Summary
The FAA proposes to supersede an existing airworthiness directive (AD) for certain General Electric Aircraft Engines (GEAE) CT7 series turboprop engines. That AD currently requires propeller gearbox (PGB) oil filter impending bypass button (IBB) inspections, oil filter inspections, replacement of left-hand and right-hand idler gears at time of PGB overhaul, and replacement of certain SN PGBs before accumulating 2,000 flight hours. This proposed AD would require the same actions, and adds additional SNs of affected PGBs. This proposed AD is prompted by reports of PGBs equipped with certain gears that do not meet design specifications, resulting in the same failure addressed in the existing AD. We are proposing this AD 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.