CM
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Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 5:59 pm

I'm starting a new conversation here.

In short:

>>The 787 uses Lithium-ion technology for its main and APU batteries. It is the first large commercial aircraft to use this battery technology in a large battery application.

>>Over a span of less than 2 weeks, 2 batteries in two separate 787s experienced thermal runaway events, causing a great deal of heat, smoke and, in the case of a JAL airplane on the ground in BOS, fire in the equipment bay.

>>After the first event, the NTSB opened an investigation and the FAA announced a full review of the 787 design and certification.

>>After the second event, ANA and JAL voluntarily grounded their 787 fleets, with the FAA issuing an AD to ground the US fleet the following day. All other regulators and airlines followed suit, with all 787s now grounded worldwide.

>>The FAA statement on the matter was, in part:

Quote:
"As a result of an in-flight, Boeing 787 battery incident earlier today in Japan, the FAA will issue an emergency airworthiness directive (AD) to address a potential battery fire risk in the 787 and require operators to temporarily cease operations. Before further flight, operators of U.S.-registered, Boeing 787 aircraft must demonstrate to the Federal Aviation Administration (FAA) that the batteries are safe.

The FAA will work with the manufacturer and carriers to develop a corrective action plan to allow the U.S. 787 fleet to resume operations as quickly and safely as possible.

The in-flight Japanese battery incident followed an earlier 787 battery incident that occurred on the ground in Boston on January 7, 2013. The AD is prompted by this second incident involving a lithium ion battery. The battery failures resulted in release of flammable electrolytes, heat damage, and smoke on two Model 787 airplanes. The root cause of these failures is currently under investigation. These conditions, if not corrected, could result in damage to critical systems and structures, and the potential for fire in the electrical compartment.

Last Friday, the FAA announced a comprehensive review of the 787’s critical systems with the possibility of further action pending new data and information. In addition to the continuing review of the aircraft’s design, manufacture and assembly, the agency also will validate that 787 batteries and the battery system on the aircraft are in compliance with the special condition the agency issued as part of the aircraft’s certification."

>>There is a great deal of speculation about what the root cause of these events was and ways Boeing might address them in order to return the aircraft to service.

This thread is for the purpose of discussing the events, the FAA action, the technologies involved, and Boeing's effort to get the aircraft back into service. This thread is not for conspiracy theories, speculation about corruption in the certification process, or other issue not directly related to the events and the technologies involved. If you want to discuss those topics, please join the threads in Civ Av, where your comments will be quite welcomed.

Thanks!

CM

[Edited 2013-01-24 04:48:33 by Wilco737]
 
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Stitch
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RE: Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 6:59 pm

Before those two incidents, the 787-8 had over 100,000 hours of in-service operation without either the Ship's or the APU battery suffering a fire or leaking electrolyte.

The NH airframe - JA804A - was delivered a year prior to the incident. It was the 9th 787 airframe to begin construction.

The JL airframe - JA829J - was delivered less than three weeks prior to the incident. It was the 84th 787 airframe to begin construction and the most recent 787 airframe delivered to a customer.

The Ship's Battery on JA804A (the NH airframe) had been replaced in October 2011. The stated reason for this was because the original battery could not start the engines. However, the Ship's Battery is not used to start the engines, so it may be a case of mistranslation (the original report was from Japanese media) or a miscommunication (the Ship's Battery can assist the APU battery in starting the APU).

There have been reports in the Japanese media that the two batteries may be from the same production batch.

The NTSB has been quoted as saying that the battery on JA829J was not subjected to charging voltages higher than it was designed to handle.

Japanese government officials have been quoted as saying that the battery on JA804A was subjected to charging voltages higher than it was designed to handle.

I have received an unconfirmed, third-hand report that a software update to the charging system was applied to a number of 787-8s recently, The details of this update are not known, though it has been said they changed the charging controls and algorithms. I also do not know which 787-8 airframes received this update (again, assuming such an update did occur).

[Edited 2013-01-22 11:00:29]
 
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kanban
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RE: Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 7:54 pm

CM, while I applaud the idea of a fact and data driven thread, the trollers and conspiracy theorists will find this sooner or later.

I'm afraid that it will still cause you, Tom, Stitch and others to be monitoring both forums and answering questions twice.

case inn point, I just finished a post in the other forum asking about the flammability or the electrolyte.. I could cut an paste it here however I'm leaving it as just one post.
 
nomadd22
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RE: Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 8:09 pm

I hear a lot about excessive charging voltage (or lack of) but that's not really the factor in the failures I'm familiar with. You always have to use a high voltage for the final portion of the charge to get that last 10% or so. Cheap batteries might just have a thermistor to limit current when the battery get to a certain temperature, but there's no chance they used that on the 787. That algorithm has to be one that analyzes the voltage to current over time curve to sense end of charge and cut the voltage back down to maintenance, or whatever they call it. I'd hope that it also predicts battery problems by sensing abnormal charging curves.
This would be a lot more fun with some details of the charging/monitoring system. Damn their proprietary eyes anyhow.
I'm guessing a two part fix. Inspection, some replacement and quality control measures to get them airborne. Maybe a 90% charge limit or additional monitoring that wouldn't change anything to the extent of needing new, drawn out certification.
Long term, something that will take a while. A major change in the charging and monitoring in order to predict trouble and disconnect cells before grief ensues. Along with procedure to make sure sub par batteries don't find their way to a plane. Much depending on if the problem was design, production or something else.

I'm not sure if I'd put my money on Japanese government official comments. It's just too easy to prevent or detect higher than designed for voltage.

[Edited 2013-01-22 12:12:11]
Anon
 
nomadd22
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RE: Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 8:20 pm

By the way. I probably missed it in the last 800 posts, but are we talking about cobalt oxide cathodes?
Anon
 
Cubsrule
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RE: Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 8:21 pm

One question I have is what assumptions Boeing and Airbus made when they incorporated lithium ion technology in to the 787 and 350. I understand the benefits, but what did Boeing and Airbus decide about thermal runaway and safety that is different today from when the 380 was developed with only minimal use of lithium ion batteries?
I can't decide whether I miss the tulip or the bowling shoe more
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 8:54 pm

I'm gonna repeat the post I just made in the civ/av thread after taking a look at the picture of the battery box after the flight (before it was cracked open):

On the surface, doesn't look too bad...I remember a battery box (containing a lead acid battery) looking like this after a coworker hooked up 28 volts DC to a poor Cessna 150 with a 12 volt electrical system and a dead battery... Fortunately, no one ever turned the master switch on in the 150 before the coworker realized the mistake. The mechanic was able to replace the fried battery and clean up the acid that boiled out of the battery box the same day. And yes, battery acid dripped down out the bottom of the cowling
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
 
CM
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RE: Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 9:00 pm

Quoting Stitch (Reply 1):
Before those two incidents, the 787-8 had over 100,000 hours of in-service operation without either the Ship's or the APU battery suffering a fire or leaking electrolyte.

Yes. Someone else suggested the total flying time between airline operations and flight test should be a bit over 100,000 hours. I could go verify that number as I have access to operational hours by tail number, but then I couldn't post on here about it - so let's call it 100,000 hours before the incidents. Sometimes it's better to not know things precisely!  

