Mystery still surrounds an airprox incident during which a Scandinavian Airlines Airbus A320-family jet unexpectedly encountered a Russian-built surveillance aircraft.
The incident took place on 3 March as the Airbus climbed out of Copenhagen en route to Rome.
It had reached 24,000ft when an unidentified aircraft – which had not appeared on the cockpit’s collision-avoidance display – flew from right to left in front of, and just above, the Airbus, says a source familiar with the investigation.
The Airbus captain initially estimated to investigators that the distance between the aircraft was around 300ft (90m).
Swedish armed forces subsequently identified the mystery aircraft as an Ilyushin Il-20M, a heavily-modified version of the Il-18 turboprop, which is used for electronic surveillance.
Russia’s air force operates the Il-20M but the origin of the aircraft involved, the reason for its presence and the status of its transponder – which should have provided data to the Airbus’s collision-avoidance system – are unclear.
The source says the event occurred over international waters in the western Baltic Sea and, because the Airbus was Danish-registered, Swedish authorities handed their information to counterparts in Denmark.
Danish accident investigation commission HCL confirms it received the data from the Swedish side, and adds that it classified the event as a “major incident”.
Under Danish legislation, it says, the details have been forwarded to the Danish Transport Authority.