United Airlines said it was taking its Boeing 787s out of its flying plans until June 5, except for a Denver-to-Tokyo route scheduled for a tentative launch in May.
United's decision came as a Japanese investigation of a fuel leak on a 787 operated by Japan Airlines indicated the cause to be a coating around the mechanism that controls fuel movement between tanks.
Japanese officials launched the investigation after two fuel leaks on the JAL 787, just days before authorities around the world grounded the new lightweight passenger jets over battery failures that sparked fires on two planes in January.
Japanese authorities still have not found the cause of the battery issue.
Airlines operating 787s are setting schedules for coming months while still uncertain about when the plane will be able to resume service following the fleet's grounding five weeks ago.
Boeing is due to meet the head of the US Federal Aviation Administration on Friday to present measures designed to prevent further battery failures, even though the root cause of the electrical problem has not been determined.
United spokeswoman Christen David said in a statement that the carrier's Denver to Tokyo Narita route, originally set to start on March 31, had been postponed to May 12.
The launch would ultimately depend on a successful resolution of the safety incidents that have grounded the 787. Other services with the 787 won't resume until after June 5, David said.
Boeing said it was maintaining communication with United as the plane maker develops a plan to resume 787 service. "We deeply regret the impact the recent events have had on the schedule for United and their customers," Boeing spokesman Marc Birtel said.
United's statement doesn't mean that the 787 won't be ready to fly again before June 5, said Carter Leake, an analyst at BB&T Capital Markets.
Rather, it means United will not put the jet into service before then. If the plane is available sooner but United cannot use it on its scheduled routes, Boeing likely would have to pay United compensation that Leake estimates at about USD$800,000 a month, based on lease rates.
"This does not tell you that Boeing's plane is grounded until June," he said. "It tells you that Boeing's costs to United could be as if it's grounded until June."
A "superbox" to contain the battery or some other fix "might come sooner, but United is not paying" to have the jet until after June 5, he added.
In a similar move, Poland's national airline LOT said last week that it would not use the 787 before October and that it is seeking compensation from Boeing.
"Airlines don't make money while their planes are on the ground," said Morningstar airline analyst Basili Alukos.
United is the only US carrier currently operating the 787 and has six of the planes, worth USD$207 million apiece at list prices. JAL and All Nippon Airways have nearly half of the 50 jets delivered to airlines so far.
Japan's Transport Ministry said it believed the manufacturing process led to deficiencies in the way electrical-insulating coating was applied to the mechanism that opened and closed the fuel-tank valve.
Investigators also found foreign matter on a switch that operated the same mechanism, causing it to send a signal that the valve was closed when it was still half open -- leading to the leak.
The ministry said four 787s in Japan, two from JAL and two from ANA, might be affected by the manufacturing process.