iowaman
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FAA Grounds 787 Part 4

Mon Jan 21, 2013 10:34 pm

As the last thread was getting quite lengthy, please continue the discussion here.

Previous thread: FAA Grounds 787 Part 3 (by NZ1 Jan 19 2013 in Civil Aviation)

Enjoy the site!

[Edited 2013-01-21 14:38:07]
 
packsonflight
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RE: FAA Grounds 787 Part 4

Mon Jan 21, 2013 11:21 pm

Quote tdscanuck

No. I claim that spilled content does not violate the FAA special condition. That would only happen if the spilled content caused meaningful damage to surrounding components...so far, no evidence of that has been put forward. I'm sure it warrants some attention, if only to confirm that what spilled was what was expected to be spilled (if any).

You maintain that: That would only happen if the spilled content CAUSED meaningful damage to surrounding components
but the FAA says: COULD CAUSE meaningful damage...

There is a big difference, but I guess the FAA has the the authority. It is good to be the king......
 
nomadd22
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RE: FAA Grounds 787 Part 4

Mon Jan 21, 2013 11:30 pm

From reply 217, previous thread.


"Oops, you are right, I was 100% sure because I have the Ultramat 14. But ... it turned out that I have the Ultramat 14 plus. Here is the right docu:
http://www.graupner.de/mediaroot/fil...4_Ultramat_14_plus_de_en_fr_it.pdf

But everything that I said is valid."

Still no. That document specifically says the balance capability is for nicad and nimh. It does not do Lithium because it's not that simple. Reduced charging current or increased voltage through a Lithium cell can mean it's charged or defective. The opposite can mean it's discharged or defective. You have to have an intelligent device that can look at the voltage/current/time charging curve to decide if the cell is losing capacity, leaking or ready to run away. That simple balancing function is just an attempt to keep nicad and nimh cells about equal to prevent reverse charging of weak cells. It would be useless in predicting and removing a Lithium cell about to run off.

I'm not denying that chargers you describe exist just because I don't know of any outside of Tesla or the ISS. (Future ISS batteries will be Lithium upgrades)
Just that the referenced charger and document ain't it, and dumb race car batteries sure the heck don't have the ability.
I'd be happy to be proved wrong. Those big oil clean up boats you saw in the Gulf a few years back could use battery upgrades for the remote skimmer controllers, and I'd like to find a charger that could predict imminent cell failure. Right now I'm dropping Radio Shack RC nicad packs in them.
Uh,,,Blah,Blah 787 Blah, (Sorry about the rambling)

[Edited 2013-01-21 15:42:29]
Anon
 
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Braybuddy
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RE: FAA Grounds 787 Part 4

Mon Jan 21, 2013 11:43 pm

Quoting Kaiarahi (Reply 247):
Hence, when a regulator uses terms such as "extremely remote", "explosion", "self-sustaining", "failure", "major or more severe failure condition" in a regulation addressed to the professional community of aeronautical engineers, it is using them as technical terms which have a defined and precise meaning that is understood by the professionals to whom they are addressed. What Wikipedia or a non-professional non-engineer thinks they might mean is irrelevant - fortunately.

Which is why it is probably not a good idea for technicians or engineers to use such terminology when aruging with people who have a different, or less esoteric, interpretation of these words.

You can argue all you like that an explosion is not an explosion, but what term do you then use when you want to actually describe an explosion? And the same goes for smoke, fire or containment.
 
JoeCanuck
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 12:50 am

Quoting Braybuddy (Reply 3):

Considering this thread is dealing with exact technicalities in a specific field, if one strives to be accurate, they should defer to language and word definitions used in that field. Of course, the lay person may not know these specific definitions, but it's good to learn new things.

As a lay person in the aeronautical fields, (but not a complete thicko), my standard definitions might not be completely accurate in the context of, say, the investigation concerning battery fires on a 787.

Semantics are crucial to the language used because these are legal definitions and liability may hang on such subtle nuances.
What the...?
 
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Stitch
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 1:19 am

Quoting JoeCanuck (Reply 4):
Considering this thread is dealing with exact technicalities in a specific field, if one strives to be accurate, they should defer to language and word definitions used in that field. Of course, the lay person may not know these specific definitions, but it's good to learn new things.

And we are fortunate that we have members who understand these exact technicalities in this specific field and have tried very hard to provide specific definitions so that these incidents can be correctly and accurately discussed.

