United Airlines drops Boeing 787 Dreamliner through June 5 United Airlines cut the grounded Boeing 787 from its flying plans at least until June and postponed its new Denver-to-Tokyo flights on Thursday, as airlines continued to tear up their schedules while the plane is out of service. Investigators are still trying to figure out what caused a battery fire in one plane and forced the emergency landing of another plane last month. The world's 50 787s have been grounded since Jan. 16. United spokeswoman Christen David said the plane could still fly earlier than June 5 if a fix is found. At that point it would be used as needed around United's system, she said. United was due to begin flying from Denver to Tokyo's Narita airport on March 31. It's postponing the start of those flights at least until May 12, or longer if the 787 isn't cleared to fly. That would be almost a year after United began selling tickets for the flight. United has said the flights are a perfect fit for the 787, which is mid-sized and very fuel-efficient. The thinking is that Denver would be unlikely to fill a bigger plane for a flight to Tokyo. But it can fill the plane's 219 seats, and the plane is fuel-efficient enough to turn a profit. LOT Polish Airlines has said it will keep its 787s grounded through October. Switching the plane to be used on a flight is more complicated than passengers might think. Pilots trained to fly one type might not be able to fly the replacement, creating scheduling problems. Seats are laid out differently, meaning seating assignments have to be redone. The Federal Aviation Administration has said it won't clear 787s to fly until Boeing can show they're safe. Boeing intends to propose a plan to federal regulators on Friday to temporarily fix problems with the 787's batteries, a congressional official told The Associated Press on Wednesday. Boeing has declined to talk about any planned meetings with federal officials. The company is in the middle of multiple probes related to the 787. The National Transportation Safety Board and the FAA are looking into the Jan. 7 battery fire on a Japan Airlines 787 parked at Boston's Logan International Airport. A Japan Airlines emergency landing in Japan is being examined by investigators in that country. And more broadly, the FAA is reviewing the design, certification, manufacture and assembly of the 787. So far industry and labor have been mostly supportive of Boeing and the government probes. Air Line Pilots Association President Lee Moak said the union is confident that when the investigations are done "we'll have known the reasons behind the system failures and we'll be able to move forward." He sidestepped questions from reporters in Washington on Thursday about how pilots would view a potential decision to return the 787 to the air before investigators have found the root cause of the battery problems. We're confident the process in place is a good one ... Once that is complete then a decision will be made. But until that time it's still an open and ongoing investigation," he said. Shares of United Continental Holdings Inc. were unchanged at $26.08 in Thursday afternoon trading. Boeing Co. rose $1.19 to $75.97.