Risk of wake turbulence at mixed-use airports

A pilot and three passengers take off on a sightseeing flight. Shortly after takeoff, the small aircraft falls into a dangerous trap: a wake vortex. The pilot tries to countersteer, but just a few meters above the ground, the maneuver is useless: the aircraft is thrown sideways at an angle of nearly 90 degrees and crashes next to the runway, quickly catching fire. Three of the four people on board are killed.” This is the tragic outcome of a planned sightseeing flight as part of an air show in Germany. What is significant is that both small aircraft and the world’s largest biplane, an Antonov 2, were operating at the airfield. The latter caused such large wake vortices during takeoff that they proved fatal for the DR400. Why? The sightseeing aircraft took off far too early after the An-2, namely after only 39 seconds. At that point, the invisible danger was still above the runway. The German Federal Bureau of Aircraft Accident Investigation has illustrated the accident involving the DR400 in an impressive video.

In Switzerland, there was also a serious incident between an airplane and a helicopter in 2016. Fortunately, this ended without serious consequences and both pilots got away with a scare. The accident report states: “Shortly after takeoff, the aircraft suddenly rolled to a 70° angle to the left. The flight instructor took control and was only just able to prevent a crash.” We have also documented this incident in a corresponding SAND recommendation.

Danger of wake turbulence from aircraft and helicopters

The danger of wake turbulence comes from both airplanes and helicopters taking off and landing, as long as they are in the air. This is because wake turbulence always occurs when lift is generated. In the case of airplanes, this is the case as soon as the nose wheel leaves the ground and until it touches down again. In the case of helicopters, however, the danger remains even in hover taxi mode until the helicopter’s own weight is fully exerted on the ground. It is therefore important to keep a safe distance from helicopters, i.e., at least three times the diameter of the rotor, both during taxiing and during takeoff and landing.

The following rule of thumb has proven useful: For both aircraft taking off and helicopters in the air, wait at least two minutes before safely crossing their flight path.

Recommendations

There are numerous materials that document the topic of “wake vortices,” such as the FAA Advisory Circular AC 90-23G. It contains important and helpful procedures for avoiding uncontrolled flight due to wake vortices. However, it also concludes that pilots who are informed about the subject are the best means of avoiding the risk of wake turbulence. And so, once again, the principle applies: only by continuously examining incidents and accidents can we make aviation safer.

Tip: There are already apps such as ForeFlight or www.flysto.net that include a “wake turbulence alert” or can be used to analyze flights retrospectively for wake turbulence. With the introduction of ADS-L in Europe and the digital networking of air traffic, there are likely to be even more options for digital wake turbulence alerts in the future.

Safety first, every flight, every time.

Image: BFU