Just one week after the much-heralded inaugural flight of the Denver-to-Tokyo nonstop flight began, a Tokyo-bound 787 Dreamliner made an emergency landing in Seattle less than four hours after taking off from Denver.

United Airlines Flight 139 took off at 1:19 p.m. MDT Tuesday from Denver International Airport headed for Narita International Airport but was diverted because of an oil-filter problem at 4:25 p.m. just as the plane reached the Pacific Ocean north of Vancouver, British Columbia.

The distressed airplane landed safely at Seattle-Tacoma International Airport at 5:10 p.m. MDT, according to FlightStats.com, which gets its data from the Federal Aviation Administration.

"We are accommodating passengers in hotels, and the plan is to get the passengers on another Dreamliner to Narita with a takeoff at 9:30 a.m. Pacific Time," said United spokeswoman Mary Ryan.

The rescheduled flight is called an "extra section," which means all of the passengers will be on a new flight and not divided among other scheduled flights.

The initial launch date for the greatly anticipated flight was pushed back twice because of battery problems with the Boeing 787 Dreamliner, which led to a worldwide four-month grounding of the aircraft while Boeing sought a solution.

Most of the Denver delegation returned without incident from a trade mission to Tokyo on Friday aboard a Dreamliner. The 787 aircraft is crucial to the route's feasibility, and United is still working to shore up support from its feeder-market clients to use Denver as its launching point for Asia travel.

Coincidentally, Tuesday's emergency landing occurred just 30 miles south of where the aircraft was developed and built by Boeing in Everett, Wash.

"We are aware of the event, and we are engaged with United to provide any support that they need," said Kate Bergman, spokeswoman for Boeing.

Earlier on Tuesday, United announced it was increasing its order of Boeing 787s to 65, including 20 of the newest model — the 787-10.

United and Boeing have not revealed what exactly went wrong with the oil filter, but according to James Simmons, professor of aviation at Metro State University in Denver, there are only two options: an oil leak or a filter clog.

"An oil leak is always a big concern, because an engine will fail completely. Sometimes, oil filters clog because of contamination in the oil," Simmons said. "It is quite common under either of those conditions to shut down one of the engines as a precautionary measure. It probably landed with one engine shut down, but we don't know for sure."

Simmons said commercial jets are designed to fly adequately on one engine and that this incident probably reflects a flight abnormality but not necessarily a flight emergency.

"But the traveling public often doesn't distinguish between the two," he said.

A third possibility is that there wasn't anything wrong with the aircraft but that the detection system alerted the crew to a nonexistent problem.

"But you don't want to go over the pond with an oil-filter bypass or not knowing what the light is saying," said Greg Feith, a former senior air-accident investigator with the National Transportation Safety Board.

The 787 has received high scrutiny since its January battery problems, but aviation experts caution against comparing those events with Tuesday's oil-filter problem.

"I would think that it is relatively unlikely that it was specific to the 787," said George Hamlin, an aviation-industry analyst. "It sounds like an unusual, but relatively routine, mechanical problem. ... To take a single incidence of anything and expand to a trend is ridiculous without pulling more information."
