Sometime in 2011 (we can’t be sure when), an airport worker hooked up an energized ground-power unit to a Cessna Citation CJ4 (525C), according to the FAA. The CJ4 was the first business jet certified with a lithium-ion main-ship battery. For whatever reason, after the ground-power unit was hooked up to the CJ4, something happened, and the result was, the FAA wrote, “a report of a battery fire.”
The agency declined to provide any more detail about the nature of this incident, whether the ground-power unit was hooked up correctly, if the CJ4’s switches were set properly, whether the battery was in a highly discharged state, excessively cold or hot or any other information that could shed more light on why the battery apparently caught fire. The FAA, in fact, doesn’t even make clear whether the battery actually caught fire or if some other element, such as nearby wiring, burned. Cessna Aircraft also declined to provide more information about this incident. However, the result was an emergency AD, calling for replacement of all CJ4 lithium-ion main-ship batteries with a heavier nickel-cadmium or lead-acid battery.
Ask about lithium battery safety, and pundits will rattle off a list of incidents that seem to point to a higher risk of thermal runaway and catching fire compared with other battery types such as lead-acid, nickel-cadmium and nickel metal hydride. Chevy Volts are exploding, you will hear, and iPhones and iPads and laptops are burning in airplanes.
The Volt does use lithium-ion batteries, but it suffered a fire after a series of test crashes. The crashes released liquid coolant that keeps the batteries at optimal temperatures, which then shorted out the batteries, causing a fire weeks later. There are no verified cases of owner-driven Volts catching fire. As a result of the tests, Chevrolet modified the battery pack design to prevent the coolant leakage from causing a fire.
In a guide about vehicles equipped with high-voltage batteries, the National Highway Traffic Safety Administration wrote, “NHTSA does not believe that electric vehicles present a greater risk of post-crash fire than gasoline-powered vehicles. In fact, all vehicles–both electric and gasoline-powered–have some risk of fire in the event of a serious crash.”
The spontaneous combustion of an Apple iPhone on an Australian Regional Express Saab 340B that was taxiing to the gate at Sydney in 2011 was due to an improper repair, according to a report from the Australian Transport Safety Bureau. Investigative firm Exponent, overseen by the FAA, found that a misplaced screw was left in the iPhone’s battery bay, damaging the battery and causing a short-circuit, which then caused thermal runaway. A repair to replace a broken screen had been done by a non-Apple-authorized facility. While the ATSB recommends not carrying lithium-ion-powered mobile devices in checked luggage, it also found, “There is no previous record in the ATSB’s databases of self-ignition involving mobile telephones or other portable electronic devices on an aircraft in Australia.”
According to a 2008 report on battery fires by the University of Alberta Department of Biological Sciences included the following three incidents that occurred on aircraft: a 2004 fire in a carry-on bag before takeoff, caused by a cordless drill with a nickel-cadmium battery; a 2006 fire involving an airplane on the ground caused by a spare lithium-ion computer battery in a computer bag; a 2007 battery fire in a carry-on bag (battery type not specified).
A search of NASA’s Aviation Safety Reporting System (ASRS) and the FAA’s Accident/Incident Data System (AIDS) databases found nine lithium-related incidents and 12 nickel-cadmium-related incidents. One of the lithium incidents involved the medicine, and two related to concerns about cargo loads that might not have been properly labeled.
These incidents highlight a bit more about the real risks of any battery technology. And it is interesting to note that there are few reports of lithium-battery problems with mobile devices. Nickel-cadmium and lithium batteries are everywhere; if they were as terribly risky as some people fear, then there would have been far more cases of mobile phones, tablets and laptop computers spontaneously combusting. That this hasn’t happened is a pretty good indicator of the relative safety of lithium technology, at least for small batteries. We don’t have information, yet, for larger lithium battery applications, but it won’t be long as all sorts of electric cars are filled with large banks of lithium-ion batteries.
New airplanes such as Boeing’s 787, Gulfstream’s G650 and the Citation Ten are or will be equipped with lithium-ion main-ship batteries. The Airbus A380 uses lithium-ion batteries for emergency lighting. The FAA has acknowledged the fact that certification regulations don’t cover this technology and has issued special conditions for lithium-ion battery installations. This occurred also when nickel-cadmium batteries became standard in aircraft, according to the FAA: “Increased use of nickel-cadmium batteries in small airplanes resulted in increased incidents of battery fires and failures, which led to additional rulemaking affecting large, transport-category airplanes as well as small airplanes.”
