Summary
The FAA proposes to supersede Airworthiness Directive (AD) 2002-03-01, which applies to all Honeywell International, Inc. (Honeywell) T53 model turboshaft engines. AD 2002-03-01 requires initial and repetitive special vibration tests of the engine, and if necessary replacement with a serviceable reduction gearbox assembly, or a serviceable engine before further flight. Since the FAA issued AD 2002-03-01, the FAA received reports that two additional Honeywell model turboshaft engines, not captured in AD 2002-03-01, are also subject to tachometer drive spur gear failures due to vibration loads. This proposed AD would require initial and repetitive special vibration tests of the engine and, depending on the results, replacement of either the reduction gearbox assembly or the engine. The FAA is proposing this AD to address the unsafe condition on these products.