New wake turbulence separation standards are improving efficiency of operations at Memphis International Airport:
  • During the busiest periods, arrivals are now about 7.5 percent and departures 5 percent closer to each other on average as they land and depart from the same runway
  • Average taxi time from the gate during the busiest departure periods is 2.8 minutes less — a 27 percent reduction
  • FedEx has been able to add an additional nine flight operations per hour — a 17 percent increase
New procedures will help recategorize how close planes can be when landing at airports. This improves efficiency of operations.

Airports referenced in this story

NextGen Implementation Plan (PDF)

Performance Based Navigation (PBN)
Addresses ways to leverage emerging technologies, such as satellite-based Area Navigation and Required Navigation Performance, to improve access and flexibility for point-to-point operations.
Separation Management
Provides controllers with tools to manage aircraft in a mixed environment of varying navigation equipment and wake performance capabilities.

If you've ever gotten too close to an 18-wheeler on the Interstate, you know that those big rigs produce a draft that can literally push your car. The same is true for aircraft. Aircraft produce a wake, similar to those large trucks — vortices of air that emanate from the wings and trail behind the aircraft, creating turbulence. Standards for the required distance between aircraft due to the wake they produce have been in place for decades, but now the FAA is overhauling those standards based on advances in wake vortex research. The result is that planes can fly closer together without compromising safety, which means that more planes can take off and land at busy airports.

Several decades ago, the FAA determined the required minimum wake turbulence separation standards, which were based mainly on aircraft weight. Of course the longer the required distance between aircraft, the fewer aircraft can take off and land, which can cause arrival delays and increase the time aircraft wait on taxiways and runways, burning fuel.

Since the weight based categories were implemented in the early 1990s, airline operations and the mix of aircraft types in airline fleets have changed dramatically, from the rise of regional jets at the light end and the A380 at the heavy end. Recent research to re-categorize wake turbulence separation standards shows that in addition to its weight, other aircraft characteristics (speed, wingspan) also affect both the strength of the wake turbulence an aircraft generates and its reaction to the wake generated by aircraft in front of it.

Through research conducted by the FAA, the Transportation Department's Volpe National Transportation Systems Center, the aviation industry and EUROCONTROL, the 39-nation European Organization for the Safety of Air Navigation, experts found that regrouping aircraft types according to similarities in their wake turbulence characteristics allows safe reduction in separation between aircraft, which will increase efficiency and airport capacity.

In November 2012, the FAA implemented an adjustment to the wake separation standards at Memphis International Airport. Since then, the throughput rate (number of departures and arrivals) at Memphis increased 2.3 percent during the busiest arrival time of the day and 1.1 percent during the busiest departure periods. There has also been an improvement in airport efficiency. Arrivals at Memphis are now about 2.5 percent closer to each other and departures 1.4 percent closer to each other on average as they are landing and departing from the same runway. During the busiest arrival and departure periods of the day the improvement is even higher: 7.5 percent and 5 percent, respectively.

Together with improved arrival routes that were implemented at Memphis in late July 2012, the new wake standards have also contributed to the efficiency of arrivals in the Memphis terminal airspace (the airspace surrounding the airport in a 30- to 50-mile radius up to 10,000 feet). On average, arriving aircraft now fly almost one minute shorter time and just under three nautical miles (nm) shorter distances in the terminal airspace, with the highest observed savings reaching almost three minutes and 10 nm.

The average taxi time from the gate during the busiest departure periods has been reduced by 27 percent — aircraft take 2.8 minutes less on average to taxi to the runway — cutting fuel consumption and emissions.

FedEx, the main carrier at Memphis, is reporting significant capacity increases since the reduced separation standards have been in place, adding an additional nine flight operations per hour, an increase in operations of 17 percent.

"I've been looking at these numbers for eight years, and the first night I couldn't believe what I was reading," said Jim Bowman, FedEx vice president of flight operations. "In the daytime now, we are rarely seeing a queue of airplanes waiting to take off. We are trying to figure out ways to get planes to the runway fast enough to feed what the new program allows us to do."

Memphis is the first airport where FAA's Phase 1 of wake recategorization separation standards has been implemented. The agency plans to expand the Phase 1 standards to other airports in 2013 and 2014, and estimates an average capacity increase of 7 percent. Individual capacity increases will depend on the mix of aircraft operating at each airport.

The second phase of the initiative will determine the optimal wake separation between two given aircraft from a sample of 100 types that represent 99 percent of the global traffic. The separation will have to meet the conditions of safe pairwise separation standards.

Recategorization Phase 2 is planned for completion in fiscal year 2015 with implementation following the approval of safety documentation and updates to the FAA order that defines separation standards in the national airspace system.