By Alwyn Scott WASHINGTON (Reuters) - The U.S. Federal Aviation Administration on Wednesday approved extended operations for Boeing's 787 Dreamliner, a move that will allow a wider range of routes and that marks a vote of confidence in the high-tech jet at a time of renewed scrutiny. The approval, known as ETOPS, will allow airlines to fly routes that are up to 330 minutes, or 5-1/2 hours, away from a landing field, versus the 180-minute, or three-hour, limit in place since the Dreamliner was launched in 2011. "Granting of the expanded operational permission will allow airlines to introduce additional routes after they meet the proof of capabilities requirements and receive approval from their own regulatory agencies," Boeing said. The FAA approval formally applies only to U.S. carriers, and within that group only United Airlines now operates the 787. But regulators in other countries typically follow the FAA's lead. Airlines apply their own rules for extended operations and could take time to actually begin flying those routes. "Airline approval is a completely different process and it can vary airline by airline," said Boeing spokeswoman Lori Gunter. United Airlines called the approval "a positive development" but said there was no immediate effect on its routes. The FAA said its decision reflected the 787's "reliability history" and Boeing's "effectiveness at addressing relevant issues during 250,000 hours of service" for each of the plane's two engine types. Last week, the U.S. National Transportation Safety Board urged further testing for the 787 to ensure that large lithium-ion batteries the plane uses are safe from overheating and fire. The NTSB recommendations came even before it had finished investigating what caused a battery to burn on a Japan Airlines Co <9201.T> 787 in January 2013. Another battery overheated on an All Nippon Airways <9202.T> plane later the same month, prompting regulators to ground the global fleet until April that year. Boeing redesigned the battery and charger and designed a steel box to contain fires and vent hot gasses outside the plane. The NTSB said tests originally devised to ensure the batteries were safe were insufficient, since they did not produce the conditions that occurred in the actual battery incidents. The board also said outside experts should be consulting in designing tests. The NTSB recommendations "are logical because we don't know yet what were the root cause or causes," said Hans Weber, a former FAA adviser and president of TECOP International, an aerospace consulting firm based in San Diego, California. The FAA approval nevertheless moves airlines an important step closer to tapping the full potential of the Dreamliner, which burns 15 percent less fuel than the Boeing 767. The approval was of little concern to investors, one Wall Street analyst said. Boeing's stock was up 0.4 percent at $134.70. But the approval appeared to come sooner than expected and its timing was seen by some as a sign of continuing tension between the two agencies, one charged with investigating accidents and the other with ensuring safety. "It certainly does seem like there's some conflict between the NTSB and the FAA," said Richard Aboulafia, an analyst at the Teal Group in Fairfax, Virginia. (Additional reporting by Ros Krasny; Editing by Marguerita Choy and Eric Walsh)