US transport safety regulators have asked Boeing for a full operating history of the lithium-ion batteries used in its grounded 787 Dreamliners.
The National Transportation Safety Board said it made the request after recently becoming aware of incidents that occurred before a January 7 battery fire in a 787 parked at Boston's Logan International Airport.
All 50 of the Boeing 787s in use around the world were grounded after an ANA flight on January 16 made an emergency landing in Japan when its main battery overheated. Lithium-ion batteries are prone to overheating and require additional safeguards to prevent fires.
Laura Brown, a spokeswoman for the US Federal Aviation Administration, said in Washington that the agency was checking whether the previous battery incidents had been reported by Boeing.
With 17 of the jets, ANA was Boeing's launch customer for the technologically advanced airliner. The airline has had to cancel hundreds of flights, affecting tens of thousands of people, but has sought to minimise disruptions by switching to other aircraft as much as possible.
The battery problems experienced by ANA before the emergency landing were first reported by The New York Times.
Japanese and US investigators looking into the Boeing 787's battery problems shifted their attention this week from the battery-maker, GS Yuasa of Kyoto, Japan, to the manufacturer of a monitoring system. That company, Kanto Aircraft Instrument Co, makes a system that monitors voltage, charging and temperature of the lithium-ion batteries.
Yesterday the US National Transportation Safety Board said it was conducting a chemical analysis of internal short circuiting and thermal damage of the battery that caught fire in Boston.
The probe was also analysing data from flight data recorders on the aircraft, the NTSB said on its website.