Pilots of a Comair jet that crashed in Kentucky, killing 49 people, failed to recognize obvious signs they were on the wrong runway -- one that was too short for safe takeoff, U.S. investigators said on Thursday.

The National Transportation Safety Board concluded after a daylong hearing the crew missed visual cues at the Lexington airport -- like runway markings, construction barricades and signs before proceeding down the incorrect path last August 27.

The crew also failed to conduct proper preflight procedures for Flight 5191 to Atlanta, confirm its position on the runway, and engaged in idle chatter on unrelated matters in violation of federal aviation and company regulations that may have distracted them, investigators said.

There were some things done in that cockpit that should not have been done and some things that weren't done that should have been done, said safety board Vice Chairman Robert Sumwalt, a former airline pilot.

Critical items were missed, vigilance was lost on this flight, Sumwalt said.

The pilots thought the Bombardier CL-600 was on the correct runway but did note that the tarmac, which was under construction, was not lighted. They realized something was seriously amiss during their takeoff roll but it was too late to stop.

The plane struck a berm and trees in the predawn darkness before exploding in flames. The co-pilot was the lone survivor.

It was the worst U.S. air disaster since the 2001 crash of an American Airlines jet in New York that killed 265.

Comair flies regional routes for Delta Air Lines

Investigators also concluded after fierce debate the lone veteran Federal Aviation Administration controller on duty did not contribute to the crash when he turned his attention to administrative matters after clearing Comair, the only plane operating at the time, for takeoff. He was not required to follow the aircraft movement from that point.

Investigators knew quickly after the crash what happened, but they spent the next 11 months trying to figure out why.

There was no 'Ah-hah!' moment, said Debbie Hersman, the lead investigator at the crash scene. In retrospect on pilot conduct, she observed, that their heads weren't in the game.

Hersman said the probe was baffling because Capt. Jeffrey Clay and First Officer James Polehinke were experienced, respected by peers and had flown at the airport previously.

The crew had enough time off before duty and weather was not a factor. The plane was mechanically sound. Two previous flights departed uneventfully on the correct runway.

The safety board said the crew did not receive proper notice on runway conditions, but said the taxi route was simple and other signs were clearly apparent that the absent notice was a non-factor.

Investigators also said they could not determine whether a second controller -- required but not staffed by the FAA -- would have prevented the crash.

The pilots' union at Comair said cockpit charts on airport ground configurations may have confused the crew.