What happened
While operating in a remote area, the pilot of an aircraft encountered severe turbulence that resulted in a loss of aircraft control. To avoid a large storm cell located 5 NM to the left of the flight path, the pilot diverted 5 NM to the right. This maneuver left a separation of only 10 NM from the weather phenomenon, which proved insufficient to avoid the encounter. While the pilot remained secured by a harness, the passengers and cabin were not adequately prepared for the intensity of the turbulence. The pilot's ability to communicate instructions to the cabin was hindered by an inability to use the intercom during the flight.
The investigation
The investigation focused on the adequacy of weather avoidance strategies and the subsequent reporting procedures. It was noted that while the pilot's operations manual suggested a 20 NM separation from such weather, the pilot had missed recent safety reminders regarding the insufficiency of 10 NM separation. Furthermore, the investigation examined the delay in reporting the incident. The pilot did not notify the operator of the turbulence encounter until after completing a subsequent passenger charter flight. Consequently, the operator did not report the event to the ATSB until seven days after the occurrence.
Regarding aircraft integrity, the pilot believed that no airframe limitations had been exceeded; however, the investigation noted that instruments may not accurately reflect the true forces experienced during severe turbulence. While the pilot performed a personal inspection of the aircraft, they did not seek a professional inspection by a licensed aircraft maintenance engineer. Although a later engineering inspection found no defects, the decision to continue operations without a formal inspection introduced avoidable risk.
Findings
- The primary cause of the encounter was insufficient separation from a storm cell.
- The pilot failed to adhere to the recommended 20 NM separation distance.
- The pilot did not immediately report the abnormal event to the operator.
- The operator lacked formal guidance for pilots regarding immediate reporting and post-event procedures.
- The lack of intercom communication prevented the pilot from instructing passengers to secure the cabin and stow loose items.