TYPES OF AIRCRAFT MAINTENANCE

Aircraft maintenance is divided into two sections called 'Scheduled Maintenance' and 'Unscheduled Maintenance'.

Standard scheduled maintenance is further divided into three types of checks called:
A Checks
C Checks
D Checks

The A Check
Usually carried out every eight to 10 weeks, filters will be changed, key systems (like hydraulics in the ‘control surfaces’ that steer the aircraft) will be lubricated and a detailed inspection of all the emergency equipment (like inflatable slides) is completed. A typical A Check on B737 takes between six and 24 hours.

The C Check
Happens every 18 months to two years or 1,800 flight hours, or 2,000 cycles (depending on type of aircraft) and takes three weeks.
C checks can be further subdivided into C1, C2, C3, and C4 where the level of maintenance increases.
During C Check, in-depth systems checks, inspection for corrosion, cracks, structural defects, in depth lube of all fittings and cables are carried out.

The D Check
This is also known as a C4 or C8 check depending on the aircraft type. This check is performed every six years and the entire aircraft is basically dismantled and put back together. Everything in the cabin is taken out (seats, toilets, galleys, overhead bins) so engineers can inspect the metal skin of the aircraft, inside out. The engines are taken off.
The landing gear is removed and overhauled with the aircraft supported on massive jacks. All of the aircraft systems are taken apart, checked, repaired or replaced and reinstalled.

Each D Check costs several million dollars and takes about three to six weeks, but it’s almost like a brand new plane by the end of it.

Most modern aircraft are designed to carry out less maintenance. For instance, the Boeing B787 only needs a D Check every 12 years compared with every six years for older aircraft.