FAA Grounds 787s
This gives the a/c an extra few minutes of emergency power when required.
Over discharge can be identified with a proper diagnostic charger.
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Hi mickjoebill
I think the over discharge is identified, that is why they replaced the batteries so many times. I think TURIN gave the most likely explanation for this also.
Over discharge can be identified with a proper diagnostic charger.
Where things have gone wrong (re: 150 batteries changed in service) is the operators have not really ensured that the people at the sharp end are thoroughly briefed as to the consequences of EG. Leaving the towing switch on.
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crappy,ill-considered system.
very early on, I was shouted-down , suggesting the battery should isolate before reaching non-rechargeable status. the argument, then, as now, was the need for that extra few minutes'power.
How about , the circuits automatically boot the APU if either battery drains down more than, say , 20% that way, the likelihood of a 2-hour battery-change delay would be virtually eliminated. In case of total in-flight generating-loss, a big red "EMERGENCY FINAL BATTERY RESERVE" switch/button could be activated....then the heroic pilots could wrestle it to the ground , safe in the knowledge that they had brakes and the tin-box would provide a bit of heat in adverse temperatures
IMO, these batteries are being used as a ground-supply as an alternative to a GPU or the APU.....It's wrong!- they're supposed to be for flight-critical emergency backup. Therefore, the APU should be the main power-source in any case where the main engine(s) are not running. I only see up-sides to an automatically-starting APU when a load is detected.
|It isn't hard! about 60 YES! 60 years ago, I stayed in a remote place in Devon, No mains services. If a light or appliance was switched-on, the generator automatically fired-up with a few seconds' time-lapse.
Job needs sorting and practical and commercial objectives need to be assessed by someone who understands the business. the present bunch of Nero wannabe's don't appear to fit the bill, having now pi55ed -off the authorities that they're supposed to work WITH....if they can't get even the basics of business right......
very early on, I was shouted-down , suggesting the battery should isolate before reaching non-rechargeable status. the argument, then, as now, was the need for that extra few minutes'power.
How about , the circuits automatically boot the APU if either battery drains down more than, say , 20% that way, the likelihood of a 2-hour battery-change delay would be virtually eliminated. In case of total in-flight generating-loss, a big red "EMERGENCY FINAL BATTERY RESERVE" switch/button could be activated....then the heroic pilots could wrestle it to the ground , safe in the knowledge that they had brakes and the tin-box would provide a bit of heat in adverse temperatures
IMO, these batteries are being used as a ground-supply as an alternative to a GPU or the APU.....It's wrong!- they're supposed to be for flight-critical emergency backup. Therefore, the APU should be the main power-source in any case where the main engine(s) are not running. I only see up-sides to an automatically-starting APU when a load is detected.
|It isn't hard! about 60 YES! 60 years ago, I stayed in a remote place in Devon, No mains services. If a light or appliance was switched-on, the generator automatically fired-up with a few seconds' time-lapse.
Job needs sorting and practical and commercial objectives need to be assessed by someone who understands the business. the present bunch of Nero wannabe's don't appear to fit the bill, having now pi55ed -off the authorities that they're supposed to work WITH....if they can't get even the basics of business right......
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It was a customer requirement that a number of the 787's systems be able to be operated without the engines or APU running or the plane having to be connected to external power.
Why Boeing didn't employ two discharge limits - one for ground operations and one for emergencies in the air - is due to it adding complexity to the fault tree and the necessity to take into account the possibility that the ground discharge limit activates during an emergency, denying the flight crew power and possibly directly leading to an accident.
The as-designed system works when operated as-designed. Ground crew need either better training as to how long they can operate the plane off just the battery and/or better supervision to ensure those limits are not exceeded.
Why Boeing didn't employ two discharge limits - one for ground operations and one for emergencies in the air - is due to it adding complexity to the fault tree and the necessity to take into account the possibility that the ground discharge limit activates during an emergency, denying the flight crew power and possibly directly leading to an accident.
The as-designed system works when operated as-designed. Ground crew need either better training as to how long they can operate the plane off just the battery and/or better supervision to ensure those limits are not exceeded.
