Ethiopean 787 fire at Heathrow
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In layman's terms, is this another battery problem with the B787? Duh....
If not, as someone has already pointed out, it is just sheer bad luck!
This was a serious incident but in fairness to Boeing, if it had occurred on any other model it would have drawn nowhere near the amount of comment and speculation that it has.
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In my mind there are 3 key elements in the AAIB report:
1) There are no other aircraft systems in this vicinity which, with the aircraft unpowered, contain stored energy capable of initiating a fire in the area of heat damage
2) It is not clear however whether the combustion in the area of the ELT was initiated by the relase of energy in the batteries or by an external machanism such as an electrical short
3) In the case of a short, the same batteries could provide the energy for an ingnition and suffer damage in a subsequent fire
My interpretation of these words is that the ELT is a suspect but is far from being confirmed as the guilty party. In simple terms, the guy was there, he had a gun, but we can't find any bullets.
1) There are no other aircraft systems in this vicinity which, with the aircraft unpowered, contain stored energy capable of initiating a fire in the area of heat damage
2) It is not clear however whether the combustion in the area of the ELT was initiated by the relase of energy in the batteries or by an external machanism such as an electrical short
3) In the case of a short, the same batteries could provide the energy for an ingnition and suffer damage in a subsequent fire
My interpretation of these words is that the ELT is a suspect but is far from being confirmed as the guilty party. In simple terms, the guy was there, he had a gun, but we can't find any bullets.
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"Mildly" Eccentric Stardriver
In all this, how about a vote of thanks to the ATC controller who first spotted it. Well done!!
Last edited by Herod; 18th Jul 2013 at 21:01. Reason: Spelling
How about moisture being the cause for a short?
In between lines it was a possible cause for the ANA event. The fix with the firebox talks about improved insulation also against humidity.
Does the no metal hull behave differently concerning condensation and causes humidity at places not expected?
In between lines it was a possible cause for the ANA event. The fix with the firebox talks about improved insulation also against humidity.
Does the no metal hull behave differently concerning condensation and causes humidity at places not expected?
Pegase Driver
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If I read the text correctly, this model of ELT has to be removed from 787s immediately ?
Since ELTs are mandatory for any large aircraft, does Boeing has a substitute certified model avail immediately to retrofit all current 787s flying ? just a question.
Since ELTs are mandatory for any large aircraft, does Boeing has a substitute certified model avail immediately to retrofit all current 787s flying ? just a question.
Batteries
There have been several previous examples of primary (non rechargeable) lithium batteries catching fire without any obvious provocation on aircraft and elsewhere ( a couple in torches IIRC).
I am not convinced by the statements on grounding and 'short circuits' etc. It is perfectly easy to provide both Thermal and Overcurrent protection to protect the Cells and therefore the system from excessive current being drawn and I am quite sure any decent designer would have done just this. Unfortunately neither protection helps if the cell structure breaks down internally and generates its own fire hazard, at that point containment or ejection are the best bets.
I am not convinced by the statements on grounding and 'short circuits' etc. It is perfectly easy to provide both Thermal and Overcurrent protection to protect the Cells and therefore the system from excessive current being drawn and I am quite sure any decent designer would have done just this. Unfortunately neither protection helps if the cell structure breaks down internally and generates its own fire hazard, at that point containment or ejection are the best bets.
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ELT source of fire
I would stick with points presented by daikilo in post #480. Going beyond that is over-interpretation.
Last edited by olasek; 18th Jul 2013 at 21:17.
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RetiredF4
To expand that a bit since there now appears to be battery related incidents with 2 very different batteries, one of which (ELT) has a significant problem free service history the question can be what is different about the 787 compared to prior design.
A couple of obviouse ones with comments.
Significantly higher "electrical content"
Certainly a factor in the main battery issues but hard to see why this would affect the ELT.
Composite construction:
Possible thermal environment changes, hotter baking in the sun etc.
Non conductive, requires explicit ground (return) paths, improperly sized/damaged these could induce unexpected voltages.
Possibly worse ESD environment.
Different cosmic ray shielding properties?
Particles that would have been blocked by metal may pass through. (Bit of a reach, pure conjecture on this one...)
Outsourcing:
Again possibly a factor in main batteries but the ELT is (so far) problem free on other types.
How about moisture being the cause for a short?
In between lines it was a possible cause for the ANA event. The fix with the firebox talks about improved insulation also against humidity.
Does the no metal hull behave differently concerning condensation and causes humidity at places not expected?