Mike Sinnett (787 Chief Project Engineer) also stated the batteries have 1.3 million total operating hours, between labs, flight test airplanes and the in-service fleet.

Quoting kanban (Reply 2):
CM, while I applaud the idea of a fact and data driven thread, the trollers and conspiracy theorists will find this sooner or later.

It is why I didn't post this link in the other thread. Perhaps this will give us a little time to discuss things intelligently.

Quoting nomadd22 (Reply 4):
By the way. I probably missed it in the last 800 posts, but are we talking about cobalt oxide cathodes?

As far as I am aware, the batteries are Lithium Cobalt Oxide. At one point the batteries were Lithium Manganese, but my recollection is the chemistry was changed for some reason. It may have been to achieve longer on-wing life for the batteries, but I may not be remembering that exactly right.

Quoting kanban (Reply 109):
we have discussed that the electrolyte is flammable.. but at what temperature? does the boiled extruded goo have the same or a significantly high ignition temperature? Does that "boiling" reduce the toxicity or encapsulate it so corrosion of surrounding metal is not at risk? My concern with building a double hull type containment is it would not allow the goo to cool which could exacerbate problems. If it runs out the port and hardens or vents from the a/c, it is less likely to ignite than if pooled around a thermal run away.

I don't know the answers to this, but I bet there is a battery expert or a fire chief out there who can help us with this. Let's hope one of those with these qualifications from the other thread drifts over.

Quoting rheinwaldner (Reply 117):
The A350 needs equally good battery solutions as the 787 obvioulsly. Airbus even mentions an additional delay, if corrections are needed. The difference is, that the total installed battery capacity is much smaller, and yet the number of cells is higher. So a single cell is less vulnerable and has less capacity to do harm.

This comment caught my attention. I have a copy of an A350 systems description which includes this explanation of the A350 batteries:

Quote:
Batteries DC generation:
Four identical Lithium-Ion batteries are connected to the 28 V DC network in order to:
- Ensure the No Break Power Transfer function
- Provide standby DC power
- Provide DC power on ground if AC power is not available .
Two out of the four batteries can provide temporary supply in an emergency configuration.

If only 2 of the 4 A350 batteries provide standby power, it is clear there was not an attempt by Airbus to reduce the size of the batteries by splitting them into 4 batteries instead of the traditional 2. Also, the standby power loads between the A350 and 787 will not be dramatically different. For example, the 787 and 777 have nearly identical standby power loads on the battery with the one difference being the need for additional capacity for electric braking on the 787 when the RAT drops below a certain speed. Because of this, I am of the opinion the A350 has 4 rather normal sized Lithium-ion batteries, not 4 half-sized batteries, as is being suggested. It adds relevance to this comment from the other thread:

Quoting Kaiarahi (Reply 111):
The Airbus Director of Programs is on record as saying that an adverse outcome of the Boeing Li-Ion issue would have a significant impact on the A350.
 
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817Dreamliiner
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RE: Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 10:04 pm

Ive havent been following the previous threads on the topic due to the Boeing haters and trolls, but im glad you've started this thread here CM. I don't want to start speculating but here's my take on the battery accidents:

Quoting Stitch (Reply 1):

Before those two incidents, the 787-8 had over 100,000 hours of in-service operation without either the Ship's or the APU battery suffering a fire or leaking electrolyte.

And you can also include the many hours of flight testing that was done with the 6 test aircraft. The only exception would be the fire that occurred on ZA002, though im sure that is not related to the current battery issue.

Quoting Stitch (Reply 1):
There have been reports in the Japanese media that the two batteries may be from the same production batch.

This is Exactly what I thought, when details of the second Incident were released. However, im sure this hasn't been fully proven as yet. As noted above the 787 has been in service for over a year, plus a year and a half of flight testing. If it really was a li-Ion battery design problem it should have came up in flight testing, which lead me to believe that the two batteries came from the same batch.

Quoting Stitch (Reply 1):

The Ship's Battery on JA804A (the NH airframe) had been replaced in October 2011. The stated reason for this was because the original battery could not start the engines. However, the Ship's Battery is not used to start the engines, so it may be a case of mistranslation (the original report was from Japanese media) or a miscommunication (the Ship's Battery can assist the APU battery in starting the APU).

Is that supposed to be October 2011 or 2012? Can you post the link to this?

Quoting Stitch (Reply 1):
I have received an unconfirmed, third-hand report that a software update to the charging system was applied to a number of 787-8s recently, The details of this update are not known, though it has been said they changed the charging controls and algorithms. I also do not know which 787-8 airframes received this update (again, assuming such an update did occur).

While unconfirmed, it would be interesting if this did occur, again don't really want to speculate, but a software update causing the problem actually sounds plausible... What would be the process of testing a software update before its released to aircraft?

Also, I read a rumour on another site that the JL 787 might be written off, but as I said that's just a rumour. I don't think the damage was that bad to write it off...
Please let me know... If you know this is the end of the world, Let me know... If you know the truth...
 
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Stitch
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RE: Tech/Ops Discussion Of The 787 Grounding

Tue Jan 22, 2013 10:16 pm

Quoting 817Dreamliiner (Reply 8):
Is that supposed to be October 2011 or 2012?

2012.
 
PITingres
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 12:46 am

Curiosity question: How much room is there around the two battery enclosures? If part of the solution is to wrap the box in a sort of "drip tray", or rework the enclosure to give some level of individual cell containment, it's obviously going to make the total package larger. Is there any room to work with or is the battery going to have to maintain its current form factor?

Quoting kanban (Reply 2):
...the trollers and conspiracy theorists will find this sooner or later.

Well, I for one will have no compunction about using the delete post button. Let's hope the mods can keep this thread clean at least for a while.
Fly, you fools! Fly!
 
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Stitch
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 1:03 am

There is a drawing of the forward and aft EE bays at the start of this PPrune thread, but I do not know how accurate they are. If the drawing is accurate to scale, then it looks like there may be room around it.

ADent in Reply 105 of the FAA Grounds 787 Part 4 (by iowaman Jan 21 2013 in Civil Aviation)#1 thread also showed a picture of the Ship's Battery on JA804A in-situ and it does look like there is a bit of extra room around it.
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 1:38 am

Quoting kanban (Reply 2):
I just finished a post in the other forum asking about the flammability or the electrolyte..

I've been searching for the answer and what I found so far says the electrolyte is flammable. Actually, when you read more it says the vapors are flammable and they would need a source of ignition to burn. It does not self ignite! There is a lot of research into new electrolytes that add flame retardants, such as this one:
http://www.targray.com/li-ion-battery/electrolyte.php

Here are the sources and excerpts:

1) http://www.sbir.gov/sbirsearch/detail/15939
Commercially available lithium-ion cells use an electrolyte containing a mixture of organic carbonate solvents combined with lithium hexafluorophosphate (LiPF6). These electrolytes have significant disadvantages limiting the performance and safety of lithium-ion batteries. First, the solvents are volatile and flammable, leading to safety issues during production, storage and use of batteries and their behavior under abuse conditions. Second, LiPF6 is not hydrolytically or thermally stable in organic carbonates, leading to degradation of electrolyte, rise in electrode/electrolyte interface impedance, dissolution of active cathode materials and limited battery life. Thirdly, present electrolyte solutions appear to be reactive towards cathode materials at high voltages, which contribute to battery performance deterioration. It also prevents further development of future higher energy cells with 5V cathode materials. Finally, present electrolyte formulations are always a compromise; no one mixture of the solvents has been shown to work well at both low and high temperatures.

2) http://prod.sandia.gov/techlib/access-control.cgi/2012/129186.pdf
For lithium ion rechargeable batteries, these electrolytes are almost universally based on lithium hexafluorophosphate (LiPF6) salts with combinations of linear and cyclic alkyl carbonates. These electrolytes enable the use of lithium as the negative electrode active component and results in the high power and energy densities characteristic of the Li-ion chemistries. However, these organic electrolyte solvents have high volatility and flammability that pose a serious safety issue for their use in the consumer and transportation markets. For example, gas generation in Li-ion cells under abuse conditions has an effect on safety because gas production, if generated at sufficient pressure will vent flammable solvent vapor into the surrounding environment. The resulting fuel-air mixture can be quite explosive and only requires an ignition source to ignite the vapors. LiPF6 is known to react with carbonate solvents at elevated temperature and in the presence of moisture to generate large gas volumes of decomposition products [2-4].

3) http://www.electrochem.org/dl/interface/sum/sum12/sum12_p045_049.pdf

4) http://144.206.159.178/ft/641/92454/1607448.pdf
The electrolyte for these batteries typically consists of ethylene carbonate with a high dielectric constant and an alkyl carbonate as a low viscosity solvent containing the LiPF6 salt. These solvents are flammable. When the internal pressure of the battery increases and the battery is mechanically destroyed, the electrolyte could be led to the dangerous situations such as fire and explosion. These accidents were thought to be related to the flammability of common carbonate-based electrolytes. Therefore, it has been becoming important to find effective method to suppress the flammability of lithium-ion batteries.

5) Wikipedia (this talks about the properties of LiPF6 salt, which by itself is not flammable)
http://en.wikipedia.org/wiki/Lithium_hexafluorophosphate
The flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air. Measuring a flash point requires an ignition source. At the flash point, the vapor may cease to burn when the source of ignition is removed. The flash point is not to be confused with the autoignition temperature, which does not require an ignition source, or the fire point, the temperature at which the vapor continues to burn after being ignited. Neither the flash point nor the fire point is dependent on the temperature of the ignition source, which is much higher.

I'm fundamentally challenged when it comes to chemistry (just a dumb economist here) so I hope this helps a bit. Please don't ask me for any follow ups.  

[Edited 2013-01-22 17:50:20]
 
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kanban
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 4:19 am

Quoting BEG2IAH (Reply 17):
I'm fundamentally challenged when it comes to chemistry

I am also.. failed chemistry so bad had to switch to an art major..
Thanks , some of it made sense.. hopefully tdscanuck or CM will translate to layman's terms.
 
tdscanuck
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 4:41 am

Quoting kanban (Reply 20):
I am also.. failed chemistry so bad had to switch to an art major..
Thanks , some of it made sense.. hopefully tdscanuck or CM will translate to layman's terms.

Hated chemistry so much I took Chemistry AP in high school just so I could avoid taking it as an undergraduate. Never took a chemistry course again, although it kept popping up annoyingly in other contexts.

Tom.
 
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Stitch
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 5:09 am

Quoting BEG2IAH (Reply 17):
I've been searching for the answer and what I found so far says the electrolyte is flammable. Actually, when you read more it says the vapors are flammable and they would need a source of ignition to burn. It does not self ignite!

So it is possible that with the outflow valve actively clearing the air in the EE bay, then even an electrolyte stream might not ignite due to the flammable vapors being expelled from the bay?
 
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CALTECH
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 5:24 am

Quoting CM (Reply 7):
As far as I am aware, the batteries are Lithium Cobalt Oxide. At one point the batteries were Lithium Manganese, but my recollection is the chemistry was changed for some reason. It may have been to achieve longer on-wing life for the batteries, but I may not be remembering that exactly right.

As relayed to us, the composition of the electrolyte was changed as the batteries were only lasting 6 months. With the new composition, battery service life has gone up to approx 4 years. Oxides had been added to the composition is what has been said.

These 787 batteries, they are high energy and high heat. There were concerns about the temperature generated during periodic main/APU battery capacity checks to be performed on the aircraft, as proposed. Believe our airline is so concerned with the heat generated and relying on a test box to prevent a thermal runaway durng the capacity check, that the batteries will be removed from the aircraft for these capacity checks.

Also, unlike the Ni-Cad batteries, if a bad cell is encountered on these 787 batteries, it supposedly needs all the cells replaced for cell voltage balancing.

787 has a voltage below which it cannot be recharged.The battery has an auto-shutdown program to prevents cell damage from further voltage loss.

In tests, the 787 batteries have been dropped from aircraft E&E hatch height, and then steel rods were driven through the battery, all with no explosive effect. It hasbeen said that the new Li-ion chemistry in this battery – the electrolyte is a paste composed mainly of Li ion solution, cobalt, and a proprietary powder – is a much more stable chemistry than earlier and other Li-ion chemistries.

It has been said that there is no going back to Ni-Cad. This is a interesting aircraft. The leap in new technologies will take some getting used to. Can not wait to fly on one .
UNITED Would Be Nice
 
BEG2IAH
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 5:54 am

Quoting CALTECH (Reply 23):
In tests, the 787 batteries have been dropped from aircraft E&E hatch height, and then steel rods were driven through the battery, all with no explosive effect. It hasbeen said that the new Li-ion chemistry in this battery – the electrolyte is a paste composed mainly of Li ion solution, cobalt, and a proprietary powder – is a much more stable chemistry than earlier and other Li-ion chemistries.

CALTECH, would that mean "flame retardant" might be part of that new proprietary chemistry?
 
CM
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 6:27 am

Quoting 817Dreamliiner (Reply 8):
Also, I read a rumour on another site that the JL 787 might be written off, but as I said that's just a rumour. I don't think the damage was that bad to write it off...

I don't have any direct knowledge of either battery incident, but the photos I've seen of the JL airplane sure wouldn't point in this direction. Let's imagine an extreme scenario: if the entire rack which housed the battery needed to be replaced (P150 panel, WIPS controller, APU battery charger, etc), plus the airplane required a major structural repair in the bilge area below the battery, I am still confident the cost of this repair would fall far short of what would make the insurer consider writing the frame off as a hull loss. I would guess the airplane to be valued by an appraiser at between $125 and $150 million. The cost of the repair would need to approach 50% of this before it would be written off.



Quoting kanban (Reply 20):
hopefully tdscanuck or CM will translate to layman's terms.

Not to create a theme, but Would you believe you can get both mechanical and aero degrees with nothing more than grade 10 chemistry? I hated it, did poorly in it, and retained none of it. I will truly be of no use to you on topics of chemistry.



Quoting Stitch (Reply 22):
So it is possible that with the outflow valve actively clearing the air in the EE bay, then even an electrolyte stream might not ignite due to the flammable vapors being expelled from the bay?

