What is an Overhaul?

The term "overhaul" has many different levels of meaning when it comes to aircraft engines. When it's time to overhaul your engine, it is critically important to understand the differences so you can evaluate the best option for you. While many companies promote a seemingly endless array of "mystical options and techniques," engine overhauls fall into four basic categories:

Service Limit Overhaul
Factory Overhauled Engines

Each engine manufacturer (with the FAA's approval) sets the minimum standards that will comply with an engine's overhaul requirements. The key word here is minimum. In a Service Limit overhaul, the engine is disassembled, parts are checked, and any part that falls within the service limits set by the manufacturer is reinstalled. This means if a given part is allowed to wear .010" before being "out of service limits" and it checks at .009" during inspection, it can be reinstalled in the engine as part of a "major overhaul". Obviously, an engine overhauled using "service limit" parts is less likely to reach TBO (Time Between Overhaul) without additional (and often costly) maintenance.

New Limit Overhaul

Just like service limits, each manufacturer also establishes the limits allowed for parts used to build a brand new engine at the factory. In a New Limit Overhaul, engine parts are reworked or replaced as necessary to meet these more stringent limits, with the final result being an engine that is functionally equal to a new engine. For those who want an engine with the best chance of achieving "new engine" reliability and longevity, this is generally the overhaul of choice.

Factory Rebuild

The Factory Rebuild is very similar to the new limit overhaul with one major exception. When the engine is rebuilt to "new limits" and completed, it is given a new logbook with "zero time since new" status. A "zero time" rebuild is presently available only from the engines manufacturer, and typically comes with a new engine warranty. A Factory Rebuild engine typically carries a 50%+ price premium above the cost of a new limit overhaul, but is priced below the cost of a new engine. However, very little is known about previous time on its major component parts.

The Quality Game

There are a number of companies that offer differing levels of "quality" in their overhaul services. The theory is to offer an overhaul that is "good enough", one that is "like a factory overhaul" and the "super duper special" version. This philosophy allows these companies to attract the price shopper, the informed shopper and the shopper who assumes "if it costs more, it must be better".

Before choosing an overhaul company, stop and consider this for a moment. Most new engines make it to TBO if operated per the manufacturers recommendations. They reach TBO because the manufacturers have spent thousands of hours and millions of dollars to arrive at the best combination of parts and assembly procedures to deliver the power, reliability, fuel efficiency and longevity demanded by aircraft owners and operators. So when it's time for an overhaul, stick with what got your engine safely and reliably to TBO the first time; a "new limit" overhaul. Accepting anything less is inviting problems; paying for anything more is just throwing good money away.