Japan’s All Nippon Airways has said it has found faulty wiring in three of its Boeing 787 Dreamliner jets.
The problem meant that if there was a fire in one of the two engines, extinguishing agent would be sprayed into the other.
Officials said that even if the wrong engine was sprayed it would not stop functioning and a fire could be extinguished by other means.
The airline has inspected its whole fleet of 20 jets. Japan Airlines said it had also begun checks.
JAL officials said they had not found any faulty connections so far, but they had to call back a flight to Helsinki, Finland, to do the check after it took off from Narita airport.
Boeing 787s were grounded worldwide in January for battery-related malfunctions. They were put back into service from April.