I doubt this very much. The normal ventilation of the equipment bays is designed with just enough pressure differential to keep steady airflow through the bay for cooling reasons. There are fans in the system, but the negative pressure at the outflow valve will keep things moving even without them. If smoke is detected, there is a second "outflow valve" (called the override valve) which automatically opens and increases the venting of the bay. Even with this second valve open, the intent is to have just enough negative pressure relative to the rest of the airplane that it would not be possible for smoke to migrate from the equipment bay into the main deck. It is by no means a massive vacuum evacuating the bay. A man wearing a toupee would certainly be safe in there, even with the override valve open  



Quoting CALTECH (Reply 23):
It has been said that there is no going back to Ni-Cad.

I know many in the other threads were asking why Boeing is not just making a Ni-Cd battery for the 787 and being done with this issue altogether. There are distinct differences in the power provided by each battery, which is why I believe your statement is mostly correct; a swap of battery technologies might be possible, but it would not be straightforward. A Ni-Cd cell has a marked voltage decay from peak charge to its depleted state. A Li-ion cell holds a much more constant voltage as it discharges. Among the many desirable aspects of Li-ion batteries, I believe the power quality they produce (and systems which were designed to take advantage of it) may make it very hard for Boeing to change battery types at this point.
 
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CALTECH
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 7:40 am

Quoting BEG2IAH (Reply 24):
CALTECH, would that mean "flame retardant" might be part of that new proprietary chemistry?

As in adding 'flame retardant' ? No. It is just a more stable chemistry. And the new composition of the electrolyte was done quite some time ago, they may play with it some more.

Quoting CM (Reply 25):
I know many in the other threads were asking why Boeing is not just making a Ni-Cd battery for the 787 and being done with this issue altogether. There are distinct differences in the power provided by each battery, which is why I believe your statement is mostly correct; a swap of battery technologies might be possible, but it would not be straightforward. A Ni-Cd cell has a marked voltage decay from peak charge to its depleted state. A Li-ion cell holds a much more constant voltage as it discharges. Among the many desirable aspects of Li-ion batteries, I believe the power quality they produce (and systems which were designed to take advantage of it) may make it very hard for Boeing to change battery types at this point.

Spot on. It is and could be possible to go to a Ni-Cad battery, but very unlikely for all those reasons you posted, at least up to this pont in time.

[Edited 2013-01-22 23:42:52]

[Edited 2013-01-22 23:43:51]
UNITED Would Be Nice
 
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kanban
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 8:02 am

Quoting CM (Reply 25):
Not to create a theme,

dang.. what a crowd!!! well maybe there is a chemist out there.

RCAIR1 had some interesting observations and new understandings about these batteries and their properties on the AV thread..
 
KC135Hydraulics
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 9:30 am

Hey guys,

Much prefer the discussion on this forum than on civil aviation! I also posted this picture there, but I thought it'd be interesting for conversation here. These are the batteries on the KC-135. They are lead-acid, 28v. These are kept in the latrine... as you can see, the toilet on the left and the urinal can to the right.




Battery charger controller is mounted just above the circuit breaker panel.
MSgt, USAF
KC-135R / C-17A Pneudraulic Systems Mechanic Supervisor
 
nomadd22
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 11:36 am

Quoting CALTECH (Reply 23):
Also, unlike the Ni-Cad batteries, if a bad cell is encountered on these 787 batteries, it supposedly needs all the cells replaced for cell voltage balancing.

It's more important for the cells to be perfectly matched in a series to prevent overcharging one of them with Lithium.

Quoting CALTECH (Reply 23):
It hasbeen said that the new Li-ion chemistry in this battery – the electrolyte is a paste composed mainly of Li ion solution, cobalt, and a proprietary powder – is a much more stable chemistry than earlier and other Li-ion chemistries.

I don't have anything to back it up, but we'd always gathered that the cobalt chemistry was one of the less safe ones and was used for greater capacity and voltage. An iron oxide setup would have needed one more cell to get the same voltage. I gather you're referring to the proprietary solution, and not being cobalt based.
Anon
 
Aviaponcho
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 11:43 am

Hello guys

Did you see (here ?) this one

http://www.usatoday.com/story/travel.../01/23/japan-boeing-probe/1857647/

Quote:

Japan Transport Safety Board chairman Norihiro Goto told reporters the jet's data recorder showed the main battery, used to power many electrical systems on the jet, did not exceed its maximum voltage. That contradicts an earlier assertion by the agency as it investigates with the U.S. Federal Aviation Administration.

All 50 of the 787 Dreamliners that Boeing has delivered to airlines were grounded after the emergency landing by the ANA flight in western Japan on Jan. 16. Boeing has halted deliveries of new planes until it can address the electrical problems.

Goto said the maximum voltage recorded for the battery was 31 volts, which was below its 32 volt limit. But the data also showed a sudden, unexplained drop in the battery's voltage, he said.

Aircraft do not usually use the kind of lithium ion battery chosen for the 787, and investigators are still struggling to figure out what may have gone wrong.

"It's not that it is difficult, but that we are not so familiar with it," Goto said.

The Transport Safety Board said it also will study the aircraft's auxiliary battery and compare data from each.

So no overcharging at the battery level for the 2 failures..
and Japanese backpedalling by the way

[Edited 2013-01-23 03:49:12]
 
rcair1
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 2:06 pm

I, too, have tried to escape the other thread here. Thanks to CM for starting it.

I posted the following in the other thread last night after spending a lot of time doing research into new areas.

To my chagrin - I found that some of the information I had posted on Li-Ion batteries applies only to Li primary (non-rechargeable) batteries.
My apologies to all for being incorrect!
------
So - I got really tired of reading patents today and so I started looking for concrete new data on Li-Ion battery fire danger and suppression techniques. I even spent a fair amount of time reading about "bricking" your Telsa.

I've discovered some errors in what has been posted here, including errors that I made.

To be clear - the information I provided was based on training I received in an alternative fuels class I took about 4 years ago - and it seems like the understanding is evolving.

First - the biggest source of misunderstanding is confusing Lithium and Li-Ion battery chemistry and the approaches to fighting a fire in both cases.

In Lithium battery fires - these are non-rechargable Li Batteries - known as primary batteries - there is significant metallic Lithium. This is a true metal class fire and requires class D extinguishing agents. Conventional extinguishers - ABC as well as Halon, and most especially water - do not work.
-> My training was focused on this - and either I missed the following, or it was not covered.

In Lithium-Ion rechargeable batteries - secondary batteries - there is little metallic Lithium. You can use water or class ABC extinguishing agents - though the efficacy of them is unproven. The primary fire hazard for a Li-Ion battery is 2 fold - heat due to thermal runaway and flammable electrolyte/vent gas. The big difference - which I have just learned - is that the electrolyte in a Li-Ion battery is more flammable that the electrolyte in other batteries (like NiCad or NiMH) because it is not water base. Those other electrolytes pose much higher corrosion and toxicity concerns, but lower fire concerns.

Tests seem to indicate that conventional techniques, if they could be applied, would be effective in extinguishing the flame - however, the danger posed by re-kindle is major.
For instance, Halon 1301 is shown to be effective extinguishing the flame (electrolyte/gas), but not cooling the battery. If you use Halon, you will likely face re-kindle. An effective suppression would need to persist - to remain on the fire long enough to extinguish re-kindles long enough for thermal runaway to terminate. Water is effective in cooling, except that the design of the battery makes it difficult/impossible to apply well enough to overcome the heating of a thermal runaway.

