PCC Airfoils and the Sixth Circuit’s Rejection of a “Clear and Convincing Evidence” Checklist for Preliminary Injunctions

1. Introduction

In PCC Airfoils, LLC v. Justin Daugherty (6th Cir. May 19, 2026), PCC Airfoils sought emergency injunctive relief after a long-time engineer, Justin Daugherty, left to become director of engineering at a competitor, Consolidated Precision Products Corp. PCC alleged Daugherty queued confidential airfoil-related documents for printing during his final days and inferred misappropriation when the documents were not found among his returned materials.

PCC sued under federal and state trade secret law—18 U.S.C. § 1836 et seq. (Defend Trade Secrets Act) and Ohio Rev. Code § 1333.61 et seq. (Ohio Uniform Trade Secrets Act)—and for breach of a confidentiality duty. It moved for a preliminary injunction to (i) prevent disclosure of trade secrets and (ii) restrict Daugherty from working on similar industrial gas turbine airfoil projects. The district court denied the motion because PCC allegedly failed to prove each preliminary-injunction factor by clear and convincing evidence.

The appeal presented a narrow but significant procedural issue: may a federal district court in the Sixth Circuit require “clear and convincing evidence” for each of the four preliminary injunction factors?

2. Summary of the Opinion

Chief Judge Sutton, writing for the panel, held that the district court applied the wrong legal standard. A movant need not prove each of the four preliminary injunction considerations by clear and convincing evidence. Instead, the court must evaluate the familiar four factors together in a sliding-scale equitable analysis and may grant relief only if, on balance, the factors clearly favor an injunction.

The Sixth Circuit reversed and remanded for the district court to apply the correct federal preliminary injunction framework in the first instance, emphasizing that the appellate court was “a court of review, not of first view.”

