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Service Bulletins Clarified

By Gregory J. Reigel

© September, 2006 All rights reserved.

Back in June of 2006, I wrote an article regarding an opinion by the National Transportation Safety Board (“NTSB”) that appeared to state that a manufacturer could specify that its maintenance manual includes all service bulletins and thereby create an obligation under the Federal Aviation Regulations (“FAR’s”) to comply with those service bulletins. The NTSB opinion contradicted the FAA’s longstanding position that compliance with service bulletins, absent an airworthiness directive, was not mandated by the FAR’s. It also created quite a stir within the aviation community, including owners, operators and maintenance professionals.

To address the situation, and in an attempt to clarify the confusion, on August 11, 2006 the FAA issued a Legal Interpretation addressing this issue. The Legal Interpretation was issued in response to a specific request regarding whether a manufacturer’s service bulletin “requiring” performance of a borescope inspection in connection with cylinder compression test revealing weak pressures during a 100 hour or annual inspection of an aircraft operated under FAR Part 91 was in fact mandatory under the FAR’s. Although the Legal Interpretation states that compliance would not be mandatory in this situation, this does not necessarily limit a manufacturer's ability to mandate performance of certain maintenance tasks.

The Request For Interpretation

Procedurally, an individual requesting a legal interpretation from the FAA must provide a specific factual scenario. The FAA will not issue general interpretations of the FAR’s. It will only address application of the FAR’s to specific facts. In this case, the individual requested a legal interpretation regarding the application of FAR 43.13(a) and FAR 43 Appendix D.

The factual scenario involved an aircraft operated under FAR Part 91 and a manufacturer-issued service bulletin specifying that a borescope inspection must be performed in connection with a cylinder compression test revealing weak pressures during an annual or 100 hour inspection performed pursuant to FAR Part 43 Appendix D. The FAA was asked to provide a legal interpretation to answer the question whether FAR 43.13(a), which requires that maintenance shall be done using methods, techniques and practices prescribed by the manufacturer or other methods, techniques and practices acceptable to the Administrator, mandated compliance with the service bulletin simply because the manufacturer required it.

The Interpretation

The FAA’s simple answer was “no”. However, it was not unqualified. The FAA stated that “unless a service bulletin is incorporated either directly or by reference into a document that makes its requirements mandatory, the answer is no.”

The FAA observed that the text of FAR 43.13(a) “provides a person performing maintenance, alteration, or preventive maintenance on a product with a number of permissible options when performing that work. A manufacturer may legitimately incorporate a service bulletin into one of its maintenance manuals by reference. If it does so, the data specified, and the method, technique, or practice contained therein, may be acceptable to the Administrator.” This means that compliance with the service bulletin in this situation would certainly be an acceptable method.

However, it went on to state “unless the method, technique, or practice prescribed by a manufacturer is specifically mandated by a regulatory document, such as an Airworthiness Directive, its contents are not mandatory.” Since FAR 43 Appendix D does not specifically require a borescope inspection as the only means for determining the internal condition of the cylinders if the compression test shows weak cylinder compression, other methods such as cylinder disassembly and inspection could be used. As a result, compliance with the service bulletin was not mandatory as long as some acceptable method was used to determine the condition of the cylinders.

According to the FAA, allowing a manufacturer to mandate compliance with a service bulletin would impermissibly authorize the manufacturer to issue substantive rules. Not only does the FAA not have the authority to delegate its ability to make rules, but allowing a manufacturer to issue rules in the form of service bulletins, without public notice and comment, would be contrary to the Administrative Procedure Act.

However, the interpretation also notes that manufacturers do have alternative methods for mandating compliance with the maintenance specified in a service bulletin. A manufacturer could petition the FAA to have the service bulletin incorporated into an AD. Alternatively, a manufacturer could incorporate the maintenance addressed in the service bulletin into its current maintenance manual or Instructions for Continued Airworthiness and, in situations in which compliance with those documents was mandated by regulation, that maintenance work would then be required.


This Legal Interpretation clarifies that compliance with a service bulletin, absent an AD or other regulatory requirement, is not mandatory simply because the NTSB says it is. Although a manufacturer can still accomplish its goal of mandating the maintenance contained in a service bulletin, it will not be able to do so unilaterally. It will need to meet additional regulatory hurdles. For now, compliance with a service bulletin on an aircraft operated under FAR Part 91, absent an AD or other regulatory requirement, is not mandatory.

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