Unraveling the FAA’s Mysterious Saga

This is a fascinating tale of intrigue, anguish, convoluted regulations, conflicting interpretations, potential fundamental law breaches, and a lot of FAA silence. 

We are talking about the strange case of the “mandatory” engine TBO for some, but not all, light sport aircraft (LSAs). People who are somewhat familiar with traditional certified aircraft know that the engine TBO for their aircraft is not mandatory unless it is being used in a Part 135 (charter) operation, been subject to an FAA approved inspection program, and not received an approved extension for that Part 135 activity. 

In all fairness, a lot of owners will still follow the TBO guidelines provided by the engine manufacturer, in the understandable belief that by doing so they are making a rational decision based on safety considerations. Ironically, as pointed out by well-known aviation writer and A&P/IA Mike Busch in his many articles, an engine that is removed for overhaul purely due to meeting TBO limitations may well have a higher probability of subsequent failure. Busch supports this position by both cross-referencing a National Transportation (NTSB) study of engine failures and from his own experience and scientific analysis. 

In short, the argument and evidence both point strongly to most engine failures occurring in the early period following an engine change (new or overhauled). Put another way, taking a well-maintained engine that is not making metal, has great compressions and running well, and deciding to overhaul it is a potential invitation to both unnecessary cost and an increased likelihood of premature failure. 

How Is Light Sport Different? 

Under the LSA regulations that were implemented in 2004, manufacturers were required to meet the new ASTM standards to qualify as a light sport but also to take on responsibility for certain safety matters relating to continued airworthiness that were normally the purview of the FAA. 

One of those responsibilities included providing service bulletins on safety matters that could be considered mandatory, if so marked by the manufacturer at its sole discretion. Mandatory service bulletins, known in the regulations as safety directives, were supposed to be the equivalent of an Airworthiness Directive (AD), which for certified aircraft, only the FAA could issue. 

The goal was to lessen the regulatory burden on the FAA and give the nascent light sport industry a chance to show it could be relied on to be co-operating safety partners without the same degree of oversight as for certified aircraft under Part 23. 

Indeed, as has been proven over time, the safety record of LSAs and sport pilots falls well within the hoped for parameters set out in the original concept—i.e., better than the barely regulated ultralight market and better than the experimental market. 

As added bonuses, we can clearly trace a number of very positive developments that were trialed through the experiences of light sport and sport pilots, including BasicMed, the ability to add safety enhancing technology without an STC (angle-of-attack monitors, for example), affordable glass panels and autopilots, and a new ASTM standard for small, certified aircraft under Part 23. Not to forget the mini revolution-in-waiting represented by MOSAIC that has recently been released in its final form and which will be in full effect on July 22, 2026. 

So, back to the story. Leaving it to the manufacturers of light sport aircraft to issue safety bulletins without direct FAA oversight was undoubtedly a well-intentioned move to demonstrate a willingness to reduce bureaucracy, but that subsequently, produced unintended consequences. A number of LSA manufacturers, possibly for perceived liability reasons, decided to issue mandatory service bulletins or put similar language into their maintenance manuals to mandate otherwise only recommended TBO intervals for engines. 

The result of this for light sport aircraft using a Rotax engine, for example, was to declare an aircraft unairworthy if it exceeded either the total hours since new/overhaul (1,500 or 2,000 depending on the date of manufacture) or years in use (12 or 15). 

This has been most evident and costly for owners of LSAs registered as Special light sport aircraft (S-LSAs), when their Rotax engines have hit the manufacturer’s recommended TBO limits. Some maintenance shops have refused to sign off annual condition inspections for aircraft that are outside of these recommendations based on the mandates of the airframe manufacturer and in line with one of two FAA legal interpretations.

But more on that later. 

In almost all cases, the engine hours have been well below 2,000 hours, but the engine had exceeded its calendar limits, so considered over recommended/mandated TBO. Depending on the route taken by the owner in response, this can become a $20,000 to $25,000 headache, or they can reregister the plane as an experimental light sport aircraft (E-LSA) and be exempt from the mandate. 

Coincidentally, the same engine in an experimental aircraft or in a fully-certified Part 23 aircraft would have no such legal limitation. Indeed, the same engine in a light sport manufactured by a different maker who did not issue a mandatory service bulletin/ safety directive or other mandate would also not require changing out. Makes perfect sense, right? 

What Is the Legal Basis??

