January 18, 2013
Credit: Photo Credit: NTSB
While the full fall-out from the grounding of the Boeing 787 fleet following two separate battery failures remains as yet unknown, there is at least one aspect over which there can be little argument.
The basic physics of the lithium-ion battery at the center of the 787 investigation cannot be changed and the focus of the investigation has already shifted rapidly from whether the safety precautions in Boeing’s design were sufficiently adequate to more urgent questions over how quickly they can be modified.
Spurred on by the U.S. airworthiness authority’s emergency directive, the U.S. National Transportation Safety Board (NTSB) probe and the broader FAA-led report will determine with Boeing what modifications are required to the battery-related aspects of the electrical system as well as whether the fire containment or protection system can, and should be, augmented. In the most extreme scenario for Boeing, this could conceivably lead to a change to alternate batteries, a new test effort, certification and modification program.
Until now, Boeing has remained unequivocal about the question of adopting or even studying different battery technology and says simply, “We have no such plans at this time.” Outwardly at least the company remains confident in its choice of technology, which was driven by the high power and energy density of the li-ion battery, its low maintenance requirements and low installed weight.
Yet the worldwide groundings, combined with NTSB images of the charred remains of the battery from the Boston incident, add to a growing litany of industry and public unease over the use of lithium-ion technology in aircraft. Even carrying lithium batteries as air cargo has proved lethal and prompted the International Civil Aviation Organization to issue stringent new rules governing their carriage as recently as Jan 1. Fires erupting in this type of battery, carried as cargo, were prime suspects in separate accidents involving two Boeing 747 freighters and a DC-8.
According to FAA figures, not counting the recent events, lithium batteries make up almost 80% of the 33 instances in which batteries have ignited on aircraft since 2009. Cessna, which introduced the CJ4 business aircraft in 2010 as the first aircraft to enter service with li-ion batteries, was forced to replace them with nickel-cadmium after a battery fire on an aircraft in 2011. As with the 787, the FAA had allowed the CJ4 to be certified under special conditions which included added safety precautions for use with the li-ion battery.
In the case of the 787, two 32-volt li-ion primary batteries provide power as key elements of the aircraft’s more-electric architecture. The main battery, located forward in the electric/electronic equipment bay below the cabin floor by the front passenger doors, provides power for aircraft startup, ground operations such as refueling and towing, and acts as a back up power for the electrically actuated brake system. It can also assist the second battery, located in the aft E/E bay, in starting up the auxiliary power unit (APU) and, in the event of a power failure, energizes essential flight instruments in the flight deck until the drop-down ram air turbine spools up.
The battery that caught fire on the Japan Airlines 787 in Boston was the second main battery. This unit’s primary purpose is to electrically start the APU when neither of the engines is running and the aircraft is not connected to external ground power. In this case, the battery energizes the right hand of the two starter/generators connected to the APU. The aft battery also provides another minor role, namely power to the navigation lights during battery-only towing operations. The unit in the second incident, which forced an ANA 787 to make an emergency landing in Japan on Jan. 16, involved the main battery in the forward E/E bay. In this case, there was less damage, though spilled electrolytes, fumes and minor thermal damage indicated signs of overheating.