Federal Circuit Insulates PTAB in Ethanol Boosting Systems Opinion
A High Bar for Challenging PTAB 'Shenanigans'
The intersection of district court litigation and administrative proceedings at the Patent Trial and Appeal Board (PTAB) frequently generates procedural friction. In Ethanol Boosting Systems, LLC v. Ford Motor Company, Nos. 2024-1381, 2024-1382, 2024-1383 (Fed. Cir., Dec. 23, 2025), the panel addressed two significant sources of such friction: the reviewability of the Board’s decision to delay institution pending a judicial outcome, and whether a district court’s unappealed claim construction binds the Board in a subsequent Inter Partes Review (IPR).
The Court’s precedential decision reinforces the high walls surrounding the Director’s discretion to institute IPRs and clarifies that the “law of the case” doctrine does not easily leap across the divide between federal courts and administrative tribunals.
For patent owners and petitioners alike, the ruling underscores the necessity of re-litigating claim construction merits in every forum, rather than relying on procedural estoppels from parallel proceedings.
Background of the Dispute
The technology at the heart of this dispute involves fuel management systems for internal combustion engines designed to mitigate “engine knock”—an unintentional detonation of fuel that reduces efficiency and damages engines (Slip Op., p. 3).
Massachusetts Institute of Technology (MIT) and its licensee, Ethanol Boosting Systems (EBS), asserted three patents (U.S. Patent Nos. 10,619,580; 10,791,760; and 9,708,965) against Ford Motor Company. The claims describe a system utilizing both port injection and direct injection to manage fuel delivery based on torque levels (p. 3).
The procedural history is intricate and highly relevant to the outcome. In prior district court litigation, the court construed the term “fueling system that uses direct injection” to require a fuel that (1) is different from the fuel used in port injection and (2) contains an anti-knock agent other than gasoline (p. 5).
EBS appealed the first part of that construction (the “different fuel” requirement) to the Federal Circuit in a prior appeal (“EBS I”; No. 21-1949, July 18, 2022), but did not appeal the second part regarding the non-gasoline agent (p. 7). IN that 2022 opinion, the Federal Circuit vacated the “different fuel” requirement and remanded (p. 7).
Parallel to this, Ford filed IPR petitions. Initially, the Board denied institution, relying on the district court’s “different fuel” construction. However, Ford requested rehearing. The Board effectively held that request in abeyance for fifteen months, waiting for the Federal Circuit to decide EBS I.
Once the Federal Circuit vacated the district court’s restrictive construction, the Board granted rehearing, instituted the IPRs, and eventually found the claims unpatentable as obvious (pp. 7-8).
EBS appealed the Board’s final written decisions, arguing that the fifteen-month “stay” of the institution decision was unlawful and that the Board was bound by the unappealed portion of the district court’s claim construction prohibiting gasoline as an anti-knock agent (pp. 8-9).
Analysis: Unpacking Section 314(d)
The Federal Circuit, in an opinion authored by Judge Chen, joined by Judges Clevenger and Hughes, affirmed the Board on all grounds. The analysis focused on two primary legal hurdles: the statutory bar on reviewing institution decisions and the scope of the law-of-the-case doctrine.
The Unreviewability of Institution “Delays”
EBS argued that the Board lacked statutory authority to “stay” a rehearing decision for fifteen months. They contended this ultra vires act tainted the subsequent institution, requiring dismissal of the entire proceeding.
The Court rejected this attempt to bypass 35 U.S.C. § 314(d), which states that the determination to institute an IPR is final and nonappealable (p. 10).
The Court reasoned that characterizing the delay as a “stay” did not alter the fundamental nature of the appeal: it was a challenge to the propriety of the institution itself (pp. 10-11).
Citing the Supreme Court’s decision in Thryv, Inc v. Click-To-Call Techs., LP, the Federal Circuit reiterated that § 314(d) bars review even when a party alleges the agency exceeded its statutory authority in the institution process (pp. 10-11), barring rare constitutional claims or “shenanigans” that implicate due process.
The Court explained:
EBS expressly challenges the propriety of institution itself by asking us to de-institute the IPRs... That looks no different from alleging ‘that the agency should have refused to institute inter partes review.’ ... Section 314(d) thus bars review of EBS’s challenge. (p. 12)
The Court further noted that the Board had “sound reasons” for the delay—specifically, waiting for the Federal Circuit to settle a claim construction issue that was dispositive to the institution decision (p. 14).
Rejecting Cross-Proceeding Estoppel
EBS’s second major argument was that the Board was bound by the “law of the case.” In the district court, the judge ruled that the direct injection fuel must be an anti-knock agent other than gasoline. Since EBS did not appeal that specific limitation in EBS I, they argued it became controlling law that the Board could not ignore (p. 8).
The Federal Circuit dismantled this argument, clarifying the boundaries of the law-of-the-case doctrine. The doctrine dictates that a legal decision governs the same issues in subsequent stages of the same case (p. 15). It does not strictly apply across separate proceedings—such as moving from a district court action to a separate IPR proceeding. The Court stated:
“EBS offers no authority suggesting that we apply these doctrines across different litigations and proceedings, particularly for a non-appealed district court construction. Indeed, we have suggested the opposite: our law-of-the-case doctrine... does not apply across different cases.” (p. 15)
Furthermore, the Court found that EBS had forfeited the argument by failing to substantively brief the claim construction issue before the Board. Instead of arguing why the term should exclude gasoline based on the patent specification, EBS merely asserted that the district court’s view was “controlling law” (p. 16).
