US National Transportation Safety Board (NTSB) officials have determined that the crew of a Comair Bombardier CRJ100 that crashed on take-off at Lexington’s Bluegrass Airport on August 27 2006 failed to use available runway environment cues and aids and did not verify they were on the correct runway before attempting a take-off.

Contributing to the probable cause were 40 seconds of “non-pertinent conversations” during a critical phase of Comair Flight 5191’s 150-second taxi from ramp to runway, and the US FAA’s failure to require specific clearances for every runway to be crossed during taxi, the NTSB concluded.

Soon after that conversation, which was prohibited by federal “sterile cockpit” regulations, the pilots attempted to take-off on an unlighted general aviation runway too short for commercial aircraft, noticing the error too late to abort the take-off.

The aircraft struck a berm off the end of the 3,500ft (1,100m) runway while the first officer pulled “full nose up control column input” in an attempt to clear the obstacles. The aircraft struck trees and burned roughly 2,000ft past the end of the runway.

The final hearing came less than 11 months after the crash that killed 49 crew and passengers on the early morning flight to Atlanta. The first officer was the only survivor. The investigation involved 31 NTSB investigators and staff and consumed 13,000 man hours.

Investigators said differences between the pilots’ airport diagram and the actual airport environment due to construction and other errors were likely not factors in the wrong runway choice, nor was similar information missing from the automated airport information service the pilots listened to before taxiing.

Further, investigators said “multiple external cues” and aids were available to help the pilots establish that their position prior to takeoff was incorrect, including cockpit instrumentation, the airport diagram and air traffic controllers.

NTSB staff downplayed the impact of the control tower being staffed by one controller rather than two for that particular shift, per verbal FAA guidance for the facility, commenting that workload was light.

Administrative tasks the controller turned to after clearing the CRJ to take-off, though not prohibited, could have waited until a more opportune time however, investigators said, as he could have elected instead to monitor the CRJ and perhaps noted and pointed out the pilots’ error.

Staffing issues at Lexington were resolved after the accident, with six new controllers hired at the facility, bringing the total to 25, according to the testimony.

Board members issued five new recommendations, adding to the six it submitted to the FAA and its controllers in December and April.

Those earlier recommendations included requiring proper runway checks and defining certain minimum runway lighting conditions for takeoff for pilots. Directed at controllers were recommendations related to fatigue and safety awareness.

The new recommendations to the FAA include requiring airline and air taxi aircraft crews to put procedures in place to verify an aircraft is positioned on the proper runway, and for those aircraft to have cockpit moving map displays or cockpit alerting systems; mandating airports to install enhanced centerline taxiway markings and painted holding position lines; prohibiting controllers from issuing a take-off clearance until all runways en route to the take-off runway are crossed; and requiring controllers to refrain from performing administrative tasks when they are controlling moving aircraft.