Preservation and Depreservation of PT6A Engines

As we head into the winter months. the question is often asked about Preservation and Depreservation of engines. To help answer some of these questions, the following information was gathered from the PT6A-34AG Maintenance manual (Manual Part Number 3021242).

An engine is considered inactive when it has not been operated either on the ground or in flight for a minimum of ten minutes after the oil temperature has stabilized, for any of the following periods. The subsequent information can be used as a helpful guide in determining if you need to perform any maintenance tasks prior to beginning your season.

Engines that are inactive for:



Requires no depreservation.


Remove covers from inlet, exhaust openings and moisture barriers.  Remove any desiccant bags and racks, if applicable.  Make sure all engine openings are clear and unobstructed.


Follow the steps above.  Fill engine oil tank.  Disconnect fuel line at flow divider inlet to permit drainage into suitable container.  Connect aircraft fuel supply.  With ignition OFF, place power control lever to TAKE-OFF and fuel condition to GROUND-IDLE.  Observing the starter motor operating limits do a normal 30 second motoring run, during which time move the power lever to GROUND-IDLE and return to TAKE-OFF, fuel condition lever to OFF and return to GROUND-IDLE until clean fuel flows from the line disconnected from the inlet.  Connect fuel inlet line to flow divider, tighten all coupling nuts 90-100 in lbs. and lockwire.  Return power lever and fuel lever to GROUND-IDLE and OFF.


Follow the steps above.  Examine all external cases for corrosion and protective coating wear, repair as necessary.  Remove inlet screen and examine case and visible flanges for corrosion.  If corrosion is found, examine internals of AGB and RGB with borescope.  If corrosion exceeds limits, send engine to an approved overhaul facility.  After completion of the steps above do the following:

Pre-op check, Pre-start check, Wet motor run, Dry motor run, Engine starting checks, Shutdown checks, Post-shutdown checks, FCU checks (idle speed only), Oil pressure check, Engine performance check, FCU manual override control check, Acceleration adjustment, Shutdown checks and Post-shutdown checks.

During motoring, check for any stiffness, audible scraping binding and/or rubbing.


After engine run and completion of all checks, examine all drain valves for oil. Examine fuel Filters and clean or replace as necessary. Examine oil filter and chip detector. Address any problems you uncover.

Remember when your season ends to give some consideration to how long your engine is going to be idle during the off-season and preserve it to insure long engine life.

One thought on “Preservation and Depreservation of PT6A Engines

  1. I’m looking for a average labor time involved for preservation and de-preservation
    of a PT6A-67R. Any information would be greatly appreciated.

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