The FAA has issued an Advisory Circular (AC 20-176) detailing best practices for drafting Service Bulletins (SBs) related to Airworthiness Directives (ADs). The AC is the result of the findings of an AD Compliance Review Team established in response to events of suspect noncompliance with ADs in early 2008.
The primary purpose of the AC is to provide best practices to design approval holders (DAHs) developing SBs in response to AD actions. The AC gives recommendations to improve the quality and usability of the SB. The first substantive chapter makes clear that a DAH drafting a SB is to strive for clarity and usability, but not at the cost of precision. The first step is to ensure that the format and content follow industry specifications listed in the AC. The AC then explains when procedures that appear in already-existing DAH documents should or should not be included in the SB, and which already-published procedures should be referred to, rather than duplicated, in the SB. The manner in which such documents should be referred to is also detailed.
The AC next focuses on ensuring the SB enhances awareness of the specific safety issue addressed. Each SB should contain a paragraph entitle “Safety Intent,” which will explain purpose of completing the SB. The statement should state the technical objective in a clear and succinct manner. It should make clear what the problem part and failure or malfunction is, and how the issue is resolved by accomplishing the SB. A paragraph entitled “Configuration Description” should also be included if accomplishing the SB will change a configuration. This too should be a detailed technical description of the resultant design change. The AC provides guidance on what should and should not be included in such a description, for instance specific features that will prevent the unsafe condition, or identification of an assembly, the part number of which cannot be rolled to differentiate configurations.
As is already apparent, the AC emphasizes clarity and precision in developing SBs. It provides a useful example table offering illustration of clear language, for instance using the precise language “inspect for minimum one inch clearance between wires” instead of the more vague “make sure there is adequate clearance.” DAHs should develop a system for ensuring ambiguous language is eliminated from SBs. The AC also advises that special precaution should be taken when including Notes in SBs. Among other requirements, care should be taken to ensure that no required steps are stated in Notes, and that conflicting Notes have a clear order of precedence.
Clarity and precision is also enhanced by limitations on figures, illustrations, drawings, and diagrams. The AC makes clear that the textual instructions must be authoritative; figures, illustrations, and drawings should be used only to supplement. Logic-based diagrams, which can offer assistance when compliance times, configurations, and alternative correction actions can be difficult to follow, similarly should be used only as a supplement. In all cases, it must be made clear that the text of the accomplishment instructions is the authoritative information.
Specific mandatory versus flexible language is articulated in the AC. When only a single method is acceptable to the FAA, the mandatory language “in accordance with” must be used. In cases when a certain method MAY be used, but other methods may be acceptable, the language “refer to … as an accepted procedure must be used. The AC provides examples of procedures and documents that frequently require either mandatory or flexible language. When using these specific phrases, a note should be included explaining the precise meaning of the language.
It is also important to identify critical tasks. Steps that have a direct effect on the unsafe condition should be identified with an “RC,” meaning “Required for Compliance.” The purpose of this step is to enhance understanding of crucial requirements in the specific AD. However, this step is only required when the SB is going to be incorporated by reference in the AD. The DAH should therefore coordinate early with the FAA to determine if it is possible that the SB might be incorporated. SBs issued prior to an FAA decision to reference the SB may be revised to include the label RC on the appropriate tasks. The AC provides lists of items that should or should not be labeled RC as well as appropriate steps for articulating RC accomplishment steps and corresponding figures, illustrations, and drawings.
It is also important for DAHs developing SBs to note that in many cases, changes will require an AMOC approval. This is possible when the SB references an external document that changes, or if an RC changes or the SB was issued without RCs noted and has been incorporated by reference in the AD.
An additional focus of the AC is avoiding overlapping and conflicting actions in SBs. Such overlaps may lead non-compliance with ADs. The AC states that a DAH should develop a SB/AD tracking system to identify and resolve conflicts between SBs, and provides a process for DAHs to follow.
The AC also encourages sharing of AMOCs between the owner/operators requesting the AMOC and the DAH. The purpose of this suggestion is to better allow DAHs to determine whether a certain AMOC is appropriate for approval as a global AMOC. More global AMOCs result in reduced costs for operators. When similar AMOCs are shared with a DAH, the DAH should determine whether a global AMOC is appropriate. If no previous AMOC exists, the DAH should determine if the condition is likely to occur again elsewhere, and if so, request approval of a global AMOC. Approved global AMOCs should be posted on a website accessible to owners and operators, and the DAH should develop a 24/7 AMOC support process. The AC also suggests using the language “later approved parts” on a case-by-case basis for ADs requiring part changes, in order to avoid repeated AMOC requests.
Finally, the AC provides guidance to DAHs for helping those performing maintenance to avoid undoing the AD-mandated designs. During the development of SBs, maintenance documents, and ICAs, DAHs need to consider the potential for the AD-mandated configuration to be inadvertently altered. DAHs therefore should update maintenance manuals and ICAs accordingly and make owners and operators aware of the updated documents. References to external manuals should be appropriately flagged, and the DAH maintenance manual should include a SB-to-AD cross reference listing to provide clarity to owners and operators. Modified procedures should be made available as early as possible to ensure compliance with the AD.