Airworthiness Directives; General Electric Aircraft Engines CT7 Series Turboprop Engines

This amendment adopts a new airworthiness directive (AD) that is applicable to certain General Electric Aircraft Engines (GEAE) CT7 series turboprop engines. This amendment requires initial and repetitive inspections of the propeller gearbox (PGB) oil filter impending bypass button (IBB) for extension (popping), requires follow- on inspections, maintenance, and replacement actions if the PGB oil filter IBB is popped, and if necessary, replacement of the PGB with a serviceable PGB. In addition, this amendment requires replacement of certain left-hand and right-hand idler gears at time of overhaul of PGBs, and the replacement of certain SN PGBs before accumulating 2,000 flight hours. This amendment is prompted by an on-going investigation that concluded that low-time PGB removals are due to accelerated wear of the PGB idler gears, rather than improperly hardened PGB input pinions. The actions specified by this AD are intended to prevent separation of PGB left-hand and right-hand idler gears, which could result in uncontained PGB failure and internal bulkhead damage, possibly prohibiting the auxiliary feathering system from fully feathering the propeller on certain PGBs.