A Guide to MRO in Aviation - The Importance of Aircraft Maintenance

What is MRO in Aviation?

MRO stands for Maintenance, Repair, and Overhaul. In the aviation industry, MRO services are focused on the repair, service, maintenance, and/or inspection of aircraft. MRO includes all of the tasks involved in keeping aircraft in safe and high-performing operating condition.

Why Is aircraft maintenance important?

As a highly complex mechanical system, an aircraft must have consistent, scheduled maintenance to ensure safety and reliability. This also is part of extending the life of the aircraft. When done robustly, a well-developed maintenance program will bring multiple benefits. When done poorly, the results can be life-threatening. Let's look at the topic deeper.

What are the MRO industry sectors involved in aircraft maintenance?

We usually see the aviation MRO sector divided into four major areas. Those are airframe heavy maintenance and modification, engine maintenance, line maintenance, and component maintenance.

According to Statista, "[In 2030], it is projected global aircraft maintenance market size…is expected to be sized at just under 20 billion U.S. dollars." Expanded to look at the entire maintenance, repair, and overhaul markets, that dollar amount is predicted to be US $64.2 billion by 2030.

Let's look at these four areas of MRO maintenance further.

Airframe heavy maintenance and modification

As explained on our Levels of Aviation Maintenance page, there are multiple levels of service for aircraft in their lifecycle. C and D checks fall into "heavy maintenance." The C level occurs every 18 months to two years (depending on the aircraft) and includes things like:

  • Visual checks of safety components for condition and operability
  • Visual checks of the condition of entry door seals, as well as engine inlet TAI ducting for cracks, stabilizer attach bolts, and floor beams
  • Detailed inspection of the wing box structure

The D check, which happens every six to ten years (depending on the aircraft), involves a complete dismantling of the whole aircraft over a month or so. All parts are inspected at this time. Using special equipment and techniques, skilled technicians probe for any signs of corrosion, structural deformation, cracking, or deterioration/distress.

During this time, there might be structural modifications, avionics modifications/upgrades, custom interior reconfiguration/modification, production skin replacements, sheet-metal modifications, or aircraft strip and paint services. After all inspections and modifications are done, the plane is reassembled and ready to fly again.

Engine maintenance

Maintenance, repair, and overhaul (MRO) is a key activity in the lifecycle of an aircraft, keeping planes in safe and functional condition to fulfill their designated operational roles. As perhaps the most complicated part of the aircraft that powers the flight, the engine needs special maintenance. Engines are exposed to the elements 24/7 and are susceptible to objects such as dust, ice, sand, ash, and even birds, as noted by Simple Flying. As they explain, a careful cleaning improves the engine's power. This can be done most practically when an engine is taken off the plane (and replaced so the fuselage can keep flying) and overhauled. But it can be done with specialized cleaning equipment when the engine is still attached.

Line maintenance

Aviation line maintenance includes any work required to be carried out on an engine in accordance with the aircraft manuals. Line maintenance areas of work include troubleshooting, inspection, servicing/diagnostic testing of the engine, and the removal of unserviceable parts requiring repair or replacement, and the refitting of serviceable parts, among other areas.

Component maintenance

The aerospace components that are inspected in detail in a specialist shop include avionics units, various mechanical and electrical aircraft and engine components, and even whole engines. This is where component maintenance comes in with a Component Maintenance Manual (CMM). The CMM is a formal document detailing how to accomplish off-aircraft maintenance tasks. It contains the information required to check, repair, adjust, and test units or assemblies in  enough detail to return the component to a serviceable condition.

What is preventative aircraft maintenance?

Aircraft maintenance checks refer to preservation or replacement tasks excluding complex assembly operations. These tasks must be done periodically on all commercial and civil aircraft after a certain amount of time or usage. Military aircraft often have their own regimented maintenance programs which might be different from commercial/civil aircraft. Preventative aircraft maintenance and inspections help prevent bigger problems through preservation. Examples of these necessities include:

    • Checking for damage
    • Running prescribed tests
    • Lubricating and cleaning specific areas
    • Replacing items as permitted

In the United States, the Federal Aviation Administration (FAA) offers an Advisory Circular (AC) to standardize the development, implementation, and update of FAA-approved minimum scheduled maintenance/inspection requirements (Maintenance Review Board Report [MRBR]).

What is accomplished with airlines and aircraft maintenance and inspection?

By carefully following a prescribed program of maintenance, aircraft assets can have their best performance for many years. Here are a few of the benefits to MRO operators.

Protect any people using the aircraft

Most important, operators protect both employees and customers by maintaining their fleet. They trust maintenance professionals to make their time in the sky comfortable and safe.

Decrease downtime

By paying close attention and catching potential problems as soon as they arise, maintenance workers can address them promptly before they cause performance or safety issues. This keeps downtime to a minimum.

Extending the life of the aircraft

A lack of good maintenance can lead to premature disposal of the plane. The converse holds true: wise managers know that they can keep an asset flying longer by investing in a strong maintenance program.

Maintenance can save unnecessary expenses

An organized way to keep track of what needs to be done and when is to use maintenance management software. The software will remind appropriate people when an inspection or repair is due. This minimizes breakdown chances and therefore maintenance expenses. It is also possible to use software that provides MRO-related data that allows for a reduction of expenses.

Increasing performance

Calibration, lubrication, and fine-tuning all help parts work optimally. Maintenance programs might also replace parts with newer, higher-performing parts, called rotables. All of this leads to increased performance.

Please don't hesitate to reach out with any further questions about aircraft maintenance. We're here to help!