor was that the Short Term Conflict Alert (STCA) system was not in use in the air traffic control at the moment.
The investigation commission made three safety recommendations of which two were to the Finnish Civil Aviation Administration (FCAA). The FCAA should take the existing STCA systems into use to the extent they can be used without a great number of nuisance alerts. The FCAA should also to acquire a well-functioning STCA system to all ATC units which give radar services. Furthermore, the investigation commission recommended that Finnair Oyj should take into account in the pilots’ TCAS training the risks associated with changing from level flight to climb or descent in accordance with ATC clearance during TCAS TAs.
The draft report was sent for comments to the UK AAIB, the Finnish flight safety authority, the ANS department of the Finnish CAA, the ANS centre for South Finland and Finnair. The Finnish flight safety authority and Finnair had no comments. The comments of the ANS centre for South Finland and the UK Accredited Representative have been taken into account in the report. Tampere ACC activated the existing STCA system soon after the incident for use above FL 200. The ANS department of the FCAA noted that a better STCA system is estimated to be taken in use with a new Eurocat 2000 v2 system in November 2003 in South Finland and in summer 2004 in North Finland. The comments of the ANS department are enclosed in the Finnish report and available in Finnish at AIB Finland.