The Terminology and Standards of Aircraft Engine Overhaul – Part 2

Last week, we discussed what various terms mean when it comes to aircraft engine overhaul. Today we’ll dig in deeper, and detail the difference between two different kinds of overhaul: service limit overhaul and new limit overhaul.

Save for factory remanufactures, all overhauls are permitted by the FAA to be performed to either new or service limits, but what’s the difference? We at Covington Aircraft are here to take the mystery out of aircraft engine overhauls and help you get the most out of your overhaul when TBO time arrives for your radial or turbine engine.


By definition, an aircraft engine overhaul involves cleaning, carefully inspecting, and repairing or replacing parts to meet service limits. It is therefore entirely legal to placea used part that meets only service limits into an overhauled engine as a replacement.

This type of overhaul is known as a service limit overhaul, and is commonly seen in factory engine overhauls. Unfortunately, this practice allows manufacturers to reinstall a part that checks out during inspection with a service limit reflecting considerable wear before that part is considered to be out of service limits. For this reason, service limit overhauls aren’t very likely to reach TBO without requiring further maintenance down the road.


While in some special cases installing a service limit part might be acceptable, given the expense and  time cost of performing an overhaul, it’s usually a good idea to request that parts used in the overhauled engine meet new limits. This type of overhaul is known as a new limit overhaul and will help you to establish a baseline of wear that is consistent with a new engine, extend the life of your engine, and preserve the resale value of your aircraft. If you’re looking for your engine to reach TBO and have reliability and longevity, a new limit overhaul is usually your best choice.

When TBO time rolls around, it’s important to remember that new engines made it there because of the new limit requirements of the engine manufacturer. So when you make your decision on aircraft engine maintenance, the safest bet is to stick with the limits that got your engine this far in the first place. Anything less could result in more costly maintenance down the road.

If you have any questions on engine overhauls or general maintenance, be sure to let us know. Happy flying!

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