Aircraft maintenance

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An A321 from Iberia having its CFM56 changed

Aircraft maintenance is the overhaul, repair, inspection or modification of an aircraft or aircraft component.[1]

Maintenance may include such tasks as ensuring compliance with Airworthiness Directives.[2] The maintenance of aircraft is highly regulated, in order to ensure safe and correct functioning during flight. National regulations are coordinated under international standards, maintained by bodies such as the International Civil Aviation Organization (ICAO). The maintenance tasks, personnel and inspections are all tightly regulated and staff must be licensed for the tasks they carry out.


A Panavia Tornado undergoing maintenance

The Maintenance, Repair, Overhaul (MRO) Market was US$135.1 Billion in 2015, three quarters of the $180.3 B aircraft production market. Of this, 60% is for civil aviation : air transport 48%, business and general aviation 9%, rotorcraft 3% ; and military aviation is 40% : fixed wing 27% and rotary 13%. Of the $64.3 Billion air transport MRO market, 40% is for engines, 22% for components, 17% for line, 14% for airframe and 7% for modifications. Its is projected to grow at 4.1% per annum till 2025 to $96B.[3]

Airliner MRO should reach $74.3 Billion in 2017 : 51% ($37.9B) single-aisles, 21% ($15.6B) long range twin-aisles, 8% ($5.9B) medium range twin-aisles, 7% ($5.2B) large aircraft, 6% ($4.5B) regional jets as turboprop regional airliners and 1% ($0.7B) short range twin-aisles.[4] Over the 2017-2026 decade, the worldwide market should reach over $900 billion, led by 23% in North America, 22% in Western Europe, and 19% in Asia Pacific.[5]

In 2017, of the $70 billion spent by airlines on maintenance, repair and overhaul (MRO), 31% were for engines, 27% for components, 24% for line maintenance, 10% for modifications and 8% for the airframe; 70% were for mature airliners (Airbus A320 and A330, Boeing 777 and 737NG), 23% were for “sunset” aircraft (MD-80, Boeing 737 Classic, B747 or B757) and 7% was spent on modern models (Boeing 787, Embraer E-Jet, Airbus A350XWB and A380).[6]

In 2018, the commercial aviation industry will need $88 billion for MRO while military aircraft should need $79.6 billion including field maintenance for 46.4%.[7] Airliner MRO should reach $115 billion by 2028, a 4% compound annual growth rate from $77.4 billion in 2018.[8] Major airframers Airbus, Boeing and Embraer enter the market, growing concerns about their intellectual property sharing, while shared data-supported predictive maintenance can reduce operational disruptions: among other factors, prognostics helped Delta Air Lines reduce maintenance cancellations by 98% from 5,600 in 2010 to 78 in 2017.[9]

Insourced maintenance can be inefficient for small airlines with a fleet below 50-60 aircraft. They have to either outsource it or sell its MRO services to other carriers for better resource utilization. For example, the maintenance on South African Comair's 26 Boeing 737s is outsourced to South African Airways' Technical Department. Another example is Spain’s Air Nostrum operates 45 CRJs and ATR72s and its 300-person maintenance department provides line, base maintenance and limited component repair for other airlines 20% of the time.[10]


The commercial aviation engine MRO market is anticipated by Aviation Week to be $25.9 billion in 2018, a 2.5 billion increase from 2017, led by 21% for the Boeing 737NG' CFM56-7B and the A320's CFM56-5B and IAE V2500 (also on the MD-90) tied for second, followed by the mature widebody engines: the GE90 then the Trent 700.[11]

Over the 2017-2026 decade, the largest markets for turbofans will be the B737NG's CFM56-7 with 23%, the V2500-A5 with 21%, the GE90-115B with 13%, the A320's CFM56-5B with 13%, the PW1000G with 7%, the Trent 700 with 6%, the CF6-80C2 with 5%, the CFM LEAP with 5% and the CF34-8 with 4%.[5] Between 2018 and 2022, the largest MRO demand will be for CFM engines with 36%, followed by GE with 24%, Rolls with 13%, IAE with 12% and Pratt with 7%.[12]

As an aircraft gets older, more of its value is transferred to its engines. Along the engine life it is possible to put value back in it with repair and overhaul, to sell it for its remaining useful time, or to disassemble it for its used parts, to extract its remaining value. Its maintenance value include the value of life-limited parts (LLPs) and the on-wing time before its performance restoration. The core value is the value of its data plate and non-LLPs.[13] Engine makers deeply discount their sales, up to 90%, to win the multi-year stream of spares and services, resembling the razor and blades model.[14]

Engines installed on a new aircraft are discounted by at least 40% while spare engine values closely follow list prices. Accounting for 80% of a shop visit cost, LLP prices escalate to recoup the original discount, until engine availability increase with aircraft teardowns. Between 2001 and 2018 for the Airbus A320 or the Boeing 737-800, their CFM56 value increased from 27-29% to 48-52% of the aircraft value. The 777-200ER's PW4000 and the A330-300's Trent 700 engines rose from a share of 18-25% in 2001 to 29-40% in 2013. For the A320neo and 737 MAX, between 52% and 57% of their value lies in their engines: this could rise to 80-90% after ten years, while new A350 or B787 engines are worth 36-40% of the aircraft. After some time the maintenance reserves exceed the aircraft lease.[15]