[Edited 2013-01-21 17:22:44]
 
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Revelation
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 1:36 am

Quoting packsonflight (Reply 1):
Quote tdscanuck

No. I claim that spilled content does not violate the FAA special condition. That would only happen if the spilled content caused meaningful damage to surrounding components...so far, no evidence of that has been put forward. I'm sure it warrants some attention, if only to confirm that what spilled was what was expected to be spilled (if any).

You maintain that: That would only happen if the spilled content CAUSED meaningful damage to surrounding components
but the FAA says: COULD CAUSE meaningful damage...

The FAA said the reason for the AD was that it could cause meaningful damage, not that it did cause meaningful damage.

I believe the special condition / design constraint is that it not cause meaningful damage.

As far as we know it did not cause meaningful damage, so the design constraint is not violated.

The FAA is concerned by the two incidents that a future one could cause meaningful damage, yet such has not yet happened.

Quoting packsonflight (Reply 1):
There is a big difference, but I guess the FAA has the the authority. It is good to be the king......

Indeed the king is concerned that something bad could happen.
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PHX787
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 1:45 am

How are some of the flights being accommodated? Has SEA been upgauged to a 772 and what about BOS?

SAN is cancelled through the 25th.
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tdscanuck
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 1:59 am

Quoting packsonflight (Reply 1):
You maintain that: That would only happen if the spilled content CAUSED meaningful damage to surrounding components
but the FAA says: COULD CAUSE meaningful damage...

The "that" in my quote refers to the incidents that occurred violating the containment. Since, as far as we know, neither event caused meaningful damage to surrounding components it's not clear that the requirements around fire containment were violated. This is in direct conflict to multiple posters in the prior thread who claimed that the incidents *demonstrated* that the containment was violated.

I agree that, if it's shown that spilled content could cause meaningful damage then Boeing would have another problem to deal with. But the events we actually know about do not show that damage occured, therefore we can't latch on to them as proof that the design features didn't work.

Tom.
 
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Stitch
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:12 am

Quoting PHX787 (Reply 7):
How are some of the flights being accommodated? Has SEA been upgauged to a 772...

I would assume it has gone back to the daily 777-300ER it was prior to the 787-8 taking over M-F (it was still a 777-300ER Sat-Sun).
 
cornutt
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:17 am

Since people have been asking, let me go over some of the hazard and probability definitions as defined by the FAA. Advisory Circular 25.1309-1A, "System Design and Analysis", is the document that lays out the FAA's general specifications for how hazards are classified and what probabilities they must meet, in regard to commercial airliners. The AC defines four categories of hazardous event, defined by severity. The terms and definitions are:

Minor: "Failure conditions which would not significantly reduce airplane safety, and which involve crew actions that are well within their capabilities." (Material in quotes is the actual words from the AC)

Major: "Failure conditions which would reduce the capability of the airplane or the ability of the crew to cope with adverse operating conditions to the extent that there would be, for example: A significant reduction in safety margins or functional capabilities, a significant increase in crew workload or in conditions impairing crew efficiency, or some discomfort to occupants."

Severe-major: "A large reduction of safety margins or functional capabilities, or higher workload or physical distress so that the crew could not be relied on to perform its tasks accurately or completely, or adverse effects on occupants." (Note here: the term "severe-major" does not actually appear in this AC. However, it is widely used in the industry to match this definition, and it is defined in the complementary AC 23.1309, which defines the standards for general aviation.)

Catastrophic: "Failure conditions which would prevent continued safe flight and landing."

The AC defines these acceptable probability levels for each category. A hazard in the category must be shown to be less likely than the standard, via the fault tree analysis:

Catastrophic: 10^-9 per flight hour, or 1 in 1,000,000,000 flight hours
Severe-major: 10^-7 per flight hour, or 1 in 10 million flight hours
Major: 10^-5 per flight hour, or 1 in 100,000 flight hours
Minor: no limit

(Note that these probabilities go out the window when it comes to software. Because software doesn't fail in a probabilistic manner like hardware does, there is a completely different way of evaluating it. If you're in the industry, you may have heard of the DO-178C standard for avionics software. It basically lays out standards and processes for software, according to the hazard severity level associated with the software. It is a *lot* of work to develop flight-critical software in accordance with DO-178C.)
 
prebennorholm
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:26 am

About this hair splitting of "contained" or "not contained". We have to look at two different things:

1. Heat
2. Residue

About heat: Those batteries went to full destruction on their known thermal runaway failure mode. We have no evidence telling that any other equipment suffered any heat damage. Therefore the heat can be assumed to be contained in these incidents.

But that's not all it takes to be "safe". If nobody know whether it takes twice as much heat to do any damage, or we came to 99% of the threshold, then we are not sure what margin we have. If such uncertainty exists, then the FAA may not at the moment consider it contained.

About residue: Residue - electrolyte - was floating on the EE-bay floor. It made cosmetic damage to the floor, but otherwise it is believed that it did no further damage.

But with chemicals on the floor it takes no more than turbulence and negative G to have it all over.

Therefore we go and ask questions to the subcontractors of all equipment in the EE-bay: "Is it okay to spray chemicals from a burst Li-Ion battery on your equipment? Was that requirement written in the specification, from which you developed your gear?"

If they all answer "Yes", and if the FAA agrees with them, then the residue contamination was contained.

Problem is that FAA already wrote the words "could damage" in their AD. If the FAA some day should eat those words again, then.... But until then it is fair to say that FAA already told us that the failure was not contained.

New subject:
Since the 2010 test incident in the EE-bay ultimately by Boeing was blamed on FOD, but too small to be positively identified, then I doubt that the EE-bay is totally Li-Ion runaway goof proof. As I read the FAA AD they seem to have the same opinion. That doesn't necessarily mean that a worst thinkable EE-bay contamination is catastrophic, but it certainly eats away redundancies and grows some really thick branches on the fault tree.
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Stitch
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:34 am

Quoting prebennorholm (Reply 11):
Since the 2010 test incident in the EE-bay ultimately by Boeing was blamed on FOD, but too small to be positively identified, then I doubt that the EE-bay is totally Li-Ion runaway goof proof.

But Boeing knows it wasn't caused by a battery leak. And considering the panels are, per reports of people who have seen them, enclosed in a case themselves, even if liquid electrolyte solution were sprayed on them, the interior should be protected.




Quoting cornutt (Reply 10):
Note that these probabilities go out the window when it comes to software.

I have heard an unconfirmed report that some 787s recently received a software update that changed the power system battery charging algorithm(s) and controls. I do not know what those changes entail, and again, it's something I heard third-hand so I cannot vouch for it's validity. However, if a change was made, and it was made to the NH and JL birds, it could be a potential source of the problem and why they occurred so close together after so many hours without incident.
 
iahmark
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:37 am

I have a quick question of some piece of information I found in other site.

It seems the importance of the APU in a 787 is much more so that a mere "Auxiliary Power Unit" to run things when the plane is on the ground.

According to these posters it also performs main duties as controlling flight control surfaces; i.e basically parts of the FBW system...this to me is crazy;...... Here's a copy an paste of the exchange between these two posters and I would like to know how true is this information: (read comments of "Blogger A")

Quote:


I have a question?
The apu is not a critical system for the plane to operate consider the word "auxiliary". The only time it is used is on the ground or in the air if an engine generator has failed. Otherwise planes really don't need them when you have air start carts and gpu's. The only reason they have them is to elimii have a question? the use of ground equipment and to fly a plane with 1 main generator inoperative. Boeing is trying to be innovating, when they should stick to what works a nicad. Lastly the FAA grounded the fleet because it started a fire multiple times in different aircraft. So they are not risking fires in transatlantic flights, can't land on water.

Blogger A
Boeing's design isn't what you'd conventionally think of in an APU. They replaced a good deal of the drive hydraulics with electro actuators. Rather than bleed off of engine power to drive all of that hardware, their APU design feeds all of the surface drive systems during flight.

I have a question?:
I'm always learning something new, but I do know is there is redundancy among aircraft's. That aircraft should be able to fly without an operative apu. Otherwise we can't call it an apu.

Blogger A
In theory, it is able to fly without an operative APU - because it has battery backup and because in extreme emergencies you have the ability to shunt main bus power to the control systems for a limited amount of time

I have a question?
I'm going to believe you because it seems like you know this aircraft very well. What powers the the main bus?
It should be in "reality" instead of theory cause the feds would not let this plane fly...

Blogger A
Main bus is supplied by engine driven generators. This is traditionally a relatively low current bus that drives things like avionics, cabin lighting & entertainment, etc. Upgrading the engine driven generators to a point sufficient to drive the control surface systems would have resulted in too much of a drain on the engines, resulting in lower fuel efficiency. Driving that set of systems off of the APU allows the main engines to operate at greater efficiency. Remember that Boeing's main selling point for this plane was that it uses less fuel.

