New wake separation rules hold capacity key

New wake turbulence separation standards could play a crucial part in developing ‘super density’ operations at established major US airports in future.

The Federal Aviation Administration (FAA) launched new wake categories in November together with revised separation standards at Memphis International Airport – designed to keep aircraft away from potentially hazardous wake turbulence while making final approaches.

The new standards were deployed on November 1 with the close collaboration of cargo carrier FedEx which uses Memphis as its principal cargo hub.

The standards were developed to increase capacity and reduce delays throughout the National Airspace System but do not add any additional cost. The impact is expected to be significant however with a potential capacity increase as much as 20 per cent at Memphis alone. If universally applied, the reductions in taxi times and departure delays are being hailed as rivalling  the same capacity boost offered by new runway development.

The method of wake turbulence categorisation until now has been based on maximum gross takeoff weight, inefficient due to the wide range of aircraft categories, and the excessively conservative separation needed for some aircraft pairs. That resulted in fewer landings and therefore less capacity.

Research efforts by the FAA, NASA and Eurocontrol over the last decade to safely reduce international separation standards for single-runway arrivals and departures have fed into the ICAO Wake Turbulence Recategorisation (ReCat) initiative, the conclusions of which the US is now applying at Memphis.

Under the new re-categorisation, aircraft are divided into one of six categories (labeled A-F) based on additional considerations such as approach speeds, wing characteristics, and lateral control characteristics. The current heavy category is now split into three wake categories, A (super); B (upper heavy); and C (lower heavy) aircraft.

When a lower heavy jet follows an upper heavy jet into an airport, the separation standard will remain the current four miles. But when an upper heavy jet follows a lower heavy jet, the separation can now reduce to three miles – a distance that is still safe, but allows for more traffic to fly into and out of an airport.

A three-phase project, Phase II will develop an overall pairwise static wake separation matrix, while Phase III will include real-time weather/wind information to permit dynamic pair-wise separation.

The FAA which is expecting a complete transition from the old wake separation standards by the end of 2014 estimates that once they are implemented across national airspace, the average capacity increase at a US airport will be around seven per cent with specific capacity gains driven by the fleet mix in operation.


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