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The resolution of the Boeing 787 Dreamliner battery crisis

17th May 2013

By: Keith Campbell

Creamer Media Senior Deputy Editor

  

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On August 26, 2011, the then Administrator (head) of the US Federal Aviation Administration (FAA), J Randolph Babbitt, gave a speech in Everett, Washington state. He described the occasion as “momentous . . . for the economy and for the global aviation system”. He was speaking at the presentation by the FAA to US aerospace giant Boeing of the type certification for the company’s new model 787 airliner, named the Dreamliner. The type certificate establishes that the aircraft model in question is airworthy. At the same function, Babbitt also presented Boeing with the production certificate for the 787, allowing the company to undertake serial production of the aircraft.

“The Boeing 787 Dreamliner is an incredible technological achievement,” he enthused, “one that sets a new standard for innovation on many levels. The 787 is the world’s first major airliner to make such extensive use of com- posite materials – over 50% by weight. This results in an airplane that will fly as fast as today’s speediest wide-body aircraft, while using 20% less fuel than airplanes of similar size. The use of composite materials, engine technology advancements and changes in systems architecture will also reduce noise.”

He also praised the new aircraft’s improved situational awareness for its flight crew and its modern communications system, which supports increased use of data transmission, compared with voice communication. He further cited its flight management system which had advanced navigation capabilities fully integrated into it.

Babbitt pointed out that, between its first flight in December 2009 until that day, the six flight test 787s had accumulated 4 645 flying hours, of which a quarter had been gained by FAA flight crews. In addition, FAA personnel had carried out 200 000 hours of technical work during the 787 type certification process.

“And our Transport Airplane Directorate developed 15 special conditions – essentially new design regulations to address innovations that existing rules don’t fully cover,” he highlighted. “At the outset of the programme, the FAA and Boeing developed a new way of working together. Rather than wait for issues to arise, we started out by working collabor-atively – and proactively – to identify certification issues expected to arise from some of the 787’s novel design features. With this high level of technological innovation, it was not possible to anticipate everything. But we had a plan for working issues to a resolution that would ensure the result we always want: a safe and compliant aircraft.”

Just ten days short of exactly 17 months later, on January 16, 2013, with 50 Dreamliners in revenue service with seven airlines, the FAA ordered that all US-registered 787s be grounded. This followed within 24 hours of a decision by All Nippon Airways (ANA) and Japan Airlines (JAL) to voluntarily ground their 787s. Within hours, all other major air safety agencies had followed suit. The 787 programme was in crisis.


Electric Jet

One of the revolutionary features of the 787 is its electrical system. Previously, airliners used electrical, pneumatic and hydraulic systems to power aircraft systems. Aeroplane pneumatic systems take (or, in aviation jargon, bleed) air from the engines and use that air to power systems such as the undercarriage, flaps, air conditioning and to de-ice the wings and tailplane. Many aircraft designs also use hydraulic systems to power the flight controls, control surfaces and the landing gear, among other things. Pneumatic systems can be used to drive the pumps controlling an aircraft’s hydraulic systems. External, ground-based and vehicle or trailer-mounted pneumatic systems can also be used to start an aircraft’s engines and auxiliary power unit (APU).

Both pneumatic and hydraulic systems are extremely reliable, proven and have high levels of safety. But they are also bulkier and heavier than electrical systems, and taking bleed air from the engines to power the pneumatics takes some energy from these engines, reducing their thrust, subjecting them to greater stress and causing them to consume more fuel. In addition, the engines need more maintenance.

To eliminate these drawbacks, Boeing sought to maximise the use of electrical systems on the 787. The design team also came up with a totally new architecture for the aeroplane’s electrical system to further reduce weight. Hitherto, the standard air- liner electrical system architecture for twin-engined aircraft (like the 787) involved one generator on each main engine, with a third generator on the APU. Heavy gauge power feeder cables run from all three of these generators to the aeroplane’s forward electrical bay.

In contrast, the 787 has two generators on each main engine and another two on the APU, giving a total of six. Heavy-gauge power feeder cables run from these to the rear electrical bay (which is actually in the middle of the aircraft). There are four alternating current (ac) buses to which the feeder cables connect; these buses either distribute the existing 235 V ac supply or convert it to whatever other systems require. There are 17 small electrical substations which provide power to local systems.

