January 21, 2013
Credit: Photo Credit: Reuters/Kyodo/Landov
While the full fallout 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 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 over the question of adopting or even studying different battery technology, saying 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 lithium-ion battery's high power and energy density and 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 (ICAO) 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 jet in 2010 as the first aircraft to enter service with lithium-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 also allowed the CJ4 to be certificated under special conditions that included added safety precautions for use of the lithium-ion battery.
In the case of the 787, two 32-volt lithium-ion primary batteries provide power as key elements of the aircraft's more-electric architecture. The main battery, located forward in the electric/electronic (E/E) equipment bay below the cabin floor by the front passenger doors, provides power for aircraft start-up, ground operations such as refueling and towing, and acts as backup 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.