It could be argued that this delegation of authority to determine conditions for continued airworthiness was clearly outlined in the enabling regulations (Federal Register/Vol. 69, No. 143/Tuesday, July 27, 2004/Rules and Regulations). But this is where the water gets decidedly muddy. 

Legislation passed in 1946, called the Administrative Procedures Act (APA), was specifically intended to govern the rulemaking and decision-making processes of government agencies in order to ensure that they were done in a predefined manner that included justification, public consultation, and notice periods prior to implementation. By extension, the logical assumption, and case law, has always been that the government could not bypass these requirements by delegating authority to private companies who could then make legally binding regulations without following any APA mandated process. 

The reason aAD has to come from the FAA is in recognition that prior to issuance (other than in an emergency) the process must include a proposal of why this is necessary, a cross-reference to the authority given to the agency to make this proposal, costs of implementation, numbers of aircraft potentially affected, a notice period, and an invitation for public comment. 

In other words, the FAA has to comply with the APA in order for the requirement to be legally enforceable. Contrast this with what has been delegated to light sport manufacturers. They could, apparently, without any public notice, analysis, comment or justification, mandate that a perfectly good engine be changed out, or declare that the aircraft would no longer be considered airworthy. This power exceeds that of the FAA itself under the strictures of the APA, which leads to the very strange result that the agency has effectively delegated powers, that it does not actually possess itself, to around 80 manufacturers around the world.

Put another way, as will be explained later, there is a very high probability that this part of the enabling legislation was, in reality, fatally flawed because it was, in legal terms, “ultra vires,” or beyond its actual powers. 

Given how embedded the APA is in established rulemaking, it might seem strange that this almost unlimited delegation ever found its way into Federal Regulations. One possible explanation is that it quite simply suited everybody at the time. Industry liked the idea of the FAA giving up something , while the FAA did not feel it had the resources to provide the same level of detailed oversight it would otherwise need. 

Interestingly, in the final 2004 rule, there was a discussion and concern about the potential for manufacturers to abuse this power by setting limits on component lives for reasons other than safety. 

Indeed, the FAA put in place a “waiver process”—(14 CFR 91.327 (b) (4) (ii)—to allow for this. This specifically relates to a safety directive that is believed not to be adhering to the applicable consensus standard. However, some manufacturers included their effective TBO mandate in the maintenance manual using words like “compulsory.” 

Did This Just Come Up? 

So, this is the fun bit, where we come up against conflicting FAA Office of the Chief Counsel opinions on this situation dating back to 2013 with one counsel opinion indicating that mandatory TBOs were not enforceable followed by another opinion in 2015 stating that failure to obey the TBO would render the aircraft unairworthy. 

Busch, specifically, asked the FAA in writing in 2016 to clarify this situation, noting that this was causing significant concern in the light sport Market. Fast-forward nine years and he, and we, have never received an answer, although, as will be shared below, the FAA has left a trail of crumbs of evidence of how this is being cleaned up, including the provisions in MOSAIC. 

So Is the FAA Aware of Likely Problems? 

Silence is always difficult to interpret, so we need to look at the circumstantial evidence that could include enforcement actions taken against owners who exceed TBO and whether MOSAIC and other FAA orders might, or already have, addressed this but not overtly. 

The FAA Press Office, in response to a yes-or-no question on whether any owner of a light sport aircraft had faced a compliance or enforcement action due to exceeding TBO, declined to respond and indicated that it would need a formal Freedom of Information Act (FOIA) to attempt to obtain this answer. An interesting response as no documents had been requested, but at least consistently coy. 

For those who are not familiar, FOIA requests involve the government/agency having to actively seek documents that relate to the requested subject matter and can involve substantial costs charged to the person requesting the information. It can take time—a lot of time. 

Does MOSAIC and/or Other FAA Orders Address This Issue? 

Yes, in several different sections of MOSAIC as well as in other FAA orders that will be considered later, but with no admission of there ever having been an issue needing to be resolved. 

MOSAIC has specifically chosen to align service bulletins and safety directives for LSAs with how other certified aircraft are treated by removing the ability for the manufacturer to make them mandatory. Indeed, the rule goes further and specifically cancels all previously issued mandatory service bulletins and safety directives with immediate effect. 

Also noteworthy is that it is the only part of MOSAIC with no waiting period. As with certified airplanes, critical safety issues going forward will be handled by ADs, which, in accordance with the APA, require public notification and consultation. The document explains that this is in line with the new idea that light sport should be considered as a certified aircraft but at the lower end of the spectrum of what the FAA has started to call the “continuum of safety.” 

