Boeing 787 battery fire was difficult to control

The National Transportation Safety Board has released 547 pages of reports and supporting materials about its investigation of the January airplane battery fire in Boston that led to the grounding of the Boeing 787.

The documents show firefighters struggling to tame a small but worrisome fire.

The smoking, hissing battery smoldered inside the belly of the parked 787 in Boston. When firefighters tried to take the battery off the plane, its six bolts held it fast. Firefighters tried a pry bar, but the battery wouldn't budge.

They finally cut it loose with a battery-operated tool and, using straps, hauled the 63-pound battery about 50 feet from the plane.

Another smoldering battery nine days later in Japan prompted the grounding of 50 787s worldwide. Investigators still don't know the root cause.

United Airlines has postponed the launch of their new route from Denver to Tokyo while federal safety agencies continue to review the Boeing 787 Dreamliner.

According to a statement from the airline, they now plan to start the route on May 12.