What happened
On August 12, 2016, at Bern Airport (LSZB), an Aero AT-3, registration HB-SRC, was performing training maneuvers consisting of touch-and-go landings. During this period, a Robinson R66 helicopter, registration HB-ZOK, was also operating at the airfield, conducting a flight for mountain training.
As the aircraft was executing a touch-and-go on runway 14, the helicopter had recently crossed the runway axis and was proceeding toward the helipads. The aircraft crossed the helicopter's previous flight path approximately 30 seconds after the helicopter had passed. Shortly after lifting off between taxiways Charlie and Delta, the Aero AT-3 experienced a sudden, violent roll to the left, reaching a bank angle of 70 degrees. The pilot managed to regain control and narrowly prevented a crash.
The investigation
SUST examined radio communications, flight records from a tablet used by the helicopter crew, and interviews with the flight crews and the Aerodrome Control Officer (ADCO). The investigation focused on the proximity of the two aircraft and the atmospheric conditions. The investigation confirmed that the aircraft were in good technical condition and the crews were properly licensed. The investigation also reviewed historical data regarding the dangers of helicopter wake turbulence, noting that such vortices can remain stationary over a runway during light crosswinds.
Findings
- The loss of control was caused by the Aero AT-3 flying into the wake turbulence generated by the Robinson R66.
- A lack of awareness regarding the specific dangers posed by helicopter wake turbulence among the air traffic controller and both flight crews was a causal factor.
- The timing of the aircraft's passage through the helicopter's path (30 seconds) fell within the known duration of helicopter-induced wake vortices.
- The flight controller and crews were primarily focused on avoiding a mid-air collision rather than the invisible hazard of wake turbulence.
Safety action
- Safety Recommendation No. 542: The Federal Office of Civil Aviation (BAZL) should work with flight schools and relevant aviation stakeholders to ensure that pilots and all personnel involved in flight operations are properly instructed and sensitized to the dangers of helicopter wake turbulence.