Every airline has its only schedule of maintenance (approved by the manufacturer and the aplicable government body).
Here, since we have such a varied fleet, we also have different maintenance programs.
Arrival Service checks whenever the aircraft arrives at a station with maintenance.
Periodic Service check every weekend, not to exceed 7 days.
Then, depending on fleet type, we will do either "A-Checks", "PS
-Checks", "PMC-Checks" or "TC-Checks." These are scheduled at intervals set out in our Maintenance Specification Manuals. basically the above checks involve lubrication, servicing, inspecting and checking systems at a superficial level.
Then we get into your heavier checks, "B", "C" & "D". These are progressively higher checks. As a guideline, "B" is done at 3 or 4 month intervals, "C" at 2 or 3 year intervals and "D" at 4-6 year intervals. I'm not sure if anyone does "D" checks anymore, since You can roll "D" check tasks into "C" checks. '
If you haven't noticed it is complicated and varied.
By the way, never heard of an "M" check.
Clear as mud.