Taking into account that there are 8 cells, the MTBF of the battery is already almost an order of magnitude lower than that for any cell...
If we are sooner or later flying around with 20 times the number of dreamliners, the MTBF should be increased by at least a factor of 100. That would still give us around one burning battery per year, possibly 3 hours away from the next airport.

I can see some customer resistance here -passengers don't like the idea of being burnt alive..................

For some reasons, I have to think of the old steam ships when reading this proposal. A century ago, a smouldering fire in the coal bunkers was considered no cause for concern. It was deemed sufficient to just use up the coal from the affected bunker first, and until then the fire was considered well contained within the ships structure. For example, the Titanic seems to have sailed under such circumstances.

Should technology really have progressed so little in the last century?

EEngr, thanks for your explanation; I'll go back to my study room and try to get a better understanding...

Airbus have stated (Very publicly) that they are reverting to NiCd on the A350, general perception appears to be that Lithium batteries and aircraft are a bad combination.

With the 787 production line still going, this suggests that whatever the solution is, it will be constrained by having to fit within the existing battery bay.

Not sure that I wouldn't have preferred a blue-sky solution where ultimate safety was the only constraint.

Surely the cells are in series; if one fails the whole battery has failed. Even if by chance it failed with zero resistance, the battery will no longer meet its voltage specification.

Given that sooner or later this problem will be resolved, its interesting to consider the impact on airline who are/were due to take delivery for this summers program here in Europe, there does not appear to be a lot of long haul capacity to lease in right now or the crews to fly parked desert ships?

Many airline will have been planning crew recruitment and training based on the now defunct delivery schedules, lots of gardening leave i suspect.

More Issues Turned Up
 

pgarner528

The problem is; these battery failures (fire or not) don't directly affect ETOPS range. The batteries are either there or not when they are needed. Their failure probability per flight may depend on the duration of that flight. Or the failure mechanism could turn out to be cycle rather than time dependent. One 'bad' charge or discharge event could initiate the fault.

That we don't understand the mechanism in play means that the probability math needed to ensure extremely unlikely events will be difficult. And involve quite a bit of Boeing/FAA hand-waving.

It's not on a common bus.

When is either battery essential?

Loss of both engines has to be "impossible" for ETOPS; is it not equally "impossible" that power from at least one generator [on one remaining engine] will not be available?

Failing that, can the APU and RAT individually supply essential power for the ETOPS period? Can the RAT be deployed at cruise? At what airspeed does the RAT become useless? - that would seem to be the moment you need a battery. Too bad Boeing's math showed it was a waste of money to add a redundancy path between the two identical batteries.


It's amusing that the Boeing CEO and the head of FAA are solving the problem. IIRC the FAA grounding order directed that Boeing engineers satisfy their Renton-area office.

It will be even more amusing (though unlikely) if another jurisdiction took a less political view of the matter. Japan probably has similar commercial pressures given that their airlines are heavily invested, but the EU might have different ideas.

EEngr - its not a case of flying without batteries for the ETOPS time, its more the worry of flying round with a battery on fire / that has been on fire while 180 minutes from the nearest airport.

In reply to MWorth, #964

"Boeing proposed a ten-point package that includes installing a fireproof container around the aircraft’s lithium-ion batteries, new venting system for fumes, and changes in the cockpit checklist. Boeing also said it plans to develop a new battery design that will measure the temperature and any voltage changes in individual cells."

without further explanations from Boeing, to me this sounds less like solving the problem, and more like they are preparing for test flights: trying to mitigate and contain damage with a new fireproof container, more spacing and venting, and at the same time gather more data by installing more sensors.

afaik the root cause is still unknown. yet Boeing claims this is "not an interim fix but a permanent fix". I hope some more information is forthcoming.

poorjohn

If its not, the obvious fix would be to eliminate the batteries. Just require ground power to fuel/maintain/start the aircraft.

Standing behind my usual claim of ignorance, I'd guess that NiCd would be fine in the APU-battery role, and it's lithium just to keep the LRU count down. The real requirements for the two batteries must be hugely different.

Any bets on who'll win the showdown between DOT and Boeing?

deptrai:
Part of it seems more likely to be to fix fundamental flaws in the original design of
the battery subsystem.

If more modern technology with a higher than average risk factor is to be used, then
you need to go further than the usual due diligence and if anything,
over-engineer until enough in service experience is gained.

I'm sure they will make it work with LI batteries, as it is proven technology in other
areas...

Adding ~100 lbs* of 1/2"-thick stainless steel fireproof case (as reported by sources not permitted to report such things) plus miscellaneous paraphenalia to permit the occasional battery to "safely" self-destruct sounds more like saving face and short-term shareholder value than good engineering. *[per battery, guestimating 12"x12"x12" case, stainless steel nominally 4.7 oz/cu-in]

"A special announcement for the passenger in seat 30H: there has been a battery explosion under the floor near you and there is no extinguishing system installed.
However there is no cause for alarm as the battery is in a heavy steel box. If you start to feel hot please contact a cabin attendant.
Our estimated flying time to the emergency alternate airport is three hours."

ARE THEY KIDDING?
.

exactly - who is going to fly on one of these planes when the cause of the problem is unknown but they are willing to ltake the risk of further fires?

Are they planning to actually carry out test flights where they set fire to the batteries in their "fire proof box" and see what happens???

Somehow I suspect this one will remain a rumour, surely there is no way anyone will certify an aircraft to fly on the basis that a known fire hazard in an emergency power system is safely encased in metal...