Dreamliner becomes Boeing's nightmare
The burnt auxiliary power unit battery removed from an All Nippon Airways 787
Boeing has made much of the innovative technologies in its 787 Dreamliner - but battery problems have seen the fleet grounded. Mark Venables reports.
For the first time since a DC-10 crashed in Chicago in 1979 killing 270 people, an entire model of aircraft has been grounded on safety concerns.
When a fire on a Japan Airlines Boeing 787 Dreamliner in Boston attributed to the lithium-ion battery system was followed a week later by smoke pouring from the same system on an All Nippon Airways plane, forcing it to make an emergency landing, the US Federal Aviation Administration (FAA) and other regulators around the world acted swiftly to ground all 787s.
Now, a month later, there is still no firm conclusion about what caused the battery to overheat, keeping the jets on the tarmac and casting doubt on the future of lithium-ion batteries for high-power functions.
"We believe this is a safe aircraft," said FAA administrator Michael Huerta. "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, including design and production."
Huerta said the FAA would focus on the electrical system, including components such as batteries and power distribution panels, as well as the interaction between the electrical and mechanical systems.
The US National Transportation Safety Board (NTSB) has carried out a microscopic investigation of the auxiliary power unit battery that caught fire on the 787 at Boston. Manufactured by GS Yuasa, this was the original battery delivered with the aircraft in December 2012. It is composed of eight individual cells, all from the same manufacturing lot.
Examination and testing of a standard battery began early in February at the Carderock Division of the US Naval Surface Warfare Centre laboratories. The tests consisted of electrical measurements, mass measurements, and infrared thermal imaging of each cell, and no anomalies were noted. The cells then underwent CT scanning to examine their internal condition.
Another group is interpreting data from the two digital flight data recorders on the aircraft, hoping that they might yield information about the performance of the battery and the operation of the charging system.
Next up is a series of non-invasive 'soft short' tests of all cells of the test battery. This will reveal the presence of any high resistance, small or 'soft' shorts within a cell. Also, an NTSB investigator has taken the JAL aircraft's battery contactor, which connects a wiring bundle to the battery, to be examined in France by manufacturer Thales.
The Dreamliner is a new aircraft, with 50 delivered to airlines so far. In hindsight it is clear that Boeing took a huge gamble when it opted to replace the heavy hydraulic systems with lightweight battery-operated electric and electronic equipment, as part of a strategy to reduce weight and increase fuel efficiency.
The use of lithium-ion batteries in the 787 was an industry first. One starts the auxiliary power generator used for electrical services when the plane is on the ground and a second powers up the pilot's computer displays and serves as a back-up for flight systems.
However, the risks were recognised. Just over six years ago a fire destroyed a Securaplane Technologies building in Arizona after a laboratory test on a lithium-ion battery got out of control.
In 2007, the FAA asked Boeing to prove the safety of the Dreamliner's batteries before granting it an airworthiness certificate. At the time, the agency noted that "lithium-ion batteries are significantly more susceptible to internal failures that can lead to self-sustaining increases in temperature and pressure". Despite that apparent misgiving it permitted the batteries to be used.
A further warning came with the crash of a UPS Boeing 747 in Dubai in 2010 that was directly attributed to lithium-ion batteries in a cargo consignment. The investigation report painted a harrowing picture of two pilots struggling to navigate their plane to an emergency landing while running low on oxygen and fighting smoke so thick they couldn't see their instruments. Both pilots were killed.
"Very early on larger batteries such as traction batteries for electric vehicles, whether hybrid or pure electric, had moved to chemically safer 'less cobalt' and 'no cobalt' formulations," explained Dr Peter Harrop, chairman of Cambridge-based IDTechEx. "The typical GS Yuasa batteries were one of the former, having lithium nickel cobalt aluminium cathodes similar to those ... used by market leaders Panasonic and others.
"In these batteries the cathode plays the largest part in controlling the characteristics of a lithium-ion battery. The leaders have shown some move to lithium manganese spinel cathodes, but just about everyone uses flammable electrolytes. In lithium polymer versions, some offer semi-solid electrolytes that reduce the chance of leakage at some reduction in certain aspects of performance."
Suba Arunkumar, industry manager, energy & environment at analysts Frost & Sullivan, warns that there is no quick fix, but he expects that all the battery manufacturers will invest more in R&D as a result, just as they did in 2005 when laptops powered by lithium-ion batteries were catching fire. "The industry learnt from these problems and improvised. Today lithium-ion batteries are ubiquitous in consumer applications."
Aside from the damage caused to Boeing, the airlines and GS Yuasa, there is a wider concern about the knock-on effects on the largest market for lithium-ion batteries - electric vehicles. "The larger a lithium-ion battery is, the more there is to go wrong," Dr Harrop said. "Those making safe small versions for phones or tablets cannot necessarily make safe big ones."
Dr Harrop believes Boeing would have been wiser to use a supplier more experienced in lithium-ion battery packs and the all-important battery-management system. "The few modest-sized batteries on the tiny number of Dreamliners should never have behaved in this way, if it is indeed the batteries that are to blame."
|To start a discussion topic about this article, please log in or register.|
"Are you a digital native or an analogue native? The analogue aesthetic is alive and well at work in art, music, fashion and many other aspects of culture"
- What to Specialise in Electronics Engineering?? [03:02 am 03/04/14]
- Britain to have just one remaining coal pit by the end of 2015 [01:11 am 03/04/14]
- LV Generator Star point earthing - UK [08:35 pm 02/04/14]
- East West Rail - the Oxford to Bedford route [07:33 pm 02/04/14]
- Small nuclear power [06:06 pm 02/04/14]
The essential source of engineering products and suppliers.