Lithium batteries that can leak corrosive fluid and start fires have emerged as the chief safety concern involving Boeing's 787 Dreamliner.
The problem is apparently far more serious than government or company officials acknowledged less than a week ago.
The US Federal Aviation Administration (FAA) grounded Boeing's newest and most technologically advanced jetliner until the risk of battery fires is resolved. The order applies only to the six Dreamliners operated by United Airlines, the lone US carrier with 787s. Others quickly followed suit.
Japan's two largest air carriers voluntarily grounded their 787s ahead of the FAA's order following an emergency landing by one of the planes in Japan. The European Aviation Safety Agency ordered all European carriers to ground the jetliner.
Only hours before the FAA issued its order, Transportation Secretary Ray LaHood reiterated to reporters that he considers the plane safe and wouldn't hesitate to fly one. LaHood and FAA administrator Michael Huerta unequivocally declared the plane safe at a news conference even while they ordered a safety review of the aircraft.
However, as details emerged of two battery failures only 10 days apart, it became apparent that the FAA wouldn't be able to wait for its safety review.
An inspection of the All Nippon Airways 787 that made an emergency landing in western Japan found that electrolytes, a flammable battery fluid, had leaked from the plane's main lithium-ion battery. Investigators found burn marks around the damage.
Transport ministry investigator Hideyo Kosugi said the liquid leaked through the electrical room floor to the outside of the aircraft.
In the first battery incident on January 7, it took firefighters 40 minutes to put out a blaze centred in an auxiliary power unit of a Japan Airlines 787. The plane was empty, shortly after landing at Boston's Logan International Airport.
The two incidents resulted in the release of flammable electrolytes, heat damage and smoke, the FAA confirmed. The release of battery fluid is especially concerning, safety experts said. The fluid is extremely corrosive, which means it can quickly damage electrical wiring and components.
The electrolyte fluid also conducts electricity, so as it spreads it can short circuits, interfere with signals and ignite fires.
The 787 is the first airliner to make extensive use of lithium-ion batteries to help power its energy-hungry electrical systems. The batteries charge fast and can be moulded to shapes.
Mike Sinnett, chief engineer on the 787, said the plane's batteries have operated through a combined 1.3 million hours and never had an internal fault. He said they were built to ensure that failures "don't put the airplane at risk".
Rechargeable lithium batteries are most widely used to power consumer electronics such as laptops and mobile phones.
Shipments of lithium batteries are suspected of causing or contributing to the severity of fires that caused two cargo jets to crash since 2010.