It is interesting to note the 2 methods discussed for aircrews to deal with runaway fires in consumer batteries (laptops) are to 1) douse them repeatedly with water or 2) put them in a containment bag. The containment bag is designed to contain the heat long enough for runaway to terminate and the fire to go out. No effort is made to contain vent gasses in these containment bags. The reports I read seemed to indicate the containment bag was a better approach - it was surer.

It is also unclear if "spreading" the electrolyte by washing it around with water is a concern.

So - the primary issue extinguishing a Li-Ion battery fire is that, while you can potentially extinguish the 'flame' you cannot effectively cool a battery in thermal runaway well enough to prevent re-kindle of either the electrolyte or gasses being expelled. A Halon extinguishing system in the EE bay would be ineffective - it may put out flames (if they are outside the containment), but would not cool the battery. Thermal runaway would continue and re-kindle would be likely.

BTW - the data I could find so far indicates that the flammability limit LFL to UFL for vented gasses is small. LFL is the concentration in air below which the gas is non-flammable (too lean) and UFL is the concentration above which it is not flammable (too rich). A narrow flammability range means that an effective control method is to either concentrate or disperse the gas. The latter is obviously the better choice. Therefore - effective and positive ventilation is important.

One of the better references I've been studying is research performed by the Fire Protection Research Foundation - funded by the NFPA (National Fire Protection Association) - an organization I work with a lot.

The report I reference is located at the link below and was dated July 2011. I might refer you to Chapter 6 (page 84) and beyond.

The obvious question one may ask is does this change my opinion on the situation the 787 and Boeing face. The answer I have is - I'm sure - not going to satisfy some. Simply stated - I don't know yet - I need more data.

It seems that containment and venting (if those are not contradictory terms) are still the best approach based on the data I have seen. Vent the gas to keep it below LFL. Contain the fire so it says in the 'box'.

I do have a concern about the leaked electrolyte. Based on the new knowledge I spent the afternoon gaining (not from a.net by the way), my level of concern is increased. If it is flammable - and it appears it may be (since we do not know the exact composition of the Yuasa batteries, I can't say for sure) it represents a hazard. Is it a hazard that can be managed by placing it in a location where, if ignited, it will consume itself and burn out without the fire extending - then - no. If it the fire could extend - then yes. I would caution you that even the NFPA report I'm citing states that Li and Li-Ion battery chemistry varies dramatically and they are careful not to point out that testing all the types of chemistry is beyond the scope of their research.

These are questions that need to be reviewed and answered. Of course - that is exactly what Boeing and the FAA is doing.
http://www.nfpa.org/assets/files/pdf...ch/rflithiumionbatterieshazard.pdf

My apologies for misinforming that re-chargeable Li-Ion secondary batteries require Class D

[Edited 2013-01-23 06:10:03]
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 2:20 pm

Quoting nomadd22 (Reply 30):
I don't have anything to back it up, but we'd always gathered that the cobalt chemistry was one of the less safe ones and was used for greater capacity and voltage.

That does appear to be the case with Lithium cobalt oxide (which is what the 787's batteries use). They are more susceptible to thermal runaway in cases of abuse such as high temperature operation (>130ºC) or overcharging.

Lithium nickel manganese cobalt appear to provide most of the benefits of lithium cobalt oxide, but is safer. This formulation was created in 2008, so it was not available at the time of the 787's development, but if it could be retrofitted into the Yuasa cels, it might provide the necessary additional level of safety.


Quoting nomadd22 (Reply 30):
An iron oxide setup would have needed one more cell to get the same voltage.

In that case, I wonder if there is enough space in the current bay location to allow a slightly larger battery using this cathode chemical.

[Edited 2013-01-23 06:28:50]
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 2:52 pm

Quoting CM (Reply 7):
I don't know the answers to this, but I bet there is a battery expert or a fire chief out there who can help us with this. Let's hope one of those with these qualifications from the other thread drifts over

The NFPA report I mentioned (re-linked here) discusses the energy content and flammability of a 16850 cell- this a typical cell used in consumer batteries. Clearly - this battery is different in the one in the 787 which is a prismatic design - but it can give us some idea of the energy content of an example battery of this type.

They do note that calculating the energy content here is difficult - this is based on a model used for fire suppression estimation. (pp88)

In the 16850 cell - they estimated the cell contain 3-6 g of electrolyte (pp 89) but to be conservative, they base the calculations on 10g of electrolyte and 1.6g of poly based separator. Based on the heat of combustion for typical materials, they estimate that battery has ~280kJ in the material. The battery itself can contain between 25 and 40 kJ of energy - so the total energy content of the battery is on the order of 300-320 kJ.

Now - this is for a n 16850 cell - this is the little cylindrical battery - kind of like a AA sized battery - used in consumer packs and they note that this estimate is not good for larger batteries because the size and composition is much different.

Suffice it to say - there is a significant amount of energy in the electrolyte - more than the stored energy.

http://www.nfpa.org/assets/files/pdf...ch/rflithiumionbatterieshazard.pdf

Regarding flammability - not energy content - the report is less revealing. This is because the chemistry is so variable. What they do discuss is the flammability of vent gasses in terms of UFL and LFL - the range of concentrations where the vent gas is flammable. I refer you to the beginning of chapter 6 - PP 86.

According to tests at Sandia - the vent gases include H2, CO, CO2, CH4, C2H4, C2H6 and some others in vary small quantities. Of those gases - CO2 is the most prevalent - in the 65% range. C2H4 is next (15%ish) followed by CO and H2. CO2, of course, is not combustible - so the most prevalent gas in these test will act more like an extinguishing agent - by displacing O2 and dispersing the other vent gases.
H and CO have large flammability ranges (4-75% and 12.5 to 74%), CH4's pretty narrow (say 1.8 to 9% +/-1) (pp87)

To determine the flammability of this gas - you must vent it into your test atmosphere with designated air flow rates and calculate the mixture present. If the mixture - for a particular gas - is within the flammability limit - and there is appropriate oxygen - and there is an ignition source - you can get a fire. There are way too many variables here that I don't know to be able to even approach the question of flammability of vent gasses in the 787 battery in a battery fire/vent.

You would have to know:
- The actual vent gasses for THIS battery
- The rate of venting
- The rate of airflow around the venting
- The concentration of oxygen and other gasses

I suspect that inside the containment - no way - it is too rich. Outside - if there is good airflow - to low. There may be an issue right at the vent location - where the gasses are vented to the atmosphere. There may be a location where the mixture is such that fire could occur. We talk about that when entering propane leak areas. Far enough away - not enough propane. Up close - too much. But somewhere in the middle, you will walk through a combustible mixture.

-- Regarding suppression mechanisms.
Halon - in particular in treating the vent gases is effective - it narrows the flammability range.
From pp 99
"When small quantities of Halon are added to a fuel/air mixture, they narrow the range
in which that mixture is flammable.176 Halon is far more effective at narrowing the flammable
range than an inert diluent. If sufficient Halon is added, the flammable range of a mixture, even
at an elevated temperature, is eliminated and the mixture cannot be ignited."