The result is that the length of both the heavy gauge cabling and all electrical cabling in the 787 is reduced, compared with previous designs. In fact, a 787 has about 32 km (yes, kilometres) less wiring in it than a Boeing 767. The consequence is greater efficiency in the generation of power and greater efficiency in its distribution, control and use as well as simplified maintenance, which result in reduced costs and less drag and noise produced by the aircraft.

In addition to these generators, the Dreamliner has two main battery systems – the main battery and the APU battery. The main battery has the main functions of powering up the aircraft’s systems before the engines are switched on, powering refuelling and braking (when the aeroplane is being towed). The APU battery can be used to start the APU generators, which then start the APU itself. Next, the APU provides power to the engine generators, which then start the engines. Both batteries serve as emergency backup power sources for key systems while the aircraft is flying.

For the 787, Boeing decided to use lithium ion batteries. There were several reasons for this. Lithium ion batteries are 30% lighter than nickel cadmium batteries and can, unlike the latter, be fully recharged. Moreover, lithium ion batteries provide 100% greater energy storage than nickel cadmium batteries and can release 100% more energy than a nickel cadmium battery of the same size. The main and APU batteries have eight large cells each, in two rows of four, with each cell rated at 3.7 V. The cells use a lithium cobalt compound chemistry and contain a flammable electrolyte fluid.

The 787 can also be hooked up to ground electrical power and has a ram air turbine to generate electricity in flight in extreme emergency situations. Boeing has shown that a Dreamliner can fly for more than 330 minutes on only one engine and with only one functioning generator, and make a safe landing.


Short Circuited

Boeing reported that, up to January 2013, the batteries on the 787 had accumulated 2.2-million cell hours on the ground and during 50 000 flying hours without any problems. But, in January, the Dreamliner was hit by a cluster of bad news events, and initial concern rapidly escalated into con-siderable alarm. On January 7, a battery on a JAL 787 caught fire and then exploded while the aircraft was on the ground in Boston, US. The very next day, another Dreamliner from the same airline experienced a fuel leak. Then an ANA 787 suffered brake problems, while another was found to have cracks in its cockpit windows.

These events led current FAA Administrator Michael Huerta to address a press con- ference in Washington DC on January 11. “[S]afety is our mission and we take this responsibility very, very seriously,” he assured. “The Dreamliner is a new aircraft with many innovations. . . . We believe this is a safe aircraft. To validate the work conducted during the certification process, we are going to work with Boeing to conduct a review of all critical systems of the 787 . . . . “We will [place] emphasis on the electrical system in the airplane. This includes components such as batteries and power distribution panels. We’ll also look at how the electrical and mechanical systems of the airplane interact with one another. Last month, we issued an airworthiness directive that required inspection of fuel line couplings in the engine pylons to verify that they were correctly assembled and installed.”

Then, on January 16, an ANA 787 on a domestic flight from Yamaguchi airport to Haneda airport, in Tokyo, made an emergency landing at Takamatsu after a battery mal- function, a smoke alert and the pilot reporting a strange smell in the cockpit. All passengers and crew were evacuated using emergency slides. The grounding orders followed rapidly after this incident.

“The battery failures resulted in the release of flammable electrolytes, heat damage and smoke on two Model 787 airplanes,” said the FAA in its statement announcing the grounding. “The root cause of these failures is currently under investigation. These con- ditions, if not corrected, could result in damage to critical systems and structures, and the potential for fire in the electrical compartment.”

“The safety of passengers and crew members who fly aboard Boeing airplanes is our highest priority,” affirmed Boeing chairperson, president and CEO Jim McNerney in a statement issued on the same day as the FAA’s grounding order. “Boeing is committed to supporting the FAA and finding answers as quickly as possible. The company is working around the clock with its customers and the various regulatory and investigative authorities. We will make available the entire resources of the Boeing company to assist. We are confident the 787 is safe and we stand behind its overall integrity.”

