Explained: The ABCDs of Aircraft Maintenance
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Explained: The ABCDs of Aircraft Maintenance

Delta TechOps Agents. Photo: Delta Air Lines

DALLAS — Thanks to technological advancements, the aeronautical industry, particularly commercial aviation, has made significant progress. As a result, it’s crucial to conduct regular maintenance to ensure that modern airliners with advanced systems operate optimally.

Commercial aviation is one of the most highly regulated industries in the world. Safety is paramount, and it can’t abide by an adequate inspection and maintenance schedule.

“Today’s aircraft are carefully tuned machines with primary systems and backup systems (and, sometimes, backup, backup systems) in order to fly up to 16 hours non-stop without skipping a beat.”

Qantas Airlines on Aircraft Maintenance

The Federal Aviation Administration (FAA) specifies stringent safety and maintenance requirements for commercial airline companies in the United States. These ensure that all aircraft in the fleet fulfill high safety measures before they depart the maintenance hangar.

As part of the Airways Explained series, this post aims to help explain aircraft maintenance and how airlines and operators keep their fleets updated.

Qantas Airbus A380-800 (VH-OQA). Photo: Tony Bordelais/Airways

Curtain Raiser


In the early days of aviation, the mavericks who designed and piloted the first aircraft carried out necessary maintenance. As airplane technology advanced, dedicated maintenance personnel were needed to perform maintenance work. That’s how the aircraft maintenance field came into existence.

There are 50-year-old aircraft still flying thanks to regularly scheduled maintenance. Some aircraft are much older than that and still take off and land frequently. Modern airliners are not operated for prolonged periods, mainly for safety; they also undergo regular complex maintenance.

There were simple maintenance schedules during the time of Boeing 707 and other narrowbody airliners. However, with the introduction of the large wide-body jets, there was a need for a more rigorous maintenance program. As a result, regulators and operators developed the maintenance schemes that came to be known as the ‘Continuous Airworthiness Maintenance Program (CAMP).

CAMP includes various routine maintenance tasks, subdivided into aircraft maintenance checks essential to ensuring an aircraft remains airworthy and safe to fly.

These checks are carried out regularly by trained maintenance personnel and are designed to identify any potential problems or issues with the aircraft before they can become serious.

SR Technics Job Portal
Photo: SR Technics

CAMP


The Continuous Airworthiness Maintenance Program (CAMP) is a comprehensive computerized aircraft maintenance management system that aviation operators and maintenance organizations implement to keep their aircraft fleets in proper shape. Think of it as a high-tech, all-in-one maintenance solution designed to keep aircraft airworthy and compliant with regulations.

With CAMP, technicians and engineers get a structured framework for managing maintenance, inspection, and repair activities for your aircraft. It covers everything from scheduled maintenance tasks and inspections based on aircraft manufacturers’ recommendations and regulatory requirements to unscheduled maintenance tasks arising from unexpected issues like malfunctions or damage.

The program aims to keep the aircraft airworthy throughout its service life by tracking maintenance tasks and inspections, recording maintenance history, and monitoring compliance with regulations. Identifying trends in maintenance cases can also help them improve maintenance practices and reduce the probability of forthcoming nuisances.

Another feature of CAMP is that it can be tailored to meet the operator’s or maintenance organization’s needs. CAMP can be implemented for various aircraft types and sizes, from small general aviation aircraft to large commercial airliners. Critical features of CAMP include maintenance scheduling and tracking, compliance monitoring and reporting, inventory management, reliability analysis, and safety management.

In a nutshell, if operators and airlines want to ensure the safety and reliability of their aircraft, they can rely on the CAMP tool for managing maintenance activities and regulatory compliance, ensuring that their aircraft remains airworthy and complies with all applicable regulations throughout its service life.

Each operator has to prepare its own CAMP, which comes under the Operations specifications (OPSPECS). Then, they must get approval for this document from the country’s civil regulatory authority—for example, FAA in the United States, TCCA in Canada, EASA in Europe, etc.

Let’s explore the different types of aircraft maintenance checks, their purpose, and their importance in ensuring aircraft safety.

Emirates engineering facility
Emirates engineering facility | Photo: Emirates Twitter

ABCDs of Maintenance


Four main types of aircraft maintenance checks are carried out regularly. These checks are known as A, B, C, and D, each more extensive than the last.