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I still have trouble understanding why Boeing had decided the 15 minute maximum tow time, if you watch a BA plane at LHR being towed from the maintenance hangar to their terminal 5 is sure as hell takes a lot longer than 15 minutes..... So how is Mr Boeing going to address this I wonder..? and I am sure at other airports around the world as well.
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Is there actually a 15 min tow time limit in towing power mode? If there is a time issue, presumably you could start the APU, Would that work?
Reading through this thread, there does seem to be a lot of opinions and guesses that later somehow become facts because "someone said it" earlier. I know it's just a rumour forum in which anyone can post but unfortunately it's easy for something that sounds clever (which was just a guess) to get taken up by others.
It would be helpful if posters background and relevant experience and qualifications appeared next to their posts on technical issues.
Reading through this thread, there does seem to be a lot of opinions and guesses that later somehow become facts because "someone said it" earlier. I know it's just a rumour forum in which anyone can post but unfortunately it's easy for something that sounds clever (which was just a guess) to get taken up by others.
It would be helpful if posters background and relevant experience and qualifications appeared next to their posts on technical issues.
Usual disclaimers apply!
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Is there actually a 15 min tow time limit in towing power mode?
There is a battery test switch primarily aimed at tow crews. Pushing the test s/w gives an indication of battery charge state.
The three lights are: High approx. 60 mins available. Med. approx. 30 mins and Low approx. 15 mins.
As said earlier the operators wanted to be able to tow without the use of the APU or other external power source.
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As said earlier the operators wanted to be able to tow without the use of the APU or other external power source.
Withy the best wil in the world, you can't expect a tug-driver to understand the ins and outs of a lithium battery's charge-discharge characteristics. they're MOVERS not scientists!...The hundreds of posts on here, by a predominantly intelligent membership, prove that the assumption that unskilled personell could be let loose on a fragile system,was deeply flawed.
In a former life, I made, and later serviced, Medical Equipment, including premature-Baby Incubators, Respirators, oxygen tents and and various pumps.
A major part of the designer's efforts , was to make everything "idiot-proof"
We had a saying....
Make it idiot-proof and it'll be ALMOST Nurse-proof.
No matter how well something is placarded, complacency and familiarity will ignore it. safety and protection need to be built-in to pre-empt misuse.
my suggestion of a "bypass" emergency-reserve switch (on the flight-deck)
addresses that issue....
Why Boeing didn't employ two discharge limits - one for ground operations and one for emergencies in the air - is due to it adding complexity to the fault tree and the necessity to take into account the possibility that the ground discharge limit activates during an emergency, denying the flight crew power and possibly directly leading to an accident.
Come on! this would be a very minor mod , in the big scheme of things.
The plane had too much design-input from smartass Graduates and bean-counters and not enough from experienced aeronautical and systems engineers. and it shows!
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"McNerney acknowledges that dealing with the 787 problems has been a "frustrating experience", but says that FAA regulators who had put the airframer "through the paces" had the country's best interests in mind."
The country's (Boeing's?) best interests. Not safety, then?
The country's (Boeing's?) best interests. Not safety, then?
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DG in the olden days
Anilv:
30 years ago a colleague handcarried a half-litre of Jet-A from a customer back to our home base for analysis. It was in a ruggedized poly bottle, wrapped in heavy polyethylene bag, in his briefcase - it probably would have withstood a 20G crash without leaking a drop.
But the young lady at security, seeing the straw-colored liquid, said "What's this?" - and said colleague professed that he raised horses, and one mare was sick, and he was rushing a urine sample to a veterinarian for a diagnosis. She turned up her nose, slammed the briefcase shut and sent him on his way!
By comparison, what about a two-litre (glass, in that day) bottle of 90-proof vodka from duty-free?
Commercial airliners are equipped with all kinds of dangerous goods, off the top of my head
-flammable liquids- a B744 can carry almost 170 metric tons of fuel. Try calling Fedex and telling them you want to ship 1 bottle of kerosene!