Investigations into the two battery failures were started by the US National Trans-portation Safety Board (NTSB) and the Japan Transport Safety Board (JTSB), supported by the FAA and Boeing. On January 24, Boeing reported that it had formed hundreds of its engineers and technical experts into teams solely dedicated to resolving the battery issue and getting the 787 flying again (the other problems were minor and/or easily solvable). The company was assisting the NTSB, the JTSB and the FAA in their enquiries as well as with its 787 customer airlines. It also pointed out that “in adherence to international protocols that govern safety investigations, we are not permitted to comment directly on the ongoing investigations”.

On February 7, the NTSB revealed that it had identified the origin of the fire in the JAL 787 APU battery at Boston. In its press release, the agency reported that its “investigators [had] determined that [most of the] evidence from the flight data recorder and both thermal and mechanical damage pointed to an initiating event in a single cell”. “That cell showed multiple signs of short circuiting, leading to a thermal runaway condition, which then cascaded to other cells.” Thermal runaway is overheating that can, and in this case did, result in a fire.

It had been determined that the problem was a malfunction in the battery, and not any mechanical impact damage to the battery or any external short circuiting. The damage to, and electrical arcing on, the battery case were the result of the malfunction and not connected to the cause of it. The NTSB had not determined the cause of the short circuit and was examining the battery design and manufacture, the manufacturing process and battery charging.

It also revealed that Boeing’s battery risk assessment had concluded that the probability of a smoke emission event involving the 787 batteries would be less than once every ten-million flying hours. In reality, there had been two “critical battery events” in less than 100 000 flying hours.

That same day, Boeing announced that the FAA had granted permission for limited test flights using the fifth flight test 787, designated ZA005, to test the aircraft’s batteries in flight. The first such test flight took place two days later, from Boeing Field in Washington state, with a crew of 13, composed of company pilots and flight test specialists. It lasted two hours and 19 minutes and was reported to be uneventful. ZA005 was fitted with special test equipment, allowing the crew to monitor and record performance data for both the main and APU batteries while in flight. The data from these missions was made available to the various aviation investigators.

Just over two weeks later, on February 27, Huerta testified to members of the US House of Representatives: “With regard to the Boeing 787, we are working around the clock to conduct a comprehensive review of the critical systems of the aircraft . . . . As part of that review, we are working on a data- driven process to identify the cause of the recent battery issues and the mitigations for them. . . . We will carefully analyse Boeing’s proposal to address these issues. But the safety of the flying public is our top priority and we won’t allow the 787 to return to commercial service until we’re confident that any proposed solution has addressed the battery failure risks.”

The NTSB issued its ‘Interim Factual Report’ on the APU battery fire on the JAL 787 on March 7. This stated that all the battery’s cells, except cell 8, were short-circuited. Each cell has a vent disc, a plate that is designed to rupture when internal cell pressure reaches a certain limit. The vent discs on cells 1, 2 and 3 were slightly open, while those on cells 5, 6, 7 and 8 were “more completely opened, giving a ruptured appearance”. The disc on cell 4 was intact, but that cell had lost some electro- lyte. The report also clarified that there had been two smoke emission events with 787 batteries in only 52 000 flying hours. The investigation was continuing. “The NTSB is also continuing to review the design, certification and manu-facturing processes for the 787 lithium ion battery system.” (As of early May, the exact cause of the battery incidents had still not been determined and the NTSB investigation was continuing, including computer tomography scans of battery cells.)
Rewired

Meanwhile, Boeing engineers were busy working out possible causes of the fires and what could be done to deal with them. Their work was double-checked by independent experts in lithium ion batteries based at national laboratories, universities and industries. The US company also worked with French group Thales, which is responsible for the 787’s integrated power conversion system, and Japanese company GS Yuasa, which manufactures the batteries.

The result was a significant redesign of the battery system and a tightening of the battery manufacturing quality control system. Thales and GS Yuasa agreed with Boeing to lower the highest charge allowed in each cell and increase the lowest level permitted for discharge. As a result, the battery monitoring unit and the battery charger have been redesigned. The battery charger has been modified to reduce the stress on the battery during charging.

Two types of insulation have been added to insulate the battery cells from each other and from the battery box. Each cell has been encased by an electrical insulation so as to isolate it from all the other cells and from the battery box. And electrical and thermal insulation has been put around and above and below each cell. Thus, a failure can be contained in the cell in which it occurs and a thermal runaway cascade can be prevented.

