In 2007, US regulators cleared Boeing's use of a highly flammable battery in the 787 Dreamliner, deciding it was safe to let the lithium-ion battery burn out if it caught fire mid-air as long as the flames were contained, and smoke and fumes vented properly, according to documents reviewed by Reuters.
Fire risk on planes has always been a major concern, especially given the amount of fuel they carry and the heat generated by jet engines. US aviation standards require planes to have numerous on-board fire-suppression systems.
But through a review of government documents and interviews with aviation and battery experts, Reuters found that the US Federal Aviation Administration (FAA) granted the Dreamliner special conditions and said its contain-and-vent system was sufficient to control the build-up of explosive or toxic gases, except in situations considered "extremely remote".
The FAA's 2007 decision is now coming under scrutiny after the lithium-ion batteries in two 787 planes failed within days of each other, sparking a fire in Boston, and generating warnings and an acrid smell that prompted the pilots of the second plane to make an emergency landing in Japan.
A key US Senate committee plans to hold a hearing in the coming weeks to examine aviation safety oversight and the FAA's certification of the 787, an aide to the Senate Commerce, Science and Transportation Committee told Reuters.
The FAA has grounded the Dreamliner in the US pending an investigation, and other aviation regulators around the world immediately followed.
The review has broad implications for other aircraft makers, including EADS unit Airbus, which also had to meet special conditions set by the FAA to use lithium-ion batteries on the A380 – a superjumbo jet that carries about 550 passengers.
A spokesperson for the FAA defended the 2007 approval, saying: "The whole aviation system is designed so that if a worst case happens, there are systems in place to prevent that from interfering with other systems on the plane."
Boeing said the 787's battery system had four layers of protection to prevent the battery from overcharging, making a fire extremely unlikely. The company said it was confident the battery could safely burn out.
The cause of the two 787 battery failures is not yet known and investigators are still determining how the contain-and-vent systems performed.
But the incidents have revived a debate on the safety of lithium-ion batteries and raised questions over whether the FAA should have consented to their use in the 787.
Depending on the outcome of the review, Boeing could face steep costs, ranging from compensating airlines to a possible major redesign and re-certification of the battery or electrical system, industry experts say.
Boeing has not commented specifically on the battery failure in the Japan incident. In the case of the Boston plane, Boeing said smoke got into the cabin because the 787 was on the ground without cabin pressure to redirect airflow.
Some experts cautioned against a rush to judgment about lithium-ion battery technology, saying the key was to understand failure rates and design a safe system.
"Everyone knew these dangers, but after it was designed, there were multiple tests and that's why it's in the final plane," said Yoshitomo Aoki, a Japanese aviation commentator.
"In no way would a fire like this lead me to say you should never have a lithium-ion battery on an airplane. That's just the wrong way to go," said Daniel Doughty, who worked on battery technology during 27 years at Sandia National Laboratory.
But Mr Doughty said the FAA's earlier decisions deserved scrutiny. "It's fair to ask about the approval process," Mr Doughty said. "There needs to be some explanation and defence of whatever they did." (Reuters)