I have a question?
I'm still having trouble wrapping my fingering around it... From what your telling me the control surfaces are controlled apu generator to save fuel? Cause running a third smaller turbine engine is using more fuel than just two big genx or rolls 1000.

Blogger A
Yes. Generators are gear driven directly off of the turbine through reduction. They introduce drag and therefore mess with your bypass ratio. GenX and Trent are both high-bypass designs. Trent especially, at 10:1, so when you start introducing drag, you lose thrust and your fuel efficiency goes into the toilet. To fix that, you'd have to essentially redesign the entire engine.

I have a question?
I would also have to say apu is not for flight controls unless you have a source or can provide one i would love to read up on it. That battery that burnt up i bet is just for starting the apu like every airplane with an apu.





[Edited 2013-01-21 18:38:02]

[Edited 2013-01-21 18:41:26]
 
tdscanuck
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:45 am

Quoting Stitch (Reply 12):
But Boeing knows it wasn't caused by a battery leak. And considering the panels are, per reports of people who have seen them, enclosed in a case themselves, even if liquid electrolyte solution were sprayed on them, the interior should be protected.

Those power panel cases have significantly sized air vents for cooling. It is not unreasonable that, under the right conditions, you could get electrolyte in there (albeit in small drops). Note that the changes made to the power system after the ZA002 event were designed to let the system respond properly *even if* you got FOD inside the panels...electrolyte drops would be considered FOD.

However, it's rather important to note that the aft EE bay contains another significant 787 technology...the power electronics cooling system (PECS), which runs a mixture of glycol, water, and some additives through an extensive set of tubes, backplanes, and connectors within the aft EE bay. Since there's no chance that the FAA would have accepted a statement that "the PECS system will never leak", Boeing would have had to design the entire aft EE bay to handle chemicals flying around anyway.

Tom.
 
CM
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:47 am

Quoting iahmark (Reply 13):
I have a quick question of some piece of information I found in other site.

The entire explanation in the thread you have posted is incorrect. See my explanations of standby power, the function of the APU, Batteries and RAT in the previous thread.
 
phxa340
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:48 am

Quoting Stitch (Reply 12):
I have heard an unconfirmed report that some 787s recently received a software update that changed the power system battery charging algorithm(s) and controls.

This would help explain why the NH bird had this happen a full 1 year after its In-Service date. That would be welcomed news.
 
RickNRoll
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:49 am

Quoting tdscanuck (Reply 8):
The "that" in my quote refers to the incidents that occurred violating the containment. Since, as far as we know, neither event caused meaningful damage to surrounding components it's not clear that the requirements around fire containment were violated. This is in direct conflict to multiple posters in the prior thread who claimed that the incidents *demonstrated* that the containment was violated. I agree that, if it's shown that spilled content could cause meaningful damage then Boeing would have another problem to deal with. But the events we actually know about do not show that damage occured, therefore we can't latch on to them as proof that the design features didn't work.

I don't know who you mean when you refer to 'other posters', but I have continually referred to the spilled content, myself, and see that as being sufficient to question the claim that it was contained adequately. I have never claimed that this is proof that it would cause severe damage, but I agree with the claim by the FAA that it is possible..
 
iahmark
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:52 am

Quoting CM (Reply 15):
Quoting CM (Reply 15):
The entire explanation in the thread you have posted is incorrect. See my explanations of standby power, the function of the APU, Batteries and RAT in the previous thread.

That's what i wanted to know, Ii seemed crazy to put all that burden on a APU!!
 
ordwaw
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 2:57 am

Quoting tdscanuck reply 270 of previous thread

"It's not a guess, it's a design condition. The battery would have burned itself out without damaging surrounding equipment, the fumes and smoke would have gone out the outflow valve and stayed out of the main deck, and the plane would have landed safely. "

Given the above statement I became curious. Let's play out the following scenario... B788 flying ORD-WAW route, just left the continental Canada an hour ago. Pilots get notified about APU battery being on fire. Should they ..

(a) start immediate diversion
or
(b) continue on knowing that it is an APU battery fire, by design it will be contained, it will go on for another 30 minutes or so when the battery will have burnt itself out without damaging surrounding equipment, the outflow valve will vent all the fumes and smoke out, we are good to continue".
or
(c) perform a different procedure (?)

What does the OP advise in the above situation?

[Edited 2013-01-21 19:02:18]
 
CM
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 3:06 am

Quoting ordwaw (Reply 19):
Given the above statement I became curious. Let's play out the following scenario... B788 flying ORD-WAW route, just left the continental Canada an hour ago. Pilots get notified about APU battery being on fire. Should they...

