Airbus has reached the final stages of regulatory reviews over a plan to use lithium ion batteries for backup and starting power on the A350-900, says executive vice-president of engineering Charles Champion.
But well-publicised safety problems with lithium ion batteries on the Boeing 787-8 and other aircraft have stretched out the regulatory review process.
“We might have to do a few more tests because authorities are extremely nervous on the subject because of the Boeing 787,” Champion says.
Airbus already has decided to make one design change to the original lithium ion battery system for the A350-900.
The original design allowed power to flow between the batteries, but that raised concerns that one overheating battery could cause another to fail.
“So we put in a non-return valve so that if it blows out, it doesn’t go back in the other battery,” Champion says.
Airbus also is still trying to persuade regulators that it is safe to install such powerful lithium ion batteries inside an aircraft without enclosing them inside a heavy stainless steel box, which Champion likens to a “huge coffin”.
Weight savings is one of the key advantages gained by switching to lithium ion batteries, so Airbus hopes to install the batteries using an enclosure made of lighter materials than stainless steel.
“If you start to put a huge coffin around the battery system in place then you lose all the benefit of the lithium ion battery,” Champion says.
But two battery fires on the 787-8 in January 2013 led the US Federal Aviation Administration to ground the fleet for four months. The grounding was lifted only after proving that a redesigned installation could prevent such a fire from causing damage to the aircraft.
One of the changes that Boeing made was to switch from a lighter aluminium enclosure for the two batteries to a stainless steel box.
Such heavier enclosures are common with older, nickel-cadmium batteries, due to lessons learned from a series of in-flight fires on aircraft when the industry transitioned from lead-acid batteries in the early 1970s.
The FAA allowed Boeing to introduce the 787-8 with an aluminium battery enclosure because certification testing appeared to prove that its lithium ion design met safety standards. But the FAA and Boeing concluded after the battery fires that those certification tests were inadequate for making such claims.
Airbus, however, remains confident that the lithium ion battery design for the A350-900 was always safer than Boeing’s original system for the 787-8, Champion says.
Boeing’s design includes two GS Yuasa-made batteries with eight 3.7V-cells each, storing a total of 72Ah of electrical power per battery.
Airbus took a more conservative design approach with the A350-900, selecting four Saft-made batteries with 14 3.6V-cells each, storing a total 45Ah of power, according to specifications released by Saft at a trade show last year. Airbus also selected Saft to supply the battery and the battery charging unit, unlike Boeing’s approach that divided the system between GS Yuasa and Meggitt Securaplane.
“We are rather confident with our system because we have a different architecture than Boeing,” Champion says.