Preliminary information about the final few minutes of yesterday's ill-fated Ethiopian Airlines flight out of Beirut indicates that the aircraft was struggling to comply with air traffic control instructions to change heading.
The Boeing 737-800, bound for Addis Ababa as flight ET409, departed towards the south from Beirut's runway 21 in darkness, but initial information suggests that the jet turned north, and was cleared to climb to a minimum crossing altitude to transit through Syrian airspace.
An air traffic control source familiar with the event tells ATI that an early exchange with Beirut centre focused on the aircraft's navigating relative to the VOR beacon identified as CAK, which lies on the Lebanese coast north of Beirut.
But he says that air traffic control needed to ensure separation between ET409 and two aircraft which were on approach to Beirut's runway 16 at the time.
In order to maintain separation, he says, ET409 was instructed to turn left onto a heading of 270° but the crew apparently failed to comply.
"Instead it turned left, further," says the source, adding that the turn continued until the 737 reached a heading of about 140°, a course which took the aircraft towards high terrain.
Controllers tried ordering the aircraft to turn right, warning that it was proceeding towards a mountainous area, but the source says that radar contact was lost with the jet shortly afterwards.
It came down off the Lebanese coast south of Beirut. Ninety passengers and crew were on board the jet but rescue teams have not found any survivors.