Guy Norris/LOS ANGELES
NORTHWEST, AMERICAN and Singapore Airlines (SIA) are set to join Delta Air Lines and United Airlines in operational trials of in-trail-climb (ITC) procedures over the Pacific.
The use of ITC is being examined as a way of preventing one aircraft becoming "trapped" beneath another in oceanic airspace. United estimates that the use of ITC could save up to 18,000kg of fuel on an average long-distance flight, compared with leaving the trailing aircraft at its original level. ITC involves one aircraft climbing over another using the traffic- alert and collision-avoidance system to maintain safe separation.
"We also have additional requests from other airlines to join the trials," says the US Federal Aviation Administration trials research specialist, Ken Peppard, who adds: "Northwest and American will soon be joining, and SIA will probably take part in some of the operational trials."
The International Civil Aviation Organisation (ICAO) separation working group, which agreed to the entry of the additional airlines to the continuing trial, has also been "the driving force" behind a major review of the first year's ITC results. This studies ITC events in Oakland- and Anchorage-controlled Pacific airspace between September 1994 and October 1995.
Revealing the first findings of the review, Peppard says: "Pilots, controllers and ARINC operators feel comfortable with the procedure, and pilots are confident in the TCAS equipment." Aircrew have, however, suggested extending the outbound display range. "They'd like to see 80nm [150km] instead of just beyond 40nm," says Peppard.
During the study period, 48 ITC requests were made and 29 approved. Of the 48 requests, 45 were made to Oakland and three to Anchorage. The reasons for declining requests included other traffic, insufficient data supplied to the air-traffic controller and cancellations by aircrew because of reports of turbulence ahead.
The bulk of requests was made between 29,000ft (9,000m) and 33,000ft, and VHF co-ordination with the lead aircraft took 1-5min on average. The average time from the crew making an ITC request to air-traffic control replying was just over 7min, and the bulk of ITC events began with the trailing aircraft 33km behind the lead aircraft and ended with the overtaking aircraft 33km ahead. Maximum measured closure from the start to the end of the climb was 5.5km.
The US Airline Pilots Association has asked the ICAO separation working group and the FAA to develop and introduce an in-trail descent procedure. This would allow aircraft to escape from unacceptable headwinds and turbulence. "We've agreed to do that as quickly as possible," says Peppard.
Source: Flight International
