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The events were the latest in a series of problems with the 787, which entered commercial service in November 2011 and has been hit by technical and electric malfunctions since then. Boeing delivered 46 planes last year, more than any analyst had predicted, and has outlined ambitious plans to double its production rate to 10 planes a month by the end of this year.

Much rides on the success of the 787 for Boeing, which expects to sell 5,000 of the planes in the next 20 years. The basic model has a list price of $206.8 million, but early customers typically received deep discounts to make up for the production delays and teething problems. All this means it could be years before Boeing starts recouping its investment costs and turning a profit on the planes.

Shares of Boeing dropped 2.6 percent to $74.13 on Tuesday, extending Monday's drop of 2 percent.

The 787 makes extensive use of new technology, including a bigger reliance on electrical systems, and is built mostly out of lightweight carbon composite materials. While the problems so far do not point to serious design problems with the airplane, they represent an embarrassment to Boeing's manufacturing ability.

"None of this is a showstopper, and none of this should signal this product is fundamentally flawed," said Richard Aboulafia, an aerospace analyst at the Teal Group, a consulting firm. "But whether these are design glitches or manufacturing glitches, either way it's a serious hit to Boeing's image."

Both of this week's incidents affected planes operated by Japan Airlines at Logan International Airport in Boston.

The fuel leak on Tuesday was spotted by another pilot as JAL Flight 007, bound for Tokyo, was taxiing and getting ready to take off, said Richard Walsh, a spokesman for the Massachusetts Port Authority. The plane was towed back to its gate and the 40-gallon leak cleaned up.

The flight with 178 passengers and 11 crew members, scheduled to take off at noon, eventually left Boston at 3:47 p.m.

On Monday, an electrical fire on a 787 was traced to a battery connected to the plane's auxiliary power unit, which runs electrical systems when the plane is not getting power from its engines.

The fire broke out about 30 minutes after the flight landed from Tokyo, and all 183 passengers and crew members had left. The smoke was first detected in the cabin by maintenance and cleaning personnel who were on the parked plane and contacted the airport's fire department.

The National Transportation Safety Board, which is investigating Monday's incident, said the battery had "severe fire damage."

New planes often experience problems, particularly in the first few years of production. But the succession of issues with the 787, which has already been marred by production delays of years, has revived concerns about the plane's reliability and safety.

Last month, the Federal Aviation Administration ordered inspections of fuel line connectors on all 787s, warning of a risk of leaks and fires. Separately, a United Airlines 787 was also diverted in December after one of six electrical generators failed in flight.

In a statement, Boeing said on Tuesday that it saw no relationship between Monday's battery problem and previous incidents with the 787's power system, which involved faults in power panels elsewhere in the electrical equipment bay.

"Boeing is cooperating with the N.T.S.B. in the investigation of this incident," the company said. "Before providing more detail, we will give our technical teams the time they need to do a thorough job and ensure we are dealing with facts, not speculation."

A Boeing spokesman, Marc Birtel, said the plane maker was aware of the fuel leak incident but declined to comment.

A spokeswoman for Japan Airlines in Tokyo said the company was still gathering the details surrounding the two incidents, and that there were no plans to change its orders for 787s. The airline has seven 787s already in service, and 38 more on order. The spokeswoman declined to be named, citing company policy.

United Airlines, currently the only airline in the United States operating 787s, said it had performed inspections on all six of its 787s after Monday's incident. It did not cancel any of its flights today, said Mary Ryan, a spokeswoman for the airline. She said United "continues to work closely with Boeing on the reliability of our 787s."

But she declined to comment on a report in The Wall Street Journal that said the airline had found improperly installed wiring in components associated with the auxiliary power unit.