While the Boeing 787’s main lithium-ion batteries have been cleared in last Friday’s Dreamliner fire in London, another type of lithium battery might have contributed to the blaze, which caused severe damage to the crown of the carbon-fiber fuselage.
Investigators there are urging U.S. aviation officials to conduct a safety review of the aircraft’s emergency locator device.
Britain’s Air Accidents Investigation Branch published the recommendation Thursday, less than a week after an unoccupied Ethiopian Airlines 787, parked at Heathrow Airport, caught fire.
Because the 787 is U.S.-built, the FAA has primary authority over its certification and safety.
An emergency locator transmitter (ELT) is a self-powered radio that helps searchers find a downed airplane. The 787’s main systems were not powered when the fire broke out.
The AAIB’s initial report has cleared the jet’s lithium-ion batteries, which are part of the main power system. In January, the FAA grounded the Dreamliner for three months following battery problems on two 787s, one of which involved a fire. The FAA approved a revised battery system design and cleared the 787 to return to service in April.
But the batteries which power the ELT could be the cause of the latest 787 problem. Those batteries are lithium-manganese-dioxide cells.
“Detailed examination of the ELT has shown some indications of disruption to the battery cells,” the report states. “It is not clear however, whether the combustion in the area of the ELT was initiated by a release of energy within the batteries or by an external mechanism such as an electrical short. In the case of an electrical short, the same batteries could provide the energy for an ignition and suffer damage in the subsequent fire.”
The AAIB noted in its report that problems with the Honeywell locator beacon have been extremely rare and that this was the first of about 6,000 units in service to have a “thermal event.”
However, “large transport aircraft do not typically carry the means of fire detection or suppression in the space above the cabin ceilings and had this event occurred in flight it could pose a significant safety concern and raise challenges for the cabin crew in tackling the resulting fire,” the British investigators wrote.
The result of the London fire was “extensive heat damage in the upper portion of the rear fuselage, with significant thermal effects on aircraft insulation and structure.”
The fire was first spotted from the airport’s air traffic control tower.
“Fire fighters equipped with breathing apparatus entered the aircraft at the L2 door and encountered thick smoke,” the report says. “As they moved to the rear of the aircraft the smoke became denser so they opened further cabin doors to clear the smoke. At the rear of the passenger cabin they observed indications of fire above the ceiling panels. They attempted to tackle the fire with a handheld ‘Halon’ extinguisher but this was not effective, so they forcibly moved a ceiling panel and tackled the fire with water from hoses. This was effective and the fire was extinguished.”
In a statement, Boeing said it supports the AAIB’s recommendations. The Chicago-based company called the precautionary action “reasonable” and said it will work with customers and regulatory authorities. “We are confident the 787 is safe and we stand behind its overall integrity,” the company said.
Boeing spokesman Marc Birtel noted that the transmitter isn’t required by U.S. aviation rules but is required by some foreign regulators for their airlines or their airspace.
Birtel said the transmitter takes about an hour to remove from a 787.
Said Honeywell in a statement: “Temporarily addressing the (transmitters) on Boeing 787s as a precautionary measure is prudent.”
Boeing’s stock price rose 2.7 percent Thursday, closing at $107.63.
The Associated Press contributed to this report.