787 Dreamliner diverted to Seattle after oil filter problem

(CNN) -- Passengers from a United Airlines 787 Dreamliner that made an unscheduled landing in Seattle were expected to resume their journey to Japan on Wednesday morning.

Flight 139 from Denver to Tokyo was diverted to Seattle on Tuesday afternoon "due to an indication of a problem with an oil filter," United said in a statement to CNN. The aircraft landed normally, said spokeswoman Mary Ryan. The plane's 210 passengers were asked to stay overnight in Seattle.

The incident comes six months after the FAA and other officials grounded the Dreamliner worldwide due to troubles with its battery system. In April, the FAA ordered all 787 operators to make specific modifications and United has been flying its fleet of six 787s since May 20.

In an apparent show of confidence in the new airliner, United announced Tuesday it was ordering 20 additional Dreamliners -- specifically the 787-10 model, which is a longer version of the plane.

Chris Seewald tweeted that he was a passenger on Tuesday's diverted flight. He said the aircraft's pilot told passengers that the "engine was not operating optimally." Seewald also tweeted a photo that he said showed the Dreamliner dumping fuel before landing in Seattle.

The 787 Dreamliner began service in the U.S. in 2012. With a fleet of six, United is the sole domestic operator of the airplane, which boasts high fuel efficiency due to the light-weight carbon-composite materials used in its wings and fuselage.

The plane represents a new generation of efficient wide-body, long-range airliners, helping to make it among the world's most watched aircraft. Airlines worldwide have committed to buy the plane, and hundreds of millions of dollars are riding on Dreamliner's success. Boeing's rival Airbus flew a similar airliner -- its highly anticipated A350 XWB -- for the first time on Friday at its facility in Toulouse, France.

The entire global fleet of 50 Dreamliners was grounded in January after two battery overheating incidents triggered concerns among safety officials. Among the Dreamliner's innovative new designs is a battery system that uses new, lighter lithium-ion batteries. Boeing and the Federal Aviation Administration collaborated on a new battery compartment which involved insulating the batteries and putting them in a ventilated armor-plated box to protect the rest of the plane.