In justifying the special conditions for lithium batteries for the G650, the FAA went on to explain, “The proposed use of rechargeable lithium batteries and rechargeable lithium-battery systems for equipment and systems on the [G650] has prompted the FAA to review the adequacy of these existing regulations. Our review indicates that the existing regulations do not adequately address several failure, operational and maintenance characteristics of rechargeable lithium batteries and rechargeable lithium-battery systems that could affect the safety and reliability of the [G650] rechargeable lithium batteries and rechargeable lithium-battery-system installations.
“At present, commercial aviation has limited experience with the use of rechargeable lithium batteries and rechargeable lithium-battery systems in aviation applications. However, other users of this technology, ranging from wireless telephone manufacturers to the electric vehicle industry, have noted safety problems with lithium batteries. These problems include overcharging, over-discharging and cell-component flammability.”
The FAA special conditions document explained, “In general, lithium batteries are significantly more susceptible than their [nickel-cadmium] or lead-acid counterparts to internal failures that can result in self-sustaining increases in temperature and pressure (thermal runaway). This is especially true for overcharging, which causes heating and destabilization of the components of the lithium-battery cell, which can lead to the formation, by plating, of highly unstable metallic lithium. The metallic lithium can ignite, resulting in a self-sustaining fire or explosion. The severity of thermal runaway due to overcharging increases with increased battery capacity due to the higher amount of electrolyte in large batteries.”
The other problem addressed by the special conditions is flammability of the electrolyte, according to the FAA. “Unlike [nickel-cadmium] and lead-acid cells, some types of lithium-battery cell use flammable liquid electrolytes. The electrolyte can serve as a source of fuel for an external fire if the cell container is breached.” The special conditions address not only installation but also maintenance instructions.
Lithium Battery Makers
A variety of companies are working on lithium battery technology for aircraft applications, ranging from Mid-Continent Instrument’s True Blue Power division (backup power systems) to Securaplane Technologies (G650 batteries) and Cessna (Citation Ten).
Cessna didn’t confirm to AIN whether it is developing the battery for the Citation Ten on its own, but that appears to be the case. “Cessna constantly researches new technologies, such as the Li-ion battery, to incorporate into our product lines,” a spokeswoman told AIN, “while ensuring that these new options meet our customers’ needs in the marketplace. We are currently in a more than year-long process of testing the Li-ion battery for use in our business jets. The Li-ion battery has great benefits for aviation use and as long as those benefits meet our customers’ needs, we will continue to look at the Li-ion battery as a viable option.”
Another source told AIN that Cessna had developed the CJ4 battery internally. According to the FAA emergency airworthiness directive, this battery was made using A123 Systems nanophosphate lithium-ion battery technology. We asked both Cessna and A123 questions about what happened to the CJ4 battery, but both companies declined to respond. Incidentally, special conditions applied to the CJ4 battery, and Cessna did comply with those.
Mid-Continent has a strong relationship with A123 and in June announced an agreement to be the distributor and supplier of A123 technology for aviation applications. The company uses the A123 technology in its True Blue Power emergency power supply, the first of which is the FAA-approved MD-835. This unit is 66 percent lighter and has a five-time greater lifetime than the comparable power supply made using a lead-acid battery, according to True Blue Power division director John Gallman.
In fact, Mid-Continent never adopted nickel-cadmium technology and went straight from lead-acid to lithium-ion. “Pretty much any place where use a battery today, lithium-ion probably can step in and in most cases do the job better,” said Todd Winter, Mid-Continent president and CEO.
Winter expects to see a number of new applications for lithium-ion batteries in aviation, and Mid-Continent is already working with many manufacturers to explore using the A123 technology. He also predicts that A123 batteries will be found in more main-ship batteries because although more expensive initially, the batteries will be more cost effective over their lifetime.