In between lines it was a possible cause for the ANA event. The fix with the firebox talks about improved insulation also against humidity.
Does the no metal hull behave differently concerning condensation and causes humidity at places not expected?
A couple of obviouse ones with comments.
Significantly higher "electrical content"
Certainly a factor in the main battery issues but hard to see why this would affect the ELT.
Composite construction:
Possible thermal environment changes, hotter baking in the sun etc.
Non conductive, requires explicit ground (return) paths, improperly sized/damaged these could induce unexpected voltages.
Possibly worse ESD environment.
Different cosmic ray shielding properties?
Particles that would have been blocked by metal may pass through. (Bit of a reach, pure conjecture on this one...)
Outsourcing:
Again possibly a factor in main batteries but the ELT is (so far) problem free on other types.
Humidity (pure water) is not a great conductor of electricity and all the short circuit discussions assume they designed an ELT battery system without a Thermal or Overcurrent fuse . .
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Jetstream67:
True but mix in a small amount a lot of things and it does conduct well enough to kill you.
An overcurrent fuse by itself would not prevent the battery from heating a low resistance (not dead short) path.
For operation it has to provide 10W or so, plenty to get a small area very hot.
Humidity (pure water) is not a great conductor of electricity and all the short circuit discussions assume they designed an ELT battery system without a Thermal or Overcurrent fuse . .
An overcurrent fuse by itself would not prevent the battery from heating a low resistance (not dead short) path.
For operation it has to provide 10W or so, plenty to get a small area very hot.
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An overcurrent fuse by itself would not prevent the battery from heating a low resistance (not dead short) path
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The more I think of it, the more convinced I am that this request is to do with the ELT's location and proximity to the composite as much as anything else. After all, these things are flying all over the world, every day without trouble.
As I said before, if this had gone up in smoke while airborne, even if it had been spotted straight away I'm not sure how much the cabin crew could do to mitigate the situation before they faced serious problems with both toxic fumes and structural integrity.
What instructions have CC been given with regard to fighting fires that may involve composites?
The LHR fire service were wearing fireproof suits, safety headgear and breathing apparatus and so were able to remain in the area while they pulled down the ceiling to get access to the fire. In flight, there would be a limited amount of firefighting time available before those in the rear of the aircraft would have to be evacuated forward while the flight crew tried to get it on the ground as soon as possible.
As I said before, if this had gone up in smoke while airborne, even if it had been spotted straight away I'm not sure how much the cabin crew could do to mitigate the situation before they faced serious problems with both toxic fumes and structural integrity.
What instructions have CC been given with regard to fighting fires that may involve composites?
The LHR fire service were wearing fireproof suits, safety headgear and breathing apparatus and so were able to remain in the area while they pulled down the ceiling to get access to the fire. In flight, there would be a limited amount of firefighting time available before those in the rear of the aircraft would have to be evacuated forward while the flight crew tried to get it on the ground as soon as possible.
Pardon me if this is a silly question, but what activates the ELT? Is it triggered by a loss of ship power, in which case could it be activated if the main battery voltage dropped?
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Only true if the number of wires connected is equal to or less than one I think!
• Four 22AWG wires to transmitter unit
provide full functionality
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Battery cells.
Something could indicate that some aircraft batteries are experiencing more frequent thermal events than consumer batteries. Why!, Size difference?
As others have already mentioned, protection of a battery cell against over current and over-voltage does not help if there is an internal fault in the cell.
As I see it, small cells have a significant lower probability of experiencing a thermal event, since they are more likely discharged before a fault in the foil (hotspot) reaches the autoignition temperature. And since they are small they can better conduct the heat from the hot-spot to the case of the cell.
A larger cell have:
1) More foil area, higher risk of faults in the foil → Higher probability of fire.
2) More foil area, more electrical energy to disparate in a fault. → Higher probability of fire.
3) Larger thermal resistance from fault location, to case. → Higher probability of fire.
As others have already mentioned, protection of a battery cell against over current and over-voltage does not help if there is an internal fault in the cell.
As I see it, small cells have a significant lower probability of experiencing a thermal event, since they are more likely discharged before a fault in the foil (hotspot) reaches the autoignition temperature. And since they are small they can better conduct the heat from the hot-spot to the case of the cell.
A larger cell have:
1) More foil area, higher risk of faults in the foil → Higher probability of fire.
2) More foil area, more electrical energy to disparate in a fault. → Higher probability of fire.
3) Larger thermal resistance from fault location, to case. → Higher probability of fire.