SEATTLE — In 2006, a devastating lab fire in Arizona showed just how volatile Boeing’s 787 Dreamliner lithium ion battery can be if its energy is not adequately contained. SEATTLE — In 2006, a devastating lab fire in Arizona showed
SEATTLE — In 2006, a devastating lab fire in Arizona showed just how volatile Boeing’s 787 Dreamliner lithium ion battery can be if its energy is not adequately contained.
A single battery connected to prototype equipment exploded, and despite a massive fire-department response, the whole building burned down.
On the finished Dreamliner, however, Boeing is confident its engineers can safely harness and contain that energy.
The 787’s battery-fire protection regime aims both to make a catastrophic blowout impossible through multiple independent controls and also to compartmentalize any less-serious battery meltdown, venting smoke outside until the high-temperature reaction burns itself out.
That approach was approved by the Federal Aviation Administration, with special conditions attached.
Yet the All Nippon Airways 787 emergency last week suggests Boeing’s containment plan — even if the engineering is technically solid — may not work for airlines in operational terms.
In the All Nippon Airways incident, the pilot made an emergency landing when he received warnings of an overheated battery and smelled a burning smell in the cockpit.
“If I’ve got an unexplained source of smoke or smell and messages indicating an overheat or a fire has been detected, frankly, I’m not going to pull out the book,” said veteran airline captain and aviation expert John Nance. “I’m just going to get the ship on the ground.”
Unless such events will occur only very rarely, Boeing’s engineering solution won’t be tenable as a practical matter.
Two 787 battery incidents in quick succession out of 18,000 in-service flights so far isn’t close to rare enough. That’s why the jet fleet is grounded worldwide as investigations continue.
The Air Line Pilots Association, or ALPA, raised concerns about Boeing’s battery-fire-protection plan in the course of the FAA certification process.
During the public-comment period in 2007, the pilots union stressed that “a fire from these devices, in any situation, is unacceptable.”
ALPA quoted a 2006 FAA report on transporting lithium ion batteries as cargo, which concluded that a relatively small amount of heat is sufficient to cause the flammable chemical inside a lithium ion cell — called an electrolyte — “to forcefully vent through the relief ports near the positive terminal.”
“The electrolyte is highly flammable and easily ignites when exposed to an open flame or hot surface,” the FAA report added.
People familiar with the investigation so far confirm that electrolytes sprayed out of the battery in the All Nippon Airways jet, leaving a dark sooty residue across the electronics bay. Photos show the insides of the battery burned out.
The 787 carries two large lithium ion batteries.
One in a rear electronics bay is used mainly to start the plane’s auxiliary power unit; the other, in a forward bay, is used to start the main engines.
In an emergency, the two batteries provide backup power for flight-control electronics and emergency lighting.
The forward electronics bay that housed the malfunctioning All Nippon Airways battery is like the “brains” of the airplane, filled with critical flight-control equipment.
In its 2007 comments, the pilots union initially asked that the FAA require “means for extinguishing fires” caused by the lithium ion batteries.
But in a subsequent email to the FAA later that year, the union switched gears and asked that the focus be “preventing a fire and not reacting to one.”
The ALPA did not respond to requests for comment Wednesday.
In any case, the FAA decided not to require fire suppressant in the electronics bay, and Boeing didn’t include it.
Mike Sinnett, Boeing vice president and chief 787 project engineer, explained why in a conference call last week and detailed Boeing’s engineering solution.
To completely rule out any catastrophic high-energy fire or explosion that could result from overcharging a battery, Sinnett said, Boeing designed four independent systems to monitor and control the battery charge.
But he conceded that if an internal cell shorts and overheats, “the electrolyte can catch on fire, and that can self-sustain.”
“Something like that is very difficult to put out,” Sinnett said. “Because the electrolyte contains an oxidizer, fire suppressants just won’t work.”
Boeing’s design solution is to contain that outcome until the combusting battery cell or cells burn out.
“You have to assume it’s not going to go out,” Sinnett explained. “You have to assume that it’s going to go and that it’s going to expend all of its energy.
“You have to be good with the amount of heat and smoke that’s generated from that event,” he added.
Sinnett pointed out that the air flow in the electronics bay will be redirected when smoke is detected, so that the smoke is vented overboard, not into the passenger cabin or cockpit.
Nance, the veteran pilot, said he assumes Boeing’s engineers have got that right — in which case, it’s possible the incident on board the All Nippon Airways jet played out as they intended.
But still, he said, Boeing “may not have adequately planned for the number of potential incidents” that might occur during a jet’s lifetime.
