The MARPA Air Carrier Committee, led by Michael Rennick, Delta Air Lines Component Engineering Manager, is hard at work supporting PMA users and MARPA members. In June, members of the MARPA Air Carrier Committee, including Air Wisconsin, American Airlines, Republic Airways, US Airways, Air Canada, and Delta Air Lines, submitted to the FAA a letter seeking clarification on the issue of PMA parts that are alternates to post modification Airworthiness Directive (AD) related parts.
This clarification is necessary because confusion has sometimes arisen between operators and local regulators over the need for an Alternative Method of Compliance (AMoC) for post-modification AD-related PMA parts. It is the position of the MARPA Air Carrier Committee that if the PMA is an alternate to an OEM part contained in a post-AD configuration, no such AMoC is required.
When a PMA is issued for a replacement part for a post-modification AD-related OEM part, it is uncommon for the PMA applicant to request an AMoC to the AD, or for the FAA to note the AD on the PMA approval. This makes some sense because a post-AD PMA part is inherently an alternative method of compliance without being described as one. However, an issue arises because many ADs call out only the modified OEM part as a means of compliance. Because ADs are technically regulations under Part 39, alternate approvals such as PMAs might not satisfy the regulatory requirement and so an AMoC may be required.
It would be beneficial to both operators and PMA manufacturers to see this change.
The OEM part is the source of the condition giving rise to the AD. The post-modification part must resolve the condition in order to satisfy the AD. During the PMA approval process for the same part, the AD is also taken into consideration.. In order to receive PMA approval, the subject PMA part must resolve the condition resulting in the AD, just as the post-modification OEM part does. There should be no need to call out an AMoC for the PMA part related to the AD; the underlying condition that necessitated the AD has changed because the approved PMA part has replaced the post-AD OEM part. The PMA should be a valid terminating action for the AD.
There are limited circumstances in which this reasoning may not apply, but these limited circumstances are not the subject upon which the Air Carrier Committee seeks clarification. For instance an AMoC may be necessary in a scenario in which an AD applies to a higher level component or assembly. In this scenario the PMA replacement for the OEM part may not address the AD for the higher assembly because it is a replacement at the piece-part level, and thus an AMoC may be necessary for the higher assembly.
Generally, however, an AMoC should be inherent in an approved PMA part and therefore unnecessary as a separate approval. This is the policy clarification that the Air Carrier Committee seeks in the form of a formal FAA communication. If an approved PMA part is a replacement for a post-AD OEM part, the FAA’s policy should clearly state that the approved PMA is a terminating action for the AD and that no additional approval or discrete AMoC is required. In the alternative, an AMoC could automatically issue for each post-AD PMA to show compliance.
MARPA greatly appreciates the Air Carrier Committee’s work on this project. MARPA will be working with the FAA and the Committee to determine whether future ADs will list an approved PMA as a valid terminating action, or whether an automatic AMoC should automatically issue with a PMA to show compliance to the AD, or some other solution is desired. We will keep our members apprised of these developments.
If you are a MARPA member air carrier and want to get involved with the Air Carrier Committee, please email Katt Brigham at email@example.com. If you are not yet a MARPA member but would like to get involved, visit our membership application page. MARPA membership is free for air carriers!
Edited to clarify that ADs are regulations and identify possible solutions to the issue raised in the Air Carrier Committee’s letter.
Those who attended MARPA’s inaugural European conference last month in Istanbul were treated to an excellent presentation by Delta Air Lines Manager of Component Engineering and MARPA Air Carrier Committee Chairman Mike Rennick on the impressive reliability benefits of PMA parts in Delta’s fleet.
As many know, Delta operates a very diverse fleet of aircraft, which are on average older aircraft than many other carriers’ fleets. Yet Delta also operates one of the most reliable mainline fleets in the world. In 2014, Delta had an impressive 169 maintenance cancellation free days; a metric that has improved each of the last three years. Mr. Rennick pointed out that one of the important contributing factors to this success was the widespread use of PMA parts.
MARPA and its members frequently tout the many benefits PMA provide to operators. Operators are generally aware of the lower prices offered by PMA parts. They are also aware that PMA parts may be their only option, or one of very few options, for replacement parts for legacy aircraft. However, operators may not be aware of the significant reliability benefits that PMA parts also provide.
