Manufacturer aims to convince ICAO to relax restriction
Airbus is to conduct a fresh series of wake vortex-encounter flight trials to persuade the International Civil Aviation Organisation to relax recommended separations on approach for aircraft trailing its A380 ultra-large airliner.
The manufacturer insists that a medium-category aircraft such as an A320 can safely fly 7nm (13km) behind a “super” category A380 on approach – a 2nm greater separation than when following a “heavy” Boeing 747 – but ICAO’s latest guidelines recommend an 8nm gap.
Also, despite ICAO’s wake vortex working group agreeing that minimum radar separation would suffice for an A380 following another A380 or a 747, “for an unknown reason ICAO has changed its mind and put back 4nm”, says Airbus senior vice-president flight tests Claude Lelaie.
Earlier this year, Airbus carried out 180h of vortex-encounter flight tests using an A380, 747, 777, A340-600 and A318. The results satisfied ICAO that in the cruise the standard spacing of 5nm/1,000ft (300m) could be retained for the A380.
Actual encounters with the wakes produced by the A380, 747 and A340-600 using an A318 were performed in the cruise, where contrails enabled the pilots of the trailing aircraft to see the vortices. “The best way to characterise the wake vortex is by the consequences of an encounter: vertical and lateral accelerations, roll, and so on,” says Lelaie.
But the runway approach tests relied on measurements by ground-based light detecting and ranging (Lidar), which were much more difficult to interpret.
“The plan is to characterise the vortex in approach by encounter, as it has been done in the cruise,” says Lelaie. “We need to review what we will do in the coming months. There are potential solutions.”
Lelaie says that under the current guidelines the industry finds itself in the “strange situation” whereby an A320 must trail an A380 by 8nm on approach, but only 6nm must separate a 747 and a light aircraft such as a Cessna. “Who is ready to fly in the wake of the 747?” asks Lelaie.
Airbus plans to take additional data to ICAO by October 2007.
Source: Flight International
