Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for Rolls-Royce (1971) Limited, Bristol Engine Division (RR) model Viper Mk.601-22 turbojet engines. That AD currently requires reducing the life of certain 1st stage turbine rotor blades from 7,000 hours time-in-service (TIS) to 4,600 hours TIS, and provides a drawdown schedule for blades that have already exceeded the new reduced life limit. This proposed AD would require the same actions but changes certain compliance times to be in agreement with RR Alert Service Bulletin (ASB) No. 72-A184, dated January 2001. This proposed AD results from comments received on AD 2004-13-03, that the AD is unnecessarily more restrictive than the requirements in the associated RR ASB No. 72-A184. We are proposing this AD to prevent multiple failures of 1st stage turbine rotor blades that could result in a dual-engine shutdown.