3. Analysis

A. Precedents Cited (and How They Shaped the Decision)

• Babler v. Futhey, 618 F.3d 514 (6th Cir. 2010)
  Used for the standard of review—denial of a preliminary injunction is reviewed for abuse of discretion—while setting up the key doctrinal move: a legal error is itself an abuse of discretion.
• Union Home Mortg. Corp. v. Cromer, 31 F.4th 356 (6th Cir. 2022)
  Reinforced that mistakes of law qualify as abuse of discretion. The court later distinguished Cromer as involving an underlying cause of action with its own clear-and-convincing standard—making it inapposite to a general Rule 65 motion absent a heightened burden source.
• Winter v. Nat. Res. Def. Council, Inc., 555 U.S. 7 (2008)
  Anchored both the four-factor test and the Supreme Court’s “clear showing” phrasing. The panel’s key interpretive move was to reject the conflation of “clear showing” with “clear and convincing evidence” for each factor. Winter also supported the sliding-scale point (balancing and weighing).
• A1 Diabetes & Med. Supply v. Azar, 937 F.3d 613 (6th Cir. 2019)
  Cited for the four-factor framework in Sixth Circuit practice post-Winter.
• S. Glazer's Distribs. of Ohio, LLC v. Great Lake Brewing Co., 860 F.3d 844 (6th Cir. 2017)
  Crucial for rejecting the idea that the factors are “prerequisites to be met.” Glazer’s supported the equitable, non-checklist character of the inquiry and was used again to underscore that the factors are weighed, not proven as elements.
• Gonzales v. Nat'l Bd. of Med. Exam'rs, 225 F.3d 620 (6th Cir. 2000)
  Supported the proposition that “no one factor is controlling,” reinforcing the balancing approach.
• Fetch! Pet Care, Inc. v. Atomic Pawz Inc., 170 F.4th 546 (6th Cir. 2026)
  Played a gap-filling role: the panel treated Fetch! and this case as clarifying Sixth Circuit law against a district-court trend of importing a clear-and-convincing requirement. The opinion positioned Fetch! as directly supporting the rejection of a heightened proof checklist.
• Trump v. Int'l Refugee Assistance Project, 582 U.S. 571 (2017) (per curiam)
  Quoted to emphasize equity’s case-specific nature and that preliminary injunctions “turn as much on the equities … as the substance of the legal issues.”
• E.M.D. Sales, Inc. v. Carrera, 604 U.S. 45 (2025)
  The most important Supreme Court authority in the opinion’s burden-of-proof analysis. The panel relied on E.M.D. Sales for the proposition that clear and convincing evidence is reserved for rare situations (constitutional/statutory command or unusually coercive government action). This undercut both the district court’s approach and the continued persuasive value of older, contrary language.
• Higuchi Int'l Corp. v. Autoliv ASP, Inc., 103 F.4th 400 (6th Cir. 2024)
  One of two “qualifications” to balancing: if there is “no likelihood of success on the merits,” the motion fails regardless of other factors.
• Friendship Materials, Inc. v. Mich. Brick, Inc., 679 F.2d 100 (6th Cir. 1982) and D.T. v. Sumner Cnty. Schs., 942 F.3d 324 (6th Cir. 2019)
  Established the second qualification: irreparable injury is mandatory in existence (even if magnitude can be weighed). The opinion used these cases to show that rejecting a clear-and-convincing checklist does not eliminate rigor—certain showings remain indispensable.
• Cutter v. Wilkinson, 544 U.S. 709 (2005)
  Invoked to justify remand rather than deciding the injunction factors anew—“a court of review, not of first view.”
• Overstreet v. Lexington-Fayette Urb. Cnty. Gov't, 305 F.3d 566 (6th Cir. 2002)
  Used to explain that “clear showing” describes the overall balance, not an evidentiary burden per factor.
• Leary v. Daeschner, 228 F.3d 729 (6th Cir. 2000)
  Addressed and limited. The court explained that saying preliminary injunction proof is “more stringent” than surviving summary judgment does not impose “clear and convincing” proof per factor; it reflects that Rule 56 does not demand irreparable harm or an overall equitable entitlement.
• Garlock, Inc. v. United Seal, Inc., 404 F.2d 256 (6th Cir. 1968) (per curiam)
  Clarified that irreparable harm must be more than speculative—a “clear case of irreparable injury”—but again not a global clear-and-convincing-evidence requirement.
• Honeywell, Inc. v. Brewer-Garrett Co., 1998 WL 152951 (6th Cir. Mar. 23, 1998)
  The principal source of the contrary “clear and convincing evidence” phrasing. The panel neutralized it on two grounds: (i) it is unpublished and nonbinding, and (ii) after E.M.D. Sales, Inc. v. Carrera, it “lost whatever persuasive value it had.”
• AK Steel Corp. v. ArcelorMittal USA, LLC, 55 N.E.3d 1152 (Ohio Ct. App. 2016) and Procter & Gamble Co. v. Stoneham, 747 N.E.2d 268 (Ohio Ct. App. 2000)
  These Ohio cases supported Daugherty’s state-law argument that Ohio equity requires clear and convincing evidence. The panel rejected their applicability in federal court under Erie principles.
• Erie R.R. Co. v. Tompkins, 304 U.S. 64 (1938) and S. Milk Sales, Inc. v. Martin, 924 F.2d 98 (6th Cir. 1991)
  The court used Erie and Martin to classify preliminary injunction standards as procedural for federal courts, governed by federal law (Rule 65 practice), even when state statutes supply the substantive claim.
• Fed. R. Civ. P. 65
  Treated as the governing procedural framework; important because it contains no heightened burden language.
• Lackey v. Stinnie, 604 U.S. 192 (2025) and Univ. of Tex. v. Camenisch, 451 U.S. 390 (1981)
  Cited to highlight the mismatch between demanding heightened proof at the preliminary stage and the reality that parties often have not had discovery and need not “prove [the] case in full” at a preliminary-injunction hearing.
• James B. Oswald Co. v. Neate, 98 F.4th 666 (6th Cir. 2024)
  Like Cromer, distinguished as involving claims with an underlying clear-and-convincing burden.
• Mktg. Displays Int'l v. Shaw, 93 F.4th 967 (6th Cir. 2024)
  Answered the concern that preliminary injunction proceedings improperly pre-decide merits: findings at the preliminary stage are “never binding” on the merits.
• Trump v. CASA, Inc., 606 U.S. 831 (2025) (Kavanaugh, J., concurring)
  Used to emphasize that interim injunctive relief can be “immensely important,” justifying careful equitable analysis without importing an across-the-board heightened evidentiary standard.

B. Legal Reasoning

The opinion’s core doctrinal clarification is the distinction between:

1. The “clear showing” requirement (from Winter v. Nat. Res. Def. Council, Inc.)—meaning that, after weighing the four factors, the movant must clearly be entitled to extraordinary interim relief; and
2. The “clear and convincing evidence” standard—a heightened burden of proof that applies only when the Constitution, a statute, or rare categories of cases require it (as synthesized in E.M.D. Sales, Inc. v. Carrera).

