Hight current?
 

Why would a control-bus carry a high current? This would be a major safety issue. I cannot believe anybody would do that.

Very true, but 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.

An internal short circuit within the battery is a much more likely cause of a high current/high temperature condition.

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

Bloomberg reporting a wire smashed under the beacons battery cover.

Boeing 787 Probe Said to Focus on Pinched Beacon Wire - Bloomberg

:ugh:

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!.

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?

Yeah, what a lousy way to win a lottery!

The AAIB stated that there have been 'no significant events' with this unit previously.

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.

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]

I've been there and you can bet your life those questions, and then some, are being asked right now!

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!

That nothing like I posted.

And assuming this is what occurred, do you think this will this event lead to tough questions about the thin insulation?

if this turns out to be a pinched wire in an ELT, what are the odds that it happens on the ground...(some operators plan to have the 787 flying up to 18 hours per day...)

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 :oh:

And not a mention of the K [TM] word.

Sorry - I must be missing something here. If - and it is still only 'if' at this stage - the problem that this thread is addressing turns out to be an internal manufacturing fault in a piece of tested, certified kit delivered by a third party who supply it to most people who build airplanes, how is that added to the 787 'teething problem' list?

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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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.

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.

If you mean the ship's wiring - no not at all - because it is the internal ELT wire that got pinched, or so we believe.

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!

I would be VERY wary of reading anything into what has been "released" so far....

Boeing 787 Probe Said to Focus on Pinched Beacon Wire - Bloomberg

:hmm: "said the person, who isn’t authorized to speak publicly." :hmm: