That raises the question of whether there were different causes for the fire in Boston and the Jan. 16 incident aboard an All Nippon Airways plane, where the battery smoldered but flames were not reported.
ANA confirmed this week that it replaced three circuit boards located in 787 electronics bays after pilots received an error message during flights in March, April and June of last year. One of those circuit boards had a “slight discoloration,” said ANA spokeswoman Nao Gunji. Nothing wrong was found with the other two, but they were replaced as a precaution, she said.
While Boeing conducted some battery testing itself before the FAA approved the 787s for flight, key tests on the battery and charging system were carried out by Thales, the French company that makes the 787's electrical system, and by GS Yuasa, the Japanese company that makes the battery, the NTSB documents showed.
The tests included a fault tree analysis, which looks at what happens as things successively go wrong with a battery. The tests were reviewed by Boeing workers, as well as another group of Boeing workers who are the FAA's authorized representatives to make sure the batteries met FAA requirements.
Boeing classified the possibility of a battery fire as “catastrophic” and built in extra safeguards to prevent overcharging.
The 787 is Boeing's newest and most technologically advanced plane. It is the world's first airliner made mostly from lightweight composite materials. It also relies on electronic systems rather than hydraulic or mechanical systems to a greater degree than any other airliner. And it is the first airliner to make extensive use of lithium ion batteries, which are lighter, recharge faster and can hold more energy than other types of batteries.
Boeing has billed the plane to its customers as 20 percent more fuel efficient than other midsized airliners. That's a big selling point, since fuel is the biggest expense for most airlines.
Airlines have been forced to tear up their schedules while the planes are out of service. United Airlines recently cut its six 787s from its flying plans at least until June and postponed its new Denver-to-Tokyo flights. United is the only U.S. carrier with 787s in its fleet.
LOT Polish Airlines has said the grounding of its two 787s is costing it $50,000 per day. The airline has said it will ask Boeing for compensation. Norwegian Air Shuttle, which was due to receive 787s this year, said it will lease two Airbus A340s along with flight crews for its planned New York-to-Bangkok flights if it doesn't get its 787s on time. The airline is allowing customers on 787 flights to change their flight date or get a refund, but “very few have taken advantage of this offer,” spokesman Laase Sandaker-Nielsen said Thursday.
Boeing is still building 787s, but deliveries are halted. It has not said how much the battery problems will cost.
UBS analyst David Strauss estimated Boeing will burn some $6 billion in cash on the 787 this year — and that's even if it delivers more than 60 of them. Every missed 787 delivery adds as much as $120 million to the plane's cash burn this year, he estimated in a note on Tuesday.