With the number of aircraft (helicopters and soon, eVTOLs) crisscrossing the skies in ever larger numbers, MRO services are in high demand – and short supply. With the purpose of MRO being to keep aircraft airworthy – that is, fit to fly – and to be safe, a shortage of MRO services, in particular MRO technicians, is concerning.
We will discuss how the industry is responding to this shortage in due course (and update our previous article on this topic) but in this blog, we explain what MRO services are, types of services and their significance.
What is MRO
Shorthand for aircraft maintenance, repair and overhaul, MRO refers to the comprehensive set of activities required to keep aircraft airworthy and operational. This includes scheduled maintenance inspections, component repairs, and the procurement of parts and supplies. For example, when a Boeing 737 undergoes its routine A-check inspection, technicians examine engines, landing gear, and avionics systems, replacing worn components and updating software as needed to ensure flight safety and regulatory compliance.
It is a highly-regulated field with a ‘robust regimen‘ of scheduled or preventive servicing, inspection, testing, repair, and overhaul or modification activities each of which is certified by MRO technicians on every aircraft in service.
Although the primary goals of aircraft maintenance are safety and performance, a comprehensive and effective maintenance program helps minimize the amount of time an aircraft spends on the ground (AOG) and maximizes the aircraft’s resale value.
The type of MRO service required to keep an aircraft safely airborne depends on the class and type of aircraft, the length of time an aircraft has been in service and the number of flight hours completed. This includes
- Line maintenance or routine inspections including regular pre-flight checks, daily fluid checks, scheduled minor repairs and modifications, and troubleshooting
- Repair or Shop maintenance: repair or overhaul of specific parts which can require specialist services
- Overhaul or Heavy maintenance which includes the thorough disassembly, repair, or replacement of major aircraft components such as engines, landing gear, and avionics systems. This type of maintenance requires large, well-equipped hangars.
Types of MRO Facilities
When it comes to MRO facilities, one size absolutely does not fit all. There are multiple categories, classes and types of aircraft that require their own specialized facilities and technicians. We list some of these below:
- Independent Repair Stations: These are small, specialist firms delivering very specific aviation MRO services to very specific types of aircraft.
- Fixed-Base Operators: Airport-based, FBOs are equipped to offer a variety of maintenance services that can include fueling, aircraft parking and storage, maintenance, ground handling, and catering.
- Commercial Airline Hubs: Many large airlines have dedicated aviation MRO centres that provide comprehensive MRO services for all their aircraft.
- Regional Airline Maintenance: Smaller airlines tend to work with regional MRO providers or FBOs
- Defense MRO Companies: These are dedicated MRO service providers for the defense industry.
Thanks to the colossal amounts of data generated by the various sensors and monitors on modern aircraft, a combination of analytics and AI is now being used to proactively predict and address problems before they occur. Digital platforms are enabling operators to streamline operations, introduce efficiencies and strike the most effective balance between managing inventory and avoiding delays due to unavailability of parts.
Glossary of MRO Terms
Some common terms and strategies are explained below:
1. Preventive Maintenance (PM)
Scheduled maintenance performed at predetermined intervals to prevent aircraft system failures. Aviation regulations mandate specific maintenance schedules based on flight hours, calendar time, or flight cycles. For instance, an Airbus A320’s engines receive detailed inspections every 6,000 flight hours, including borescope examinations of turbine blades and replacement of filters and seals before wear could cause in-flight failures.
2. Predictive Maintenance (PdM)
Advanced maintenance approach using data analytics and sensor monitoring to forecast component failures before they occur. Modern aircraft generate thousands of data points per flight through Engine Health Monitoring (EHM) systems. For example, vibration sensors on jet engines can detect bearing deterioration weeks before failure, allowing airlines to schedule engine changes during planned downtime rather than experiencing costly flight delays.
3. Work Order Management System (WOMS)
Digital platform that manages all maintenance activities from initiation to completion. When a pilot reports cabin pressure irregularities in the aircraft logbook, the system generates a work order, assigns qualified technicians, tracks required parts availability, and documents all corrective actions taken. This ensures regulatory compliance and provides complete maintenance history for each aircraft tail number.
4. Mean Time Between Failures (MTBF)
Statistical measure of component reliability expressed in flight hours or cycles between failures. An aircraft hydraulic pump with an MTBF of 12,000 flight hours indicates the component typically operates reliably for that duration before requiring replacement. Airlines use MTBF data to optimize spare parts inventory and schedule component changes during routine maintenance visits rather than during unscheduled repairs.
5. Root Cause Analysis (RCA)
Systematic investigation methodology to identify underlying causes of aircraft maintenance issues or incidents. When multiple aircraft in a fleet experience similar avionics failures, RCA might reveal that the root cause is contaminated wiring harnesses from a specific supplier batch, rather than individual component defects. This analysis prevents recurring problems and improves fleet-wide reliability.
6. Planned vs. Unplanned Maintenance
Planned Maintenance: Scheduled maintenance activities such as C-checks, engine overhauls, and component replacements performed according to manufacturer and regulatory requirements. Unplanned Maintenance: Immediate corrective actions required when aircraft systems fail unexpectedly, such as replacing a faulty navigation radio discovered during pre-flight inspection, potentially causing flight delays and increased operational costs.
7. Asset Lifecycle Management
Strategic approach to managing aircraft and components from acquisition through retirement. This includes initial purchase or lease decisions, operational maintenance costs, modification programs, and eventual disposal or resale. For example, an airline evaluates whether to extend a Boeing 767’s service life through major structural modifications or replace it with newer, more fuel-efficient aircraft based on total lifecycle economics.
8. Key Performance Indicators (KPIs) in MRO
Metrics used to measure maintenance effectiveness and operational efficiency. Common aviation MRO KPIs include aircraft availability rates (percentage of time aircraft are serviceable), on-time maintenance completion, and maintenance cost per flight hour. For instance, achieving 98% aircraft availability means only 2% of the fleet is out of service for maintenance at any given time, maximizing revenue-generating flight operations.
9. Spare Parts Inventory Management
Strategic management of aircraft components and consumables to ensure parts availability while controlling inventory costs. This includes managing line-replaceable units (LRUs) such as avionics boxes, rotable components like landing gear assemblies, and consumable items such as hydraulic fluid and brake pads. Airlines must balance having sufficient spare parts to minimize aircraft downtime with the high carrying costs of aerospace inventory.
The MRO industry is a highly specialized, technical space being rapidly transformed by technological innovations. Stay tuned to read about them in our next blog.
KAMS Global provides end-to-end advisory services to aviation industry leaders worldwide. Combining in-house expertise and local insights with international partners and global expertise we offer strategic planning, design and implementation services across aviation infrastructure, MRO, technical and asset management services. Contact our regional practice for market entry assessments and partnership enquiries.