Mr. Rennick explained that in order to maintain its fleet to the level it requires Delta wants options. Service experience has demonstrated that PMA parts match, and in some cases exceed, the performance of OEM parts. Based on this experience Delta has found PMA parts to be acceptable for use throughout the aircraft, components, and engines.
Mr. Rennick’s presentation included exciting metrics showing an upward trend in Mean Time Between Unscheduled Removals (MTBUR) and Mean Time Between Failures (MTBF) on certain applications in which Delta had utilized a PMA solution. Metrics like these indicate the great value proposition that PMA’s can offer air carriers; not only from a purchase price standpoint, but importantly, from a reliability standpoint. These metrics, along with shortened lead times, are part of the greater holistic value proposition offered by PMA parts and something we should remember to emphasize when talking to potential customers.
Mr. Rennick also stated that because of Delta’s close cooperation with its vendors it is able to address issues more quickly than might otherwise be possible.
Delta’s comfort level born of experience with PMA parts has led to the carrier using PMAs in even very critical applications, including engine gas path and rotating parts, life limited parts, and power generation.
The emphasis on the reliability of PMA parts is one that we, as an industry, should be sure to promote to our customers. Cost savings means more than just lower prices (an obvious benefit of PMA!) Keeping aircraft safely and reliably operating without unscheduled removals and increasing time between failures generates cost savings for operators by allowing them to get planes turned quickly and keeping their passengers happy. MARPA always makes it a point to emphasize the reliability benefits of PMA wherever we go.
If you were unable to join us in Istanbul you will still have a chance to see this great presentation on the reliability benefits of PMA parts. We anticipate Mr. Rennick giving a similar presentation at the 2015 MARPA Annual Conference. This will be a great opportunity for PMA manufacturers to hear directly from Delta on the air carrier’s take on PMA parts, and an excellent opportunity for operators to see how one carrier is making PMA parts an important element of their maintenance program success. Register today to take advantage of Early Bird rates!
The FAA has released two new advisory circulars that may affect the PMA community. Both advisory circulars are issued by the Transport Aircraft Directorate and apply to Part 25 aircraft (and parts thereof).
We would be interested in hearing from any MARPA member who is affected by one of these new advisory circulars.
The FAA has issued a new advisory circular for statistical analysis. This AC only applies to engine and APU parts.
The new advisory circular uses statistical analysis to arrive at correct sample sizes. This sample size formula is introduced for persons who are trying to correlate two populations of parts. MARPA had pointed out to the FAA that typically a PMA applicant does not correlate two different populations of parts – instead they derive the reasonable tolerances on one population of parts, and then design and produce within those tolerances. The FAA would like PMA applicants to arrive at their appropriate sample size, test the parts being reverse-engineered, and then produce an equivalent number of pre-PMA parts to test for the same properties (and then correlate the two populations). This is contrary to current FAA regulatory guidance, which requires the design to be approved and the requires the production quality system to ensure that parts are all produced within the approved design parameters. In essence, ACO engineers will now take control of the quality assurance system through the design process.
One of the problems with the AC is that it relied on statistical analysis for clinical trial sample size as the basis for assessing statistical analysis of reverse-engineering sample size. Clinical trials for pharmaceuticals typically rely on populations of hundreds or even thousands of people. Trying to test hundreds or thousands of parts in order to reverse-engineer them is simply not realistic. Furthermore, the degree of part-to-part difference under modern quality assurance systems does not support such large sample sizes.
For those cases where the equations in the advisory circular give a lower number for the appropriate sample size, the FAA has also established minimum sample sizes. The AC sets some minimum limits for the number of parts that must be tested in order to derive certain values (remember that you need that number of PC parts and also that number of reverse-engineered parts to meet the AC’s requirements):
Minimum Number of Parts to be Sampled
- For basic material properties that are more dependent on alloy constituency than on part manufacture process – 10 approved parts from three separate lots with at least three parts per lot
- For properties affected by how the material is processed during part manufacture such as high-cycle fatigue, low-cycle fatigue, creep, tensile strength, crack growth, etc. – 30 approved parts
- For fatigue testing – at least 25 tested parts that are run until they crack
- For parts exhibiting complex geometry or complex manufacturing variables, additional specimens may be required
- For parts considered to have a high degree of criticality, greater sample sizes may be required
No statistical basis is offered for these minimum sample sizes.
