The pilots of the Comair Bombardier CRJ100 that crashed on take-off at Lexington, Kentucky's Blue Grass airport on 27 August last year were apparently lured by "confirmation bias" into believing they were lined up on the correct runway in the pre-dawn darkness that morning.
They had "ample time" and a variety of runway environment cues and air traffic control resources they could have used to verify their actual position, the US National Transportation Safety Board has revealed in its final analysis of the crash.
Contributing to error were 40s of "non-pertinent conversations" during a critical phase of the 150s taxi of Comair Flight 5191 from ramp to incorrect runway, say investigators.
Soon after that conversation - which was prohibited by federal "sterile cockpit" regulations and Comair guidelines - the pilots attempted to take off on an unlit general aviation runway.
The aircraft struck trees and burned roughly 610m (2,000ft) past the end of the 1,100m runway, half the length of the correct runway. Forty-nine passengers and crew perished in the accident, with only the co-pilot surviving.
Investigators say differences between the pilots' airport diagram and the actual airport environment due to construction were probably not factors in choosing the wrong runway, nor was similar information missing from the automated airport information service listened to by the pilots before taxiing.
Rather, "multiple external cues" and aids were available to help the pilots establish that their position before take-off was incorrect, including cockpit instrumentation, the airport diagram and help from air traffic controllers, investigators have concluded.
The NTSB downplays the impact of the control tower being staffed by one controller rather than two for that particular shift, per verbal US Federal Aviation Administration guidance for the facility, commenting that workload that morning was light.
Administrative tasks the controller turned to after clearing the improperly positioned CRJ to take off, although not prohibited, could have waited until a more opportune time however. Some NTSB members chided the controller for not continuing to monitoring the flight through the tower windows, perhaps noting the pilots' error.
NTSB members have issued five new recommendations, adding to earlier calls for requiring proper runway checks and calling on controllers to address possible fatigue issues - the controller had obtained only 2h of sleep in the 24h preceding the crash.
As well as requiring airline and air taxi aircraft to have moving map displays or runway advisory alerting systems in the cockpit, the NTSB wants the FAA to require airports to install enhanced taxiway markings and asked that controllers do not issue take-off clearances until all runways en route to the take-off runway are crossed.