Check A
Light check
- Every 400-600 flight hours (1 month)
- Duration 10 hours
Check B
Light check
- Every 6-8 months
- Duration 1-3 days
B checks are increasingly incorporated into successive A checks, i.e. checks A-1 through A-10 complete all the B check items.
Check C
Heavy check
- Every 2 years
- Duration 1-4 weeks
Check 3C
Heavy check
Some authorities use a type of check, known as a 3C check or Intermediate Layover (IL), which typically includes light structural maintenance, including checks for corrosion, or on specific high-load parts of the airframe.
The 3C check may also be used as the opportunity for cabin upgrades, e.g. new seats, entertainment systems, carpeting. This shortens the time the aircraft is out of service, by performing two distinct tasks simultaneously.
As component reliability has improved, some MROs now spread the workload across several C checks, or incorporate this 3C check into D checks instead.
Check D
Heavy check
- HMV Heavy Maintenance Visit
- Every 6-10 years
- Duration 6 months to a year
