Aircraft engine overhaul: Everything MROs need to know

Aircraft engine overhaul: Overview

An aircraft engine overhaul is a comprehensive inspection and refurbishment of the powerplant.

Usually performed at certain intervals based on flight hours and/or a calendar, the process includes disassembly, cleaning, inspection, repair (or replacement) of parts, reassembly, and testing.

The goals of an engine overhaul are to:

• Address wear 
• Prevent failures 
• Increase reliability and safety 
• Ensure the engine meets manufacturer and regulatory standards 

Rules and regulations

MROs must adhere to relevant regulations and approved data when performing engine overhauls, including:

• FAA and EASA requirements
• OEM manuals (e.g., Aircraft Maintenance Manual, Component Maintenance Manual, and Engine Maintenance Manual)
• Airworthiness directives
• Service bulletins

Release to service requires complete documentation, such as FAA Form 8130-3, and traceable records of the work performed.

How to perform an aircraft engine overhaul in 8 steps

A successful engine overhaul means following a clearly structured process that upholds safety, quality, and compliance standards.

It also means robust documenting and tracking at every stage. MROs should take care to maintain part-level traceability, life-limited-part records, repair histories, test data, and conformity statements.

Below is an outline of the typical aircraft engine overhaul process.

Step 1: Induction and receiving inspection

Verify the engine identity, configuration, shipping condition, and documentation. Record serial numbers, prior findings, and customer instructions.

Step 2: Disassembly

Remove accessories, split cases, and separate modules in accordance with OEM work instructions. Tag and segregate parts to preserve traceability.

Step 3: Cleaning

Use approved chemical cleaners and ultrasonic or media methods to remove contaminants while protecting coatings and base materials.

Step 4: Inspection

Conduct dimensional checks, nondestructive testing (fluorescent penetrant, magnetic particle, eddy current, and ultrasonic), borescope examinations, and visual assessments against limits.

Key inspections at this stage include:

• Borescope evaluations of hot and cold sections
• Nondestructive testing on critical rotating hardware
• Dimensional and runout checks
• Bearing assessments
• Leak checks

Step 5: Repair and replacement

Perform approved repairs (welding, blending, and coating restoration) and replace parts beyond limits. OEMs like Continental, General Electric, Lycoming, Pratt & Whitney, and Rolls-Royce offer a broad inventory of parts.

Be sure to also incorporate mandatory service bulletins and airworthiness directives as you repair and replace parts.

Step 6: Component balancing and assembly

Balance rotating components to OEM tolerances, apply correct torques and fits, and install new seals and fasteners.

Step 7: Test cell run

Validate thrust or power output, fuel flow, exhaust gas temperature margins, vibration, and system integrity. Apply oils and lubricants, such as AeroShell and ExxonMobil, to ensure smooth operation.

Step 8: Final inspection and release

Close discrepancies, update life usage, and issue airworthiness release with complete documentation.

Controlling costs for aircraft engine overhauls

Engine overhauls aren’t cheap, often costing tens of thousands — even millions — of dollars.

Higher-than-expected costs not only hurt the customer but also the MRO performing the overhaul. Unexpected cost increases can push customers to seek alternative providers or defer aircraft maintenance altogether.

Controlling cost starts with accurate diagnosis. You should use engine health monitoring, borescope history, and FADEC logs to separate root causes from symptoms. Doing this can reduce labor costs, test-cell hours, and parts consumption.

Here are more ways MROs can control aircraft engine overhaul costs:

• Use condition-based tools: Engine Health Management (EHM) platforms and predictive analytics allow you to schedule engine overhauls as needed instead of via a fixed calendar.
• Upgrade your inspection tech: Advanced borescope systems and automated nondestructive testing can detect issues early and reduce full teardowns.
• Improve digital workflows: Utilize Computerized Maintenance Management Systems (CMMS) and engine records that centralize history, parts provenance, and approvals to speed decision-making without raising costs.
• Integrate financial tools: Regularly using job-costing systems and dashboards that track data, like cost per overhaul and first-pass yield, can help you identify potential improvement areas.

Key takeaways: Aircraft engine overhaul

Successful engine overhauls are rooted in accurate diagnostics, standardized workflows, and strategic parts management. MROs should not only aim to reduce risk and meet compliance standards but also work to ensure clear communication with customers at all stages of the process.

Frequently asked questions about aircraft engine overhauls

What triggers an engine overhaul?

Engine overhauls are driven by several factors, including:

• OEM-recommended TBO
• On-condition findings (such as borescope results and performance margin loss)
• Whether any life-limited parts have met their predetermined lifespans
• Mandatory airworthiness directives

MROs might also choose engine overhauls to incorporate service bulletins that improve reliability or performance.

How long does an engine overhaul take?

Typical turnaround time for an aircraft engine overhaul is 30 to 90 days, depending on engine type, parts availability, and scope. Module exchanges and pre staged materials can shorten this estimate.

What documentation is required for return to service after an engine overhaul?

After an aircraft engine overhaul, MROs must present:

• Complete work-order records
• Parts traceability
• Nondestructive testing and test-cell data
• Conformity checks to OEM standards
• Appropriate airworthiness release documents (such as FAA Form 8130-3)

You should also maintain electronic copies for audits and future planning.

Are partial engine overhauls acceptable?

Yes, many MROs perform partial engine overhauls, depending on what kind of maintenance is required to meet airworthiness and performance standards. Many aircraft engines support modular or partial overhauls, such as hot-section and core modules.