An aircraft maintenance plan has several different sources that are used in creating it. When the sources are combined, they reflect that specific aircraft and so the maintenance plan is now customised accordingly. The multiple sources will determine tasks and apply instructions on when to carry these tasks out.
The tasks are from a multitude of sources such as Certification Maintenance Requirements (CMR) which are essential tasks to keep the aircraft safe and airworthy through to documents nonmandatory service bulletins (SB) or information letters.