Between 2019 and 2038, 5,200 spare airliner engines will be required with at least half leased.[16]


A Power by the Hour program provides budget predictability, avoids installing a loaner during repairs when an engine fails and enrolled aircraft may have a better value and liquidity.[17] It was coined by Bristol Siddeley in 1962 to support Vipers of the British Aerospace 125 business jets for a fixed sum per flying hour.[18] A complete engine and accessory replacement service was provided, allowing the operator to accurately forecast this cost, and relieving him from purchasing stocks of engines and accessories.

In the 1980s, Rolls-Royce plc reinstated the program to provide the operator with a fixed engine maintenance cost over an extended period of time. Operators are assured of an accurate cost projection and avoid the breakdowns costs; the term is trademarked by Rolls-Royce but is the common name in the industry.[19] It is an option for operators of several Rolls-Royce aircraft engines.[citation needed] Other aircraft engine manufacturers such as General Electric and Pratt & Whitney offer similar programs.

Jet Support Services provides hourly cost maintenance programs independently of the manufacturers.[20] GEMCO also offers a similar program for piston engines in general aviation aircraft.[citation needed] Bombardier Aerospace offers its Smart Services program, covering parts and maintenance by the hour.[citation needed]


Aircraft maintenance is highly regulated, because the smallest slip can lead to an aircraft crashing with consequent loss of life. The International Civil Aviation Organization (ICAO) sets global standards which are then implemented by national and regional bodies around the world.

Local airworthiness authorities include:


Field maintenance on a Cessna 172 being conducted from a van used to carry tools and parts

The International Civil Aviation Organization (ICAO) defines the licensed role of aircraft maintenance (technician/engineer/mechanic), noting that "The terms in brackets are given as acceptable additions to the title of the license. Each Contracting State is expected to use in its own regulations the one it prefers."[21] Thus, aircraft maintenance technicians, engineers and mechanics all perform essentially the same role. However different countries use these terms in different ways to define their individual levels of qualification and responsibilities.

Recognised licenses for aircraft maintenance personnel include:

As there will be 41,030 new airliners by 2036, Boeing expects 648,000 new commercial airline maintenance technicians from 2017 till then: 256,000 in Asia Pacific (39%), 118,000 in North America (19%) and 111,000 in Europe (17%).[22]

European authorities[edit]

Aircraft maintenance personnel in Europe must comply with Acceptable Means of Compliance (AMC) Part 66, Certifying Staff, issued by the European Aviation Safety Agency (EASA).

AMC Part 66 is based on Joint Aviation Regulations (JAR) promulgated by the Joint Aviation Authorities and on Air Transport Association (ATA) Specification 104. There are four levels of authorization:

  • Level 1: General Familiarisation, Unlicensed
  • Level 2: Ramp and Transit, Category A
    • can only certify own work performed for tasks which he/she has received documented training
  • Level 3: Line Certifying Staff and Base Maintenance Supporting Staff, Category B1 (electromechanic) and/or B2(Avionics)
    • can certify all work performed on an aircraft/engine for which he/she is type rated excluding base maintenance(generally up to and including A-Check)
  • Level 4: Base Maintenance Certifying Staff, Category C
    • can certify all work performed on an aircraft/engine for which he/she is type rated, but only if it is base maintenance (additional level-3 staff necessary)
    • this authorization does not automatically include any level 2 or level 3 license.

Checks and inspections[edit]

Technicians work on a Bombardier airplane in Dallas, Texas

Routine checks[edit]

Aircraft maintenance checks are periodic inspections that have to be done on all commercial/civil aircraft after a certain amount of time or usage.

Airbus has indicated that data diagnostics could put an end to aircraft unscheduled grounding for fault repairs around 2025, supported by big data and operational experience. Predictive maintenance, diagnostics and health monitoring could eliminate unscheduled groundings, by making maintenance schedule intervals more frequent to avoid AOGs and the associated operational interruptions, ultimately eliminating them. Data or monitoring can tell that some parts do not need a scheduled check, but a full transition to this model will need much greater experience. With more history, examples and regulatory confidence, the maintenance manual could become a dynamic document for each specific aircraft with every check and interval based on its operational history.[23]

Maintenance release[edit]

At the completion of any maintenance task a person authorized by the national airworthiness authority signs a maintenance release stating that maintenance has been performed in accordance with the applicable airworthiness requirements. In the case of a certified aircraft this may be an Aircraft Maintenance Engineer or Aircraft Maintenance Technician, while for amateur-built aircraft this may be the owner or builder of the aircraft.[24] A maintenance release can be called a certificate of release to service (CRS).[25]

Automated inspection[edit]

Autonomous Donecle UAV performing an aircraft inspection.

