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System Tackles Wake Vortex Spacing Issues-NASA Technology Will Reduce Flight Delays

Trailing vortices in flightAirline passengers frustrated with ever-increasing delays at U.S. airports may be able to reach their destinations faster, because of a revolutionary new technology developed at the NASA Langley Research Center in Hampton, Va.

NASA researchers have designed a system to predict aircraft wake turbulence on final approach, so airliners can be spaced more safely and efficiently. The technology is called AVOSS or Aircraft Vortex Spacing System.

Photograph to the left shows aircraft during take off with trailing vortices.

AVOSS determines how winds and other atmospheric conditions affect the wake vortex patterns of different types of aircraft. The system uses laser radar, or lidar technology, to confirm the accuracy of those forecasts. This information is processed by computers, which can then provide safe spacing criteria automatically.

Wake vortices can cause crashes

All aircraft produce wake vortices . . . much like two small horizontal tornadoes trailing behind the wing tips. The larger and heavier the plane the stronger the wake. That means small aircraft that follow larger ones can encounter turbulence if they are not kept far enough apart. The turbulence can be severe enough to cause a plane to crash.

Weather plays a big part in the motion and decay rate of these trailing twisters. There has been no system to accurately predict wake vortex patterns and quantify the spacing needed for safety. This lack of information forces air traffic controllers to use rigidly fixed distances to separate different classes of aircraft during bad weather, causing air traffic delays that disrupt flight schedules and increase costs.

NASA’s Aircraft Vortex Spacing System can provide that information. The system was installed at Dallas-Fort Worth International Airport in 1997 and has undergone development and testing since then. Initial results show that AVOSS can increase individual runway capacity as much as 15 percent depending on weather conditions and the number of "heavy" aircraft arriving.

How AVOSS works

The Aircraft Vortex Spacing System concept integrates the output of a number of subsystems:
  • weather
  • wake prediction
  • wake sensors
Weather gear at the airport measures winds, temperatures and turbulence levels aloft. The equipment also makes short term predictions of potential weather changes.

AVOSS establishes an invisible aircraft approach corridor with multiple wake prediction windows.

Approach corridor illustration

That information is fed into the wake prediction subsystem, which predicts the time it will take for wake vortices to decay or drift away from the flight path. This computer model uses not only the weather data, but also descriptions of the aircraft to forecast wake behavior. The prediction subsystem calculates spacing criteria and potential runway capacity. It then provides appropriate aircraft separation distances for the next 30 minutes.

Sensors measure actual wake vortex behavior to verify the accuracy of the predictions.

AVOSS integrates the data from the three subsystems to establish a sort of invisible approach corridor. The system predicts the time it will take for wakes to clear the corridor at multiple windows. The end result is automatic, accurate, safe and efficient aircraft spacing information for air traffic controllers.

DFW sees the benefits

AVOSS spacings would have increased runway arrival rates an average of six percent during tests at Dallas-Fort Worth International Airport. At DFW, that means six additional planes that would normally face delays would be allowed to land each hour.

If airports could install an automated wake turbulence system, such as AVOSS, they would be better able to handle unexpected weather delays and expected growth.

NASA worked with the Federal Aviation Administration, Dallas-Fort Worth International Airport, Massachusetts Institute of Technology Lincoln Laboratory, Transport Canada, and Volpe National Transportation Center to develop the Aircraft Vortex Spacing System.