Piston engine helicopter pilots are reminded to be alert for unexpected yawing and transient reduced engine performance during flight, following an Australian Transport Safety Bureau investigation into the forced landing of a Robinson R22 near Geraldton earlier this year.
On the morning of 20 February 2021, a R22 Beta helicopter was to be repositioned from a storage depot near Geraldton Airport to Murchison House Station near Kalbarri, Western Australia.
Shortly after lifting off, at about 30-40 ft above the ground, the engine’s performance reduced and the helicopter began to descend. The pilot completed a forced running landing in a yard adjacent to the point of departure.
“The ATSB found that an inlet valve in the engine’s number-four cylinder sustained thermal damage, which led to reduced engine performance, resulting in the forced landing,” ATSB Director Transport Safety Stuart Macleod explained.
A short time after the forced landing, the pilot elected to reposition the helicopter. However, on becoming airborne, the helicopter began to immediately rotate nose-right, and the pilot again landed the helicopter.
The ATSB investigation found that the loss of directional control was the result of a loss of drive from the helicopter’s tail rotor, due to a fracture in the tail rotor drive shaft close to its connection with the tail rotor gearbox.
“This incident serves as a reminder for all pilots of piston engine helicopters to be alert for unexpecting yawing during flight,” Mr Macleod said.
“Additionally, when a loss of engine power or abnormal operation is encountered, an appropriately licensed maintenance engineer should complete an engine cylinder inspection in accordance with the helicopter and engine manufacturer’s most recent service instructions, before any further flight takes place.”
The ATSB’s investigation also highlighted the utility of borescope inspections.
“Maintenance organisations should note that when completing a differential compression test of the engine cylinders, an accompanying borescope inspection of the cylinders and valves will provide an effective method to visually assess the condition of these components.”Last update 16 December 2021