-flammable liquids- a B744 can carry almost 170 metric tons of fuel. Try calling Fedex and telling them you want to ship 1 bottle of kerosene!
But the young lady at security, seeing the straw-colored liquid, said "What's this?" - and said colleague professed that he raised horses, and one mare was sick, and he was rushing a urine sample to a veterinarian for a diagnosis. She turned up her nose, slammed the briefcase shut and sent him on his way!
By comparison, what about a two-litre (glass, in that day) bottle of 90-proof vodka from duty-free?
Paxing All Over The World
cockney steve
There is an old saying, origins unknown:
It takes one generation to start a company,
A second generation to run the company,
A third generation to close the company.
Boeing is not going to close over this but it will not be forgotten. Hopefully, it will be used in business schools and text books.
The plane had too much design-input from smartass Graduates and bean-counters and not enough from experienced aeronautical and systems engineers. and it shows!
It takes one generation to start a company,
A second generation to run the company,
A third generation to close the company.
Boeing is not going to close over this but it will not be forgotten. Hopefully, it will be used in business schools and text books.
cockney Steve, #1487
I tend to agree. I different sort of "enough of the bo***cks", right ?.
You can only take things so far via the use of diplomacy
The number of areas that have been identified here as indicative of poor
design are many, but for yet another, consider this: If the battery system
is designed to disconnect when the voltage reaches a low limit, the
contactor in the box must be energised (Normally closed contact). When
the battery reaches a low enough level for the contactor to drop out, the
battery becomes connected again. This would eventually discharge the
battery to zero volts, turning it into scrap.
As for the low voltage limit "reserve", I find it difficult to believe
that such a design would pass any design review. Consumer electronics,
perhaps, but not for aviation...
crappy,ill-considered system.
You can only take things so far via the use of diplomacy
The number of areas that have been identified here as indicative of poor
design are many, but for yet another, consider this: If the battery system
is designed to disconnect when the voltage reaches a low limit, the
contactor in the box must be energised (Normally closed contact). When
the battery reaches a low enough level for the contactor to drop out, the
battery becomes connected again. This would eventually discharge the
battery to zero volts, turning it into scrap.
As for the low voltage limit "reserve", I find it difficult to believe
that such a design would pass any design review. Consumer electronics,
perhaps, but not for aviation...
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Syseng68k, post # 1496
I'm not disagreeing with design issues, however if the only source of power is the battery, then it's a question of how long before the plane gets to the ground, if the battery lasts that long then it's fulfilled it's purpose.
If there is one other source of power, wouldn't the contactor remain powered? The battery system doesn't exist as self-contained system although there are degrees of isolation.
I'm not disagreeing with design issues, however if the only source of power is the battery, then it's a question of how long before the plane gets to the ground, if the battery lasts that long then it's fulfilled it's purpose.
If there is one other source of power, wouldn't the contactor remain powered? The battery system doesn't exist as self-contained system although there are degrees of isolation.
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@syseng68k
If I may, I think the action you describe above (energized coil drops out on low coil voltage) to indicate the behavior of a "normally closed contact" instead describes the behavior of a "normally open contact". That is to say, the ordering description for the contactor which produces the behavior you envision as cause of trouble would be "NO". The "normal" position is the position of the contacts with the coil not energized. "Normal" for a coil device does not refer to the customary position of the contacts when the circuit is in some particular configuration which is considered the normal position when operating.
So, if the contactor is NC, it is not energized when the battery is connected to the bus. Current to lift the contactor armature is only drawn when it is commanded to break the circuit by opening the normally closed contacts. In this application a mechanical latch would be applied and either this latch or the main armature by way of auxiliary contacts, would provide what's called coil clearing. That is, the latch hold the armature up, and once latched the coil clearing removes the operation current from the coil.
Such a contactor (as I described it) cannot be reset other than manually. [There are latching relays that are electrically locked, but I don't think this one would be.] Speaking of relays, the coil current may be provided by a mechanical relay, as a very substantial current would be required to lift a 400-ampere contactor, even more so if it were a motor contactor compared to a lighting contactor.
