Pilots and controllers will still need to check in with each other to be assured that the two-way voice channel is there, but even check-in and acknowledgement can be carried out and confirmed on both the controller's and pilot's human/machine interfaces.
The datalink connection is initiated by the pilot operating the aircraft datalink initiation capability service. The pilots will see their clearances and handovers pop up on their datalink communications display unit, and the controllers will be able to see all the detail they need about a datalink-equipped aircraft, its performance and intentions on its electronic flight progress strip, so there should be no need to confirm details or to issue instructions unless a change is needed. This aircraft is inbound to a busy airport. A system known as the controller access parameter service (CAP) enables the controllers to interrogate the aircraft flight management system for its current vertical rate of change, indicated airspeed or Mach number, magnetic heading, selected flight level and wind vector.
As usual, the en route controller clears the arriving aircraft to descend to an initial level on course for one of the terminal area holding fixes, then hands the aircraft over to approach control via the ATC communications management service, uplinking the handover advice to the crew. This unambiguously transfers control from one sector to the new controller, who can use the CAP to check the aircraft is complying with the 250kt (460km/h) speed restriction at the standard point approaching the holding fix, and show whether the aircraft's height, heading and rate of descent put it on the right profile for vectoring to intercept the final approach. If it is, approach can hand the aircraft over to the director, who can check the speed of sequenced aircraft to ensure continued separation. On passing the outer marker, the crew is transferred to the tower. At any time, if an aircraft is blocking the voice channel with a stuck transmit switch, the controller can use the ATC microphone check service to uplink to all datalink-equipped aircraft a message for crews to check their switches.
Source: Flight International
