What happened
On 20 July 2018, a Cessna 182T Skylane, registration G-ORDM, was taxiing at RAF Brize Norton behind a Hercules C130J Mk 4, registration ZH878. The pilot of the Cessna believed they were maintaining a separation of between 50 and 100 metres from the larger aircraft. As the Cessna began turning into the wind to perform engine power-up checks, the crew of the stationary Hercules began a propeller overspeed check, which required increasing engine power from ground to flight idle.
During this power increase, the Cessna was struck by intense, turbulent airflow from the Hercules' propellers. The force of the propwash lifted the Cessna's nosewheel and caused the wings to rock violently. In an attempt to avoid being flipped, the pilot steered right, but the aircraft was ultimately tipped onto its right wingtip. The aircraft slid approximately 8 metres on its wing and nosewheel, during which the propeller struck the ground multiple times, leading to engine failure. The pilot was uninjured and able to exit the aircraft without assistance.
The investigation
An investigation conducted by the aircraft operator and the pilot's employer examined the separation between the two aircraft and the nature of the engine checks. While the pilot had estimated a much larger gap, evidence and eyewitness accounts indicated the actual separation was only about 25 metres. The investigation found that the C-130J crew performed the overspeed check as a standard procedure at the holding point and did not view it as a high-power event requiring notification to Air Traffic Control.
Findings
- The primary cause of the incident was insufficient separation between the two aircraft at the holding point.
- The pilot of the Cessna underestimated the intensity of the propwash and overestimated the distance between the aircraft.
- The C-130J crew did not consider the propeller overspeed check to be a high-power ground run, and therefore did not alert ATC or the following aircraft of their intent to increase thrust.
- There is a lack of published data regarding the intensity of propwash for the C-130J, and no specific warnings exist in the aircraft's manual.
- Pilots transitioning from large aircraft to light aircraft may become desensitised to the risks posed by jet blast and propwash.