Aircraft Maintenance: Line Maintenance and the A, C, D’s of It All

Aircraft are under a constant state of stress when logging flight hours. Boeing aircraft, for example, have the ability to fly upwards of 14 hours non-stop and their lifetime can extend anywhere from 20 - 27 years in operation. In this time, an aircraft will experience about 35,000 pressurization cycles and will undergo the associated, and often expected, degradation and parts fatigue. So, how do modern aircraft maintain their reliability and safety over time?

Beginning at the production level, an aircraft undergoes FAA regulated inspections and checks to ensure quality control and safety. Manufacturers of commercial airliners usually resort to a non-destructive evaluation (NDE) when an aircraft is on the production line. This program is structured to ensure that components are free of defects before they even see a buyer. Companies that consult these large-scale evaluations include the likes of Boeing and Airbus, among many others.

Maintenance checks are regulated by the FAA and scheduled over the life cycle of an aircraft. Standard parameters set forth by manufacturers by these regulations will include the following: line maintenance, A checks, C checks, and D checks. B checks have actually been absorbed into the A category, as B checks have become obsolete or covered by the A category with the advancement of aviation technology.

Line maintenance of an aircraft often involves up to 12 hours of inspection per week. System checks include some of the elements you may have seen in standard automotive servicing. The assessment will survey the brakes, wheels, fluid levels and landing gear of an aircraft. Any necessary repairs are also attended to during this phase of maintenance.

Proceeding through the life cycle of the aircraft, the next inspection it will encounter is the A-check. These checks are required after every 100 flight hours. Processing of the inspection takes longer than line maintenance, often totaling over 12 hours. Under this careful examination, lubrication and oil are changed, and systems and functional checks should be performed.

Defined as a heavy maintenance check, a C-check is completed between 18 months and 2 years, 1800 flight hours, or 2,000 pressurized cycles. It is typically a 3-week process in which airlines might make changes to interior cabin design or amenities.

Lastly, a D-check is performed after the aircraft has been in service for about 6 years, or after it has received a total of four C-checks. This assessment is broken up into a series of steps, often referred to as C4 or C8 checks. During this inspection, the aircraft is dismantled including the cabin, landing gear, and any applicable accessories. The airframe is then removed, and the engine/s undergo routine maintenance checks.

Despite inspection during and post production, it is crucial to stay up to speed on the durability limits specified by a parts manufacturer. Each aircraft will encounter different levels of pressurization and degradation, and each part’s component will have its own established flight cycle limit. With proper care, following manufacturer and FAA parameters will promote the longevity of the aircraft. 

1. mary wilson
2. Posted on March 7, 2019
3. aviation

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