Overview by Sofema Online (SOL) www.sofemaonline.com

Airworthiness Directives (ADs) are legally enforceable rules issued by the FAA in accordance with 14 CFR part 39 to correct an unsafe condition in a product.

• 14 CFR part 39 defines a product as an aircraft, aircraft engine, propeller, or appliance

Maintenance Planning Document (MPD) – The MPD is essentially generic across a particular fleet, is issued by the aircraft manufacturer and applies to many aircraft, it is not customized and several (hundreds of) tasks are dependent for example on the aircraft modification status and its serial number.

It cannot under any circumstances be considered as a final list of tasks for a given tail number.

Aircraft Modification Status – The applicability of multiple tasks may be affected by the aircraft modification status. (The MPD may list a task as “pre mod” or “post mod”.)

To correct set the tasks we must know the mod status of the aircraft in order to know which tasks are applicable and should be carried out.

Also, the aircraft may have custom modifications embodied, which often come with their own maintenance tasks. (Via Supplemental Type Certificate (STC) controlled by Part 21 Subpart J Design organisations)