Turbulence arises from all aircraft, but the world’s largest passenger aircraft – the new Airbus A380 doubledecker super-jumbo – poses new challenges for the aviation industry.
Demanding safety criteria for super-jumbo
Turbulence arising from the new Airbus A380 exceeds all other aircraft. That is why new safety criteria had to be defined before this aircraft enters service.
All aircraft generate turbulence as they lift. The strength of this turbulence is proportional to many factors, including the aircraft’s weight, and may cause trouble for other aircraft entering the disturbed airspace. As the A380 is about 40% heavier than other common large aircraft flying today, new safety criteria had to be defined.
By any standards, the Airbus A380 is a big aircraft. For example, it is 40% heavier than a Boeing 747-400 and capable of carrying many more passengers. However, its greater size means that it may create stronger turbulence than existing aircraft, and this turbulence can cause loss of control or even structural damage to aircraft entering the disturbed air if the risks are not properly controlled.
“If a smaller aircraft encounters such disturbed air – or vortex wake – in ‘exactly the wrong way’ then severe acceleration or even structural damage can occur,” explains Paul Wilson, Head of the Airport and Environmental Division of Brussels-based EUROCONTROL. He has formerly been an air traffic controller at Heathrow Airport for 18 years and general manager of the Stansted Control Tower for six years.
One way to mitigate wake vortex encounter risk is by ensuring that the wake is sufficiently decayed so that unacceptable effects are not encountered by following aircraft.
“The primary means of control are separation criteria between aircraft that are sufficient to allow the vortices to decay in strength,” explains Mr Wilson.
In 2003, an international team of wake vortex and operational experts was established, drawn from US and European aviation organisations, including Airbus. The objective was to derive and agree on a revised set of separation criteria for the A380 prior to this aircraft entering passenger service.
Mr Wilson participated in this project from the beginning.
“In addition to the technical work of establishing the vortex separation criteria for the A380, it was essential that a full safety assessment report was produced to support this work,” he says.
Fresh pair of eyes
To enhance the quality of the safety assessment, it was decided by the steering group that this should be undertaken by an external body who would act as a fresh pair of eyes and ensure that every possible hazard was identified and dealt with.
“This was groundbreaking work. It had never been accomplished before, and due to its complex nature it turned out to be more time-consuming than first thought,” Mr Wilson continues.
After the initial work, in devising the technical process to establish the required separations, was complete, it was time to enlist the support of a safety team to construct and complete the safety assessment on behalf of the steering group. For this task DNV was selected, led by Dr Tim Fowler from the company’s London transport team.
Finally, in September 2006, after full agreement was achieved in the multi-stakeholder team, the safety case was completed. Then the safety requirements were presented to the International Civil Aviation Organization (ICAO) in November.
Fully supported conclusion
“DNV was an essential part of our team that brought this project to a successful result,” says Mr Wilson.
In terms of vortex wake separation criteria between aircraft, the aviation industry divides aircraft into three broad weight categories, known as Heavy, Medium and Light. According to the new vortex wake separation criteria, aircraft in these categories should be separated by a minimum of 6, 8 and 10 nautical miles respectively when landing behind an A380 (the current criteria are 4, 5 and 6 nautical miles respectively for aircraft landing behind conventional Heavy aircraft). These figures are important parameters for the future safety and capacity of airport operations.
Great impact
“The successful results and lessons learnt from this project will have a huge impact on the aviation industry in a 4-5 year time frame. Significant improvements can be made to aircraft operation as a result of this work,” concludes Mr Wilson.