So, when this NC contactor lifts, it breaks the circuit, latches open, and disconnects its own coil. There is no resetting this puppy without breaking the seal on the battery box. Possibly its setting permits a special charging protocol at the factory to make it serviceable again, possibly not; in any case with remaining capacity around 15 or 20%, lifting the contactor to open the circuit should be no problem (the action is very fast) for the battery in the simple case of nav lights on too long.
An internal cell fault could be a different story, however. Some of the reported data in the cases involving cell damage suggest the contactor may not have opened immediately, and possibly not at all, in at least one of these cases.
As for a design to permit irreparable battery discharge, I have made designs where considerable heating of equipment was permitted by the controls. This involved a battery of motors, in a situation of very substantial life safety hazard. The idea was to get into shortening the ultimate life of the motors, as a reasonable expense in very unusual circumstances, but to stop short of fire.
There were other changes made to the manner in which the motors operated, the type of motor, the equipment building, and the location of the motors and their controls within it. So if maximum possible energy delivery was part of this 787 design, I can see that point of view even if it cost $16k. But I think it is necessary to stop short of fire-- although where that point is, is not easy to judge, it appears.
This was also true of insulation life in motors, in the example I gave. It followed a real failure of the system, very luckily without injuries, which was not our design-- although it had been a very standard design (and so "protected" the motors in preference to the mission), excepting possibly one or two details. Well, the details were important. IIRC, mission failure resulted in the loss of the motors anyway; ditto expensive controls ($10 million worth, years ago).
...If the battery system is designed to disconnect when the voltage reaches a low limit, the contactor in the box must be energised (Normally closed contact). When the battery reaches a low enough level for the contactor to drop out, the battery becomes connected again.
So, if the contactor is NC, it is not energized when the battery is connected to the bus. Current to lift the contactor armature is only drawn when it is commanded to break the circuit by opening the normally closed contacts. In this application a mechanical latch would be applied and either this latch or the main armature by way of auxiliary contacts, would provide what's called coil clearing. That is, the latch hold the armature up, and once latched the coil clearing removes the operation current from the coil.
Such a contactor (as I described it) cannot be reset other than manually. [There are latching relays that are electrically locked, but I don't think this one would be.] Speaking of relays, the coil current may be provided by a mechanical relay, as a very substantial current would be required to lift a 400-ampere contactor, even more so if it were a motor contactor compared to a lighting contactor.
So, when this NC contactor lifts, it breaks the circuit, latches open, and disconnects its own coil. There is no resetting this puppy without breaking the seal on the battery box. Possibly its setting permits a special charging protocol at the factory to make it serviceable again, possibly not; in any case with remaining capacity around 15 or 20%, lifting the contactor to open the circuit should be no problem (the action is very fast) for the battery in the simple case of nav lights on too long.
An internal cell fault could be a different story, however. Some of the reported data in the cases involving cell damage suggest the contactor may not have opened immediately, and possibly not at all, in at least one of these cases.
As for a design to permit irreparable battery discharge, I have made designs where considerable heating of equipment was permitted by the controls. This involved a battery of motors, in a situation of very substantial life safety hazard. The idea was to get into shortening the ultimate life of the motors, as a reasonable expense in very unusual circumstances, but to stop short of fire.
There were other changes made to the manner in which the motors operated, the type of motor, the equipment building, and the location of the motors and their controls within it. So if maximum possible energy delivery was part of this 787 design, I can see that point of view even if it cost $16k. But I think it is necessary to stop short of fire-- although where that point is, is not easy to judge, it appears.
This was also true of insulation life in motors, in the example I gave. It followed a real failure of the system, very luckily without injuries, which was not our design-- although it had been a very standard design (and so "protected" the motors in preference to the mission), excepting possibly one or two details. Well, the details were important. IIRC, mission failure resulted in the loss of the motors anyway; ditto expensive controls ($10 million worth, years ago).
Momoe, #1497
Correct me if i've got this by the wrong end, but the argument seemed to
be suggesting that the battery would be run outside cell data sheet limits
to get that final reserve, which I find difficult to believe.
