Boeing’s three-layered fix for the Dreamliner batteries approved for testing

Boeing’s planned fix for the Dreamliner’s lithium-ion battery has been approved by the FAA and while this is only approval of the plan it at least represents the start of the process to get the Dreamliner back into the air. The FAA approval will allow two Dreamliners to return to the air to test various aspects of the proposed fix. Results from both in-flight and laboratory tests will have to be evaluated to obtain the new certifications and approvals necessary to get back into the air.

NY Times: The F.A.A. could still demand changes if problems develop in the laboratory and flight tests. While Boeing hopes to begin fitting its redesigned batteries in the grounded 787 fleet by mid- to late April and resume commercial flights quickly after that, government officials are not sure the process will move that fast. …

….. the tests would subject the battery to the most extreme conditions it was likely to face and determine if the case could withstand a battery explosion. The tests will include bursts of power to put stress on the battery and check its flammability as well as how it performs in hot weather.

The F.A.A. has also approved limited test flights for two aircraft. One plane will test the old battery, while the other will test how the new system performs under normal flight conditions. The flight tests will begin within a week.

The agency will approve the redesign only if the company successfully completes all required tests and analyses. The F.A.A. said it was continuing a review of the 787’s design, production and manufacturing.

But there is a downside. The fixes being introduced will increase the weight of the aircraft by 150 lbs which almost nullifies the advantage gained by using the lighter lithium-ion batteries in the first place. The fuel efficiency gains – at least those due to the lighter battery – will no longer be available and no doubt customers will want compensation for this. An extra 150 lbs is just about equivalent to one passenger and compensation claims could also be for the equivalent of one passenger less for every commercial flight through the life of the aircraft. This would be in addition to any compensation claims for losses suffered during and because of the grounding  and for delivery delays.

The three-layered approach that Boeing is taking consists of

  1. preventing a fire within any individual battery cell,
  2. preventing the fire from spreading to other cells in the event that a fire does occur, and
  3. preventing the fire from spreading or impacting anything outside the battery enclosure in the event that the fire does spread to multiple cells
Dreamliner Battery Fix (via Aviation Week, Credit Boeing)

Dreamliner Battery Fix (via Aviation Week, Credit Boeing)

The Dreamliner still has a way to go to complete all the testing and while Boeing is talking about “weeks rather than months”, it seems unlikely that the planes will be released for commercial flying before June.

Aviation Week: Among the tougher tests to be conducted will be an evaluation of the containment system’s ability to withstand a deliberately induced thermal runaway. This self-propagating phenomenon was cited by the National Transportation Safety Board (NTSB) in its March 7 interim report on the first battery failure on a Japan Airlines 787 in early January. Although not identifying a specific cause, the report described several shortcomings in both the baseline battery system design and the original means of testing and certification of the device.

The NTSB has announced plans to hold a forum and investigative hearing in April to review the battery’s technology, safety and process used in its certification. The agency’s investigation found—among other things—no record of the final production-standard charging system having been tested with the actual GS Yuasa-made battery. According to the NTSB report, Securiplane, the charging system developer, tested the unit with a simulated electric load instead of an actual battery. The company apparently took this precaution after having earlier suffered a fire at its facility during battery testing.

The three layers of the Boeing fix are structured as below:

1. The first layer of improvements is taking place during the manufacture of the batteries in Japan. Boeing teamed with Thales, the provider of the integrated power conversion system, and battery maker GS Yuasa to develop and institute enhanced production standards and tests to further reduce any possibility for variation in the production of the individual cells as well as the overall battery.  … Four new or revised tests have been added to screen cell production, which now includes 10 distinct tests. Each cell will go through more rigorous testing in the month following its manufacture including a 14-day test during which readings of discharge rates are being taken every hour. This new procedure started in early February and the first cells through the process are already complete. There are more than a dozen production acceptance tests that must be completed for each battery. Boeing, Thales and GS Yuasa have also decided to narrow the acceptable level of charge for the battery, both by lowering the highest charge allowed and raising the lower level allowed for discharge. Two pieces of equipment in the battery system – the battery monitoring unit and the charger are being redesigned to the narrower definition. The battery charger will also be adapted to soften the charging cycle to put less stress on the battery during charging.

2. Changes inside the battery will help to reduce the chances of a battery fault developing and help to further isolate any fault that does occur so that it won’t cause issues with other parts of the battery. To better insulate each of the cells in the battery from one another and from the battery box, two kinds of insulation will be added. An electrical insulator is being wrapped around each battery cell to electrically isolate cells from each other and from the battery case, even in the event of a failure. Electrical and thermal insulation installed above, below and between the cells will help keep the heat of the cells from impacting each other. Wire sleeving and the wiring inside the battery will be upgraded to be more resistant to heat and chafing and new fasteners will attach the metallic bars that connect the eight cells of the battery. These fasteners include a locking mechanism. Finally, a set of changes is being made to the battery case that contains the battery cells and the battery management unit. Small holes at the bottom will allow moisture to drain away from the battery and larger holes on the sides will allow a failed battery to vent with less impact to other parts of the battery.

3. The battery case will sit in a new enclosure made of stainless steel. This enclosure will isolate the battery from the rest of the equipment in the electronic equipment bays. It also will ensure there can be no fire inside the enclosure, thus adding another layer of protection to the battery system. The enclosure features a direct vent to carry battery vapors outside the airplane. New titanium fixtures are being installed in the electronics equipment bays to ensure the housing is properly supported. “Our first lines of improvements, the manufacturing tests and operations improvements, significantly reduce the likelihood of a battery failure. The second line of improvements, changes to the battery, helps stop an event and minimize 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 to the airplane,” said Sinnett.

Two aircraft will be used for the testing:

Flight tests of the prototype revised battery containment system will be conducted using Line No. 86, an aircraft designated for LOT Polish Airlines. Aviation Week was the first to report this same aircraft being previously used for ground tests of the battery system in mid-February (AW&ST Feb. 18, p. 32). The modified battery has also been installed in test aircraft ZA005, though Boeing says this is to allow testing to resume of the planned General Electric GEnx performance improvement package (PIP) II engine upgrade. The FAA says flight tests will validate instrumentation for the battery and testing its enclosure in addition to improvements for other systems.

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