The lone US air traffic controller on duty the morning Comair Flight 5191 crashed had cleared the jet for takeoff, then turned his back to do some “administrative duties” as the aircraft veered down the wrong runway, a federal investigator said in Kentucky.

Investigators in Kentucky, probing a weekend plane crash in which 49 people were killed, were today trying to determine why the commuter aircraft used a runway that was too short for take-off.