The new advisory circular provides guidance for statistical analysis of sample-size despite the fact that no regulation actually requires such a broad-based sample. The advisory circular appears to potentially change the regulations by increasing the burden on applicants. To the extent that this is true, it is inappropriate.
Our concern is that despite warnings that this is non-mandatory guidance, this guidance may be used as if it were a regulation, with offices refusing to accept PMA applications that are otherwise valid, but that failed to use this AC as a basis for identifying sample size.
If you find that this AC effectively changes the application obligations imposed on you as a PMA applicant, STC applicant, or other FAA-approval applicant, then please contact MARPA so we can raise this concern with the appropriate personnel at the FAA.
AC 33-10 is known by its full title: Statistical Analysis Considerations for Comparative Test and Analysis Based Compliance Findings for Turbine Engine and Auxiliary Power Unit Replacement, Redesign and Repaired Parts.
Some of you may be wondering where to find the FAA’s policy memo on design approval holder restrictions on ICA availability. Older MARPA links to the original position of that guidance are no longer valid because it has been moved. But it is still available if you know where to look!
Many MARPA members look for this policy memo because it clarifies that anti-competitive language in ICAs (restricting use of PMAs or third party repairs) is unacceptable to the FAA:
While not exhaustive, the FAA finds the following practices of using restrictive language in the ICA or through restrictive access or use agreements unacceptable under the provisions of 14 CFR §21.50(b) and related ICA airworthiness requirements:
1) Requiring the owner/operator to only install DAH-produced or authorized replacement parts, articles, appliances, or materials.
2) Requiring that alterations or repairs must be provided or otherwise authorized by the DAH.
3) Requiring the use of only maintenance providers or other persons authorized by the DAH to implement the ICA.
4) Establishing, or attempting to establish, any restriction on the owner/operator to disclose or provide the ICA to persons authorized by the FAA to implement the ICA.
MARPA had a very good meeting today with Mark Bouyer and Ann Azevedo of the FAA’s Engine and Propeller Directorate (EPD).
The focus of the meeting was status on EPD policy that may affect PMA manufacturers.
Azevedo explained that she has responded to the comments on the Statistics Advisory Circular (AC), and hopes to have the final draft of that guidance available to the public by September. The Statistics AC is meant to address FAA concerns that have been recognized in practice, such as misusing statistical methods to show equivalence, and underestimating the appropriate sample sizes.
Bouyer expects the Materials AC to go out for public comment this month. The Materials AC will identify the essential data that is necessary when a PMA applicant is trying to replace the material used in the type design. MARPA members should watch for this one, and be prepared to offer their comments.
The FAA had published the Geometry AC for comment. This AC is meant to enhance awareness of how reverse engineering can introduce dimensional differences in replacement parts. MARPA Board members have expressed that the draft of this proposed guidance appeared to be very helpful to the industy.
The Burner Rig AC, which was also previously out for comment, is expected to be issued by September. It is expected to provide a method for establishing functional equivalence for certain degradation modes in parts such as oxidation, hot corrosion, erosion, etc. The AC is expected to identify existing technology as a means of compliance.
Finally, the FAA is internally reviewing AC 33.8 with a plan to update and clarify the AC. The updates are intended to make the AC easier to use.
The FAA has been very active and diligent in preparing guidance. In the immediate future (before the Conference), MARPA members should expect to see the release version of the Statistics AC and the Burner Rig AC, and they should expect to see the Materials AC go out for comment.
MARPA recently filed comments on the FAA Engine and Propeller Directorate’s draft Advisory Circular 33-Geometry, discussing geometry and dimensional considerations for comparative test and analysis for turbine engine and APU replacement parts. In a previous blog post we observed that AC identified a number dimensional and geometric factors that the FAA expects to be assessed in ensuring the integrity of dimensional characteristics for the purposes of showing similarity.