Always option A. Divert.

Every fire event on the airplane is designed to be managed or suppressed, but the crew procedure is always to divert. In teh case of the 787, cargo fire suppression systems are designed for 5.5 hours (ETOPS 330), but you would certainly choose a closer airport if one is available.

[Edited 2013-01-21 19:10:21]
 
prebennorholm
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 3:07 am

Quoting Stitch (Reply 12):
But Boeing knows it wasn't caused by a battery leak.

Of course the 2010 incident wasn't a battery leak. If it had been that simple, then Boeing would have known immediately.

Quoting Stitch (Reply 12):
And considering the panels are, per reports of people who have seen them, enclosed in a case themselves, even if liquid electrolyte solution were sprayed on them, the interior should be protected.

And problem is that this contradicts FAA when they write "could damage".

But as I wrote in reply #11, don't ask "people who have seen them". Ask the subcontractors about what specifications they had to fulfill when they designed and built them. And ask FAA for approval.

"People who have seen them" may see totally enclosed boxes. Still they may have fan driven cooling ventilation on the back side. Just one thing which.....

We will again enjoy flights on the beautiful 787 when the FAA has approved it. "People who have seen them" boxes do not decide.
Always keep your number of landings equal to your number of take-offs
 
CM
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 3:17 am

Quoting CM (Reply 15):
The entire explanation in the thread you have posted is incorrect. See my explanations of standby power, the function of the APU, Batteries and RAT in the previous thread.
Quoting iahmark (Reply 18):
That's what i wanted to know, Ii seemed crazy to put all that burden on a APU!!

I just went looking for my previous posts and can't even figure out what thread they are in! I guess I shouldn't expect you to be able to find them. Man, this topic is out of control! Here is a thumbnail explanaiton:

For normal operations, the APU is started when the airplane is on the ground and is used to provide power for main engine start. For most every flight you will fly on, the APU is then shut off and will remain off for the rest of the flight. It's only other purpose is as a redundant power source (bleed and electric on most airplanes) for when the engine sources cannot supply the power.
 
dfambro
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 3:18 am

Quoting tdscanuck, prior thread
Quoting dfambro (Reply 256):
WingedMigrator is correct, you can calculate confidence interval for a rate from a single event. You can calculate it for zero events.

Yes, you can calculate it, but you can't do anything with the information because the confidence interval is infinitely wide.

************************


If you're using the word "infinitely" in regard to the zero event case, it's true. I just brought it up as illustration to counter the claim that there is no rate information in a single event. Of course there is, and there is even rate information in the zero event case. I also stated the rate is unbounded on one side (=infinitely wide) in the zero event case. But that's the uninteresting case, as you know. The interesting case is what a single event tells you about rate, and that is not infinitely wide. And it will be actioned, if the time to first event is sufficiently rapid, because you can exclude with statistical confidence that the rate is very low.

What's intriguing to me is how you deal with the multiple-hypothesis testing problem when looking at isolated failures in a system as complex as a cutting-edge airliner.

Here, the first battery event occured a year into service and (so I read) greater than 1 million flight hours into the program, which does not exclude with statistical confidence that the failure rate is appropriately miniscule. And it wasn't actioned with a grounding, rather it was just targeted for investigation. And then a second battery event/fire occurred...
 
CM
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 3:20 am

Quoting prebennorholm (Reply 21):
But as I wrote in reply #11, don't ask "people who have seen them". Ask the subcontractors about what specifications they had to fulfill when they designed and built them. And ask FAA for approval.

"People who have seen them" may see totally enclosed boxes. Still they may have fan driven cooling ventilation on the back side. Just one thing which.....

Protection from PECS coolant spray is a design requirement for all equipment / racks / boxes in the aft equipment bay.
 
prebennorholm
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 3:46 am

Quoting CM (Reply 24):
Protection from PECS coolant spray is a design requirement for all equipment / racks / boxes in the aft equipment bay.

