General Electric says cleaning systems at both its US engine assembly site and the Italian supplier Avio have been changed to prevent particle contamination in CT7-8A turboshafts, following bearing failures in early engines powering Sikorsky S-92 helicopters.
The US Federal Aviation Administration issued an airworthiness directive (AD) to all operators of CT7-8A-powered S-92s calling for repetitive inspections following “two failures of the No 3 bearing” caused by aluminium oxide contamination. The AD says the contamination came from particles “left in the air cavity of the front frame core after cleaning, that entered the bearing and caused damage and metal loss at the roller ball and race interface”.
The resulting chip detector warning led to the pilot in one case shutting down the engine in flight. A subsequent inspection revealed bearing damage. GE says it is “working with the FAA to see how long the operators have to continue with the inspections”. The AD, issued on 17 March, covers removal of the electrical chip detector assembly, and replacement of the engine if bearing material is found.
Source: Flight International