Unfortunately - Halon is a problem.
"Note that production of Halon was banned by the Montreal Protocols, as this material contributes to the destruction of
the ozone layer. Halon in use today is from recycled sources only, primarily for protection of aircraft."
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 3:47 pm

Quoting CM (Reply 25):
I am still confident the cost of this repair would fall far short of what would make the insurer consider writing the frame off as a hull loss. I would guess the airplane to be valued by an appraiser at between $125 and $150 million. The cost of the repair would need to approach 50% of this before it would be written off.

If it even got to that point, I suspect Boeing might eat some (or most) of the cost of repairs simply to avoid the PR issue of having a 787 written off at this stage of the game.

Quoting KC135Hydraulics (Reply 29):
These are the batteries on the KC-135. They are lead-acid, 28v. These are kept in the latrine... as you can see, the toilet on the left and the urinal can to the right.

And it was never that bright in there. Aim carefully!

Let me add my thanks to CM for starting this thread - it was difficult to find the useful information hiding amongst the dreck in those CivAv threads.
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 5:45 pm

NTSB update from Jan 20 that I haven't seen referenced (although I could have missed it on the CivAv compost heap). Major points:

JL battery being disassembled for examination of cell internal components.

Test plans developed for various components:

The team has developed test plans for the various components removed from the aircraft, including the battery management unit (for the APU battery), the APU controller, the battery charger and the start power unit. On Tuesday, the group will convene in Arizona to test and examine the battery charger and download nonvolatile memory from the APU controller. Several other components have been sent for download or examination to Boeing's facility in Seattle and manufacturer's facilities in Japan.

Does any of this (e.g. testing the APU controller / start power unit) suggest an investigative direction?

JTSB and BEA have accredited representatives to the NTSB investigation (there's no indication on the BEA site that they've started their own, contrary to "info" on the other thread).
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 8:15 pm

a revision from AV Herald

http://avherald.com/h?article=45c377c5&opt=6144

"Attending emergency services found no trace of fire, however traces of smoke released from the electric compartment were found on the outside of the fuselage. Investigators found the main battery, a lithium ion battery same type as the APU battery, had buckled at the upper cover and was leaking, the inside showed hydrocarbons. The main battery was removed from the aircraft on Jan 17th, the undamaged APU battery was removed from the aircraft on Jan 18th, following a first examination of the main battery on Jan 20th the battery has been dispatched for detailed examination on Jan 22nd."

the posting goes on to show pictures of both the a/c's batteries side by side.

The only thing puzzling is the insistence that the residue under the fuselage is 'smoke' residue rather than liquified electrolyte residue.
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 9:11 pm

Quoting Kaiarahi (Reply 42):
Does any of this (e.g. testing the APU controller / start power unit) suggest an investigative direction?

I'm not sure...it looks like they took the battery and everything the battery interfaces with. That seems more like the shotgun approach (investigate everything in the hope that we find the culprit).

Tom.
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 9:49 pm

Quoting tdscanuck (Reply 45):

If I remember (not sure of the source of the info, though), the APU was running in BOS. Which means it was started relatively recently before the fire was discovered - although we don't know if it was started before powering off the engines.
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 10:17 pm

Folks,

I tried to have this question answered in the "other" dreaded thread as well, so here goes:

Is Boeing physically checking each airframe delivered, in other words: are they dispatching personnel to NRT, SCL, DOH etc? Or is it just a check in general, concentrating on the batteries?
Same question for the NTSB, or do they leave that the local authorities in each country?

Has the B787 in question left Takamatsu yet?


Thanks,


FH
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RE: Tech/Ops Discussion Of The 787 Grounding

Wed Jan 23, 2013 10:29 pm

Quoting CM:

here are some personal thoughts on the FAA statement:
[...]
The statement talks about the failure mode, the conditions it may create, and the potential consequences:

Failure Mode:
>> Battery failure by thermal runaway

Conditions it may Create:
>> Heat
>> Release of flammable electrolytes
>> Smoke
>> Fire

Potential Consequences:
>>Damage to critical systems and structure

Hi CM (and everyone)
I've been meaning to build on your thoughts in reply 38 from FAA Grounds 787 Part 4 (by iowaman Jan 21 2013 in Civil Aviation) for a couple of days, but I don't have much free time.

Anyway, I used your ideas to propose this somewhat crude (!!) fault tree representation :



It starts with the root causes, which remain unknown, and could be a problem from any one among design, manufacture, assembly, in flight ops, ground ops, maintenance ops..., and probably a combination of the above.
I represented these root causes at a same level '-x' (-xvious event happened (everything is represented as independant - big approximation...)

Again this is very simplified, and is meant for illustration purposes only.

I did modify a little your interpretation of the "fire" part ; I kept the "EE bay fire" stated by the FAA, but put it as a terminal consequence. But I added a "battery fire" as immediate consequence, which could itself lead to both "bay fire" and "system damage".




Assuming the Boeing design and failure analysis people are competent - which I will   - the battery thermal runaway and its consequences (= the lower part of the tree, levels >= 0) are not a surprise, and should have been considered and the relevant occurance probabilities would have been analyzed and calculated. This would be based on a model of the fire/smoke/electrolyte propagation, itself based on some hypotheses.

As I see it, the problem is :
......1) the fact that 2 events happened in rapid succession could indicate that the calculated probability of the main failure is lower than it should be, if this is a systemic failure. The probabilities of all the subsequent events would be automatically increased, resulting in the terminal consequences having too high a probability (>1e-9)
and/or
......2) the observations made after the two incidents could invalidate the hypotheses used to calculate the conditional probabilities of the consequences (arrows leading to events at levels >= 1). The resulting calculated probabilities for the terminal consequences would then be invalidated also. If the model seems to be very wrong, the probabilities could be sufficiently off to climb above the 1e-9 threshold.

Alternative 2) seems to unlikely to me (or at least, unlikely that the hypotheses would be so wrong as to invalidate all calculations). And if this is a defect of a limited batch of equipment, then alternative 1) should be cleared also.

At least that is what I see so far, with the little data publicly available
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 12:17 am

Quoting airmagnac (Reply 50):
I used your ideas to propose this somewhat crude (!!) fault tree representation :

Thanks for this. I always do better when I can visualize things! Just a couple quick comments:

First, I agree with your modification and distinguishing between a fire inside the containment and a fire in the equipment bay. That's a good modification/improvement to how I had worded things before.

Regarding #1. I agree. It seems most likely that the original fault tree had a probability error in Level X or Level -1 than the alternative - that we just witnessed two remote or perhaps even extremely remote events within a relatively small number of operational hours. Lightning doesn't strike twice...

One of the possible precursors to a runaway event is a manufacturing defect inside the battery cell. The manufacturing process will have been studied and approved to validate that the likelihood of this defect occurring during manufacturing, so that some quantifiable probability can be inserted into the fault tree. Not personally knowing any details of the 787 battery fault tree, this probability could range anywhere from 1 to 1e-9, although I would be shocked if the probability wasn't quite remote. If the failure is at this level and if 1e-9 is in reality 2 in 200, you are absolutely correct that everything downstream needs to be revisited.

