Extreme teetering in the main rotor has been identified as a contributing factor in the in-flight break-up of a Robinson R22, according to an ATSB investigation report released yesterday.
R22 VH-RAS was on a private flight from Koorda to Jandakot, WA, in October 2022 when the aircraft lost altitude rapidly and collided with the ground. Both the pilot and passenger died in the crash.
Evidence showed the helicopter climbed sharply by 100 feet before entering an almost vertical descent to a salt pan below. It was later determined the aircraft broke-up in flight.
ATSB investigators found "signatures consistent with the main rotor assembly being subject to excessive teeter and mast bumping – where the main rotor spindle impacts the mast."
Investigators examined the dual RPM gauges fitted to RAS, both of which showed low RPM conditions prior to impact. The ATSB believes the near-vertical descent was characteristic of a rotor stall condition.
ATSB Director Transport Safety Kerri Hughes the mast bumping was likely caused by poor pilot response to a rotor stall.
“It was likely the helicopter entered either a low-g and/or a low rotor RPM/rotor stall condition," Hughes said, "which, along with delayed and/or inappropriate control inputs, resulted in extreme teetering of the main rotor assembly, and the in-flight break-up ...
“A pilot’s ability to identify the developing condition and promptly apply the correct flight control inputs is vital to effective recovery and continued safe operation."
The ATSB explored multiple scenarios to determine the reason for the extreme teetering and mast bumping, and the investigation would have been considerably aided had the helicopter been fitted with an in-cockpit video recorder.
One of the scenarios included the passenger in the left seat inadvertently providing control inputs as the R22 was fitted with quick-disconnect dual controls.
“When carrying passengers, the helicopter manufacturer recommends removing the passenger-side controls to avoid inadvertent bumping or interference,” Hughes said.
Hughes stressed there was insufficient evidence to determine if the passenger made any control inputs or if they were operating any of the controls during the flight.
“Where dual controls cannot be removed, the passenger should be fully briefed to keep their hands and feet clear.”
Other scenarios the ATSB considered were bird strike, door loss and engine failure.
The full report is on the ATSB website.