Review by Sofema Aviation Services (SAS) www.sassofia.com

Introduction Role & Purpose of an STC

An STC attests the approval of a major change, classified in accordance with Article 21A.91 of Annex Part 21 to Commission Regulation (EC) No. 748/2012, to an approved type design where the designer of the major change is not the Type Certificate holder.

The supplemental type certification shall be performed in accordance with the provisions of Annex II of the Basic Regulation and Annex Part 21, Subpart E of Commission Regulation (EC) No. 748 /2012 laying down implementing rules for the airworthiness and environmental certification of aircraft and related products, parts and appliances and the related Acceptable Means of Compliance (“AMC”) and Guidance Material (“GM”).

Steve Bentley MD of Sofema Aviation Services www.sassofia.com – explains

A type certificate holder (TCH) can produce parts for its airplanes through the process of the manufacturers authorisation FAR Part 21 / EASA Part 21 Subpart G has the authorization to manufacture those parts on the basis of its type certificate, and production certificate.

However organisation who are authorised as PMA-holding manufacturers are permitted to make replacement parts for aircraft, even though they are not the original manufacturer of the aircraft. An applicant for a PMA applies for approval from the FAA.

An STC is a certificate. It defines the product design change, states how the modification affects the existing type design, and lists serial number effectivity. It also identifies the certification basis, listing specific regulatory compliance for the design change. Information contained in the certification basis is helpful for those applicants proposing subsequent product modifications and evaluating certification basis compatibility with other STC modifications.

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)