Many of the technical publications and regulations issued by the FAA are
complex in nature and often require additional explanation.
As a result, the FAA issues Advisory Circulars (ACs) to inform, explain,
and provide further guidance.
Advisory circulars are informative only and cannot be used as
approved data unless incorporated into a regulation or an airworthiness
directive.
Advisory circulars are listed in a numerical sequence closely following the
same subject areas covered by the FARs.
For example; AC43.13-1A, Acceptable Methods; and AC43.13-2A,
Acceptable Methods, Techniques, and Practices – Aircraft Alterations,
correspond with FAR 43.13, which lists the performance rules for the repair
and alteration of aircraft.