THE US Federal Aviation Administration gave formal approval yesterday for a new lithium-ion battery system for Boeing's 787 Dreamliner, ending a three-month ban and clearing airlines to fly the plane with passengers again.

The FAA's "airworthiness directive" technically applies just to United Airlines, which so far is the only US carrier with the new high-tech jet, but it will set the standard that regulators in Japan, Europe and elsewhere will follow. Other US carriers with 787s on order will eventually come under the new rule.

The FAA pegged the cost of repairing United's six jets at about US$2.8 million.

The approval caps a tumultuous period for Boeing and its airline customers, beginning when two lithium-ion batteries overheated on two Dreamliners in separate incidents less than two weeks apart in January.

The two planes are owned by Japan Airlines and All Nippon Airways, which together own nearly half the fleet of 50 Dreamliners delivered so far. The ban on flights effectively halted deliveries of new planes to customers.

Boeing devoted thousands of hours to developing a fix, even before investigators found what caused the batteries to overheat, emit smoke and, in one instance, catch fire. That probe continues, led by the US National Transportation Safety Board.