Power-wise, this unit is completely self-contained, self-testing and with a ten year battery life.

The only electrical integration with the aircraft's systems would seem to be this connection to a flight deck 'test switch'.

Are all Honeywell ELTs connected to the flight deck or just those fitted to the 787?

I am struggling to see how a low voltage/data connection can cause a fire, even when incorrectly connected. And the unit itself in a quiescent state is unlikely to draw more than a few milliamps from the onboard battery, not unlike an electric clock battery which can tick for several years on a single AA 1.5 volt cell.

I can only imagine that if the beacon is the cause of the fire, it somehow suffered some mechanical damage either inflight or during manufacture and installation.

The requirement for a remote switch in the cockpit on all new installations has been around in the US for 10+ years. All aircraft all installations.

ELT - a good idea in any and all aircraft
 

It is self contained and there to help SAR teams get to you in the event of a crash. Of course you are right in that most all commercial operators have satellite tracking regardless of control zone type. What if aircraft power is lost suddenly or standard communication equipment fails? Or what about a sudden event where the crew could not get out a distress call?

Modern 406 ELTs transmit exact position for an extended period of time. Very useful if one ever had to ditch and was floating around in the sea. Also useful regardless because the ELT will outlast any other electrical communications after an event.

Bottom line: one faulty ELT is hardly cause to discuss getting rid of them all together on scheduled airliners.

I wonder if Boeing EE's are tracing the route of electrons from the ground power receptacle throughout the aircraft to see how current could leak into the ELT circuit. Let us suppose that they find something that allows a stray voltage to wander here or there. Hmmm.

Other than putting all ELT's in the bin, as some Aussies seem to suggest, maybe one could return the ELT to the condition of entirely isolated from all of the aircraft elecrical systems. This would lead to a pre flight test where a CC or maintenance crew accesses the ELT test switch, and either confirms the light or the flight deck crew are listening up on the ELT's freq and confirm via intercom good test or bad.

Yes, it's a crew coordination drill, but you don't need an ELT unless you are intending to fly in the first place. You always fly as a crew. It may also be in the too hard category, in terms of getting access to a test switch from inside the cabin.

Just thinking aloud here ...

Suggesting that these things are switched off rather than removed, suggests that there may be a problem with their operation rather than their manufacture or installation.

Can they know that by now? :confused:

SOS:This could point to environment as well, is the 787 ELT subject to deeper temperature cycles due to it's location compared to other aircraft?

The larger the temperature swing the more mechanical stress there is.

Wonder how hot the unit gets when parked in the sun in Africa?

The Bulletin doesn't recommend just turning the unit off, it recommends making it inert. Big difference.

here is a report
 

My reading of the AAIB safety recommendations is that it is only the fixed ELT that is required to be switched off and NOT the portable devices or those attached to life rafts.

Could that be because they are different units or because they are not located in close proximity to a composite structure and are difficult to access in flight?

I take some poster's points about a crew in flight having a time advantage over the ground firefighting crews when tackling the fire. But reading about the firefighting efforts in the report, I doubt it would be easy for crew members to do this in flight given that the firefighters had to hack away at ceiling panels to tackle the fire with water after failing to control it with halon extinguishers.

This could have been extremely nasty! :(

I bet they are! I'm not familiar with this kit but, given I understand it is not powered from any aircraft bus, I would have expected any external control wires to be galvanically isolated from the ELT electronics via an opto or something, so there should be no possibility of any sneak back-feeds, but you never know, I have had someone tell me in the past "I don't need to isolation from the system, it's battery powered". Only true if the number of wires connected is equal to or less than one I think!

I presume it has an external antenna? I hope nobody did a bad thing with antenna grounding.

Don't forget in all this that 'in flight' would probably result in depressurisation of the aircraft making life a lot harder!

To make it truly inert would require it to be disconnected from any other aircraft systems and the battery to be removed. As access is the problem with this device, wouldn't it be easier to remove it altogether once it was 'exposed'?

Pitts #452, the version of the report I have downloaded interestingly states "the only _significant_ thermal event".

Murphy, on smaller aircraft (think King Air, small jet) they are usually aft of the pressure bulkhead in the tail. On larger aircraft (think G-IV and up) they are usually inside the pressure vessel, to prevent cold soak problems on long flights.

Living very close to the threshold of EGLL as I do, I can vouch for the volume from the outside as well.

The 787 and the A380 are remarkably quieter than the aircraft they are replacing.

Ban Lithium-anything batteries from ANY airborne system!!!!

AAIB recommends review of all lithium-powered ELTs after 787 fire | Reuters

Lithium-Manganese Dioxide (LiMnO2) batteries are actually at the lower energy/greater safety end of the Li-Ion scale. If these are now catching fire without an external ignition source, it's not good. :eek:

The guilt or innocence of the ELT will become clear in due course.

Of more concern are the problems that the firefighter(s) had in getting to the fire and extinguishing it.

Also, the lack of detail of the damage is interesting (I still await the videos of the fire and the close-up photos).

When we installed the ELT on the '380 the most "difficult" part was wrapping the antenna feeds with fireproof material to ensure that the installation as a "whole " met regulation re-fire/heat resistance.

It seems a somewhat moot point that there is no airframe insulation in that self same area of the 787 by design....:\

True, but we don't know that to be the case yet, as Lonewolf_50 pointed out, folks will be looking for possible sneak circuits that could have caused the problem. If I have correctly identified the ELT on Honeywell's site there are a number of remote connections available so, although it should be unlikely, perhaps there is a back-feed from the airplane system that caused the issue? It is very bad luck for Boeing that with over 3000 of these ELTs out there, the very first one to combust was one of the 50 or so in a 787!

Edit to add link:

http://www51.honeywell.com/aero/comm...06_AFN_ELT.pdf

Don't know how the AAIB does investigations, but if the damage did not shed light on causative factors, a detailed evaluation of the damage was not always a required part of the investigation when I was doing them for the US Army. The technical investigation is for prevention purposes - identify causes that can be avoided.

Yeah, therefore we may get something concrete in months rather than years...

Only if it was actually the battery, and the incident was directly related to its location, installation, use, integration with other systems, and maintenance.

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. :*

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.

Scuffers & Speedo


UK Board: Remove Honeywell Beacons After 787 Fire - ABC News

In all this, how about a vote of thanks to the ATC controller who first spotted it. Well done!!:ok:

1. ELT source of fire BUT no determination why it ignited
2. No reaction from Boeing apart from an acknowledgment
3. No FAA response

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?

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.

Incorrect, as I understand, it may have to be deactivated on all aircraft on which it is fitted in an equivalent location.

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.

This is not certain.
I would stick with points presented by daikilo in post #480. Going beyond that is over-interpretation.

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.

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 . .

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.

True, also it provides no protection if something was trying to 'charge' a non-rechargable cell but I really can't believe Honeywell won't have thought of that and ensured that even if volts were applied where they shouldn't be, no reverse current can reach the battery. If it is the first ever 'spontaneous combustion' of this ELT Boeing must be thinking someone hates them or the planets are very badly aligned right now, some reports say over 6000 of this type are out there!

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.

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?

A 'G' switch.

I guess the irony is so obvious it's gone unsaid, but it looks like the ELT here "located" the emergency all right.