In Zunun Aero, Inc. v. The Boeing Co., No. 24-5212 (9th Cir. Aug. 26, 2026), on a petition for panel rehearing, the Ninth Circuit holds that a federal court may exercise supplemental jurisdiction over state-law claims, under 28 U.S.C. § 1367(a), even where the federal-law claim is a permissive counterclaim under Fed. R. Civ. P. 13(b).
Rule 13(a) provides, in relevant part, that a defendant or third party “must state as a counterclaim any claim that—at the time of its service—the pleader has against an opposing party if the claim . . . arises out of the transaction or occurrence that is the subject matter of the opposing party’s claim.” Any counterclaim not falling within the “transaction or occurrence” compass is a permissive counterclaim under Rule 13(b).
The classification of a counterclaim as compulsory or permissive became relevant in this case because it potentially affected which U.S. Court of Appeals had appellate jurisdiction to review the decision in this case.
The underlying matter was a suit filed by Zunum in state court raising Washington state law contract, tort, and statutory claims against Boeing. Zunum alleged that “Boeing had breached its contracts with Zunum by misusing confidential information and tortiously interfered with Zunum’s business expectancies by using Zunum’s confidential information to develop its own hybrid electric aircraft.” In relevant part, “Zunum alleged that the Active Voltage Control for Hybrid Electric Aircraft patent (‘Active Voltage patent’)” held by Boeing contained information that “relates closely to issues addressed by . . . [a] patent filed by Zunum in August 2018.”
Boeing “counterclaimed in state court and sought a declaration that Boeing’s ‘employees, affiliates, or associates’ were the ‘sole inventors’ of the Active Voltage patent.” Boeing then removed the dispute to federal court “under 28 U.S.C. §§ 1331, 1338(a), 1454(a), on the sole basis of its patent inventorship counterclaim . . . . Boeing also invoked supplemental jurisdiction over Zunum’s state law claims . . . on the basis that those claims were related to the only federal claim in the case at the time, i.e., Boeing’s counterclaim seeking declaratory judgment to establish the validity of its Active Voltage patent.”
Following a jury trial, with a verdict in favor of Zunum, “the district court granted Boeing’s motion for judgment as a matter of law (‘JMOL’) and Boeing’s motion for a conditional new trial and thus vacated the jury verdict. On appeal, this panel reversed the district court’s grant of JMOL and conditional grant of a new trial and remanded with the instruction that this case be assigned to a different district judge on remand.”
It was at this point – on a petition for rehearing – where Boeing sprung its appellate jurisdiction argument. It argued that the panel was on the horns of a dilemma. If Boeing’s federal patent claim were deemed a compulsory counterclaim to Zunum’s state law claims under Rule 13(a), then appellate jurisdiction was vested in the Federal Circuit by 28 U.S.C. § 1295(a)(1) rather than the Ninth Circuit; that is, Zunum fatally took its appeal to the wrong courthouse. But if the counterclaim were deemed permissive, then the district court supposedly lacked supplemental jurisdiction over Zunum’s claims all along because they lacked a “common nucleus of operative fact” to the federal counterclaim under 28 U.S.C. § 1367(a). However considered, the Ninth Circuit (by Boeing’s lights) lacked power to review the district court’s grant of JMOL in its favor.
The Ninth Circuit affirms jurisdiction and denies rehearing, although the panel divides on the exact reasoning.
First, the panel finds that Boeing’s patent claim was a permissive, not compulsory, counterclaim to Zunum’s action because it did arise out of the same transaction or occurrence.
“Boeing’s counterclaims arose out of just two of the 576 paragraphs in Zunum’s complaint. Zunum had many theories to support its trade secret misappropriation claim. Specifically, Zunum alleged in its FAC that Boeing had misappropriated over 30 alleged trade secrets by either using or disclosing those trade secrets in many different contexts, of which Boeing’s patents were just one. Additionally, Boeing won on its patent inventorship counterclaims at summary judgment whereas Zunum won on its trade secret misappropriation claim at a jury trial. Thus, there was no need for Zunum to prove that Boeing was not the sole inventor of Boeing’s patents to prevail on Zunum’s trade secret misappropriation claim.”
(Judge Bade, concurring, would find Boeing’s counterclaim permissive by another route. “[A] claim is generally not a compulsory counterclaim ‘to the original suit which furnishes its predicate’ . . . . Here, as Boeing acknowledges, the predicate condition for asserting its counterclaims for a declaratory judgment—a substantial controversy between the parties over the inventorship of the ’635 and ’811 patents—did not arise until Zunum filed its complaint . . . . [And] the possibility that both the plaintiff’s claim and the defendant’s counterclaim could be successful often, but not always, indicates that the two claims arise from different transactions.”)
Second, the panel holds that even a permissive counterclaim may furnish the basis for supplemental jurisdiction, because the “common nucleus of operative fact” standard of 28 U.S.C. § 1367(a) is broader than the “transaction or occurrence” standard of Rule 13(a). “Every circuit to have addressed this question since 28 U.S.C. § 1367(a) was enacted has held that the supplemental jurisdiction test is broader than the compulsory counterclaim test . . . . In this case, Boeing’s permissive counterclaim and Zunum’s state law claims share a ‘common nucleus of operative fact.’ Id. Boeing’s patent inventorship counterclaims and Zunum’s trade secret misappropriation claim, breach of contract claims, and tortious interference claim are all related to Boeing’s access to and alleged misuse of confidential information regarding Zunum’s hybrid electric aircraft technology.”
Even a “loose connection” between the claims, the Ninth Circuit concludes, can bring the entire action within a single constitutional case. “Accordingly, the district court properly exercised supplemental jurisdiction over Zunum’s state law claims under 28 U.S.C. § 1367(a).”
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