While many battery makers employ lithium-iron phosphate chemistry, A123’s secret sauce is nanophosphate technology. The A123 batteries use lithium-iron phosphate chemistry, but the cathode surface material inside the battery is impregnated with tiny graphite particles, which adds surface area so the battery delivers, according to an A123 white paper, “higher power, excellent safety, long life and greater usable energy.”
Another advantage of nanophosphate technology, according to Gallman, is that “it is more abuse-tolerant and less reactive when the product is abused.” Products using A123 batteries still require protection circuits to prevent over-charging or other problems that could lead to thermal runaway. But in a nanophosphate battery, he said, the chemical reaction that leads to a thermal runaway is less energetic than in ordinary lithium-iron phosphate batteries.
When working with customers to develop lithium battery products, Mid-Continent offers three options: providing the A123 batteries to a customer who knows how to make a battery and protection circuits and offering consulting services; providing a module of battery cells already welded together (this is a special skill by itself) and the customer makes the protection circuitry; or making a complete solution, including the batteries and safety/performance-management circuitry.
According to a Securaplane spokesman, the batteries developed for the G650 use lithium-iron phosphate technology, which “is more tolerant to abusive conditions such as excessive ambient temperature or excess voltage charge conditions, and mechanical shock/crush conditions outside of specification. Securaplane cells may be overcharged or punctured without demonstrating any flame.”
Features that keep the batteries safe include the cell design itself and high discharge capacity and a built-in charger, which, according to Securaplane, “result in excellent charge recovery rate from 100 percent depth of discharge (less than 60 minutes to 90-percent-charged condition), ensuring effective charge recovery following a complete discharge event. The cell/electronic architecture is configured to allow multiple levels of failure redundancy. Loss of several cells [is] required before loss of required function is realized. Modular cell pack design allows cells to be readily replaced at end of life or due to individual cell failure. Unique thermal monitoring and cell balancing during discharge ensures maximum battery capacity even after many internal cells have reached end of life.”
For Gulfstream’s G650, Securaplane is developing not only main-ship batteries but also emergency and flight control batteries (for the fly-by-wire controls). The total weight saving for the G650, compared with lead-acid or nickel-cadmium batteries, is about 170 pounds, the spokesman said. And the lithium batteries take up half as much space and have an energy density twice that of lead-acid or nickel-cadmium.
The lithium batteries are also much easier to maintain, with “built-in chargers, push-to-test state-of-charge and health determination, less scheduled maintenance, Arinc 429 interface, MSG-3 maintenance and internal heaters for faster dispatch,” he explained. “The G650 will use nickel-cadmium batteries on entry-into-service,” according to a Gulfstream spokeswoman. “We may look at using lithium-ion inthe future as the technology surrounding those batteries matures.”
Concorde Battery is now developing its own line of lithium-iron phosphate batteries, according to Dave Vutetakis, director of advanced battery technology. The company’s lithium-ion batteries should weigh about 50 percent less than lead-acid batteries, he said, but the new batteries will use the same volume to make them more interchangeable with lead-acid batteries. Concorde’s lithium-ion batteries will include electronics to manage charging safely.
Vutekakis believes that adoption of lithium-ion batteries for certified general aviation applications will be a slow process, notwithstanding the work done by Cessna and Boeing and the development of lithium-ion batteries for the G650. “Weight is not as important for general aviation,” he said. Paying five times the cost of a lead-acid or nickel-cadmium battery to save 20 pounds just isn’t worth it, he explained. Manufacturing lithium-ion batteries is a tricky process, specifically the need to eliminate any moisture. And the batteries’ electrolyte is flammable. “It’s not just fire, it’s the smoke. Iron phosphate is not as susceptible to thermal runaway.” But if the battery does catch on fire, it can emit a lot of smoke, which means that even though such a scenario is highly unlikely, aircraft installations may require the ability to vent smoke from a battery fire overboard, adding more expense to the installation.
The lack of charge protection circuitry in lithium-ion batteries for the experimental market is a problem, he added, because if a battery is over-discharged, then trying to charge it generates heat and can cause thermal runaway. And if a lithium-ion battery gets below 5-percent charge, it is probably damaged and won’t be recoverable. So, for example, if a pilot leaves the master switch on and kills the lithium-ion battery, it will have to be replaced.