Aviation kit is generally designed with parts having generous operating
margins to improve reliability and/or safety. The worst case operating
conditions are analysed and components sized accordingly. If a proposed
battery doesn't meet the load requirements, they just fit a bigger one.
It's that simple.
Other than the ntsb report, there seems to be very little added info at
present and the proposed box solution looks more and more surreal with
each week that goes by. Come clean Boeing, tell the truth and publish
everything. It's the only way to really restore confidence. Otherwise
there will always be doubt and the tech pundits will never let the story
die...
Correct me if i've got this by the wrong end, but the argument seemed to
be suggesting that the battery would be run outside cell data sheet limits
to get that final reserve, which I find difficult to believe.
Aviation kit is generally designed with parts having generous operating
margins to improve reliability and/or safety. The worst case operating
conditions are analysed and components sized accordingly. If a proposed
battery doesn't meet the load requirements, they just fit a bigger one.
It's that simple.
Other than the ntsb report, there seems to be very little added info at
present and the proposed box solution looks more and more surreal with
each week that goes by. Come clean Boeing, tell the truth and publish
everything. It's the only way to really restore confidence. Otherwise
there will always be doubt and the tech pundits will never let the story
die...
Old Engineer, #1498
If you look at the schematic in the ntsb report, it's quite clear that the
contactor is drawn with normally closed contacts, which is the contactor state
with the coil / solenoid unenergised. While it may be latching to the open
state, there's no evidence for this and in fact, the contactor looks fairly
standard in that respect, but yes, it could be latching to the contacts open
state.
I originally brought this up in tech log, (#902), which might better explain why
this isn't a very good idea..
I think the action you describe above (energized coil drops out on low coil
voltage) to indicate the behavior of a "normally closed contact"
voltage) to indicate the behavior of a "normally closed contact"
contactor is drawn with normally closed contacts, which is the contactor state
with the coil / solenoid unenergised. While it may be latching to the open
state, there's no evidence for this and in fact, the contactor looks fairly
standard in that respect, but yes, it could be latching to the contacts open
state.
I originally brought this up in tech log, (#902), which might better explain why
this isn't a very good idea..
Last edited by syseng68k; 1st Apr 2013 at 16:11.
...
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My car has "always-live" convenience outlets (e.g., the ubiquitous cigarette lighter plugs) which incorporate a protective monitoring circuit that keeps them live, but disconnects them before the battery charge state reaches the point where it will not start the car. It seems to me that if it can be done in a car, the Boeing system could monitor battery state and "disconnect" the towing lights when the battery charge state reaches a low, but not damaging state. Full use (even to the point of damage) would be allowed for in-flight non-routine operations (gen failure, etc.). The SOP would call for battery replacement after such an event.
It's interesting, I read the list of "improvements" to the battery system proposed by Boeing, and many of them were things that I (and others) suggested early on in the thread. It seems to me that if these things are obvious to me, they would be obvious to anyone with even a modicum of engineering experience. Given that, I can only conclude that the battery system at Boeing was designed to the requirements of the bean counters rather than the engineers. And is so often the case, designing to a price, has a price, and Boeing sure seems to be paying it.
It's interesting, I read the list of "improvements" to the battery system proposed by Boeing, and many of them were things that I (and others) suggested early on in the thread. It seems to me that if these things are obvious to me, they would be obvious to anyone with even a modicum of engineering experience. Given that, I can only conclude that the battery system at Boeing was designed to the requirements of the bean counters rather than the engineers. And is so often the case, designing to a price, has a price, and Boeing sure seems to be paying it.
Why Boeing didn't employ two discharge limits - one for ground operations and one for emergencies in the air - is due to it adding complexity to the fault tree and the necessity to take into account the possibility that the ground discharge limit activates during an emergency, denying the flight crew power and possibly directly leading to an accident.
A simple big fat mechanical switch between the flight battery and the ground battery would not take much of a redesign?
Captain Macgyver could use the ground battery in the event of an inflight emergency.