Airbus flight-test managers are questioning the validity of data on which the International Civil Aviation Organisation (ICAO) based its recommendations to greatly increase separation distances for the A380, and say they were “surprised” by the timing of the advisory letter published last month. The manufacturer, meanwhile, is planning to carry out back-to-back wake vortex tests of the A380 with a Boeing 747-400 and 777 at Istres next year.
Until ICAO issued its “interim policy” letter on 10 November, Airbus had believed that because A380 wake vortices are only slightly greater than the 747’s, the existing separation requirement for “heavy aircraft” of 4nm to 6nm (7km to 11km) during approach and 5nm in the cruise would be applicable. However, ICAO has ruled that approach separation should be increased to 10nm for any size of aircraft following the A380, and 15nm in the cruise.
“We were somewhat surprised by the timing as we’re still gathering wake-vortex data,” says Airbus vice-president flight test Fernando Alonso. “The ICAO policy is based on a type of computation that has not been validated by flight-test measurements. We disagree with its recommendation.” Airbus senior vice-president flight test Claude Lelaie adds: “We strongly believe there is something fundamentally wrong with ICAO’s reasoning.”
Alonso says that now the new distances have been adopted in France, they threaten to cause disruption to the A380 flight-test programme because much of the flying is undertaken from Toulouse-Blagnac airport. “When we are doing touch and goes, or have two A380s in the circuit, we can virtually close the airport,” he says.
Airbus has been conducting wake-vortex trials since almost the start of the flight-test programme and Alonso says the trials show that “on average, A380 wake is at a slightly higher level than the 747”. However, he adds that, for both aircraft, the raw data shows a high scatter of results, but the average difference between the wakes of the two aircraft is far smaller than the scatter of the measurements. “There has been no demonstration that the 747 is the limit for the ‘heavy’ category,” says Alonso.
“Next year we will make comparative measurements of wake vortex of the 747-400, 777, A340 and A380 in sequence, the same day with the same weather conditions,” he adds.These tests will be carried out at the Istres test centre in southern France. Airbus also plans to fly trials with a small-class airliner – an A320 – trailing the A380.
Max Kingsley-Jones /