Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Rolls-Royce, plc (R-R) Viper Models Mk.521, and Mk.522 series turbojet engines. This proposal would require replacement of certain high pressure (HP) fuel pumps with an improved design which is more tolerant of water contaminated, low lubricity fuels. This proposal is prompted by reports of HP fuel pump drive shaft failures resulting in inflight engine shutdowns and at least two reported near dual engine events. These failures have been attributed to the low lubricity properties of water contaminated fuel. The actions specified by the proposed AD are intended to prevent HP fuel pump failures, which can result in inflight engine shutdowns and the possibility of dual engine events.