The planes are quite detailed and great vehicles. It is not difficult to estimate the volume of work that arises if we consider dozens or even hundreds of airplanes in fleets. In aviation, some say airplanes are like ladies because they need certain attention and they have major expenses. We can see below that we have justification in this analogy because of reasons;
Continuity is essential in aviation. So a job is done as many times as if it had never been done before. For example, the exterior of the aircraft is checked in detail after every flight. Tire pressures are measured, systems oil and water is checked. Electronic (avionic) systems are checked for malfunctions. Pilots are also briefly negotiated and asked if they have any negative findings, so necessary precautions are taken. These are repetitive operations performed daily as long as the aircraft continues to fly. It is known as aviation transit or daily checks.
There are also some more detailed inspections done at longer intervals. Even though some special crews and equipment are used for these inspections, there is no need for the aircraft to enter the hangar. It can be done with a relatively limited number of people. It usually takes a few days to complete and return to the flights. Such treatments are called line maintenance or light (A) checks.
Apart from these inspections, there are much more detailed controls that are made at less frequent intervals, where the aircraft has to enter a closed hangar environment. Special controls, equipment and supplies are required for these checks. The plane’s panels, various parts, seats, engines and even wing parts are disassembled. The necessary parts are tested. Some parts are checked for damage or not, and if no problem is found, they are installed back. Some are replaced by new ones due to safety reasons, even if they have no problems. Such checks are done every 2 to 3 years. The more detailed ones are made at intervals of 5 to 6 years. This type of maintenance is called heavy (C) or structural (D) maintenance.
In addition to the detailed controls in the hangar environment, the landing gear and engines are also disassembled and sent to special maintenance centers. Since the control of these basic parts requires special processes and applications, it is done by specialized centers in this business. These operations are much more extensive and are even less frequent than hangar maintenance, ranging from once in a 10 to 12 years or about 20,000 flights. Such maintenance, which is carried out by a special authorized maintenance center, is also referred as shop maintenance (or visit).
All of these transactions are supported with paper documents and recorded. A record of all controls, operations and repairs carried out on the aircraft, including the production phase of the aircraft, is kept. All accumulated records are archived in boxes. Accumulated boxes are stored in a safe environment until the aircraft leaves the service. Even if the plane changes hands, even if the country of operation changes, all boxes are transferred to the new owner or place with the plane and continue to be kept.
As a result, the aircraft are checked at regular intervals and with variable precision. No matter how good they look, they are inspected repeatedly, regardless of their appearance. Each control is recorded and stored until the end of its life. In other words, planes are sensitive vehicles that demand close attention and consistency at the same rate of speed and comfort they provide.