A and B checks come under Line maintenance or Light Checks, while C and D checks are categorized under Base or Heavy maintenance.

Many operators and airlines have combined A and B checks under A-1 to A-10, but some small operators still use these terms. So, we will also provide details about B-Checks for a general overview.

The man hours and flight cycles mentioned below are general outlines, and we suggest you refer to the approved CAMP to comprehend specific information on the respective aircraft type.

By SuperJet International - Line Maintenance Performing, CC BY-SA 2.0,
By SuperJet International – Line Maintenance Performing, CC BY-SA 2.0

A Checks

The A-check is the most basic aircraft maintenance check every 100 to 300 flight hours. This check is usually completed within a few hours and is designed to identify defects or aircraft issues.

According to the Aviation Maintenance Management book, A check is accomplished around every 400-600 flight hours or every 200–300 flights, depending on aircraft type. It takes ten to 24 hours to complete with 50-70 technicians for single-aisle aircraft.

Operators or Maintenance, Repair, and Overhaul (MRO) organizations can also delay some tasks in these checks if they follow specific predetermined provisions. Some of these items are categorized under Minimum Equipment Lists or MEL.

During an A-check, MROs:

  • Inspect the aircraft’s exterior for signs of damage or wear and tear.
  • Check the aircraft’s fluid levels, such as oil and fuel.
  • Inspect the tires and brakes for any signs of wear or damage.
  • Check the aircraft’s avionics systems, including radios, transponders, and navigation systems.
  • Check the aircraft’s flight controls, such as flaps and ailerons.
Photo: Ramco
Photo: Ramco

B Checks

The B-check used to be a more extensive aircraft maintenance check than the A-check. It was usually carried out after every 600 to 800 flight hours or approximately every six to eight months.

Depending on the aircraft type, this check typically takes between one and three days to complete with 160-180 man-hours and involves a more thorough inspection of the aircraft’s systems and components. As mentioned above, these checks are more intensively incorporated into their predecessor, A-Check.

During B Checks, operators usually:

  • Perform A Check
  • Check the aircraft’s engines and associated systems, including oil filters and fuel nozzles.
  • Inspect the aircraft’s landing gear and associated systems, such as hydraulic and pneumatic systems.
Lufthansa Technik
Photo: Lufthansa Technik via LinkedIn

C Checks

The C-check is usually carried out after every 18 to 24 months. The aircraft must be pulled out from operations because it’s categorized under heavy checks. As it’s more extensive, it demands a considerable prevalence of the aircraft’s components to be inspected.

 This check places the aircraft out of service for one to four weeks. Here’s the catch: the plane cannot leave the maintenance hangar without completing the tasks mentioned in this check.

The C-check requires more space, so operators carry out this check at their base locations. It usually needs nearly 6,000 man-hours to complete all the inspections and tasks.

During a C-check, operators typically:

  • Perform A-B Checks
  • Inspect the aircraft’s structural components, such as wings and fuselage.
  • Inspect the aircraft’s electrical systems, including wiring and connectors.
By Apetrov09703 - Own work, CC BY-SA 4.0,
By Apetrov09703 – Own work, CC BY-SA 4.0

D Checks

Finally, we have the D-check, also known as the structural check; it is the most extensive check and undergoes complete aircraft inspection and overhaul. It costs operators and carriers millions of dollars.

The D-check is also referred to by some as Heavy Maintenance Visit (HMV) and requires six to ten years to complete. Practically, a massive team of aircraft mechanics and engineers disassembles the whole aircraft and puts it back concurrently again over a few months or so.

The aircraft undergoes meticulous inspection, overhaul, replacement, and maintenance during this check. This is a resonant operation of the structure itself, scrutinizing for any signs of corrosion, structural deformation, splintering, or deterioration/distress using special tools and procedures. D check includes all the tasks carried out in A, B, and C checks as well.

During a D-check, operators:

  • Perform A and B Checks
  • Inspect the aircraft’s electrical systems, including wiring and connectors.
  • Complete overhaul of the aircraft’s systems, including engines, landing gear, avionics, and structural components.

The list can include more tasks depending on the CAMP approved by respective regulatory authorities.

As reported by Aircraft Value News in 2018 that the cost of D checks for Boeing family jets is in millions of US dollars.

