A new warning system is being developed in Germany to protect aircraft during takeoffs and landings from dangerous wake turbulence from aircraft ahead of them.

Wake turbulence has various components, the most hazardous of which are known as wake vortices. This is due to counter-rotating trails of turbulent air streaming behind an aircraft in flight they are caused by higher-pressure air beneath the wings curling around the wingtips to the lower-pressure area above.

Occurrences of trailing planes flying into the vortices are “frequent, but there are relatively few accidents,” noted Stefan Levedag, director of the German Aerospace Centre’s (DLR) Institute of Flight Systems in the German city of Braunschweig. He and his team are working on the warning system.

Accidents are infrequent because planes taking off or landing are required to keep a safe distance from preceding aircraft. The amount of separation depends on the size of the planes. A smaller aircraft trailing a jumbo jet must keep a distance of up to 15 kilometres, for instance.

Nevertheless, accidents do happen. The most serious was in November 2001, when an Airbus A300 crashed in the New York City borough of Queens shortly after takeoff from John F. Kennedy International Airport.

The accident was attributed to pilot error in the presence of wake turbulence from a Boeing 747, which caused the Airbus’s vertical stabilizer (or vertical tail) and rudder to break off in flight. All 260 people aboard the Airbus and five people on the ground were killed.

The strength of wingtip vortices is determined primarily by an aircraft’s wingspan, weight and airspeed. “When an airplane is flying more slowly, wake turbulence increases,” Levedag said. It can remain in the air for several minutes after the passage of an aircraft and drift laterally depending on the wind direction. Gradually sinking, it finally dissipates.

The Wake Encounter Avoidance and Advisory system (WEAA) being developed by DLR scientists uses information on an aircraft’s technical data, takeoff weight, speed and altitude, along with wind and atmospheric conditions. Using that data, it continuously computes where turbulence in its trail is most likely to be located in the sky. “We’ve tested the system a number of times already,” Levedag said.

In April the DLR used a Dassault Falcon jet as a vortex generator. It made repeated passes across the flight path of an Airbus A320 converted into a research aircraft.

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