The crew of a Japan Airlines Dreamliner loaded with 181 passengers apparently was unaware of fuel spewing from a wing as the jetliner prepared to thunder down the runway on Tuesday in Boston.

It was only due to an alert from the pilot of another plane that Flight 7's takeoff for Tokyo was abandoned and the Boeing 787 towed to the gate, the second problem in two days for a JAL Dreamliner at Logan International Airport.

An electrical fire on Monday damaged an empty Dreamliner on the same tarmac.

The unusual twin incidents added to service questions about the highly touted plane that experienced a very difficult development and clearly has growing pains, according to safety experts.

Boeing's chief project engineer for the 787 said in a conference call with reporters Wednesday that he is "100 percent convinced the airplane is safe to fly."

"There are issues we have seen that we will need to work through, and just like any new airplane program we work through those issues and we move on," said Mike Sinnett.

The fuel leakage was due to an open valve, Japan Airlines spokeswoman Sze Hunn said Wednesday.

The leak came from the left wing surge tank vent, Hunn said.

"Further inspection of the cockpit messages showed that one of four valves connecting the center tank and left main tank was opened and had resulted in fuel flowing from the center tank to the left main tank and subsequently into the surge tank near the wing tip and out the vent," Hunn said.

"The valve that the indicator showed was opened (the left outboard refuel valve), was deactivated/made inoperative and the flight was cleared to depart again," Hunn said in a statement.

Air traffic control recordings from LiveATC.net captured Tuesday's incident as the the wide body was on the taxiway.

"Hey, that Japan Air may know it but they have fuel spewing out the leftward wing quite a bit," the pilot of another plane told the control tower, which radioed the JAL crew and halted takeoff.

"You mean fuel leak from left wing?" came the response from the JAL cockpit, according to LiveATC.net.

"Yes ... there appears to be a fuel leak from your left wing," controllers said again.

Airport fire and cleanup crews responded to the spill.

The Federal Aviation Administration said it was investigating the matter, but the National Transportation Safety Board said it would not do so.

No safety board involvement indicated the reason behind the leak was probably determined quickly and remedied. The flight took off later in the day.

It appears Monday's electrical fire that injured a firefighter was a more pressing issue for investigators, the manufacturer and the global airline industry that has embraced the 787 as a technologically advanced and efficient long-haul aircraft.

Fire in the belly of the aircraft broke out not long after arriving in Boston from Tokyo. All of the 172 passengers and 11 crew had already disembarked.

Boeing said in a statement that the fire was traced to a battery unit that helps power electrical systems when the engines are idle -- typically while a plane is being serviced or cleaned. The Dreamliner was being readied at the time for a return flight to Japan.