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All Rolls-Royce/Allison 250-C20, 250-C20B, 250-C20F, 250-C20J, 250-C20R/2 and 250-C28 engines.
To advise affected helicopter operators and maintainers of recent reports of finding oil system contamination and blocked accessory gearbox oil pressure inlet screens on three Rolls-Royce 250 Series II engines. For further details of the contamination found on the accessory gearbox oil pressure screen, refer to the photograph below.
This Continuing Airworthiness Notice (CAN) is prompted by reports of finding blocked accessory gearbox oil pressure screens on three Rolls-Royce 250 Series II engines. The reason for the contamination is still under investigation. The accessory gearbox oil feed tube supplies the compressor and turbine main thrust bearings (i.e. #2 and #5), the gearbox pinion gear support bearings (i.e. #3 and #4) and the gears within the accessory gearbox. A blocked accessory gearbox oil pressure screen will restrict the oil supply to the bearings and gears of all three engine modules. Unless the helicopter is fitted with a bypass indicator/Facet filter, the only early warning indication that the accessory gearbox oil pressure screen may be blocked is an increase in indicated engine oil pressure.
Rolls-Royce advise that if a sudden increase in oil pressure is experienced, or a higher than normal oil pressure persists after trouble shooting, then any further flights should cease and the engine should be removed and sent to a maintenance facility for disassembly and inspection. For further information refer to the applicable Rolls-Royce Operation and Maintenance Manual.
There is also the possibility that oil system contamination may be caused by replacing non HTS oil with HTS oil.
This CAN is considered an interim action and further CAA action may follow.
The CAA strongly recommends the following:
If any oil system contamination is found on a Rolls-Royce 250 Series II engine, then complete a CA005 Defect Report form and submit the completed form to the CAA at CA005@caa.govt.nz
Please include all findings and any other relevant technical information.