Concern over radio transmission reliability discussed days before regional jet’s encounter with US presidential helicopter.
Investigators have revealed that two transmissions from the US presidential helicopter, advising preparation for take-off, were not received by air traffic control before a loss-of-separation incident involving an Embraer 170 departing Washington National airport.
The incident occurred on 4 August, just five days after a meeting between National air traffic tower personnel and the helicopter squadron responsible for presidential transport, to discuss concerns that required 3min lift-off warnings were not being received by tower controllers.
Bound for Pensacola, the Sikorsky VH-3D – operating with its ‘Marine One’ callsign – had been preparing to lift off from The Ellipse, an oval of ground adjacent to the White House. The helicopter was operating temporarily from this location owing to construction.
Its crew attempted to contact Washington National airport’s helicopter controller, to give the 3min notification. Less than a minute later the crew made a second attempt to reach the controller, asking whether the notification had been received.
Neither message could be heard on the air traffic control frequencies, says the National Transportation Safety Board in preliminary findings.
It says the helicopter controller, who had previously been briefed on a pending VIP movement, received only an “unintelligible transmission” and broadcast an advisory that it had been broken and unreadable.
The helicopter crew had also unsuccessfully tried to relay the 3min call through the Anacostia-Bolling military base.
Almost 3min after the helicopter crew’s first attempt at contact, a separate local tower controller cleared the Envoy Air Embraer 170 to take off from National’s runway 1.
The pilots received a collision-avoidance system traffic advisory but neither saw the southbound helicopter, which was passing about 0.82nm to the right, and 700ft below.
No resolution advisory was displayed or commanded, according to the Embraer’s captain.
Departures from National would normally be halted upon receiving the 3min call from the presidential helicopter.
But with this transmission not having been received, the local controller proceeded to clear the Embraer for take-off. The presidential helicopter, in the meantime, had lifted off and its crew was able to contact the tower once it reached sufficient height.
According to the safety board, the helicopter crew “immediately reported” visual contact with the Embraer. None of the occupants on board either aircraft was injured.
US FAA technicians carried out a coverage analysis as a result of the missed transmissions on the day of the incident, and determined there was “not adequate line-of-sight” to ensure communications with The Ellipse.
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