What happened
On 15 September 2018, a Quik GT450, registration G-DTAR, was engaged in a training flight at Perth Airfield. The flight was performing circuits using Runway 27. While the aircraft was on its downwind leg, a helicopter departed from a pad located south of the runway.
At the time of the incident, the wind was light, estimated at less than 5 knots from 2D0°.
Although the instructor had considered the potential for wake turbulence from the helicopter, they believed the vortices would have dissipated by the time the aircraft reached the runway. However, as the aircraft flew a few feet above the runway, it encountered turbulence. In response, the instructor applied full power, but the aircraft made heavy contact with the runway surface before the crew proceeded with a go-around. During the subsequent circuit, the throttle became stuck at cruise power, requiring the instructor to release it before the aircraft completed a successful glide landing.
The investigation
Investigators examined the conditions surrounding the departure of the helicopter and the atmospheric state at Perth Airfield. The investigation focused on the behavior of helicopter-generated vortices in light wind conditions. It was noted that helicopters produce radial vortices during hover and trailing vortices during forward flight. When these vortices reach the ground, they can split and move laterally at approximately 5 knots in near-still air. The investigation also reviewed the impact of the light prevailing winds on the persistence and movement of the turbulence toward the active runway.
Findings
- The aircraft sustained damage to the landing gear and minor distortion to the underside.
- There were no injuries to the two crew members on board.
- Light winds were conducive to sustaining a helicopter vortex and allowing it to drift toward the runway.
- The instructor's assessment that the wake would dissipate before the aircraft reached the runway proved incorrect.