The district court, relying on certain district court decisions and the unpublished Honeywell, Inc. v. Brewer-Garrett Co., treated “clear and convincing” as a universal requirement for each factor. The Sixth Circuit rejected that approach as inconsistent with federal equity practice and its own precedent describing the factors as considerations to be weighed on a sliding scale.

The panel also sharpened two important guardrails that preserve rigor without importing a heightened burden:

• Likelihood of success floor: if there is “no likelihood of success on the merits,” the motion fails (Higuchi Int'l Corp. v. Autoliv ASP, Inc.).
• Irreparable injury requirement: irreparable harm must exist; it is mandatory in kind, even if degree is weighed (Friendship Materials, Inc. v. Mich. Brick, Inc.; D.T. v. Sumner Cnty. Schs.).

Finally, the court rejected the attempt to import Ohio’s preliminary injunction burden through state trade secret law. Under Erie R.R. Co. v. Tompkins and S. Milk Sales, Inc. v. Martin, preliminary injunction standards are procedural and governed by federal law in federal court, including in cases asserting Ohio statutory claims.

C. Impact

• Immediate procedural correction in the Sixth Circuit: The decision forecloses a district-court practice—particularly in trade secret and restrictive covenant disputes—of demanding “clear and convincing evidence” on each preliminary injunction factor absent a specific legal source requiring it.
• Recalibration of early-stage litigation leverage: In employee mobility and trade secret cases, a heightened evidentiary burden at the preliminary stage can functionally determine outcomes before discovery. By rejecting that blanket requirement, the Sixth Circuit reduces the risk that plaintiffs (or defendants) win purely because an evidentiary hurdle is set too high too early.
• Uniformity across federal claims and state-law supplemental claims: The opinion reinforces that parties cannot use state preliminary-injunction burdens to alter federal equitable procedure in federal court—important for mixed DTSA/OUTSA pleadings.
• Guidance for future disputes over “clear showing” language: The court’s clarification that “clear showing” is a holistic entitlement determination, not a factor-by-factor evidentiary burden, will likely be cited whenever litigants argue that Winter silently raises burdens of proof.

4. Complex Concepts Simplified

• Preliminary injunction: A temporary court order entered early in a case to prevent harm before final judgment. Because it can effectively shape real-world conduct immediately, it is considered “extraordinary” relief.
• Four-factor test: Courts consider likelihood of success, irreparable harm, harms to others, and public interest. In the Sixth Circuit, these are weighed together rather than treated as four separate elements each with its own fixed proof burden.
• Sliding-scale balancing: A stronger showing on one factor (e.g., irreparable harm) may compensate for a weaker showing on another (e.g., likelihood of success), provided mandatory minimums are met (no “zero” likelihood of success; irreparable harm must exist).
• “Clear showing” vs. “clear and convincing evidence”: “Clear showing” describes the overall conclusion that the equities and merits favor an injunction; “clear and convincing evidence” is a heightened burden of proof usually reserved for specific contexts (e.g., certain constitutional or statutorily defined situations).
• Erie doctrine (procedural vs. substantive): Federal courts apply state substantive law for state claims, but apply federal procedural rules. The standard for obtaining a preliminary injunction is treated as procedural, so federal standards apply even in state-law trade secret cases litigated in federal court.
• “Court of review, not of first view”: Appellate courts generally correct legal errors and send the case back rather than deciding fact-intensive equitable questions that the trial court has not evaluated under the correct legal standard.

5. Conclusion

PCC Airfoils, LLC v. Justin Daugherty establishes (and, together with Fetch! Pet Care, Inc. v. Atomic Pawz Inc., cements) a clear Sixth Circuit rule: district courts may not require “clear and convincing evidence” for each preliminary injunction factor unless a statute, the Constitution, or a rare recognized category demands it. The proper inquiry is a federal, equitable, sliding-scale assessment of all four factors, with the movant entitled to relief only when those factors—taken together—clearly favor an injunction.

The opinion’s practical significance extends beyond trade secret disputes. It is a procedural precedent about how federal courts must approach emergency equitable relief: rigorous, context-sensitive, and faithful to Rule 65 practice—without importing heightened burdens by habit, misunderstanding, or nonbinding authority.