Airworthiness Directives; Dowty Propellers Constant Speed Propellers

We are revising airworthiness directive (AD) 2010-17-11R1, which applies to all Dowty Propellers R408/6-123-F/17 model propellers. AD 2010-17-11R1 required initial application of sealant between the bus bar assembly and the backplate assembly of certain line-replaceable units (LRUs) and repetitive re-applications of sealant on all R408/6- 123-F/17 model propellers. AD 2010-17-11R1 also provided an optional terminating action to the repetitive re-application of sealant. This AD increases the interval allowed between the required re-application of sealant, and specifies an additional acceptable sealant. This AD was prompted by failure of the propeller de-ice bus bar due to friction or contact between the bus bar and the backplate assembly, consequent intermittent short circuit, and possible double generator failure. We are issuing this AD to prevent an in-flight double generator failure, which could result in reduced control of the airplane.