What happened
On January 24, 2007, at approximately 08:15 UTC, an Antonov aircraft, registration MTL5HD, deviated from its assigned taxi route while operating at Helsinki-Vantaa Airport. At the time, the airport was utilizing runway 15 for arrivals and runway 22L for departures, though the departure runway was being transitioned to 22R due to ongoing snow removal operations.
Due to poor weather conditions, visibility was limited to approximately 1100 meters. The ground controller issued a taxi clearance for MTL5HD to proceed from stand 803 to holding point ZS. However, the aircraft instead turned onto taxiway Z and proceeded to holding point ZJ. Because of the low visibility, air traffic controllers had no visual contact with the aircraft, and it was not being tracked on the ground movement radar.
During the incident, the tower controller observed a radar blip from a service vehicle, SÄHKÖ10, located near holding point ZR/ZS. The controller mistakenly identified this vehicle's radar signal as the Antonov and subsequently cleared the aircraft to cross runway 22L to proceed to holding point 22R. The error was discovered when a snow removal vehicle, HARJA82, operating on runway 22L, spotted the aircraft stationary at holding point ZJ and alerted the tower.
The investigation
The investigation focused on why the aircraft deviated from its path and why air traffic control failed to maintain accurate positioning of the aircraft. Investigators examined radar data, radio communications, and the operational workload of the controllers. The investigation noted that the ground controller had to hand over the aircraft to the tower controller without specific identification data.
Analysis of the radio transcripts revealed that the pilot's responses were highly unclear and imprecise. For instance, when asked for its position, the pilot reported being at "Z7," a response that was easily confused with the intended destination of "ZS." Furthermore, the investigation looked into the radar presentation system, noting that the lack of aircraft labels on the ground movement radar contributed to the difficulty in monitoring the aircraft's movement.
Findings
- Poor weather conditions significantly reduced visibility to 1100 meters, preventing visual identification of the aircraft.
- The misidentification of a service vehicle's radar signal as the aircraft led the controller to issue an incorrect crossing clearance.
- The aircraft's unclear radio communications and imprecise readbacks made it difficult for controllers to verify the aircraft's actual location.
- The sudden change in departure runway requirements and the issuance of new taxi instructions increased the complexity of the taxi sequence.
- The ground movement radar system lacked sufficient identification features (labels) to easily distinguish the aircraft from other ground traffic.