What happened
On October 29, 2002, at 14:33 local time, a serious air traffic incident occurred approximately 50 km south of Jyväskylä, Finland. Two aircraft, a Virgin Atlantic Airways Ltd Airbus 340-600 (call sign Virgin 901) and a Finnair Oyj MD-83 (call sign Finnair 473), passed each other on crossing tracks at approximately 11,000 meters.
At the time of the encounter, both aircraft were flying at flight level 360, which violated the required separation minima. The aircraft had deviated from their original assigned altitudes; the Finnair 473 was flying higher than its assigned FL 340 due to its light weight, while the Virgin 901 was flying lower than its assigned FL 380 due to heavy traffic in that sector.
The aircraft were flying in visual meteorological conditions above the clouds and were able to see one another. The encounter triggered the Traffic Alert and Collision Avoidance System (TCAS), resulting in a Resolution Advisory (RA). The Virgin 901 performed a climb, while the Finnair 473 performed a descent. The minimum horizontal distance between the two aircraft was approximately 1,610 meters, with a vertical separation of 360 meters.
The investigation
The investigation examined the air traffic control (ATC) environment and the actions of both flight crews. Investigators found that the air traffic controllers (R1 and R2) had assumed that traffic from the east (Russia) and traffic from the north (Finland) would remain separated because they believed the eastbound traffic was at FL 380 and the southbound traffic was at a lower level.
Crucially, the investigation established that the controllers did not notice the two aircraft approaching each other at the shared FL 360. Just before the encounter, the controller (R1) cleared the Finnair 473 to descend, leaving the execution to the pilots. The controller only became aware of the conflict once the separation minima had already been breached and the Finnair 473 had begun its descent.
Findings
- The primary cause of the incident was the failure of air traffic controllers to detect the approaching aircraft due to an incorrect assumption regarding the flight levels of the two traffic flows.
- The controllers' oversight was exacerbated by the fact that the Short Term Conflict Alert (STCA) system was not in use at the time, as it had been previously deactivated due to a high frequency of nuisance alerts.
- The Finnair 473 crew initiated a descent following an ATC clearance during the TCAS Traffic Advisory (TA) phase, but before the Resolution Advisory (RA) was issued. This created a risk that the subsequent RA could have required a climb instead of a descent.
Safety action
- The investigation recommended that the Finnish Civil Aviation Administration (FCAA) implement STCA systems in a manner that minimizes nuisance alerts.
- The FCAA was advised to provide well-functioning STCA systems to all radar-service ATC units.
- A recommendation was made to Finnair Oyj to enhance TCAS training for pilots, specifically addressing the risks of executing ATC-mandated altitude changes during a TCAS Traffic Advisory.