An Advance Change Notice (ACN) would be received when?

An Advance Change Notice (ACN) is issued specifically to communicate changes in existing maintenance requirements. This ensures that all relevant personnel are informed of updates that might affect maintenance scheduling, procedures, or policies. The issuance of an ACN reflects a need for timely dissemination of information regarding alterations that have been implemented, enabling effective operational planning and compliance with updated guidelines.

In contrast, the other options suggest predetermined scheduling intervals—monthly or semi-annually. However, the nature of an ACN is not based on a regular schedule but rather is dependent on the necessity of communicating modifications as they occur. Therefore, the correct understanding aligns with the fact that an ACN is generated whenever a change has been implemented, rather than at fixed time intervals.