On 2 July 2008, a Boeing 737-700 being operated by Air Tran Airways on domestic scheduled passenger flight from Baltimore to Seattle-Tacoma had, in normal ground visibility at night, failed to hold clear of runway 34R during taxi in after landing on runway 34C at destination and had passed almost directly underneath a North West Airlines Airbus 330-200 which had just become airborne on a flight to London Heathrow.
An Investigation was carried out by the National Transportation Safety Board (USA) (NTSB). It was found that the A330 had been in compliance with a valid take off clearance and that the 737 had been in breach of its taxi in clearance.
It was established that having landed on runway 34L and taken Rapid Exit Taxiway ‘F’, the 737, with the First Officer as PF, had then failed to hold short of runway 34 as instructed and was crossing the runway as the A330 passed almost directly overhead after it had become airborne on runway 34R between taxiways M and N with an estimated vertical clearance of just over 400 feet between the two aircraft. It was noted that the hold short clearance had been acknowledged twice but that the 737 crew claimed that they had not seen the illuminated hold short line prior to the incursion. They also stated that they had not heard the 330 being given take off clearance on the same frequency.
The 330 flight crew subsequently advised that they had not seen the 737 and had been unaware of the incursion.
It was note that taxiway F had enhanced hold short lines that were 77 metres from the Runway 34R left hand edge markings and that taxiway F had a lit centreline and elevated runway guard lights at the holding point concerned.
It was noted that Airport Surface Detection Equipment, Model X (ASDE-X) had been activated as the incursion occurred with both an aural and visual alert but no useful response had been available to the TWR controller.
The Investigation concluded that the Probable Cause of the conflict was “the diverted attention during taxi of the flight crew in the (Boeing 737)” and that contributing to the incident was the fact that the 737 had not followed its air traffic control clearance.
The Final Report of the Investigation was adopted on 26 September 2008. No Safety Recommendations were made.