What You Should Know About Aircraft Engine Overhauls

Engine overhauls have evolved into an extremely specialized operation, as most mechanics do not prefer doing an entire engine overhaul or rebuild on their own. Usually, the engine is taken out and sent for an inspection. Keep reading to find out everything you need to know about aircraft engine overhauls, including the cost of an overhaul vs. that of a rebuild, what overhauls are, and why they’re so important in modern aviation.

What is an Aircraft Overhaul?

The design and operational capacity of engines are built around tolerances. Thus, when the engine of an aircraft is new or has recently undergone an overhaul, the tolerances adhere strictly to stated regulations and specifications. However, as the aircraft performs various functions internal components undergo normal wear and tear, which, in turn, causes the tolerances to widen. The wider the tolerances become, the more the motor’s design and overall performance suffer. When this happens, the amount of motor oil used increases, power declines, and the likelihood that an engine component will fail rises. Most importantly the safety of crew and passengers can become at risk. All these factors combine to bring about the need for an aircraft engine overhaul.  It’s often said that if cars were maintained like commercial aircraft they would last millions of miles on the road. Engine overhauls are a cost-effective exacting, but necessary process for the safety and reputation of the entire airline industry.

Taken directly from the FAA, Service Limits form a key component of airline safety. It’s important to remember that  “service limits are dimensions representing limits that must not be exceeded and are dimension limits for permissible wear.” When a total overhaul is necessary that means that “consists of the complete disassembly of an engine. The overhaul facility inspects the engine, repairs it as necessary, reassembles, tests, and approves it for return to service within the fits and limits specified by the manufacturer’s overhaul data.” Thus aircraft engine overhaul typically refers to the intensive process of inspecting, maintaining, and repairing the engine components of an aircraft to ensure maximum efficiency. The inspection aspect of an aircraft engine overhaul is perhaps the most critical step — it aids in identifying issues before they cause a significant and costly failure in the aircraft. It is vital to note that an aircraft engine overhaul can help extend the engine’s lifespan and the entire aircraft, make the aircraft more secure to fly, and even increase its market value. While we would all like to maximize safety and performance, the FAA is aware that maintaining aircraft entails a complex balance between safety, performance, and cost-effectiveness. Thus they acknowledge that the “average aircraft owner usually selects an overhaul facility based on the cost quoted by the engine overhauler. Engine overhauls are accomplished to a variety of standards….The selection of an overhaul facility can and does, in most cases, determine the standards used during overhaul.” Read on to learn more about the specifics of this essential process.

What Does an Aircraft Engine Overhaul Look Like?

The phrase ‘engine overhaul’ refers to performing maintenance checks and repairs, where necessary, to ensure that a component, machine, or system is in serviceable condition. This entails disassembly, inspection to find worn, broken, or defective parts, replacement or repair of those parts, and then reassembly, testing, and trial run before the entire machine is put back together and returned to its full operating capacity.

However, before conducting an aircraft engine overhaul, you must ascertain that the engine components are actually in need of an overhaul. It is not always necessary to perform an engine overhaul just because it has been a while since the previous one. Those operating under the Federal Aviation Administration (FAA) Part 135 must legally follow the recommended intervals between overhauls set by engine manufacturers. For everyone else, the engine’s condition is the only indicator that your aircraft requires an engine overhaul.

An engine that operates at least once per week, has good cylinder compression, and has no exhaust valve leakage shows that it is in good condition to keep running. In addition, routine maintenance checks and oil changes must constantly show that the engine is not producing too much metal. Such an engine can be in use legally and safely beyond the interval time between overhauls (TBO), as suggested by the manufacturer. However, you must ensure that it functions according to the required airworthiness rules and service bulletins. In addition, your mechanic must also certify that the aircraft’s engine meets the airworthiness requirements. 

So, how can you tell if your aircraft requires an engine overhaul? Here are some key pointers:

  • If an excessive quantity of metal can be identified emanating from the underside components. These include crankshaft bearings, gears, lifter bodies, and camshaft
  • If there are larger cracks on the crankcase than those legally permitted
  • If an engine struggles to produce its rated power despite having functional ignition and fuel systems as well as acceptable cylinder compressions
  • If there are larger cracks on the crankcase than those legally permitted
  • If an engine struggles to produce its rated power despite having functional ignition and fuel systems as well as acceptable cylinder compressions

Now that you understand when you should get an aircraft engine overhaul, it is time to discuss the actual process of engine overhauling. Generally, there are two types of engine overhaul. They are:

  • Top Overhaul: This involves repairing engine components outside the crankcase without completely disassembling the entire engine. It may also include piston rings and piston replacement, as well as repairs to the valve seats, valve guides, valve-operating mechanisms, pistons, and cylinders. After this, the engine components are reassembled and tested to guarantee a problem-free return to service life.
  • Major overhaul: This involves completely disassembling the aircraft engine and examining each component, then repairing or replacing them, reassembling, testing, and approving service return. However, this is only provided it adheres to the manufacturer’s overhaul documentation parameters. This might be a return to acceptable limits or the fits and limits of new.

Cost of Aircraft Engine Overhaul vs Rebuild

While some may use the terms’ overhaul’ and ‘rebuild’ interchangeably, the truth is that these terms have different meanings and processes. Generally, an engine overhaul refers to inspecting and conducting maintenance checks and repairs to worn parts, while those whose wear limit has not been exceeded remain in place. On the other, an engine rebuild refers to replacing all the engine components with new ones and testing them to ensure they are working optimally.

Regarding costs, aircraft engine overhauls are cheaper than rebuilding an engine. This is because of the expenses associated with the actual overhauling process and the workmanship involved in removing and replacing the motor. 

To take just one example from Sean Lynch, Program Coordinator for Engine Assurance Program, a Hawker 800XP or Falcon 900’s Honeywell TFE 731-5BR overhaul costs range from $500k to $800k. In addition, the operator must also spend an extra $125,000 to remove and replace the engine. Furthermore, operators who choose to continue flying their aircraft during the overhaul, which usually takes four to six weeks, will need to spend roughly $40k to borrow a replacement engine, provided one is available. Most rental engines are saved for overhauls carried out under hourly service maintenance contracts.

Likewise, installation and removal will cost approximately $12,000, raising the total overhaul cost of a Hawker 800XP or Falcon 900 to about $650k -$900k. However, if an aircraft is under a maintenance plan, this cost subsides drastically to about $200k -$300k. 

When it comes to rebuilding an aircraft engine, apart from the significant difficulties an operator may experience when trying to find a suitable option on the general market, an aircraft engine’s price ranges from $12 million to $35 million, depending on the brand, its specifications, and condition.

PartsBase for Aircraft Parts and Expertise

If you are looking for aircraft parts, including aircraft engine components, for an overhaul, PartsBase has got you covered. PartsBase is a global ecommerce platform that serves as an integrated and comprehensive solution for business, commercial, military, general aviation, major assemblies, and aircraft nuts-and-bolts.

Whether you are looking to buy or sell on the platform, you can find a wide range of high-quality aircraft parts available at affordable prices. Our inventory comprises more than 15 billion aircraft parts, including valves, floodlights, seats, engine components, processors, batteries, coffee makers, and so much more. 

Thanks to our over 25 years of experience in the aviation industry, we can give you insights on performing a successful engine overhaul and help you with any concerns you may have. Browse or sell aircraft and aircraft parts on PartsBase PartsStore or contact us for more information about our services. 


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