We are part of a heavily regulated industry in aviation. In the United States, the Federal Aviation Administration (FAA) establishes rigorous safety and maintenance requirements for commercial airline companies. These ensure that all aircraft meet high safety standards before they leave the hangar.
As part of that, commercial airline companies must create and sustain a Continuous Airworthiness Maintenance Program (CAMP). This page is a general overview of the scope of work that an aviation maintenance technician will perform on a regular basis. That includes line maintenance checks, A Checks, C Checks, and D Checks (there used to be a B Check, but it was assimilated into the other checks for more modern aircraft).
Let’s first look at the legal requirements of the types of aviation maintenance. According to the FAA, a CAMP must “contain the person’s entire inspection program and the program covering other maintenance, preventive maintenance, and alterations, which constitute the maintenance part of the person’s required manual. The identified documents (including those referred to within) are the prescriptive methods, techniques, and practices individuals must follow when performing maintenance activities on the person’s aircraft. A CAMP contains 10 elements and must be comprehensive in scope and detail to fulfill the certificate holder/program manager’s responsibility to ensure:
- Maintenance, preventive maintenance, and alterations performed by it, or by other persons, are performed in accordance with the certificate holder/program manager’s D072-authorized manual;
- Competent personnel and adequate facilities and equipment are provided for the proper performance of maintenance, preventive maintenance, and alterations; and
- Each aircraft released to service is airworthy and properly maintained for its operation.”
For the aviation maintenance technician, line maintenance checks are the most common. Broadly, they happen after 24 to 60 hours of accumulated flight time, which varies per plane, and they are usually performed at the gate.
A line technician monitors fuel levels and maintains fuel inventories, ensuring that each and every plane has the correct quantity of fuel for each flight. That means making sure that fuel trucks are full and ready to distribute fuel. These professionals also do things like checking oil levels, hydraulics, wheels, brakes, and the body of the plane for any visible damage. This process is also called transit checks, post-flight, maintenance pre-flight, service checks, and overnight checks. It ensures airworthiness and basic safety.
The next kind of aviation maintenance check we will look at is the A Check. This happens approximately every 400-600 flight hours or every 200–300 flights, according to specifications for an individual aircraft. For an A Check, the aircraft will be taken to a hangar, usually overnight so that it is not out of commission during busy daytime flight times. The A Check requires careful examination of the body of the aircraft for evidence of damage, deformation, corrosion, or missing parts. Technicians change filters, lubricate key systems, and inspect all the emergency equipment (like inflatable slides and emergency lights).
As an example, a typical A Check on B737 takes between six and 24 hours.
Now we are getting into the “heavy maintenance” portion of aviation maintenance. The C Check happens between 18 months to two years (depending on the aircraft). This is likely performed in a special facility, taking 1-2 weeks. During a C Check, an aviation maintenance technician performs an extensive check of individual systems and components for serviceability and function.
Here are some examples of C Check items, per Aviation Pros:
- Visually check flight compartment escape ropes for condition and security
- Check operation of DC bus tie control unit
- Visually check the condition of entry door seals
- Operationally check flap asymmetry system
- Pressure decay check APU fuel line shroud
- Inspect engine inlet TAI ducting for cracks
- Inspect stabilizer attach bolts
- Inspect floor beams
- Detailed inspection of wing box structure
This is also known as a structural check, the most extensive of them all, costing several million dollars. A D Check happens every six to ten years and basically, a crew dismantles the entire aircraft and puts it back together again over a month or so. The cabin is taken apart and inspected and even the engines and landing gear come off. This is a deep process of the structure itself, looking for any signs of corrosion, structural deformation, cracking, or deterioration/distress using special equipment and techniques. The D Check includes all the lower checks, too.
As Qantas said a few years ago, “It’s easy to forget when you board a modern jet aircraft that you’re stepping onto one of the most complex machines ever created.” We hope this page has helped clarify some areas of aircraft maintenance. We're here to help!