The Australian Transport Safety Bureau (ATSB) advises all pilots, operators and maintainers of recently-built Robinson R22 and R44 helicopters to monitor for intermittent or abnormal operations of the helicopters’ engine RPM governor, which can lead to engine overspeed or underspeed conditions.
A small number of recent incidents have been reported to both the ATSB and to the Civil Aviation Safety Authority (CASA) where the governor has not controlled engine RPM under normal conditions.
“This has led to either a rotor overspeed or underspeed condition, requiring the pilot to override the governor by applying collective throttle inputs,” noted ATSB Chief Commissioner Angus Mitchell.
None of the occurrences reported to the ATSB have resulted in a serious incident or accident, Mr Mitchell said, although some have resulted in precautionary landings.
Other incidences have been reported separately to CASA via the Defect Report Service (DRS).
“The ATSB encourages all pilots, operators and maintainers of R22 and R44s purchased after 15 January 2020 to familiarise themselves with the CASA’s recently released airworthiness bulletin, and to continue to report such instances via the CASA DRS portal,” Mr Mitchell said.
“In addition, any incidents where the safety of flight is affected should also be reported directly to the ATSB.”
The engine RPM governor senses engine RPM and makes adjustments to the throttle control to maintain a constant engine RPM, which leads to a constant rotor RPM in flight, and it may not prevent over or under speed conditions during aggressive manoeuvres.
“As per the CASA AWB, pilots are encourage to exercise care not to unintentionally override governor by squeezing throttle twist grip too tightly, and to monitor governor operation during flight by keeping hand lightly on throttle twist grip,” Mr Mitchell said.
“A properly-functioning governor will provide relatively slow, small, and frequent twist grip rotation in both directions. If twist grip rotation becomes erratic or stops altogether, the governor may be malfunctioning.”
The AWB notes that if a governor malfunction is suspected, switch the governor off, assume manual RPM control using the twist grip, land as soon as practical, and have the governor serviced by qualified maintenance personnel.
The helicopter manufacturer, Robinson Helicopter Company, is currently investigating the circumstances of the malfunctions to identify causal factors and solutions.
Last update 04 February 2022
