The Terminology and Standards of Aircraft Engine Overhaul – Part 1

This is the first post of two in our efforts to educate aviation enthusiasts, aircraft owners, and business fleet aircraft managers on the terminology of an aircraft engine overhaul.  If you are in need of maintenance or overhaul for your radial or turbine engine, make sure you visit Covington Aircraft’s website for more information!

When TBO time rolls around, are you ready to speak and understand the language enough to make an informed decision?

Air-Tractor-Landing-at-Hangar-1024x676Parents everywhere tell their children, “Read everything before you sign it.”  What good is this advice if you have no understanding of what you are reading?  Sure, many things are intuitive, but a clear understanding of what is offered for services further ensures that you will get value for your dollar.  The following is a listing and discussion of what various terms mean when it comes to aircraft engine overhaul. You may not know how to check the free-play on a valve tappet after reading this, but at least you should know your O.E.M from aftermarket enough to discuss your options.

Terms that are used and approved by the FAA.


A new engine is one that has been manufactured from all new parts and tested by an FAA-approved manufacturer.  The engine will have no operating history except for test cell time when received.  No FAA-approved manufacturer can approve another entity to manufacture or assemble a NEW ENGINE.


These are the FAA-approved fits and clearances manufacturers adhere to with new engine.  This may be accomplished using standard or approved undersized and oversized dimensioned parts.


The service limits are the FAA-approved allowable wear fits and tolerances to which a new limit part may deteriorate and still be a useable component.  This may also be accomplished using standard and approved undersized and oversized dimensions.


Chey-5-300x225An engine that has been disassembled, cleaned, inspected, repaired in accordance with manufacture overhaul instructions and tested using FAA-approved procedures.  The engine may be overhauled to new limits or service limits and still be considered an FAA-approved overhaul.  The engine’s previous operating history is maintained and it is returned to you with zero time since a major overhaul and a total time since new.  Of course, the total time since new is the same as before the overhaul.


This is an engine that has been overhauled using new and used parts to new limits by the manufacturer or an entity approved by the manufacturer.  The engine’s previous operating history is eradicated, even though the engine may have used components installed that have many hours of operating history, and it comes to you with zero hours total time in service


When an engine is overhauled or rebuilt, the new parts that are used during the repair process can come from a variety of sources.  An “O.E.M.” part is a new part that is manufactured by the original engine manufacturer to stringent FAA standards.  An “aftermarket” part is a new part that is manufactured by someone other than the original engine manufacturer and meets or exceeds the same stringent FAA guidelines as a new O.E.M. part.

So, now you know enough to be dangerous! However, put your aircraft engine overhaul into the hands of the experts who have performed thousands upon thousands, either at the Hangar in Okmulgee, OK or wherever you are located, and give Covington Aircraft a call today!  Next week we will go over some other aircraft maintenance terminology. Happy Flying!

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