Ethiopean 787 fire at Heathrow
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DWS,
Sort of depends on what the control-data circuit wiring was shorted TO external to the ELT --for example like a 32 vdc bus bar or any power circuit or sneak circuit.
Speed of Sound,
... this would almost certainly fry the IC which would usually lead to an open circuit somewhere along the path to ground. A dead short of the battery via a damaged IC
is also likely to result in an open circuit condition. I'd also be surprised if there wasn't a fuse or diode to protect the battery itself from a short circuit condition.
I'm trying to think through the implications of these interesting posts, while remembering that there are two batteries involved in the above scenarios. [One feeding the bus,
the other within the ELT.]
A hypothetical situation is that a fault in the wiring causes the plane's battery to fry the ELT's IC, raising the temperature within the ELT.
In a related scenario the plane's battery might be able to feed current into the ELT's battery via the damaged IC.
Regards, Peter
Sort of depends on what the control-data circuit wiring was shorted TO external to the ELT --for example like a 32 vdc bus bar or any power circuit or sneak circuit.
Speed of Sound,
... this would almost certainly fry the IC which would usually lead to an open circuit somewhere along the path to ground. A dead short of the battery via a damaged IC
is also likely to result in an open circuit condition. I'd also be surprised if there wasn't a fuse or diode to protect the battery itself from a short circuit condition.
I'm trying to think through the implications of these interesting posts, while remembering that there are two batteries involved in the above scenarios. [One feeding the bus,
the other within the ELT.]
A hypothetical situation is that a fault in the wiring causes the plane's battery to fry the ELT's IC, raising the temperature within the ELT.
In a related scenario the plane's battery might be able to feed current into the ELT's battery via the damaged IC.
Regards, Peter
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Bloomberg reporting a wire smashed under the beacons battery cover.
Boeing 787 Probe Said to Focus on Pinched Beacon Wire - Bloomberg
Boeing 787 Probe Said to Focus on Pinched Beacon Wire - Bloomberg
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I was not aware of this '32VDC bus', can anyone enlighten me?
However - and this is making the assumption that the ELT was indeed the cause and not a victim - all the 'evidence' we have to date makes the most likely cause internal to the ELT. Given the way these things should be protected, for instance if there was a failure mode that could lead to data lines 'back-feeding' the battery a diode would be fitted, likewise a non-resettable fuse in the battery pack to protect against overcurrent, it almost sounds as if the wire that got 'pinched' was within the pack itself and upstream of the protection. That would not be good but I can't see how it would have got through a design review - it's the sort of thing one focuses on big time in battery powered equipment!.
However - and this is making the assumption that the ELT was indeed the cause and not a victim - all the 'evidence' we have to date makes the most likely cause internal to the ELT. Given the way these things should be protected, for instance if there was a failure mode that could lead to data lines 'back-feeding' the battery a diode would be fitted, likewise a non-resettable fuse in the battery pack to protect against overcurrent, it almost sounds as if the wire that got 'pinched' was within the pack itself and upstream of the protection. That would not be good but I can't see how it would have got through a design review - it's the sort of thing one focuses on big time in battery powered equipment!.
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As someone posted earlier, is this the first ever incident of this kind in this ELT? If so, and it was on a 787.......................what odds
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As someone posted earlier, is this the first ever incident of this kind in this ELT?
The 'pinched' wire, if more than just rumour, puts the ball back in Honeywell's court as the ELT is a customer specification which is simply fitted by Boeing during assembly.
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So I take it the we are to assume an internal short circuit is the "fault"?
Then why didn't it show up during unit assembly or testing??
[However it could also be chaffing/fretting of wire to expose conductors in a longer timescale, but I find it hard to believe an ELT Tech working at a bench in the factory wouldn't spot this during assembly]
Then why didn't it show up during unit assembly or testing??
[However it could also be chaffing/fretting of wire to expose conductors in a longer timescale, but I find it hard to believe an ELT Tech working at a bench in the factory wouldn't spot this during assembly]
Last edited by glad rag; 21st Jul 2013 at 08:57.
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Then why didn't it show up during unit assembly or testing??
