Aircraft

Airbus claims unprecedented tests of conditions experienced by aircraft following the Airbus A380 in flight demonstrate that the wake turbulence it creates is no worse than that produced by any other heavy aircraft.

Official standards, however, require that the A380 have its own 'super-heavy' category, extending separation for aircraft trailing the A380 by 2nm (3.7km) compared with in-trail separation for 'heavy' category jets.

Airbus senior vice-president for product safety Capt Claude Lelaie admits he does not see any indication that the ICAO-led steering group on the subject is likely to change that standard any time soon.

At an international aviation safety seminar held in Honolulu by the Flight Safety Foundation, IATA and the International Federation of Airworthiness in late October, Lelaie revealed more details about the nature of Airbus's in-trail tests.

The company flew types such as the Airbus A318 into the A380's wake - made visible by smoke streaming - and then compared the smaller aircraft's reaction with its behaviour when flying into the wake of an Airbus A340-600.

Measurements were taken in the A318, says Lelaie, with the pilot flying stick-free - releasing controls on entry to the wake - and with the pilot allowed to use manual control inputs.

Lelaie says they showed roll, pitch and altitude-deviation rates that, compared with those measured following the A380, were "so similar that the differences were of no significance".

Rates measured following deliberate wake encounters 11-12nm (20-22km) behind the A380 were a 15° per second roll rate with negligible pitch impact. The A380's wake behaviour showed the disturbed air tended to dip by about 1,000ft (300m) at 12-15nm behind the aircraft, a figure considered normal for other heavy types.

The number of light-detection and ranging scans of A380 wake behaviour on airport approaches now amounts to 280 runs, with 87 comparison runs for Boeing 747s and 39 for 777s. None of the information gained, says Lelaie, justifies a system like that which now exists, whereby an aircraft classified 'light' may fly 6nm behind a 747, but the same separation applies when a 747 is following an A380. A 747 can follow any other 'heavy' aircraft at 4nm.

Lelaie says the problem with securing acceptance of changes to current standards is the need to persuade "a lot of experts to agree on a lot of data".