Eighteen months after the US Federal Aviation Administration lifted the grounding order on the Boeing the 787-8 fleet, the two rechargeable lithium-ion batteries installed in the aircraft produce mixed reactions among operators.
For some, Boeing’s redesigned installation and improved battery monitoring software that lifted the FAA’s nearly four-month grounding order in 2013 is enough.
“As long as it’s reliable, we don’t have any issues with [the battery],” says Michal Leman, LOT Polish Airlines director of product development. The “FAA approved it. All security institutions approved it. We don’t have any issues of [overcharging] or getting hot. Nothing such as that has happened.”
Other operators in the fleet are less comfortable. Boeing redesigned the internal layout of the battery but retained the lithium-cobalt-dioxide chemistry with eight cells storing 72Ah of power.
“For me, the message [from Boeing] is the battery will still catch fire probably,” says Yohannes Hailemariam, Ethiopean Airlines chief test pilot. “But when it catches fire, the smoke will not come to you. That is what they say to us, I think. That is what I understood.”
Although Hailemariam used the word "fire", Boeing says the redesigned installation should prevent any flames in the first place. The new installation, however, does not prevent a cell from "venting", a thermal event that spews heat and vapour from burning electrolyte outside the cell container. The new design is intended to keep the heat contained to the venting cell, while the heat and smoke are channelled directly off-board. The goal is not to guarantee that a battery will never fail, but to prevent a venting cell from causing further damage to the aircraft or its crew and passengers.
Hailemariam is well briefed on the new battery system, but Boeing's explanation does not satisfy him completely. Asked if he would prefer a different kind of battery, he replies, “Yes. Number one, what caused that issue, you know? Why did the battery catch fire?”
So far, investigation teams in Japan and the USA have not been able to answer what caused the 787 batteries to malfunction. The US National Transportation Safety Board plans to release a final report within weeks, but so far it has not identified the root cause of the battery meltdown in a Japan Airlines 787-8 parked at Boston Logan International airport on 7 January 2013.
The Japan Transport Safety Board (JTSB) investigated the 16 January 2013 battery failure on an All Nippon Airways 787-8. The final report identifies an internal short circuit in one of the eight cells as the likely reason the battery overheated, but the investigators do not understand what caused the short circuit.
After the second battery failure, the FAA grounded the six 787-8’s United Airlines had in service, and regulators all over the world followed the US government’s example. While the root cause is still a mystery, Boeing addressed the risk in two ways, making it harder for the battery to overheat with better monitoring software and preventing a battery that does overheat from damaging the airplane or exposing passengers and crew to fumes and smoke.
“Overall, we’re satisfied that the fixes we’ve implemented do prevent any airplane-level event,” says Mike Fleming, Boeing’s director of 787 services and support.
The redesigned installation received its first test a year after the battery groundings. Earlier this year, on 14 January, a single cell of a lithium-ion battery on a parked JAL 787-8 vented. Boeing’s new system worked. The overheated cell did not propagate enough heat to cause adjoining cells to vent. Smoke generated by the malfunctioning cell was vented directly outside, where it was spotted by airport staff. There was no damage besides the battery cell.
The incident, however, did not go unnoticed. The JTSB noted in its final report that the cell overheated in January, the same month as the two previous battery failures. The Japanese investigators were unable to confirm the timing as a factor, but they raised the possibility of a cold-soak problem.
Not all of Boeing’s customers are satisfied that the redesigned battery installation is a sufficient answer. In addition to concerns about cell venting, some airlines are dissatisfied with the functional reliability of the battery.
“Actually, the rate of failures and frequency of failures is more than what the design is intended to be,” says one senior airline executive. “In that sense, we are not satisfied. So we are talking to Boeing about the possibility of design improvement. Also, in terms of manufacturing process management, there may be an opportunity for an improvement.”
So far, Boeing is not promising any further changes, but it certainly has not closed the door.
“When you ask if we’re satisfied, we’re going to continue to look for improvements in the battery system and every system on our airplane,” Fleming says. “From that standpoint, we’ll continue to be participants to the investigations into why a battery cell vented, and then we’ll take appropriate action to address any findings.”
Meanwhile, airlines continue to keep a close eye on the battery system’s reliability and safety.
“Every day, real-time, we are monitoring the voltage and the current,” says Masaru Nishiwaki, ANA’s deputy director of engineering and maintenance. “We sometimes sample [at intervals] of three months, six months and 12 months. We remove the battery and send it [to battery supplier GS Yuasa], and ask them to review if something is wrong. At this point, no negative report has come from them.”
For now, Boeing’s options are limited as it waits for the NTSB to release a final report on the first JAL battery incident.
Airbus adopted a completely different approach when it decided to make lithium-ion batteries standard on the A350-900. Instead of using two large batteries containing eight cells, the A350-900 is equipped with four smaller batteries, each divided into 14 cells.
“While our customers understand and are comfortable with the changes that we’ve made on the airplane,” Fleming says, “there are some that would still like to see a battery that doesn’t vent.”
Check out our dedicated 787 in-service report page here
ANALYSIS: After three years in service, how is 787 performing?
ANALYSIS: Airlines satisfied with 787 engines despite efficiency miss
Boeing fields permanent APU fix for 787-8
Source: Cirium Dashboard