We requested feedback from our members describing to what extent the FAA’s expectations were reasonable and practicable, and identifying any issues with the proposed guidance on which MARPA should comment. We received several very helpful responses from our members that helped us shape our comments to the proposed AC. Among the issues members identified were:
Feedback from our members is both helpful and valuable to our comments, as it helps us to identify issues that directly affect members’ businesses, and helps us to better focus our resources on those matters that are important to the PMA community. The result is more detailed and on-point responses to the FAA to better help shape the guidance material that will ultimately be issued.
We greatly appreciate the feedback we received from our members on this Advisory Circular, and we hope that our members will continue to answers our requests for responses as additional guidance and rulemaking documents are issued. Together we can work with the FAA to develop the best possible guidance for our industry.
The FAA is currently seeking comments on its Draft Advisory Circular Engine Overtorque Test, Calibration Test, Endurance Test, and Teardown Inspection for Turbine Engine Certification (§§ 33.84, 33.85, 33.87, 33.93).
As the title suggests, the AC offers guidance on compliance with the engine overtorque, calibration, and endurance tests, and teardown inspection called out in Part 33 of the Federal Aviation Regulations. Although the guidance is directed at engine manufacturers, foreign regulatory authorities, applicants for engine type design approval, and FAA designees, it also notes that parts manufacturer approvals “may require running certain endurance testing for compliance with § 33.87″ and refers to AC 33.87-2 for guidance on showing compliance by comparative test methods.
MARPA would like to know to what extent members anticipate this AC might effect them, and whether we should submit comments. If you plan on submitting comments, or have already done so, we would would like your feedback so that we can incorporate member concerns into our comments.
Comments on the Draft AC are due next week, so if you have feedback for us please submit them to firstname.lastname@example.org soon!
Today, the FAA announced the issue of AC 21.3o3-4. The title of this AC will be “Application for Parts Manufacturer Approval Via Tests and Computations or Identicality.”
As of this time, the AC is not yet available to the public. When it is available to the public, it is expected to be posted online at this location:
Note: the issue date published on the FAA’s website is March 21, 2014; however the AC is not yet available through the FAA’s online advisory circulars, nor through the Regulatory and Guidance Library (RGL). The note on the FAA’s website states “This document‘s content is not currently available.”
The FAA Engine and Propeller Directorate has issued a new draft Advisory Circular that could have a significant effect on companies seeking PMAs, STCs, or approval of repair or alteration of turbine engine and APU parts. Draft AC 33-Geometry: Geometry and Dimensional Considerations for Comparative Test and Analysis for Turbine Engine and Auxiliary Power Unit (APU) Replacement, Redesign, and Repaired Parts is directed at applicants who use comparative techniques to reproduce dimensional characteristics of parts during the reverse engineering process.
The AC is intended to provide guidance to help PMA (and other) applicants assess their reverse engineering methods to identify possible causes of dimensional inaccuracies, as well as helping applicants develop adequate criteria for determining dimensional similarity between the PMA design and the sample. To that end, the draft AC identifies several dimensional and geometric factors that the FAA expects should be assessed in seeking to ensure the integrity of dimensional characteristics for the purposes of showing similarity. These factors range from geometric relationships to precision and accuracy to influence on critical parts.
The background section of the draft AC states that because reverse engineering methods vary in their measurement techniques, interpretation and combination of data, and in dimensioning systems, they do not typically produce a design with the exact same dimensional properties as the type design part. It further explains that because dimensional differences may exist, functional assessments–which may include both test and supplemental analytical data–will be necessary to safeguard type design functional properties, as well as capabilities of interfacing and higher level assemblies. Such explanations help to illuminate the FAA’s expectations of an applicant in making showings of dimensional similarity. MARPA would like feedback from our members describing to what extent such test data is currently available and practical within the industry.
Although this AC, like all Advisory Circulars, is neither mandatory nor regulatory, such guidance documents do sometimes become ingrained and relied upon in considering applications. It is therefore important to review the draft and offer comments to the FAA to ensure the guidance reflects the realities of our industry. MARPA will be closely reviewing the guidance and offering comments on behalf of the PMA community. If you identify any particular issues within the guidance, please bring them to our attention so we can incorporate them into our comments. Email your concerns to email@example.com. We also recommend that members who identify concerns file their own comments on the guidance. Comments are due July 3, 2014 and should be submitted to Mark Bouyer of the Engine and Propeller Directorate, at firstname.lastname@example.org