That seems to really rock the FAA wording "could damage" etc, which to me at least seems to be their major reason for grounding. If the boxes are totally PECS coolant spray resistant, then I doubt that any Li-Ion goof can do any damage either except exterior cosmetic damage.
Always keep your number of landings equal to your number of take-offs
 
RickNRoll
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 3:51 am

They refer to the leakage as 'flammable'.
 
bellancacf
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 3:58 am

Perhaps the following site and thread have been mentioned, but there's a drawing, some photos, and, as here, back and forth commentary:

http://www.pprune.org/tech-log/505695-787-batteries-chargers.html
 
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7BOEING7
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 4:03 am

Quoting dfambro (Reply 23):
Here, the first battery event occured a year into service and (so I read) greater than 1 million flight hours into the program, which does not exclude with statistical confidence that the failure rate is appropriately miniscule

Don'y know where you're getting the "1 million flight hours" from, including flight test it's probably closer to 55,000 at best.
 
dfambro
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 4:12 am

Quoting 7BOEING7 (Reply 28):
Don'y know where you're getting the "1 million flight hours" from, including flight test it's probably closer to 55,000 at best.

Thought I saw that written somewhere, but yea, after a moment's thought it can't be nearly that many.
 
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Aesma
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 4:13 am

Glycol/water cooling for the electronics, cool, I use that in my computers too. If it leaks it can cause shorts but shouldn't start a fire.
New Technology is the name we give to stuff that doesn't work yet. Douglas Adams
 
WingedMigrator
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 4:30 am

Quoting dfambro (Reply 23):
there is even rate information in the zero event case.

   indeed there is, although this can be hard to grasp. If the 787 fleet had accumulated 0.13 million flight hours when the first battery event occurred, that was sufficient to bound the failure rate to somewhere between zero and X, where X depends on the chosen confidence level. Intuitively you can think of it this way: if you make it to 0.13 million hours with no failures, the hourly failure rate is extremely likely below 0.1 per hour (with a confidence of many nines). Pick any confidence level, say 95%, and you can compute the upper bound of the failure rate... with ZERO events. Well, actually 0.13 million successful 1-hour trails...

The first event changed the lower bound of the estimate to something non-zero. The second event narrowed the estimated failure rate, for the same given confidence level.

For a Poisson process you do not need two failures to establish an estimate of the failure rate. That being said, a Poisson process assumes the underlying failure rate is constant, which it may not be in this case.

[edit: fixed fleet hours - was erroneously quoted as 1.3 million, should be closer to 130,000]

[Edited 2013-01-21 21:15:51]
 
smolt
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 4:40 am

I'm afraid this has already been told here, but a TV special program of ANA 787 I watched yesterday showed,

1. There was a hole of several centimeters under belly, and, from which, a mark of something brown (soot?) having
flowed backwards. (what is this hole for?)
2. After emergency landing, white mist is seen going downwards out of around nose gear onto the ground.

plus in the other news they told that the battery has lost its weight by 4.5kg out of 29kg.

smolt
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 5:02 am

Quoting tdscanuck (Reply 14):
However, it's rather important to note that the aft EE bay contains another significant 787 technology...the power electronics cooling system (PECS), which runs a mixture of glycol, water, and some additives through an extensive set of tubes, backplanes, and connectors within the aft EE bay. Since there's no chance that the FAA would have accepted a statement that "the PECS system will never leak", Boeing would have had to design the entire aft EE bay to handle chemicals flying around anyway.

That is a very interesting piece of information that should,but probably will not, silence many naysayers that seem to think Boeing somehow forget how to build certain fail-safes into their plane designs.

It is always fantastic to get factual information from people in the know. Thanks again Tom.

Paul
 
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DocLightning
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 5:02 am

Quoting tdscanuck (Reply 14):
Since there's no chance that the FAA would have accepted a statement that "the PECS system will never leak", Boeing would have had to design the entire aft EE bay to handle chemicals flying around anyway.

But glycol and water may have very different properties than electrolyte. Is electrolyte caustic or alkaline? How reactive is it? Will it burn if it gets hot or if current passes through it? I do not know. I do know that most coolants are chosen to be minimally reactive.
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 5:06 am

Quoting WingedMigrator (Reply 31):
The 787 fleet had accumulated 1.3 million flight hours when the first battery event occurred

How could the 787 fleet have accumulated 1.3 million flight hours by now?

That's equivalent to over 100 planes flying 24 hours a day, nonstop, from service entry to today.
The plural of Airbus is Airbuses. Airbii is not a word, and doesn't even make sense.
There is no 787-800, nor 787-900 or 747-800. It's 787-8, 787-9, and 747-8.
A321neoLR is also unnecessary. It's simply A321LR.
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 5:13 am

Quoting DocLightning (Reply 34):
But glycol and water may have very different properties than electrolyte. Is electrolyte caustic or alkaline? How reactive is it? Will it burn if it gets hot or if current passes through it? I do not know. I do know that most coolants are chosen to be minimally reactive.

