US investigators probing the weekend's fatal crash of the Comair Bombardier CRJ100 in Lexington, Kentucky have disclosed that the single air traffic controller on duty only had two hours’ sleep in the 24h prior to the accident – a period which included two shifts totalling over 14h.

It follows the revelation that Lexington Blue Grass airport had been concerned about potential difficulties in meeting US Federal Aviation Administration requirements demanding that separate controllers be assigned to cover radar and tower control functions.

Investigators from the US National Transportation Safety Board (NTSB) conducted a second interview with the controller on duty at the time of the 27 August accident, when the CRJ mistakenly attempted to depart from the shorter of the airport’s two runways.

They discovered that he had worked an eight-hour shift from 06:30 to 14:30 the previous day but had slept for only two hours before going back on shift at 23:30. This second shift period had been due to last until 08:00 on the day of the accident, which occurred shortly after 06:00.

“In this interview with the controller [we asked], did he obtain any sleep between the two shifts when he went off duty at [14:30 on 26 August] and went back on duty [at 23:30]?” said NTSB board member Debbie Hersman, speaking at a briefing on the Comair investigation. “He advised our team that he got approximately two hours of sleep.”

A memorandum dated 16 November 2005, apparently from Lexington’s air traffic manager, cites the FAA requirement for separation of tower and radar functions but points out that the facility would find it difficult to meet the demand.

“Our staffing rarely allows for a second controller to be assigned to the [overnight shift],” it states. To satisfy the FAA requirement, Lexington planned to hand radar control to the Indianapolis area traffic centre between midnight and 06:30, leaving the airport’s tower as a non-radar facility providing services under visual flight rules.

The communication goes on to state that, until Indianapolis centre controllers were trained to handle Lexington’s airspace, there would be occasions when a second controller would be assigned to the overnight shift in order to keep the tower and radar functions apart.

It is unclear whether, or when, the intended handover of overnight radar control to Indianapolis centre took place.

Forty-nine of the 50 passengers and crew on board the CRJ were killed when it crashed just off the end of Lexington’s short runway 26. The jet had been cleared to depart from runway 22, which was twice as long.

Although both pilots arrived in Lexington the day before – the captain at 15:30 after deadheading on an inbound service, the first officer at 02:00 as crew on flight 9471 from New York JFK – the nature of the early-morning flight, and the information about the controller, has raised questions on whether fatigue played a role in the accident.

Hersman had previously mentioned a curious aspect of the crew’s preparations for the fatal flight: for reasons as-yet unknown, the pilots originally boarded a different aircraft, a Comair CRJ200 with serial number 7824, and began start-up procedures before being advised that they were on the wrong jet.

Read Airline Business deputy editor Brendan Sobie on how people were too quick to blame pilot error in the immediate aftermath of the fatal Lexington Comair CRJ100 crash