Boeing admits the hunt for battery fault is inconclusive as replacement battery systems are fitted to 787 Dreamliners.
Larry Loftis, Boeing’s General Manager of the 787 division, said "It is possible we will never know the root cause. It is not uncommon not to have found the single root cause. So industry best practice is to look at all the potential causes and address all of them."
The batteries are only in use when the planes are on the ground to power brakes and lights. Speaking at a press conference, Loftis said 3000 engineers spent 200 000 hours investigating the problems before admitting the cause may never be known.
"We did an exhaustive study of potential causes, and addressed all of them. We do feel that with all the work we have done, we have tackled the potential problems." Loftis added.
When the planes are operational again, the batteries will have additional safety features, such as cooler working temperatures and ventilation from the stainless steel enclosures to the exterior of the plane to contain the battery should it encounter problems and vent any gases or smoke immediately.
Randy Tinseth, Vice President of Boeing Commercial Airplanes said: "The battery is now contained in stainless steel, so should there be overheating, there is no chance of flames or fire because there's no oxygen present. If there were any fumes from a fire there's no chance of entering the cabin or cockpit.”
The cost of replacing the batteries has not yet been disclosed. The planes are expected to resume flights in the next few weeks.