According to the FAA, they are concerned about flammable material coming from the batteries.
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 5:14 am

Quoting hOmsAR (Reply 35):
How could the 787 fleet have accumulated 1.3 million flight hours by now?

Sorry, I read that somewhere and must have mis-remembered it. It obviously can't be that high... probably closer to 130,000.  
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 5:19 am

Quoting 7BOEING7 (Reply 28):
Don'y know where you're getting the "1 million flight hours" from, including flight test it's probably closer to 55,000 at best.

I think it was Mike Sinnett who mentioned the battery had 1.3 million operational hours, between lab, flight test and commercial operations.



Quoting prebennorholm (Reply 25):
That seems to really rock the FAA wording "could damage" etc

Not really. There is always the forward equipment bay to consider, which has no PECS fluid and where the equipment does not carry the same requirements as the aft bay.

That being said, here are some personal thoughts on the FAA statement:

>> In my opinion, it is quite awkwardly worded, which is not helping us dissect the words with any success.

>> It talks about "conditions" and "results", but then seems to mix the two, which is unfortunate.

>> It talks about "results" such as "damage to critical systems and structure", but then adds on "fire" as a result.

Here is their statement:

Quote:
"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."

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

The FAA released the statement with very little time to work through the details, so I don't fault them too much for what seems to me to be a jumbled statement. The way I interpret their statement is this:

Quote:
"There have been battery failures on two separate Model 787 airplanes. The battery failures included the release of flammable electrolytes, heat, and smoke, and the potential of a fire in the electrical compartment. If not corrected, these conditions could result in damage to critical systems and structures."

According to the way I understand their statement, the concern is not electrolyte getting onto/into systems and damaging them. The concern is the potential of a fire. Fire is the only thing which could create the damage to critical systems and structure they mention. Obviously a panel or other component does not need to have openings, fans, vents, etc which let the electrolyte seep inside, in order for a fire to be a problem.

Let me underscore, this is a personal interpretation of what I see in the FAA statement. It may well be I am mistaken about the meaning of their statement.



Quoting smolt (Reply 32):
1. There was a hole of several centimeters under belly, and, from which, a mark of something brown (soot?) having flowed backwards. (what is this hole for?)

From the photo I saw, it is the equipment cooling smoke/override port. The dark streak was identified by the JTSB as material which seeped out of the battery.
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 5:33 am

Quoting CM (Reply 38):

I think that is pretty much how I understand it. Well written.
 
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7BOEING7
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 5:35 am

Quoting smolt (Reply 32):
1. There was a hole of several centimeters under belly, and, from which, a mark of something brown (soot?) having flowed backwards. (what is this hole for?)

Probably one of the "body drains" which run along the bottom of the airplane.

Quoting WingedMigrator (Reply 37):
Sorry, I read that somewhere and must have mis-remembered it. It obviously can't be that high... probably closer to 130,000.
Quoting CM (Reply 38):
I think it was Mike Sinnett who mentioned the battery had 1.3 million operational hours, between lab, flight test and commercial operations.

The hours that count are the ones in the airplane and the number that was mentioned in a previous thread on this or another 787 topic was 50,000 which didn't count the almost 5,000 flight test hours.
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 5:44 am

Quoting smolt (Reply 32):
1. There was a hole of several centimeters under belly, and, from which, a mark of something brown (soot?) having
flowed backwards. (what is this hole for?)
Quoting CM (Reply 38):
From the photo I saw, it is the equipment cooling smoke/override port. The dark streak was identified by the JTSB as material which seeped out of the battery.
Quoting 7BOEING7 (Reply 40):
Probably one of the "body drains" which run along the bottom of the airplane.

Was that where all of that smoke came from in the earlier linked videos from TAK?
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 6:03 am

Quoting 7BOEING7 (Reply 40):
Probably one of the "body drains" which run along the bottom of the airplane.

Which fits with my observation of a fluid on the ground below the a/c and the "smoke" actually being (maybe) condensation (like the peoples breath) from the warm fluid.

Quoting PHX787 (Reply 41):
Was that where all of that smoke came from in the earlier linked videos from TAK?

When I look - it seems the "smoke" may be coming from the puddle on the ground. I've wished for a definitive statement regarding that - but have not seen it. Consider the temps in the area are near freezing, warm fluid on the ground could certainly 'steam'. You can certainly see the breath of passengers and crew in the video.
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 6:19 am

Wait, what "valve actuator" ? Also, is the investigation taking a serious turn, or is the press fishing for a story?