It will be interesting to see the degree to which manufacturers contact the FAA to convert their safety directives and mandatory service bulletins into ADs given that they will need to provide a very clear safety justification for doing so. 

The original MOSAIC Notice of Proposed Rulemaking (NPRM) never brought up engine or other TBOs explicitly, but 12 comments, including one from this author, requested “clarification” of their enforceability. In the final document the FAA addresses these comments by indicating that they were “outside the scope of this rulemaking” but, nevertheless, referred the reader in a footnote to “existing guidance that explains the requirements for meeting manufacturer’s specified TBOs or other time-life intervals.” 

The cross-reference given was to FAA Order 8900.1. In short (Volume 3, Chapter 15, Section 1, para 3-595 (c)), this basically states that “since Part 91 operators are not required to comply with a manufacturer’s entire maintenance program, overhauls are not mandatory for Part 91 operators… in most circumstances.” 

One exception identified in the Order 8900.1 is for an “FAA Approved Inspection Program.” However, also in MOSAIC, the FAA writes the following: 

“3. Maintenance and Inspection Program (§ 21.190(c)(3)) A commenter asked if the maintenance and inspection program in § 21.190(c)(3) was accepted or approved. FAA will not accept or approve light-sport category aircraft maintenance and inspection manuals.” 

This statement clearly closes that door as well. 

Another piece of confirmatory evidence comes in the form of FAA orders 8620.2A (2007) and its successor, order 8620.2B (2019), addressed to FAA personnel. These orders cover all “U.S. Registered Aircraft,” while making it clear that an OEM (original equipment manufacturer) cannot mandate compliance with something that would put itself in the position of issuing “substantive rules” or “enable them to impose legal requirements on the public that differ from 14 CFR requirements.” It is not a stretch to interpret this as being a clear statement against the imposition of legally enforceable TBOs on engines by manufacturers. 

Despite requests for clarification during the latter part of December 2024 as to whether this would effectively eliminate enforceable TBOs for light sport aircraft, the FAA remained resolutely silent, other than to acknowledge the question. However, in a response to the same question sent to the FAA Press Office in June 2025, the agency did confirm that for the purposes of this order, a light sport aircraft was, indeed, a “U.S. registered aircraft” as defined in orders 8620.2A and 2B, and therefore, by extension, covered by this order. 

Two additional questions were addressed to the FAA Press Office just prior to the publication deadline for this article. 

The first was whether the FAA planned to withdraw the previous legal interpretation that supported the mandatory nature of light sport engine TBOs, and the second was to ask why the agency had remained unresponsive to this issue for so long. 

The first question was responded to with, “The FAA is evaluating legal interpretations to ensure they align with the updated regulations.” The second question, as befits past experiences, failed to elicit any response. 

Given the overwhelming weight of evidence from the various FAA orders and MOSAIC, there does not appear to be any logical explanation as to why the agency has continued to remain silent on this matter for so long. 

Conclusion 

A number of owners of LSAs have had their aircraft grounded by a rule that was probably always defective and likely could never have passed full legal scrutiny in any enforcement action.As a consequence, these owners have been forced to replace a perfectly operating and safe engine or find a different solution, such as converting their plane to an experimental certificate (E-LSA) as allowed under the regulations. 

Expressions of concern on this issue have been communicated on many occasions to the FAA dating back to at least 2013 with two contradictory FAA counsel opinions made in 2013 and 2015. But there has been complete silence since—for reasons that remain unexplained. 

The combined wording of MOSAIC, order 8900.1 and order 8620.2A and 2B, make it crystal clear that an engine or other TBO-referenced component in an S-LSA that has exceeded its manufacturer-recommended or mandated TBO would not, in itself, render the airplane unairworthy. 

Moreover, even going back to the original 2007 version of order 8620.2A, the FAA explains why OEMs cannot mandate TBOs: “This would be objectionable for two reasons. First, the FAA does not have authority to delegate its rulemaking authority to an OEM. Second, ‘substantive rules’ can be adopted only in accordance with the notice and comment procedures of the Administrative Procedures Act (APA), which does not apply to an OEM.” 

There are very reasonable questions remaining unanswered as to when the FAA realized that it might have exceeded its powers of delegation, why the chosen strategy was to decline to answer questions for the last nine years and how to justify, provide, and maintain a legal interpretation that was diametrically contradicting a very clear agency order (8620.2A). 

Given that this has likely cost some individual owners in the tens of thousands of dollars—and collectively, potentially well into the millions—LSA pilots affected by this might justifiably expect a clear answer.