FARNBOROUGH — After more than two weeks of espousing daily hope that four Lockheed Martin F-35Bs would make a historic debut in the U.K., the Pentagon has finally announced that the single-engine, stealthy fighters will be a no show, even though the fleet has been approved to resume limited flight operations.

This is the result of an engine fire that erupted in a Pratt & Whitney F135 engine on an F-35A preparing for takeoff June 23 at Eglin AFB, Florida, only days before the four F-35Bs were due to take off for the Atlantic crossing.

The cancellation of the appearance only adds to Pratt’s disappointing showing at Farnborough. Bombardier’s CSeries was also prohibited from flying here after leaky oil seals in a Pratt engine grounded that fleet.

Pentagon officials said this week that the F135 engine fire was the result of excessive rubbing between the third- stage fan of an integrally bladed rotor and an abradable strip lining the casing of the engine. Though some rubbing is acceptable, F-35 AF-27 experienced extreme friction, creating excessive heat that eventually caused the engine to burst into flames; the pilot safely egressed. F-35 Program Executive Officer U.S. Air Force Lt. Gen. Christopher Bogdan said July 14 that data from inspecting all 98 operational engines indicates that the problem is not endemic to the entire fleet.

Pentagon spokesman Rear Adm. John Kirby made the cancellation official late July 15 in Washington. "In concert with our partners in the U.K.—[the Defense Department] has decided not to send Marine Corps and U.K. F-35B aircraft across the Atlantic to participate in the Farnborough air show," he told reporters at a Pentagon press briefing. "This decision was reached after consultation with operational commanders and airworthiness authorities, despite the decision by airworthiness authorities to clear the aircraft to return to flight."

The decision came at 7 p.m. local time in Farnborough, after show crowds had left and only hours after Kirby and other officials—including Air Force Secretary Debora Lee James, speaking at the show today—had expressed hope that the jets could perform a flying display during the air show hours after the U.S. Air Force and Navy lifted the grounding. "If I were a betting woman, I would say the odds just got better" that the F-35Bs would fly at the show, James said in a speech at the U.S. pavilion here just before noon.

The Pentagon’s statement in Washington barred a bevy of reporters who have been reporting daily on the situation here from asking questions on the decision, and about whether more technical insight has come to light about the mishap. Prior to the no-show at Farnborough, the F-35s were also absent from the Royal International Air Tattoo last week, where they were set to make their official international debut.

With the U.S. armed services willing to allow a return to flight, it appears that the notoriously risk-averse aviation authorities in London nixed the deployment, though officials from both governments insist it was a joint decision.

"We are pleased that the Lightning II has returned to flying although it is disappointing that it has been unable to come to the U.K. for the Farnborough air show," a British Ministry of Defense spokesman said. "However, the safety of pilots and aircraft must always be our priority and we fully support the decision not to carry out a transatlantic crossing with limited flight clearances. We remain committed to the F-35 program and are on track for the U.K.’s aircraft to achieve their initial operating capability in 2018." The U.K. is the only tier 1 international partner on the $398 billion U.S. fighter project.

The mood at the show today went from upbeat—with the return-to-flight notice—to disappointed once the deployment was halted.

On July 14, the U.S. Navy and Air Force allowed for a return to flight with limited clearances, though program officials have not said specifically what portions of the envelope are limited. One source close to the program suggested the g loads will be restricted while work is ongoing in the investigation. Officials have also not said whether any F-35s have actually flown since the limited clearance was provided earlier today.

It is also unclear whether the aircraft involved in the fire will be a total loss. The target price of the latest aircraft is $98 million.

"While we are disappointed, we remain fully committed to the program and look forward to future opportunities to showcase its capabilities to allies and partners," Kirby said.

It is not clear when the next such opportunity will occur given the F-35’s testing schedule, or whether deployment plans will allow for another attempt at an international debut soon. A demonstration is unlikely to happen at the Paris air show next year unless the aircraft is based elsewhere, as U.S. officials are skittish about basing stealthy aircraft in France.