David Kaminski-Morrow / London
Scheme could be extended after lateral offset procedure cuts risk of collision in high-density area off US East Coast
Organisers of a trial to cut mid-air collision risks by encouraging airlines to fly a lateral offset procedure in West Atlantic oceanic airspace are hailing the test as a success - despite a lack of data to quantify the results.
US Federal Aviation Administration officials initiated the trial two years ago in a bid to counter the potential collision hazard posed by the implementation of reduced vertical separation minima (RVSM) to increase capacity in the busy West Atlantic Route System (WATRS). Although the trial was due to end in November, having already been extended by a year, there is support for keeping it active.
The WATRS area, part of which includes the New York flight information region, is a complex area of high-density traffic with two dominant traffic flows - the transatlantic flow from North America to Europe and a strong crossing flow from North to South America via the Caribbean and Bermuda.
"With the increasing accuracy of [satellite-based navigation], RVSM created a lateral overlap [collision] risk which was far higher," says an FAA source involved in the trial.
Once a suitably equipped aircraft passes through the gateway to WATRS oceanic airspace, its crew can exercise an option to offset to the right of the centreline track by either 1nm (1.9km) or 2nm, reducing the head-on collision risk by distributing traffic across three separate tracks.
But under the trial's rules, aircraft had to return to the centreline before re-entering radar airspace. For the north-south traffic flow this would typically occur around Bermuda. This requirement, says the FAA source, has made it almost impossible to calculate with any accuracy how many aircraft are opting to offset.
"It has always been optional for the operator. If they want to participate, they can," he says. "But the only way we can determine who's doing the offset is by using the radar data. Our hope was to gain data [on the number of participants]. But we're finding it very difficult to do that."
Another problem has been incompatibility with North Atlantic wake turbulence mitigation procedures. While the WATRS trial prohibits offsets to the left, the North Atlantic procedure allows offsets either side; this has led to confusion, with some WATRS aircraft offsetting to the wrong side.
Even though the trial is short on quantitative data, the official says it has been worth implementing: "Even having a [number] of aircraft offsetting can reduce the [collision] risk, he says."
Source: Flight International