The absolutists in the other thread are quite hung up on the thermal runaway of the battery - that it must not happen under any circumstance, no exceptions. I think we both know this is not true for any battery on any airplane, and this is not how the 787's problem will be solved. From a "Failure Modes & Effects" standpoint, they are only thinking about the FM, they just assume the "E in FME is catastrophic or otherwise unacceptable. That sentiment in Civ Av (probably because they don't understand how AC 25.1309 or the EASA equivalent works) has them looking for solutions which will likely never even be considered by Boeing and the FAA.

Instead, I say let the fault tree take us to the Level 0 event with an assumed probability of 1. If I was involved with trying to solve this, I would certainly assign a team to go see how they would solve the problem under that assumption - that every battery will go into thermal runaway at some point in its life. This would get the team focused on mitigating the effects of the event and may result in an acceptable fault tree, even with a battery that occasionally misbehaves. (Please note, I'm not saying I would accept the demonstrated failure rate of the batteries, but you get my point)

Lastly, I probably should re-state the fact I was not involved at all in the 787 battery design. With that disclosure, you can take my comments as from someone who is well informed about Boeing design practices and FAA certification, but not from an expert on the failure modes within this particular system.
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 12:24 am

I might be one of the (few?) non-chemistry-haters here, although I never studied it at an advanced level. (Did plenty of messing around in the basement as a teen, though.) I happened to run across this haiku in the "Lamentations on Chemistry" blog and thought it might amuse the folks here:

Mighty exotherm
Sleeping in reaction mass
Please stay home today

 
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rcair1
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 1:00 am

Quoting airmagnac (Reply 50):
Anyway, I used your ideas to propose this somewhat crude (!!) fault tree representation :

I like your representation. I do have some comments.

For instance, you show the "release of flammable electrolyte" and "battery fire inside container" pointing at "EE bay fire.

I don't think that a fire inside the container would combine with electrolyte outside in that way. I think is is more likely that "heat" would combine with 'release" and lead to EE bay fire (not that I think it is likely).

You need to add 'venting gases' too. It may be they are more likely to ignite than the electrolyte - I don't know.

Also - the presence of heat and electrolyte would not, in all cases, lead to fire. Instead - there would be a probability factor (sent that become involved (extension), then it could damage critical components.
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 2:04 am



Quoting WingedMigrator (Reply 19):
Fun with Poisson statistics:

If we assume the underlying failure rate is constant, i.e. we are not dealing with an infant mortality issue
If we assume the battery system has accumulated 1.3 million hours of operation (as stated by Boeing exec)

Do you think Poisson is the right distribution model to apply here? I know we don't know the underlying failure mechanism but I have a tough time thinking of any mechanism that would have a constant rate with time.

Quoting TheSultanOfWing (Reply 49):
Is Boeing physically checking each airframe delivered, in other words: are they dispatching personnel to NRT, SCL, DOH etc? Or is it just a check in general, concentrating on the batteries?

I doubt they're doing that yet...unless they already know what they're looking for and that just hasn't been made public yet. As soon as they do know what to look for, I'd expect a joint NTSB/FAA/JCAB/Boeing/Yuasa team to visit all 50 airplanes.

Quoting TheSultanOfWing (Reply 49):
Same question for the NTSB, or do they leave that the local authorities in each country?

By treaty, the local authorities own the investigation. So NTSB has the Boston event and JCAB (or whoever their investigative branch is) has the Japan event. In many countries the local authorities have very limited resources and request help from a bigger outside agency (BEA, NTSB, etc.). Japan, however, has a very good investigation board so they wouldn't drag NTSB in on that basis. However, it's normal courtesy to bring the investigating body from the country of certification in. And, when two events might be coupled, they cooperate.

Quoting PITingres (Reply 52):
I happened to run across this haiku in the "Lamentations on Chemistry" blog and thought it might amuse the folks here:

Mighty exotherm
Sleeping in reaction mass
Please stay home today

The very sardonic part of me wants to see this written in as a footnote to a battery spec somewhere.

Quoting rcair1 (Reply 53):
You need to add 'venting gases' too. It may be they are more likely to ignite than the electrolyte - I don't know.

In one of the bazillion posts buried in the CivAv theads, somebody stated that it was only the gases that were flammable (or electrolyte vapour, also a gas). However, I have no idea if that was accurate.

Tom.

[Edited 2013-01-23 18:27:09]
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 10:17 am

From the following thread in Tech/Ops:

Battery Container Contributing To Li-Ion Failure? (by faro Jan 18 2013 in Tech Ops)

I thought a couple of questions may perhaps be better nested here:

Quote:
I wonder whether the container which serves as fire/leak shield for Li-ion batteries may be reflecting back into the battery the (strong) electromagnetic fields which are produced by the movement of lithium ions within it. Depending on the 3D geometry of the container, such retro-reflection may become amplified and focused on a local point within the battery. If such is the case, this point may become susceptible to heat damage and maybe ultimately lead to thermal runaway.

Is this shielding container metallic in the first place? If yes, it is designed to preclude retro-reflection of electromagnetic radiation produced internally by the battery?
Quote:

DC current through a relatively straight path isn't going to produce that much of a field. I don't know if they have something as simple as a large filter cap to keep high speed current pulses out of the battery.
But, it must be either something like that, where field conditions don't match lab conditions or the batteries being used are different than the ones that were tested. I'd think they would have had a full size pack in the the same boxes they'd be using in the plane being tortured under all possible environments for certification.
Quote:
The EM field will however peak as the current goes from nil to full discharge current. Given the power of the APU batteries, I dare say that the peak EM field on initial discharge could be quite significant.
Quote:
That's what I meant regarding the filter cap. It slows down the rise and fall time of the current changes and reduces the fields caused by such quite a bit.

I trust there is a filter cap in place on these powerful batteries. Can it be ruled out as a causal factor in the thermal runaway with any degree of confidence?


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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 10:57 am

I was reading a presentation on the B787 at work, and there was one slide about batteries.
It showed that Yuasa also makes the batteries for the flight control computor. There are two of these batteries on board.
It also states that all these four Yuasa batteries are subject to IATA Dangerous Goods Regulations and cannot be carried on passenger aircraft as cargo.
So are these Flight Control batteries Lion as well?
Are they being investigated?
Just curios
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 1:22 pm

Quoting Tristarsteve (Reply 39):
Are they being investigated?

I think anyone that has flown electric models knows that if one tries hard enough, one can make any sort of battery technology from any manufacturer to become unstable if they are not changed correctly.

I think it is a little early to point fingers at a particular battery manufacturer or battery technology, it is only one part of a larger system, it just happens to the most visible part that appears to have failed.

As you would know in flight the main and APU batteries should be receiving next to no change.
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 2:50 pm

Quoting Tristarsteve (Reply 39):
I was reading a presentation on the B787 at work, and there was one slide about batteries.
It showed that Yuasa also makes the batteries for the flight control computor. There are two of these batteries on board.
It also states that all these four Yuasa batteries are subject to IATA Dangerous Goods Regulations and cannot be carried on passenger aircraft as cargo.
So are these Flight Control batteries Lion as well?
Are they being investigated?
Just curios

Besides the Main and APU battery set, there are 3 sets of flight control emergency batteries. Haven't heard of any problems with these.

Quoting zeke (Reply 40):
As you would know in flight the main and APU batteries should be receiving next to no change.