AircraftEstimatedActual
Boeing 777-200ERUS$2.5US$4.0
Boeing 777-300ERUS$2.7US$4.5
Boeing 747-400US$4.0Us$6.0
Boeing 737-800US$0.65US$1.0
Source: Aircraft Value News
AIESL - AI Engineering Services Ltd
Photo: AIESL – AI Engineering Services Ltd.

Airlines with HMV facility


The A and B checks are usually performed at airlines or operator facilities and are sometimes contracted to MROs. While most airlines outsource C and D checks to specialized maintenance organizations, a few prefer to have greater control over their maintenance schedules and reduce costs by doing it themselves.

Take Emirates Airlines (EK). This airline has its own maintenance facility in Dubai, United Arab Emirates, where it can perform C and D checks and other maintenance services. The facility is loaded with advanced technologies and can handle multiple aircraft types.

Then there’s Lufthansa Technik, the maintenance division of Lufthansa (LH) Group, which operates several maintenance facilities worldwide, including in Hamburg, Germany, and Budapest, Hungary, where it provides C and D checks and other services.

Along with EK and LH, other carriers have all four check facilities. A few to name are Air India (AI), British Airways (BA), Singapore Airlines (SQ), Qantas (QF), Turkish Airlines (TK), Delta Air Lines (DL), and Air France (AF), and KLM (KL) joint Engineering & Maintenance facilities.

Of course, airlines having their own maintenance facilities requires a massive investment in equipment, facilities, and personnel, which may not be feasible for smaller airlines.

But for those who can afford it, having their own HMV check facilities can help them save time and money while maintaining greater control over their maintenance schedules.

PT-MUA LATAM Airlines (Star Wars-Galaxy’s Edge Livery) Boeing 777-32W(ER) B77W JFK KFJK. Photo: Francesco Cecchetti/Airways

Importance of Checks


Aircraft maintenance checks are crucial for ensuring aircraft and passengers’ safety. These checks help identify any potential problems or issues with the aircraft before they can become serious. They authorize maintenance personnel to take corrective action to preclude these situations from occurring.

In addition, routine maintenance inspections can help prolong an airliner’s lifespan and its components. By identifying and addressing issues early on, maintenance personnel can help prevent premature wear and tear on the aircraft’s systems and components, leading to longer service life and lower operating costs.

Ultimately, These checks are required by regulation for all commercial aircraft. This means that airlines and other operators are legally obligated to ensure that their aircraft are adequately maintained and inspected on a regular basis. Failure to comply with these constraints can result in fines, penalties, and even the grounding of an aircraft.

Apart from these checks, we have other types of maintenance tasks. These are divided into Planned and Unplanned maintenance. The planned checks include daily, transit, and pre and post-flight inspections. The A to D checks are also part of Planned maintenance.

While Unplanned is such that we cannot predict in advance and can be caused by a bird strike, lightning strikes, hull damage, ground handling damage, heavy landings, and more.

N143DU Delta Air Lines A220-300 KSMF SMF #GOLDENHOUR. Photo: Jinyuan Liu/Airways

Bottom Line


The CAMP maintenance framework and the aforementioned checks are essential for ensuring the safety and airworthiness of aircraft. From routine checks to heavy maintenance checks, each plays a crucial role in keeping aircraft operating safely and efficiently.

With technological advances and the increasing complexity of modern aircraft, the role of maintenance checks has become even more critical. Computerized maintenance management systems have revolutionized the way aircraft maintenance is managed, helping to ensure that aircraft remain airworthy and in compliance with regulatory requirements.

Airlines have recognized the importance of maintenance checks and have invested in their own maintenance facilities to better manage their maintenance schedules and costs. This investment helps airlines ensure that their aircraft are maintained to the highest standards, providing their passengers with safe and reliable flights.

Ultimately, aircraft maintenance checks are a critical component of aviation safety, and it is essential that they are carried out thoroughly and effectively. Aircraft maintenance checks are the reason flying on a commercial aircraft is safer than riding a bike.

By prioritizing maintenance checks and investing in the necessary resources, airlines can continue to provide safe and reliable air travel for passengers worldwide.

Have you seen these metal birds undergo maintenance? Let us know in the comments on our social media channels.


Feature Image: Delta TechOps Agents. Photo: Delta Air Lines

Aircraft maintenance engineering graduate and Aviation enthusiast with more than four years of experience in running a successful aviation startup.

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