Quote:
Investigators also are being sent to the U.K. to probe a valve actuator maker for the 787, the ministry said, without identifying the target company.
GS Yuasa Searched After Boeing 787s Are Grounded (Bloomberg)

[Edited 2013-01-21 22:19:28]
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 6:38 am

Thank you for many informative replies. I am sorry I got many facts wrong (like believing there are other battery packs in the rack). Looking into the presented facts about the incident, I now believe that the second incident is the one that forced the FAA to act, as the flammable liquid escaped the battery pack, while the 2 failures of the batteries could be seen as an idication that the failure rates might be above the expected range.

Thei first incident should have only pointed to some minor modifications like having some heat shields in the venting area or such things.
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 6:55 am

Quoting DocLightning (Reply 34):
But glycol and water may have very different properties than electrolyte. Is electrolyte caustic or alkaline? How reactive is it? Will it burn if it gets hot or if current passes through it? I do not know. I do know that most coolants are chosen to be minimally reactive.

The point is that everything is fairly well shielded against a spray of (conductive!) coolant (of drastically lower viscosity) anyway. A bit of corrosive electrolyte paste leaving a chemical burn on the outside of a cabinet is not going to be a big issue - everything is covered.

Obviously the electrolyte *is* different than the coolant, and those special attributes (like flammability and corrosiveness) are clearly in need of attention not required of a glycol-based coolant.

BTW, most glycols are at least moderately flammable, although when used as coolants, they are usually mixed with water, which considerably reduces that.
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 7:07 am

Quoting CM (Reply 38):
Not really. There is always the forward equipment bay to consider, which has no PECS fluid and where the equipment does not carry the same requirements as the aft bay.

That being said, here are some personal thoughts on the FAA statement:

>> In my opinion, it is quite awkwardly worded, which is not helping us dissect the words with any success.

>> It talks about "conditions" and "results", but then seems to mix the two, which is unfortunate.

>> It talks about "results" such as "damage to critical systems and structure", but then adds on "fire" as a result.

Here is their statement:

I actually find it a bit concerning that you take it upon yourself to reinterpret the words of the NTSB, its a bit patronising don't you think? You talk as if the statement was written by idiots who have no clue as to what they are saying.

On one hand you say that the NTSB are the only agency authorised to issue statements then on the other you as a Boeing employee denigrate the statements that the NTSB make and interpret them in a way favourable to your employer.

Does this not bother anybody else?
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 7:21 am

Quoting boacvc10 (Reply 43):
Wait, what "valve actuator" ? Also, is the investigation taking a serious turn, or is the press fishing for a story?

Could be in connection with the inadvertent fuel dumping.
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 8:27 am

Quoting bellancacf (Reply 27):
Perhaps the following site and thread have been mentioned, but there's a drawing, some photos, and, as here, back and forth commentary:

Thanks for the link. I had previously only seen a photo of the damaged battery when it had already been removed... there's another photo of it still installed on page 3 of the thread.

Quoting BoeingVista (Reply 46):
On one hand you say that the NTSB are the only agency authorised to issue statements then on the other you as a Boeing employee denigrate the statements that the NTSB make and interpret them in a way favourable to your employer.

I find it a bit puzzling myself, to be honest... regardless of whether or not such comments are prefaced with "personal thoughts" or "opinion".

Quoting boacvc10 (Reply 43):
Wait, what "valve actuator" ? Also, is the investigation taking a serious turn, or is the press fishing for a story?

As yeelap mentioned, it's related to the fuel spill. Battery investigation aside, there's still the review process going on.
 
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RE: FAA Grounds 787 Part 4

Tue Jan 22, 2013 8:35 am

Quoting BoeingVista (Reply 46):
On one hand you say that the NTSB are the only agency authorised to issue statements then on the other you as a Boeing employee denigrate the statements that the NTSB make and interpret them in a way favourable to your employer.

Does this not bother anybody else?

The 787 emergency airworthiness directive was issued by the FAA, not the NTSB, and is in the public domain.

CM's personal interpretation of the AD, while not speaking on the behalf of any other party, doesn't bother me at all. This is an international forum, where the definition of technical terms may not have always translated well, as we've seen in some of the earlier posts. A bit of clarity was in order at this point in time, and there are few here as well educated/informed as CM regarding the subject matter to put the semantics issues to rest so we could move on.

In his post, I see no attempt to circumvent the NTSB's rules regarding the release of non-public information.

If you have a different personal interpretation of the FAA's AD, I doubt if anyone would oppose your posting it here as well.
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