A, B, C & D Checks

Imagine a car's maintenance schedule, a quick oil check every few weeks, a more thorough service every year, and eventually a major overhaul after many years of heavy use, and then imagine that same escalating logic applied to an aircraft, except with dramatically higher stakes and considerably more rigorous inspection at every single stage. Aircraft maintenance follows exactly this escalating structure, organised into four standard check levels, A through D.

An A Check happens frequently, roughly every few hundred flight hours, and covers routine visual inspections and basic servicing that can typically be completed overnight without taking the aircraft out of active service for long, while a B Check, somewhat less common in modern maintenance programmes which often fold it into A or C checks, covers a moderately deeper inspection.

C Checks represent a genuinely significant step up, occurring roughly every one to two years, requiring the aircraft to be taken out of service for several days to a couple of weeks while extensive systems and structural inspections are carried out, work substantial enough that it usually happens at a dedicated maintenance facility rather than at a regular airport gate.

The D Check is the big one, a complete teardown occurring roughly every six to ten years, where the aircraft is essentially stripped down to its structural frame, every system inspected, and worn components replaced, work so extensive it can take a month or more and represents one of the largest single maintenance expenses an airline incurs on any aircraft, exactly the kind of specialised, capital-intensive work the MRO, Maintenance Repair and Overhaul, industry covered elsewhere on this site exists specifically to provide.