Boeing announced this week their proposed alterations to the 787 lithium-ion batteries to prevent any major incidents in flight. Tellingly, the company has not announced the cause of he problem which suggests they do not still know it. The changes are designed not only to improve safety but reassure regulators, carriers and the public that the plane is safe.
The changes include:
- improving the insulation between the eight cells in the battery. The batteries’ original insulation was made of polyvinyl chloride (PVC) which can withstand heat of 300 degrees Fahrenheit (149 degrees Celsius). The cells will now be wrapped with another insulating material called phenolic glass laminate, made of thin layers of a fiberglass material and resin. This will give with a resistance of more than 900 degrees Fahrenheit (482 degrees Celsius)\
- reducing vibrations inside the battery that might have been one of the possible causes of the short circuits
- gentler charging to minimise “stress”
- installing a new titanium venting system.
- sealing the batteries in a steel box, which would contain any smoke and fire. The box adds 150 pounds (68 kilograms) which almost negates the point of using the lighter weight battery in the first place. Boeing has been testing the steel casing for three weeks and has found it can withstand three times the pressure generated when a battery “fails”.
If a cell did combust, the steel casing would contain the smoke and fire, the venting tube would open, and the smoke would be pushed outside the plane and out of the cabin.
The FAA Federal Aviation Administration approved these changes on Tuesday. Boeing has since begun a series of certification tests -20 over one to two weeks. Most of the tests will be conducted inside Boeing labs but one will be a test flight.
The company have also disputed the National Transportation Safety Board analysis of the original January 7 Boston airport fire which triggered the plane’s grounding. The NTSB said a short circuit led to “thermal runaway” and fire in the battery. Boeing says it was “thermal propagation.” and state the fire was not in the battery box.
Boeing said yesterday: “We think the likelihood of a repeat event is very unlikely,”
This is either good news or an expression of hope.
We shall see what the FAA says after the tests have concluded.