The FAA has made a change to the rules concerning vibration testing (14 C.F.R. § 33.83). The change was published in the July 5th Federal Register on page 39623.
Under both rules, a vibration survey is necessary for engine certification, and also it is required for any part that is “subject to mechanically or aerodynamically induced vibratory excitations.” So any part that vibrates in an engine, has to be subject to a vibration survey as part of the process of developing data to support the PMA application. Examples of parts subject to vibration survey requirements are blades, vanes, rotor discs, spacers, and rotor shafts.
Under the old rule, the engine survey is based upon an appropriate combination of experience, analysis, and component test. A full engine test was not required. Many PMA companies confirm that they have been obtaining PMAs for parts like blades and vanes by using comparative analysis supported by component-level testing. This sort of approach is also supported by FAA Advisory Circular 33.83-1, which provides guidance on performing shaker tests for blades and vanes.
The new rule changes this standard by eliminating the option to perform component-level testing and replacing it with an obligation to perform full engine testing. The preamble to the rule clarifies that the FAA’s intent is for applicants to perform full engine testing (the preamble claims that this has always been FAA policy, but FAA-industry common practice belies this claim), and that this obligation should apply to PMA applicants and repair data approval applicants as well. For PMA parts, and for FAA-approved repair data, this requirement would effectively eliminate many of the smaller competitors because of the cost, but it does not appear to provide any additional safety benefit.
Here are the two rules, for comparison purposes:
§ 33.83 – Vibration test.
(a) Each engine must undergo vibration surveys to establish that the vibration characteristics of those components that may be subject to mechanically or aerodynamically induced vibratory excitations are acceptable throughout the declared flight envelope. The engine surveys shall be based upon an appropriate combination of experience, analysis, and component test and shall address, as a minimum, blades, vanes, rotor discs, spacers, and rotor shafts.
§ 33.83 Vibration test.
(a) Each engine must undergo vibration surveys to establish that the vibration characteristics of those components that may be subject to mechanically or aerodynamically induced vibratory excitations are acceptable throughout the declared flight envelope. Compliance with this section must be demonstrated by engine test, and must address, as a minimum, blades, vanes, rotor discs, spacers, and rotor shafts. The conduct of the engine test should be based on an appropriate combination of experience, analysis, and component test.
What’s Wrong with the Rule?
The rule was published without any prior “notice and comment.” Instead, it was offered as a direct final rule. Normally, the FAA only issues a rule as a direct final rule when it is non-controversial, and FAA regulations dictate that if someone provides adverse comments within the comment period, then the rule is withdrawn (because this is evidence that it was NOT non-controversial).
In this case, though, the rule was immediately effective and no comment period was offered at all. So there was no reasonable opportunity for anyone to offer a comment before the close of the (non-existent) comment period.
The new rule was labeled as a non-substantive technical amendment, and this claim was used as a justification for not offering the change up for notice-and-comment; however the rule change appears to be a substantive change that should have been open to prior public comment. Had it been open to public comment, then MARPA and others would have commented that it undermines the existing regulatory system, rather than improving it, and that it imposes unnecessary burdens on both the applicant and the government with no commensurate safety benefit.
In short, the promulgation appears to have violated based procedural laws that are designed to protect the public from activity like this.
What Are We Doing?
MARPA has been in consultation with the Board, the Technical Committee, and the FAA on this matter. We have asked FAA Headquarters to help us out with this issue. On Friday, August 3, we filed a note with the FAA seeking formal withdrawal of the rule change. We have pointed out to the FAA that:
- this is a substantive rule change,
- this was issued without opportunity for comment, and
- industry would have opposed this change if it had been permitted to provide comment, and
- the manner of promulgation violated FAA regulations and the Administrative Procedures Act.
Based on these facts, MARPA has requested that this rule be withdrawn.