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Boeing’s 787 Dreamliner suffered a fresh setback after ANA, the model’s biggest operator, said it discovered wiring defects in the fire-suppression system on three aircraft.

The fault, first detected on a 787 due to depart Tokyo’s Haneda airport Wednesday, would trigger the wrong extinguisher in the event of a blaze in one of the two engines, ANA said. Japan Airlines recalled a 787 flying to Helsinki from Tokyo as a precaution, and Boeing said it was investigating the flaw.

“These things happen with a new aircraft,” said Robert Stallard, an analyst at RBC Capital in London with an “outperform” rating on Boeing. “When the airlines ground the plane or regulators start becoming involved, then it becomes something to watch out for.”

Boeing’s flagship jet, which made its commercial debut in 2011, is already under scrutiny after a fire in London last month that U.K. investigators linked to an emergency beacon. The 787 returned to service with ANA and Japan Airlines on June 1 after a global grounding spurred by a pair of meltdowns in the lithium-ion batteries on the carriers’ jets.

Boeing fell 2 percent to $104.16 at the close in New York as broader U.S. stock indexes declined. That pared the shares’ gain to 38 percent this year.

ANA’s parts were replaced in two of the jets in which the Tokyo-based carrier found the defect, which must have occurred during the manufacturing process, said Megumi Tezuka, a spokeswoman. She said the third aircraft would be fixed by the end of the day.

Japan Air brought back the 787 from Helsinki to Narita airport in Tokyo as a precautionary measure after being informed of the new wiring issue, company spokesman Seiji Takaramoto said. The airline subsequently inspected all 10 of its 787s and found no issues, he said.

United Continental Holdings, the only U.S. Dreamliner operator, was inspecting its 787 fleet after “preliminary instructions from Boeing,” said Christen David, a spokeswoman.