Airlines participating in a trial of datalinked position reports over the North Atlantic are to be allowed to stop making additional voice reports on high frequency radios as early as 8 may following the initial success of the work.
Air Canada is optimistic that minor upgrades to ground systems in the UK will satisfy reliability criteria and enable aircraft to transmit their positions solely through automatic dependent surveillance (ADS) as they cross mandatory waypoints.
The trial, which began last July under the auspices of ICAO, is being conducted in the Gander and Shanwick oceanic control areas. Aircraft equipped with FANS-1/A avionics are able to log on to a ground processor as they enter the trial airspace.
As the aircraft reaches each of the waypoints programmed into its flight management system, it automatically transmits the waypoint coordinates to the processor. The processor then turns the data into a standard position text message and sends it to the air traffic centre where it is displayed alongside regular HF voice reports.
Air Canada director of aeronautical services Grant Wilson says: "Our initial analysis shows that datalink is more efficient than HF voice by about 400%. Typically a voice report takes up to eight minutes to reach the controller. But we’re seeing 98% of the ADS reports coming through within two minutes."
Air traffic services provider Nav Canada is confident that its Gander Automated ATC System is ready to accept the ADS messages. However, its UK counterparts at National Air Traffic Services are still upgrading flight-data processors to deal with the information.
A spokesman for NATS says: "We’re not 100% convinced about the May starting date. It’s based on the requirement to obtain clean data; we have to be able to convince our regulators.
"We still need to fix it so that the transmitted ADS data is accepted by flight-data processors, without too many referrals or rejections. But although we might not go operational in May, we’re only talking about a difference of weeks."
Until then, pilots must still make voice reports as backup. Air Canada's Wilson says: "We’re hoping to hear that the next upgrade to filters will satisfy all the requirements, so that the ADS part can go truly operational.
"I have to emphasise that this needs to be done incrementally. We’ll only have a small sample of aircraft - maybe 10% - participating. But if they’re no longer required to do HF voice reports, then we can begin looking at opening up frequencies."
While the FANS-1/A operational trial specifically excludes tests of controller-pilot datalink (CPDLC), Nav Canada says it is carrying out its own North Atlantic CPDLC tests with Air Canada.
Following months of ground simulations, initial airborne tests were conducted in January. Pilots flying an Air Canada Boeing 747-400 from Toronto to Paris downlinked pre-formatted clearance requests to the Gander Automated ATC System.
Controllers uplinked clearances back to the aircraft, and free-text messages were also exchanged to coordinate the tests. Further tests were carried out in the same week on a London-Toronto flight.
Wilson says CPDLC transmissions were exchanged over both VHF and satcom, with successful switching between the two media.
Air Canada and Nav Canada are planning further transatlantic CPDLC tests in the next few weeks, during which controllers will communicate with two aircraft simultaneously.
Nav Canada believes CPDLC will reduce the problems associated with HF voice on North Atlantic routes. It says: "HF quality varies depending on atmospheric conditions, and the increasing growth in the number of flights over the North Atlantic further emphasises the problems of HF communication due to frequency congestion."
The organisation anticipates that an ICAO-endorsed operational trial of CPDLC, running along similar lines to that for ADS waypoint reporting, will begin by the autumn of this year.
A spokesman at ICAO’s North Atlantic regional office says that the ADS operational trials is effectively "a done deal" and that, although no decisions have been made, such a CPDLC trial is likely to feature on the agenda at its upcoming FANS Implementation Group meeting in Paris in late March.