All Aeronautical Accessories Pc Safety Valve Kits.
Compressor discharge pressure (Pc) Safety Valve Kits are known to be installed on Rolls-Royce 250-C28 and 250-C30 fitted to Bell 206L helicopters in New Zealand.
Note: These Pc Safety Valves may also be installed on other engine types.
The CAA has received a report of an aircraft accident which resulted from an in-flight engine roll back to ground idle. The engine roll back appears to have been the result of a failed engine compressor discharge Pressure (Pc) Safety Valve.
The intent of this CAN is to raise awareness of this event, and to draw attention to the requirements provided in the Aeronautical Accessories Instructions for Continued Airworthiness (ICA) and Aeronautical Accessories Alert Service Bulletin (ASB) No. AA-06107.
Laboratory analysis of the failed Pc Safety Valve identified that the valve stem head fractured as a result of fatigue. See photo of the failed valve below.
Following this incident, Aeronautical Accessories released ASB AA-06107 which includes a caution that the Pc Safety Valve is designed for hand operation only and that tools should not be used.
Operators and maintainers are advised to be make themselves familiar with the requirements for operation of the Pc Safety Valve, and to ensure that the requirements in the Pc Safety Valve ICA are included in their aircraft maintenance programme.
Aeronautical Accessories Alert Service Bulletin AA- 06107(external link)