The Board, not being bound by the district court, adopted the plain and ordinary meaning, which the Federal Circuit affirmed on the merits.
The Court noted that the specification explicitly disclosed a “gasoline only” mode, which contradicted EBS’s proposed limitation:
“Nothing in the claims suggests that the DI Fuel terms disavow gasoline as the anti-knock agent... Indeed, the specification counsels against adopting EBS’s constraint on the anti-knock agent because it teaches a gasoline-only embodiment.” (p. 18)
Key Takeaways and Practical Implications
This decision solidifies the insulation of the PTAB’s institution phase and highlights the risks of relying on procedural arguments over substantive ones in patent disputes.
1. The “Shenanigans” Exception to § 314(d) Remains Narrow
Practitioners often attempt to frame procedural irregularities at the institution stage as jurisdictional defects to escape the bar of § 314(d). This case demonstrates the futility of that strategy absent a clear statutory violation that reaches beyond the institution decision itself.
The Court noted that allegations of “acting in excess of statutory jurisdiction,” without more, “do not overcome § 314(d)’s bar” (p. 13). Parties should assume that once an IPR is instituted, the path to vacating that institution based on pre-institution conduct is nearly nonexistent.
2. Separate Forums Require Separate Substantive Arguments
The most critical lesson for counsel is that a victory or a settled point in district court does not automatically translate to the PTAB. The “law of the case” is not a bridge between the two forums.
When defending a patent in an IPR, the patent owner must re-establish favorable claim constructions on their merits.
Relying solely on the argument that a district court has already decided the issue is a high-risk strategy that failed here, as the Court affirmed the Board did not abuse its discretion by “not evaluating a claim construction argument that neither party raised” (p. 17).
3. Specification Support is Paramount
On the merits, EBS lost the claim construction argument because the specification contained an embodiment (a “gasoline only” mode) that conflicted with their proposed claim limitation.
The Court reiterated the canon that “[w]e normally do not interpret claim terms in a way that excludes embodiments disclosed in the specification” (p. 18).
This serves as a reminder during patent drafting and prosecution: specific embodiments can and will be used to broaden claim scope against the patent owner’s wishes during enforcement.
Strong PTAB Powers
Two short months ago, USPTO Director John A. Squires issued an “Open Letter” and a binding Memorandum restructuring how Inter Partes Reviews (IPRs) are instituted. Effective October 20, 2025, the authority to institute trials has been reclaimed by the Director, ending the long-standing practice of delegating this power to the PTAB (see Memo, p. 1).
This case, Ethanol Boosting Systems, arrives at a pivotal PTAB moment, effectively reinforcing the Director’s broad discretion just as the agency centralizes control over the institution docket (Letter, p. 2).
By affirming that even significant procedural delays—characterized by appellants as “stays”—are unreviewable under § 314(d), the Federal Circuit has effectively insulated the Director’s new centralized institution process from judicial scrutiny (Slip Op., p. 10).
Director Squires’ stated goal to “eliminate the appearance of self-interest” by separating institution from trial adjudication is now bolstered by the court’s refusal to micromanage how and when those institution decisions are made (Letter, p. 2).
Practitioners and parties should recognize that the “shenanigans” exception to unreviewability remains exceedingly narrow (Slip Op., p. 13), leaving the Director with seemingly unchecked authority to shape the IPR landscape through institution denials or delays.
While the Squires PTAB Memo aims to align agency procedure with the “clear language” of the AIA (Letter, p. 2), Ethanol Boosting Systems may be viewed as ensuring that the Director’s interpretation of that statutory mandate will largely be the final word.
Consequently, the Director’s ability to manage the patent ecosystem through threshold institution determinations is now more potent than ever, having been both administratively centralized and judicially fortified.
Conclusion
Ultimately, Ethanol Boosting Systems v. Ford Motor Company stands as a definitive statement on the sovereignty of the PTAB within the patent ecosystem. By insulating institution delays from review and rejecting the cross-forum application of the “law of the case” doctrine, the Federal Circuit has empowered the Board to chart its own procedural and substantive course, unfettered by the shadow of district court litigation (pp. 10, 15).
For practitioners, this decision emphasizes the need for comprehensive advocacy in every venue: procedural victories in one forum offer no safe harbor in another. A claim term construed favorably in district court must be fought for and won anew before the Board, armed with the specification rather than reliance on judicial estoppel (p. 17).
As patent disputes increasingly play out across these disconnected parallel tracks, successful strategy demands a comprehensive approach—where every venue is treated as a distinct battleground requiring its own independent, merit-based defense.
Disclaimer: This is provided for informational purposes only and does not constitute legal or financial advice. To the extent there are any opinions in this article, they are the author’s alone and do not represent the beliefs of his firm or clients. The strategies expressed are purely speculation based on publicly available information. The information expressed is subject to change at any time and should be checked for completeness, accuracy and current applicability. For advice, consult a suitably licensed attorney and/or patent professional.