Airworthiness Directives; AlliedSignal Inc. ALF502 and LF507 Series Turbofan Engines

This amendment revises an existing airworthiness directive (AD), applicable to AlliedSignal Inc. ALF502 and LF507 series turbofan engines, that currently requires initial and repetitive inspections of the oil system chip detectors and oil filter bypass valve, and optional installation of an improved oil filter bypass valve, to ensure the integrity of the reduction gear system and overspeed protection system. This amendment adds an initial inspection threshold for the oil maintenance requirements that was inadvertently omitted from AD 97-05- 11, and makes editorial corrections. Paragraphs (b) through (f) of AD 97-05-11 have been rearranged in this AD to make these corrections. This amendment is prompted by the inadvertent omission of the initial inspection threshold. The actions specified by this AD are intended to prevent No. 4 and 5 duplex bearing failure, which can result in a Stage 4 low pressure turbine (LPT) rotor failure, an uncontained engine failure, and damage to the aircraft.