All commercial and private aircraft need to undergo proper maintenance and periodic inspections to ensure their airworthiness.
Image source: dorsetcollege.bc.ca
A daily check is the lowest scheduled inspection, and it includes post-flight, basic pre-flight maintenance, and service and overnight checks. A cursory examination of the aircraft, along with the checking of fluid levels, general condition and security of the airplane, and installed emergency equipment, is conducted to ensure the airplane is in working order.
For heavier checks, more detailed inspections are categorized into the following maintenance plans:
‘A’ check: An ‘A’ check is performed every 400-600 hours of flight. It is typically done in designated maintenance hangars in the route structure. A minimum of 10 hours is required, and limited special tooling, servicing, and test equipment are required for the maintenance procedures.
Image source: af.mil
‘B’ check: Conducted every six to eight months, a ‘B’ check is completed within one to three days. While a detailed examination of components and systems is conducted, there is no need for detailed disassembly or removal of aircraft parts.
‘C’ check: Much more extensive than a ‘B’ check, a large majority of the components are thoroughly and individually probed for serviceability and function. It is performed every 20-24 months, and the general time of completion is around one to two weeks.
‘D’ check: The most comprehensive among the four checks, it is also known as a heavy maintenance visit. A ‘D’ check is accomplished every six years. A complete inspection and overhaul of every component and system is undertaken in approximately two months.