Yup. A checks are typically prefomed every 250 flights and are not heavy maintenance. They are typically done overnight and are just checking more general things.

B checks are usually included in an A check and still not heavy maintenance. Can be completed in 1-4 days.

C checks are different for each aircrat but can take thousands of hours to complete. This is what is happening with our planes at SIN most of the time.

The D check is done every 5-10 years which involves completely stripping the aircrat of everything and then placing it back together. Ths makes refits during the D check time appealable, as the can strip everything and the whack the new cabin in all in one visit. These typically take up to 50,000 hours