Vutekakis is participating on industry committees to work with the FAA on standards and regulations that will eliminate the need for special conditions each time an aircraft manufacturer wants to install lithium-ion batteries.
He would prefer that risks of lithium-ion batteries be covered by adequate standards and that a serious safetyincident doesn’t occur and cause regulators to shy away from the benefits of the technology. “That’s why we’re trying so hard to come up with adequate standards that will not allow that to happen. Murphy’s Law is alive and well, if anything bad can happen, it will. If that doesn’t happen, then more and more new designs are going to go to lithium-ion.”
For ultimate safety, battery manufacturers are pursuing what Vutekakis said is the “holy grail” of lithium-ion battery design, a non-flammable electrolyte. “A lot of top companies are working on that.”
As for portable devices with lithium-ion batteries, Vutekakis doesn’t worry about those too much, because a thermal runaway in one of those is easier to deal with, provided the device is readily accessible. The FAA, in Safety Alert for Operators 09013, recommends knocking down these types of fire with either Halon or water, although water is not able to get into a sealed battery and might not have any effect until the runaway is finished. Many pilots are carrying fire-containment bags on board, in case of a portable device fire. The bags are designed to keep the fire from spreading. Industrial Fire Products makes the Fire-Fighter bag, which is distributed by Ship-it AOG. Aircare Access Assistance offers a bag called the FireSock.
What is abundantly clear from the research conducted for this article is that all types of battery have risks and can cause problems. Pilots need to know as much as possible about the type of battery installed in their aircraft, how the charging systems work and how they protect the batteries. Pilots also need to be aware of what mobile devices passengers are carrying and where they are located (and if any are stowed in non-flight-accessible baggage compartments). They need training for battery-related emergencies, not only in how to deal with battery problems, but in how not to let the problem overwhelm the primary duty to keep flying the airplane during the emergency.
Batteries Fall Under the Safety Spotlight
FAA’s Accident/Incident Data System database:
• 2004: A lithium camera battery exploded, setting a passenger seat on fire in a Boeing 727 while airborne. Flight attendants extinguished the fire, and the pilots declared an emergency and landed at the departure airport.
• 1984: A nickel-cadmium “battery system” overheated on climb-out, but there was no damage or fire.
NASA’s Aviation Safety Reporting System database (lithium):
• 2011: A lithium-battery-powered flashlight in the captain’s computer bag made “popping noises and smoke.” The flight continued to the destination.
• 2009: The cabin crew of a Boeing 757 detected a strong smoke odor. Passengers were asked to turn off all electrical devices in case of a lithium-battery fire. No cause of the smoke was found.
• 2007: A checked piece of luggage caught fire during boarding of an Airbus. The fire occurred in a handheld video game device. According to the reporter, “An alert ramper saw the bag in flames. He saved the day.”
ASRS database (nickel-cadmium):
• 2011: The pilots of a Galaxy business jet declared an emergency and returned for landing after a “battery hot” message illuminated on the crew advisory system. “The fear, of course, is a nickel-cadmium battery thermal runaway,” the reporter wrote. The problem turned out to be a faulty temperature sensor.
• 2004: A ramper noticed smoke from luggage before loading onto a Boeing 717. The airport fire department extinguished the fire. It was believed to have been caused by either a hand drill that was left running or the battery slipping out of the drill and shorting out.
• 2003: The pilot of a Pilatus PC-12 saw an overcharge indication for the airplane’s battery while at 4,000 feet and asked for priority handling. While trying to comply with ATC instructions and deal with the battery problem, the pilot lost communication momentarily and the controller became worried about separation with another aircraft.
• 2003: After a battery charger light illuminated, the pilots of an MD-80 diverted to a nearby airport and made an overweight landing.
• 1993: A nickel-cadmium battery showed an overtemp indication in a turboprop twin, but it turned out that the wires for the number one and two batteries were reversed. The pilots ended up isolating the good battery, while the bad battery remained energized and subsequently destroyed itself.
• 1992: An overheat warning in a piston twin resulted in the pilot’s departing from an assigned altitude. The problem was caused by a runaway nickel-cadmium battery with reversed cells.
• 1990: A series of problems caused the crew of a twin turboprop to deviate from an assigned altitude, following a cockpit indication of overheat of the nickel-cadmium auxiliary battery.