Automated aircraft inspection systems have the potential to make aircraft maintenance safer and more reliable.[26] Various solutions are currently developed: a collaborative mobile robot named Air-Cobot,[27][28] and Unmanned aerial vehicles from Donecle or Easyjet.[29][30]

See also[edit]


  1. ^ Transport Canada (May 2012). "Canadian Aviation Regulations 2008-1, Part I - General Provisions, Subpart 1 - Interpretation". Archived from the original on 27 December 2012. Retrieved 9 December 2012.
  2. ^ Transport Canada (March 2002). "Canadian Aviation Regulations 2008-1, Part V - Airworthiness, Standard 593 - Airworthiness Directives". Archived from the original on 18 May 2013. Retrieved 9 December 2012.
  3. ^ Kevin Michaels (April 28, 2016). "MRO Industry Outlook" (PDF). ICF International.
  4. ^ "2017 MRO Market Share by Category". Aviation Week Network. Jul 12, 2017.
  5. ^ a b "Top 10 Engine MRO Demand: 2017-26". Aviation Week Network. Aug 16, 2017.
  6. ^ Kevin Michaels (Jan 16, 2018). "Opinion: OEMs Focus On Mature Aircraft For Aftermarket Growth". Aviation Week & Space Technology.
  7. ^ Lee Ann Shay (Jan 2, 2018). "Commercial Spending Will Lead MRO Field In 2018". Aviation Week & Space Technology. Comparing civil, helicopter, business aviation and military MRO forecasts for 2018.
  8. ^ Aaron Chong (26 Jan 2018). "Global MRO spend to reach $115 billion by 2028 - Wyman". Flightglobal.
  9. ^ Jon Hemmerdinger (25 Apr 2018). "Airframers set out on differing aftermarket paths". Flightglobal.
  10. ^ Henry Canaday (Mar 12, 2018). "Outsourcing Versus In-Sourcing For Small Fleets". Aviation Week Network - MRO.
  11. ^ James Pozzi (Nov 24, 2017). "Life In The Old Dogs Yet". Aviation Week Network.
  12. ^ "Engine MRO Demand - Top 5 Engine OEM: 2018-22". MRO Network. Aviation Week Network. May 30, 2018.
  13. ^ Alex Derber (Oct 16, 2017). "Keeping An Eye On Engine Values". Aviation Week network.
  14. ^ Ernest S. Arvai (January 19, 2018). "The Meaningless Game of List Prices". AirInsight.
  15. ^ David Griffin (21 June 2018). "Analysis: The influence of engines on aircraft values". FlightGlobal.
  16. ^ Alex Derber (Oct 22, 2018). "Engine Leasing In Rude Health". Aviation Week Intelligence Network.
  17. ^ William Garvey (Nov 3, 2017). "How Hourly Maintenance Provides Shelter From Explosive Surprises". Aviation Week & Space Technology.
  18. ^ "Rolls-Royce celebrates 50th anniversary of Power-by-the-Hour" (Press release). Rolls-Royce. 30 October 2012.
  19. ^ "'Power by the Hour': Can Paying Only for Performance Redefine How Products Are Sold and Serviced?". Knowledge at Wharton. Feb 21, 2007.
  20. ^ "Jet Support Services, Inc". Bloomberg Businessweek.
  21. ^ ICAO; Doc 7300, Convention on International Civil Aviation (also referred to as the Chicago Convention), 9th Edn. (2006), Annex 1, Chapter 4. Licenses and ratings for personnel other than flight crew members.
  22. ^ "Pilot and Technician Outlook". Boeing. 2017.
  23. ^ Max Kingsley-Jones (12 Dec 2017). "Airbus sees big data delivering 'zero-AOG' goal within 10 years". Flightglobal.
  24. ^ "Canadian Aviation Regulations (CARs)Part V - Standard 571 - Maintenance". Transport Canada. 2010-12-01. 571.10 Maintenance Release.
  25. ^ Airworthiness Manual, Doc 9760 (3 ed.). Montreal (Canada): International Civil Aviation Organization. 2014. p. 375. ISBN 978-92-9249-454-4.
  26. ^ "Robots in the hangar". November 23, 2015. Retrieved May 20, 2016.
  27. ^ Jovancevic, Igor; Larnier, Stanislas; Orteu, Jean-José; Sentenac, Thierry (November 2015). "Automated exterior inspection of an aircraft with a pan-tilt-zoom camera mounted on a mobile robot". Journal of Electronic Imaging. 24 (6).
  28. ^ I. Jovancevic, I. Viana, T. Sentenac, J.J. Orteu and S. Larnier, Matching CAD model and images features for robot navigation and inspection of an aircraft, International Conference on Pattern Recognition Applications and Methods, pp. 359-366, February 2016.
  29. ^ "Donecle - lightning fast aircraft inspections". Retrieved May 20, 2016.
  30. ^ "EasyJet's Using Drones to Check Planes for Lightning Damage". Retrieved May 20, 2016.

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