Sonex, LLC has shut down. The Wisconsin-based kit aircraft manufacturer — one that spent more than two decades making high-performance experimental aviation accessible to everyday builders — ceased all operations and filed for bankruptcy effective March 27, 2026. Owner Mark Schaible broke the news via a video posted to the company’s website and YouTube channel on or around April 14, 2026, calling the collapse a “perfect storm” that left him no real choice but to close immediately.
The timing was brutal. The April 2026 issue of Kitplanes hit mailboxes the same week the announcement dropped, featuring Sonex as its cover story under the headline: “2026 promises to be another big year for Sonex Aircraft.” As recently as January 23, 2026, the company had announced it was shipping tail kits for the much-anticipated Sonex Highwing, with production scheduled to run into mid-February. Less than five weeks later, it was over.
What Killed It
Schaible was unusually candid. He cited a compounding list of pressures: a sharp drop in new kit sales, rising material costs, bank pressure following several unprofitable years, and — critically — competition from the used aircraft market Sonex itself had created. Nearly 700 completed aircraft were already flying, with another 1,398 kits listed as under construction in the company’s builder database (based on voluntary self-reporting by builders). That healthy secondary market was undercutting demand for new kits. Schaible named it directly:
“This decision is necessitated by a severe drop-off in sales and our bank’s unwillingness to carry-forward our debts given some unprofitable years. We’ve had to make this decision very suddenly as a perfect storm of bank pressure, lack of sales, increasing costs, competition from our own aircraft in the used market, and cashflow realities are not allowing us to continue our work.”
Some industry observers have pointed to the “Osborne Effect” as a partial explanation — the theory that pre-announcing the Highwing caused prospective buyers to hold off on existing kit purchases while waiting for the new model, strangling cash flow during the development stretch. Whether or not that analysis holds, Schaible acknowledged the closure follows several years of unprofitable work toward the Highwing launch.
He also drew a pointed comparison to Van’s Aircraft’s Chapter 11 reorganization, making clear Sonex’s situation was categorically worse. “Barring an 11th hour investment or purchase allowing the operation to continue, this will not be a reorganization of our debts but will be much more severe,” he said. He confirmed that he and his wife intend to file for personal bankruptcy as well.
What Sonex Was
John Monnett founded the company in 1998, following the first flight of serial number SX1 at Wittman Regional Airport in Oshkosh. Mark Schaible purchased the company in January 2022, forming the new entity Sonex, LLC, and remained owner at the time of closure. Sonex built its name on affordable, all-metal, low-wing kit aircraft — the Sonex, Waiex, Onex, and Xenos motorglider — powered primarily by automotive engine conversions through its AeroConversions subsidiary. That subsidiary produced the AeroVee, a custom aircraft implementation of the Volkswagen air-cooled engine. Then there was the SubSonex — a single-seat personal jet powered by a PBS TJ-100 turbojet producing 258 pounds of thrust, first flown by test pilot Bob Carlton on August 10, 2011. Niche, but the kind of headline-grabbing product that kept the brand visible. At the time of closure, the company employed nine people and operated a factory and 5,600-square-foot parts distribution warehouse and flight center adjacent to Wittman Regional.
A Door Left Open — Barely
Schaible hasn’t entirely ruled out a rescue. In a March 31 follow-up email reported by AOPA, he said he had received an “overwhelming” number of inquiries — spanning investment, outright purchase, manufacturing rights acquisitions, and grassroots fleet-support efforts. He and Monnett said they had “a lot to sift through” with attorneys and advisors.
Longtime Sonex customer Michael Jackson, who completed his Onex more than a decade ago, put the community’s reaction plainly: “It was like a gut punch. I think most of us were surprised by the announcement. I always felt that Sonex ran their business the right way. They didn’t grow too quickly, and they kept their designs simple.”
For the wider kit aircraft industry, the timing is uncomfortable. Coming on the heels of Van’s Aircraft’s financial crisis, Sonex’s hard closure has pushed homebuilder forums to openly question the long-term viability of the kit aircraft business model — as material costs keep outpacing what budget-conscious builders can absorb. Developments will be tracked here as the bankruptcy process moves forward and any potential acquisition talks take shape.
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