The National Transportation Safety Board (NTSB) is investigating a March 23rd incident in which the only air traffic controller on duty at the Ronald Reagan Washington Washington National Airport (DCA) apparently fell asleep, thwarting attempts by two flight crews and other controllers to make contact with him.

The incident occurred between 12:04 a.m. and 12:28 a.m., when American Airlines flight 1012 executed a missed approach after numerous attempt to make contact with the supervisory controller in the DCA control tower failed.

According to the NTSB, the crew reported their situation to controllers at the Federal Aviation Admininstration’s Potomac Terminal Radar Approach Control (TRACON0), who vectored the aircraft back to the airport for another approach.

The approach controller and the TRACON supervisor on duty made several attempts to contact the tower controller via telephone, but were unable to establish contact. The TRACON approach controller advised the crew of American flight 1012 that the tower was apparently unattended, and that the flight would be handled as an arrival to an uncontrolled airport.

The flight was again cleared for approach, and instructed to switch to the tower frequency. At 12:12 am, the crew returned to the tower frequency, still unable to make contact with the tower, made position reports while inbound, and landed on runway 1.

United Airlines flight 628T (UAL628T), operating as a scheduled 14 CFR 121 passenger flight from Chicago-O'Hare International Airport to DCA, was advised of the service interruption by the TRACON approach controller and subsequently transferred to the tower frequency at 12:22 am.

The United flight, also unable to make contact with the tower, made position reports on the tower frequency while inbound, and landed at 12:26 am. At 12:28 am, American flight 1012, on the ground at DCA, established contact with the tower controller, and normal services were resumed.

The controller had been working his fourth consecutive overnight shift

Human fatigue issues are one of the areas being investigation by the NTSB. The controller in the tower at the time of the incident, along with other FAA officials at DCA, has been interviewed. The controller, who had 20 years' experience -- 17 of those at DCA -- indicated that he had fallen asleep for a period of time while on duty. He had been working his fourth consecutive overnight shift (10 pm - 6 am).

The NTSB will also interview officials at the TRACON facility tomorrow.

NTSB Air Traffic Control specialist Scott Dunham is the investigator-in-charge. He is being assisted by an NTSB human performance specialist. Parties to the investigation are the FAA and the National Air Traffic Controllers union.

Citing a fatal aircraft accident and two incidents that occurred in a 23-month period between 2007 and 2009, on Monday, March 21, the NTSB issued a safety recommendation letter to the FAA asking the agency to improve the safety of air traffic control operations by prohibiting air traffic controllers from providing supervisory oversight while performing operational air traffic duties.