In normal flight, until you lose a engine or engine generators, then the batteries will receive a charge, especially after the APU starts up.
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 4:50 pm

I'm reposting portions of a previous post that was removed because it quoted a post that quoted a post that quoted a post that was removed because that post violated rules. I actually don't know which was the offending post - but when a post is removed - every post that quotes it is removed - and if a post quotes one of the quoted ones, its removed- and so on.
It cascades - kind of like a Li-Ion Battery that has a cell in thermal runaway.

Sometimes it can be a lot of posts. In this case at least 16 posts were removed.

Reminds us all how important it is to follow the rules- I'm sure we lost some great discussions because of this - but I appreciate the mods trying to keep this thread focused.

I'm only posting the parts that I'm sure did not quote the post that quoted the offending post.

Quoting tdscanuck (Reply 37):
In one of the bazillion posts buried in the CivAv theads, somebody stated that it was only the gases that were flammable (or electrolyte vapour, also a gas). However, I have no idea if that was accurate.

Tom - let me help you with that one.
In this post, in this thread - I discuss the findings in a 2011 study performed for the NFPA on the characteristics of Li-Ion rechargeable (secondary) cells.

Quoting rcair1 (Reply 26):
In the 16850 cell - they estimated the cell contain 3-6 g of electrolyte (pp 89) but to be conservative, they base the calculations on 10g of electrolyte and 1.6g of poly based separator. Based on the heat of combustion for typical materials, they estimate that battery has ~280kJ in the material. The battery itself can contain between 25 and 40 kJ of energy - so the total energy content of the battery is on the order of 300-320 kJ.
Quoting rcair1 (Reply 26):
Regarding flammability - not energy content - the report is less revealing. This is because the chemistry is so variable. What they do discuss is the flammability of vent gasses in terms of UFL and LFL - the range of concentrations where the vent gas is flammable. I refer you to the beginning of chapter 6 - PP 86.

According to tests at Sandia - the vent gases include H2, CO, CO2, CH4, C2H4, C2H6 and some others in vary small quantities. Of those gases - CO2 is the most prevalent - in the 65% range. C2H4 is next (15%ish) followed by CO and H2. CO2, of course, is not combustible - so the most prevalent gas in these test will act more like an extinguishing agent - by displacing O2 and dispersing the other vent gases.
H and CO have large flammability ranges (4-75% and 12.5 to 74%), CH4's pretty narrow (say 1.8 to 9% /-1) (pp87)

While both are flammable, it seems that vent gasses may pose the highest risk of ignition outside the containment because they must be allowed to escape. Whether or not that is a hazard - in the sense of the FAA understanding - I can't say. Vent gas fire would probably be hot, but short lived. It may re-kindle.
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 5:09 pm

Ditto here... re-posting deleted stuff:

If we assume the underlying failure rate is constant, i.e. we are not dealing with an infant mortality issue
If we assume the battery system has accumulated 1.3 million hours of operation (as stated by Boeing exec)

Then:

With zero observed failures, the failure rate would have to be 2.3e-6 per hour (1 in 430,000 hours) to ensure there is only a 5% chance that they got lucky and saw "only" zero failures in 1.3 million hours.

With one observed failure, the failure rate would have to be 3.7e-6 per hour (1 in 270,000 hours) to ensure there is only a 5% chance that they got lucky and saw "only" one failure in 1.3 million hours.

With two observed failures, the failure rate would have to be 4.8e-6 per hour (1 in 208,000 hours) to ensure there is only a 5% chance that they got lucky and saw "only" two failures in 1.3 million hours.

Quoting tdscanuck:
Do you think Poisson is the right distribution model to apply here? I know we don't know the underlying failure mechanism but I have a tough time thinking of any mechanism that would have a constant rate with time.

I agree that the current circumstances probably do not jive with the assumption of a constant failure rate. Subject to that (poor) assumption, and subject to one failure having occurred after 1.3 million battery hours, the odds of another failure within (50 airplanes x 2 batteries/airplane x 12 operating hours/battery/day x 2 days = 2400 hours) are roughly 1 in 125, based on a generously large failure rate that corresponds to 95% confidence level. That by itself is a red flag, a mathematical way of saying "lightning never strikes twice"... There's got to be something more than bad luck here.

The failure rate may not be constant in the same battery over time.
The failure rate may vary from battery to battery.

All that being said, the Poisson distribution is a fundamental building block of any reliability analysis. Without it, you cannot make the leap from discrete test outcomes to a calculated failure probability. There are surely more sophisticated versions of it that account for a variable failure rate, and no doubt powerful numerical simulation tools to synthesize all that, but then you have to guess what the failure rate curve looks like (the bathtub parameters). You can quickly find yourself grasping at unobservable straws.

If only these batteries didn't fail so damn rarely, we'd have better data to work with  
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 5:20 pm

Quoting Tristarsteve (Reply 39):
So are these Flight Control batteries Lion as well?

I think so. The use of Li-ion in small backup emergency batteries is pretty well established (the A380's been doing it without issue for many years). The ISS also uses them.

Quoting Tristarsteve (Reply 39):
Are they being investigated?

Not that I'm aware of. If they crack open *that* can of worms, it's going to impact a lot more than 787's...it will completely kill off flight deck iPads and laptops, for example.

Quoting WingedMigrator (Reply 43):
If only these batteries didn't fail so damn rarely, we'd have better data to work with

Good point.

Tom.
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 6:00 pm

Quoting CALTECH (Reply 41):
In normal flight, until you lose a engine or engine generators, then the batteries will receive a charge, especially after the APU starts up.

In brand A aircraft I am only used to seeing batteries receiving a short charge in flight and then disconnecting from the charge (to bring the battery back up to its nominal voltage range). Most of the time they do not receive a charge, they are simply connected to the DC bus, however the DC bus is normally powered by normal power sources (AC BUS and TR to the DC BUS) and taking next to nothing from the batteries.

The 787 manual shows the 28 Vdc bus being normally powered by the 235 Vac bus via a power converter. I read the 787 FCOM on this part, it lacks any real depth to tell a lot of detail on the system. It does not show any input bus to charge the APU battery. I wonder if the main battery is continuously being charged, or if it has smarts in the system so it is only charged when required.
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 6:33 pm

I'll also repost my wild-eyed notion of using an aerogel within the containment case to enhance cell separation. The stuff is supposed to be an excellent insulator, is lightweight and heat resistant, and an extremely poor heat conductor. You could probably cast some sort of vent baffling into it for venting isolation. I don't know if an aerogel is or can be made corrosion resistant, though, and I don't know how well it withstands shock and vibration.
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 7:05 pm

Anybody has gen on the NTSB press conference that was supposed to happen @ 0230pm est ?
/

[Edited 2013-01-24 11:06:38]
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 7:25 pm

Quoting Pihero (Reply 47):
Anybody has gen on the NTSB press conference that was supposed to happen @ 0230pm est ?

Looks to still be planned to start in 10 minutes. There does not appear to be a public-facing option to follow in real-time - no webcast and CSPAN/CSPAN2 are not carrying it. There is a teleconference line, but you must RSVP and it appears to be limited to the press.
 
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RE: Tech/Ops Discussion Of The 787 Grounding

Thu Jan 24, 2013 7:46 pm

I know we can count on you for a report !   
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