Central to the Washington mid-air collision inquiry is whether the military helicopter crew correctly identified the inbound PSA Airlines regional jet, having apparently been informed of its position and intention some 2min before the accident.
The MHIRJ CRJ700, arriving at Washington National from Wichita on 29 January, had initially been flying north along the Potomac river, in the approach stream for runway 1.
Shortly before reaching the Woodrow Wilson bridge, the CRJ crew accepted an air traffic control offer to switch to runway 33, which involved deviating to the right and flying just east of the Potomac, allowing the crew to align with the runway centreline before crossing the river on final approach.
The Sikorsky Black Hawk, its crew conducting a night proficiency flight, was nearing the airport from the opposite side, following the river on a southeast heading.
While investigators have yet to verify the precise communications between National tower controllers and the helicopter crew, archived air-ground transmissions indicate that the crew was advised of the CRJ’s presence as the jet prepared to manoeuvre for the runway change.
Using the helicopter’s callsign, ‘PAT25’, a controller refers to traffic “just south” of the Woodrow bridge, identifying the aircraft as a CRJ and giving its altitude, before stating that it is “[preparing] for runway 33”.
According to the transmissions, archived by LiveATC, the helicopter crew responds by stating that the traffic is “in sight” and requesting visual separation – a procedure under which the pilot is responsible for maintaining safe distance from the other aircraft.
The National Transportation Safety Board’s inquiry will need to ascertain whether the Black Hawk crew correctly identified the CRJ – which had separated from other traffic in the runway 1 approach stream – and, if so, whether it maintained visual contact as the jet turned for the runway.
While visual meteorological conditions prevailed, and visibility was good, the jet would have been flying at low altitude against a backdrop of city lights and its relative motion from the helicopter crew’s perspective would probably have reduced as it turned to align with runway 33.
Transmissions from the tower indicate that, moments before the collision, the helicopter crew was asked whether they had the CRJ in sight.
The inquiry will aim to determine the status of collision-avoidance equipment on each aircraft, and whether either crew, or the tower controllers, received any kind of automated conflict warning.
Although carriage of traffic collision-avoidance systems is mandatory on commercial aircraft, the response of such systems at low altitude is modified.
Typically the system will not issue a resolution advisory – a command for an evasive manoeuvre – if the aircraft is below about 1,000ft, as determined by the radio altimeter.
None of the 64 occupants of the CRJ, nor the three helicopter crew members, survived the accident.
