Japan Airlines and All Nippon Airways are conducting inspections of their Boeing 787 fleets after faulty wiring was discovered by ANA in an engine fire extinguisher.

JAL opted to turn back an airborne 787 to Tokyo Narita Airport so it could be inspected. It was replaced by another 787 that had already been cleared, and the flight to Helsinki was scheduled to depart after a 7-hr. delay.

The carrier says three of its 10 787s have been inspected so far, and it has not yet found evidence of improper wiring. The remainder of the fleet will be examined by the end of Aug. 14.

ANA discovered improper wiring in the engine fire extinguisher of a 787 (registration JA813A) during a pre-takeoff inspection. The carrier subsequently found the problem in two more of its 787s, and has reportedly replaced parts in two of the three aircraft.

This is the latest in a string of issues discovered by 787 operators this year. In January the worldwide 787 fleet was grounded due to problems with lithium-ion batteries, and in July widespread inspections were carried out due to wiring problems on emergency locator beacons.