[However it could also be chaffing/fretting of wire to expose conductors in a longer timescale, but I find it hard to believe an ELT Tech working at a bench in the factory wouldn't spot this during assembly]
[However it could also be chaffing/fretting of wire to expose conductors in a longer timescale, but I find it hard to believe an ELT Tech working at a bench in the factory wouldn't spot this during assembly]
However a pinched wire would not necessarily be visible from an external inspection and could well not have created a short straight away. My guess is the combination of a pinched wire followed by the temperature cycling eventually ruptured the wire insulation and if, as I speculated earlier, the fact the wire was pinched also compromised the hermetic seal and allowed the damp in, well - there you go!
Last edited by fenland787; 21st Jul 2013 at 09:14.
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As someone posted earlier, is this the first ever incident of this kind in this ELT? If so, and it was on a 787.......................what odds
so far I dismissed all the speculations about the 787 having more than it's fair share of teething problems, but the way this is developing, I think it's legitimate that some people are starting to ask questions about quality and testing processes, particularly those who built the plane should
Last edited by deptrai; 21st Jul 2013 at 10:42.
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so far I dismissed all the speculations about the 787 having more than it's fair share of teething problems, but the way this is developing, I think it's legitimate that some people are starting to ask questions about quality and testing processes, particularly those who built the plane should
I agree there are teething problems, just this isn't one of them, or did I misunderstand your post?
The Main & APU batteries are not manufactured by Boeing either.
Quality control?
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Quality control?
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I was as just irritated by the odds of this happening in a 787, and expressed myself in a misleading way. I dont think this is necessarily Boeings responsibility, and a 787 issue, from the little we know so far. but in the end they put their name on the airplane, and if I was them, I would be asking some questions, and I am pretty sure they do.
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I've read through all of these posts since this thread was created.
There are three things that may, or indeed may not, be related to one another.
A mention of sparks seen well before the fire though to be from an aircon unit. If that was correct could that have affected the humidity in the area on that day?
The pinched wire discussions as a possible cause to failure of the ELT unit.
The attachment of the cables from the aircraft to the ground cart. Now it is stated that the power was disconnected and observed to be so by the flight engineer, however my question is whether the connection of those cables presented a passive electrical characteristic of some kind. e.g. a ground connection that was significantly related to a fault condition on that day. Note I've said 'fault' because normally it should not be a problem.
I'm not an avionics engineer, btw, but I have experience of EMC and have tested military gear. Some of EMC work is passive where you listen to signals emitted from a system and decide whether they are supposed to be there or not. Other tests involve introducing electrical conditions to see if anything changes.
There are three things that may, or indeed may not, be related to one another.
A mention of sparks seen well before the fire though to be from an aircon unit. If that was correct could that have affected the humidity in the area on that day?
The pinched wire discussions as a possible cause to failure of the ELT unit.
The attachment of the cables from the aircraft to the ground cart. Now it is stated that the power was disconnected and observed to be so by the flight engineer, however my question is whether the connection of those cables presented a passive electrical characteristic of some kind. e.g. a ground connection that was significantly related to a fault condition on that day. Note I've said 'fault' because normally it should not be a problem.
I'm not an avionics engineer, btw, but I have experience of EMC and have tested military gear. Some of EMC work is passive where you listen to signals emitted from a system and decide whether they are supposed to be there or not. Other tests involve introducing electrical conditions to see if anything changes.
Last edited by old dawg; 21st Jul 2013 at 11:31.
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And assuming this is what occurred, do you think this will this event lead to tough questions about the thin insulation?
If you mean will Honeywell be looking at the insulation of whatever wire they used in their box? Well they may, but much more likely they will be figuring out how to re-route the wire so it can't happen again!
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because it is the internal ELT wire that got pinched
Boeing 787 Probe Said to Focus on Pinched Beacon Wire - Bloomberg
"said the person, who isn’t authorized to speak publicly."
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Glad Rag,
My apologies, I jumped ahead of myself in my reply. You asked how come it was not picked up during assembly and test, my point is that as it is thought from the reports that the outer battery cover did the pinching, there would be nothing to see during the assembly process and once it is assembled, inspection and test is all that is left to you. It is possible that inspection would not show anything and if the insulation was not compromised at that time then the unit would pass it's tests too.
Quote: (mine)
However a pinched wire would not necessarily be visible from an external inspection
However a pinched wire would not necessarily be visible from an external inspection
(yours)
That nothing like I posted.
That nothing like I posted.