February 04, 2013
Credit: Photo Credit: Cessna Aircraft
Two years ago, Boeing, Cessna and Gulfstream were the leading edge for introducing lithium-ion main-ship batteries into new aircraft in the civil aviation market. But by late 2011, evidence had emerged that the technology was not yet mature, spurring business aircraft makers Gulfstream and Cessna to return to more traditional, lower-performance and heavier batteries for the G650 and CJ4, respectively. Boeing however went forward with its original choice of lithium-ion batteries for the 787 widebody, a decision that is now under the microscope given the grounding of the fleet (see p. 20).
Gulfstream decided to switch battery types barely a year before the G650's final FAA certification in September 2012, and Cessna abandoned the lithium-ion batteries on the nascent CJ4 fleet less than two years after first delivery. The abrupt reversal followed a November 2011 FAA emergency airworthiness directive (AD) involving a thermal runaway and fire in a CJ4 battery on the ground. Both Cessna and Gulfstream say they could revisit lithium-ion battery technologies in the future but offered no timetables.
They are not alone. Embraer too is planning to use lithium-ion batteries and associated electronics built by Meggitt subsidiary Securaplane on the new Legacy 500 and 450 business jets, slated for entry into service in late 2013 and 2014, respectively. Securaplane was also to be the supplier of lithium-ion batteries and systems for the G650. Embraer is holding to its plans at the moment, though officials say the company is watching closely the FAA's deliberations on the Boeing batteries.
Gulfstream's decision to switch batteries so close to the final certification of its flagship $65 million G650 ultra-long-range business jetsurprised some industry insiders. The company had declared its intention to use lithium-ion batteries in marketing materials starting in 2008, and in June 2011 selected Securaplane to supply the main battery as well as the emergency and flight-control backups, along with integral charging and control electronics. In January 2012, the FAA granted “special conditions” that Gulfstream could use to certify the lithium-ion batteries, virtually the same nine conditions that Boeing had received for the 787 batteries in 2007 (see p. 22).
Gulfstream launched an internal battery-test program in parallel with a flight-test effort that used legacy nickel-cadmium batteries in the flight-test aircraft. According to Gulfstream officials, the lithium-ion battery could not pass the gauntlet of internal tests, and in late 2011, they decided the technology was too unstable. Securaplane documents show that Gulfstream was to use a lithium-iron-phosphate coating on the cathode and says the alternative nickel-cadmium batteries weigh 150 lb. more. The 787's batteries use a lithium-cobalt oxide powder as a cathode coating. As a comparison, a lithium-ion battery using a cobalt oxide cathode has five-times the energy density of a nickel-cadmium battery, though nickel-cadmium has twice as many cycles of battery life.
Like Gulfstream, Cessna knew the risks of lithium-ion batteries but believed that its chemical formula and extensive company-funded testing rendered them safe. In August 2009, the FAA approved special conditions allowing Cessna to certify the batteries, pending certification tests.
Post-Boeing's 787 battery incidents, Cessna has not commented on the type of lithium-ion battery it used for the CJ4. However, a research paper written in part by its then-principal engineer for technical development, John Gallman, discusses the nanoscale phosphate-based lithium-ion cathodes Cessna used and the rigorous ground- and flight-testing program it conducted. Testing was based on a modified version of RTCA guidelines for nickel-cadmium batteries as lithium-ion-specific guidelines had not yet been completed. The installed batteries and charging systems for the CJ4 were built by A123 Systems. Gallman left Cessna in 2011 to become division director of Mid-Continent Instruments' True Blue Power, a distributor of A123 batteries.
The CJ4's phosphate-based lithium-ion batteries weighed 30 lb. less than the equivalent nickel-cadmium battery that was available. Though packing about half the energy density of a cobalt oxide cathode battery, the phosphate-based chemistry has four-times the number of life cycles while having “inert” failure modes, according to Gallman.