German investigators have disclosed preliminary details of a three-way encounter between an Airbus A380, an Antonov An-124 and a Boeing 747-400 near Frankfurt.
The An-124 suffered an in-flight disturbance moments after passing the A380, and subsequently came into conflict with the 747.
German investigation agency BFU states that the A380 and An-124 had been on opposing adjacent tracks, 37nm east Frankfurt Main.
The An-124 had been flying westward on airway UL984, at flight level 320. This was 1,000ft below the A380 which was travelling at flight level 330 in the opposite direction with the 747 flying 20nm behind.
One minute after passing the A380, says the BFU, the An-124 lost 200ft in height over the course of 15s, dropping to FL318 some 6nm after they crossed. Flight-recorder data, says the BFU, shows the An-124 also rolled 15° both left and right.
After passing the A380 the An-124's altitude "reduced and subsequently increased so that the original FL320 altitude was exceeded", says the BFU.
It climbed by 700ft over another 15s period, to FL325, passing beneath the 747 at FL321 as it did so.
BFU says the An-124 pilots received a traffic advisory from the collision-avoidance system as the jet climbed, followed by a resolution advisory instructing them to adjust vertical speed just after passing the 747. The An-124 stabilised at FL320 about 2.5min after the deviation began.
Investigators have not specified whether the disturbance was caused by the A380's wake.
"All three flights continued according to plan," says the BFU, which disclosed the 10 February incident in its latest bulletin.
Visual conditions prevailed. There was no significant weather in the vicinity at the time, according to the German meteorological service, which states only that there was a 30kt wind from the west-north-west at FL340.