The wire sleeving and wiring inside the battery have been made more heat resistant and stronger to better withstand chafing. The metallic bars which connect the battery cells have been fitted with new fasteners that can be locked. The battery case, which encases the cells and the battery management unit, has been changed to incorporate larger apertures on the side to allow a failed cell to vent with less effect on the other parts of the battery and small apertures in the bottom to permit moisture to drain away.

Moreover, the battery case is itself now contained within a new stainless steel enclosure. This isolates the battery from the remaining equipment in the electronic bays and is designed to eliminate oxygen, thereby making fire impossible. Should any battery cell vent vapour, the enclosure will directly vent that vapour outside of the aircraft. New titanium supports have been designed to properly secure the new enclosure inside the electronic equipment bays. All these modifications have been rigorously tested.

With regard to the manufacturing of the batteries, the monitoring of the process has been increased with four new or revised tests added during production, taking the total to ten separate tests. Following full assembly, each battery is now subject to more than 12 production acceptance tests, including a continuous 14-day test, in which discharge rates are recorded every hour.

“Our first line of improvements, the manu-facturing tests and operations improvements, significantly reduce the likelihood of a battery failure,” highlighted Boeing Commercial Airplanes VP and 787 chief project engineer Mike Sinnett. “The second line of improvements, changes to the battery, helps stop an event and minimise the effect of a failure within the battery if it does occur. And the third line of improvements, the addition of the new enclosure, isolates the battery so that even if all the cells vent, there is no fire in the enclosure and there is no significant impact on the airplane.”


Cleared for Take-Off
On March 12, the FAA announced that it had approved Boeing’s plan to certify the modified battery system. The certification programme included a test flight, conducted on April 5. This involved 787 Line number 86, an aircraft built for LOT Polish Airlines but which, at the time, was still Boeing property. The flight was from Paine Field at Everett, in Washington state.
On April 16, Huerta testified to the US Senate that Boeing “has redesigned the internal battery components and conducted extensive testing”. “This includes limited test flights – without passengers – using the redesigned battery prototype. The FAA is reviewing these test reports and analysis to make sure that the 787’s new battery system ensures the safety of the aircraft and its passengers.”
Three days later, the FAA announced that it had approved the redesigned battery system. Once fitted with the new battery system, US-registered 787s would be allowed to return to revenue service. “FAA approval clears the way for us and the airlines to begin the process of returning the 787 to flight with continued confidence in the safety and reliability of this game-changing new airplane,” affirmed McNerney. The European Aviation Safety Agency approved the redesigned battery system on April 25 and Japan’s Ministry of Transport followed suit the next day.
About 300 Boeing personnel in ten teams fanned out across the world to modify the grounded airliners. The aircraft were scattered across every continent except Australasia, with one each at Boston, Chicago and Los Angeles and four at Houston, in the US; one each at London, Frankfurt and Warsaw, in Europe; four at Addis Ababa, in Africa; and four at Doha and six at Mumbai, in Asia. In Japan alone, there were 23, with eleven at Tokyo Haneda airport, eight at Tokyo Narita, and one each at Kumamoto, Matsuyama, Okayama and Takamatsu.
It takes about five days to modify each aircraft and the modifications add some 70 kg in weight. Interestingly, LOT Polish Airlines has decided to send its two already delivered 787s to Addis Ababa to be fitted with the modified battery system at Ethiopian Airlines’ facility.
The cost of the modifications was covered by the guarantee. However, the London Financial Times reported on April 30 that the grounding of the 787 had cut the combined operating profits of ANA and JAL by more than $100-million.

On April 27, Ethiopian Airlines undertook the first 787 revenue flight in the world since the grounding orders in January, from Addis Ababa to Nairobi, Kenya. “We are excited to resume our service with the Dreamliners,” said airline CEO Tewolde Gebremariam in a press release before that flight (on which he was one of the passengers). “During the five months our four Dreamliners were in service, we were very pleased with their performance, and the feedback from our passengers has been overwhelmingly positive.”

Edited by Martin Zhuwakinyu
Creamer Media Senior Deputy Editor

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