Looks like there are four wires connecting the ELT to the outside world.

• Four 22AWG wires to transmitter unit
provide full functionality

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.

In the transmission business, a good ground plane is essential in getting a solid signal off the antenna, while using the least amount of power. In a traditional metal fuselage, that ground plane would obviously be the fuselage itself. In this bird however, a large piece of conductor for the antenna to work against may be more difficult to come by, especially at the ELT's required frequencies of operation (121.5 and 406 MHz).

If the ELT was activated some how, there is a possibility that a highly inefficient transmission scenario was occurring. This usually results in higher transmitter temperatures and/or higher battery drain.

I don't have a Honeywell ELT battery, but here is a picture of the lithium pack for an Artex C-406

[IMG]http://i1365.photobucket.com/albums/...psc3dfebb9.jpg[/IMG]

The 4 green cells are each about the size of a D battery. The small circuit board has 2 fuses and a small ic for monitoring the condition of the battery.

You can see 4 small black parts, 1 across each cell. They are diodes so if a cell goes flat it won't see reverse polarity.

But if one of those diodes short, you will have a dead short across that cell.

I am trying to work up the nerve to short a diode out and see what happens, but I'm a little chicken at this point. :} And the boss said if I burn down the hanger I'll be in trouble. :eek:

ABOUT HUMIDITY ON 787
 

From a few friends involved in 787, and a few not well publicized comments/documents about the 787. One selling feature was to be able to have higher humidity in the 787 than on a regular aluminum bodied airliner due to less or virtually zero corrosion issues resulting from passenger breath and temperature deltas in flight, along with a lower cabin altitude.

But during early flight tests, some wags considered renaming it the rainliner, due gto unexpected amounts of condensation in the cabin. Which admittedly was not in a well finished cabin configuration, but filled with instrumentation racks, exposed insturmentation wiring, etc.

Business & Technology | Dreamliner's woes pile up | Seattle Times Newspaper

. . .
The latest delay will at least give engineers more time to test design fixes, including some for less consequential troubles, not uncommon on new jets, such as the maddening drip, drip, drip of "rain in the plane." On 787 flight tests, drip trays padded with squares of absorbent cloth are positioned to collect the condensation.
Fancher said "a good design fix" to dehumidify the interior is being installed and will be tested when the Dreamliners resume flying.
Employees working on the 787 complain about insufficient oversight of suppliers and a management system that the senior engineer called "totally broken."
"This program is not like anything we've seen," said the veteran 787 employee. "It's a screwed-up mess." . . .




Now add to that the wonderous decision to use predominately aluminum wiring to save weight instead of copper or copper/silver alloy or similar.

http://www.safran-group.com/IMG/pdf/EN_mag2_29-31-2.pdf

Now for flight data and computer data lines with low voltage and low current, aluminum ** might ** be an acceptable choice.

But years ago, the push for house wiring of aluminum met eventually with corrosion or similar problems due to buildup of non conductive films on aluminum, resulting in hot spots and IF I RECALL a few fires.

Check your local replacement power plug or switch in the us and the warning re cu aluminum and the availability of a cu-al grease/coating to preven oxidation.

Surely BA would have considered that ???????????

With 6000 similar ELT units in service it would be hard to believe that this was the first one to sufffer a battery problem.

It would be interesting to know how many batteries have been replaced, per qouted 10 year life any replacement would be a failure not end of life.

The really ineresting question would be the condition of the replaced cells,
what if failure is "rare but happens" but on metal aircraft "thermal event" energy is insufficient due to heat sinking etc to light a fire or even be noticed?

md80fanatic
Large ground planes are a requirement with transmitters operating on much lower frequencies. That's why cellphones don't use the 27MHz band ;)

The 121.5MHz transmitter in the ELT works at very low power, a mere 150mW. I wouldn't worry too much about power drain, even with a not-so-efficient antenna configuration, unless I'd want to power the thing from a 9V transistor battery.
The 406MHz transmitter has a rated output of 5W, but at such a high frequency you really do not need a large ground plane - a piece of alu foil a foot square would be quite OK. Also, the 406MHz signal is made up of short bursts, with a low duty cycle: overall power drain is fairly modest.

LASJayhawk
A silicon diode like the one in the picture shorting out spontaneously is a very unlikely event. More so when, as in this type of circuit, they are not under any significant stress.
Well, if you want to do a little experiment, here's how I'd do it:
Solder a few feet of heavy gauge wire (12AWG) to both cell terminals, connect the other ends to a heavy duty switch (make sure the switch is open!).
Close the switch and get away real quick.
The total circuit resistance will be in the order of 0.03 ohms or so if the connections are nice and solid and you use a good quality, 30A rated switch.

Of course you'd only ever do this out in the open, away from any flammable materials.

DEJA VU?
 

Is this another Swissair MD11 accident, except it happened on ground, without crew & pax being involved and too far from professional firefighters with proper kit?

I reword the question I posed in the original 787 grounding discussion:

Was there one or more grumpy old f**t with a long flying/line-engineering pedigree on the Boeing design team, and if not, then why not?

Perhaps such an animal would ask questions and quote incident/accident reports which would make the rest of the "Children of Magenta" team squirm uneasily in their seats and possibly think long and hard before venturing down the Li-On and other innovative but risky solutions?!

Other postings here imply that all is not harmonious sunshine and happiness in the Boeing family, so maybe those at the top of the food chain there had better review their choice of whizz-kids who drool at the thought of new and unproven technology and get back to K I S S basics whilst still producing good kit, or Monsieur HiTecq in Toulouse may win the war in the end? :eek:

Presume?
 

They presume it was the ELT, it hasn't been confirmed, why let this dangerous aircraft fly, again they should all be grounded until the cause of the fire is established. The C of A should be revoked!
I wouldn't fly in one of these death traps! :=

Alumium wiring
 

Aluminium wiring has been used in cabins for years to save weight. Back when I was an avo I dealt with it regularly in AB cabins. Just wack up the voltage and it works fine. Only area you MUST use copper is around the engines and APU due to temperatures (melting point of copper being higher). I havn't worked in an MRO for years so I'm sure somebody else who has can elaborate.....

While we stretch for ever more remote possibilities, just wondering if they had flown through an electrical storm on their last flight and if so whether lightning dispersal across the 787 skin could have set off a slow reaction within the ELT batteries?

Presume!
 

GD Slacker, get a life!!

Transportation of goods or people, by whatever form, involves risk. The trick is to be able to assess probabilities dispassionately.

You clearly cannot!l You probably take bigger risks when you cross the street!

:D:D

olandese:

Seems like a diode shorting or a major defect in the cell are the only reasons I can think of for an ELT to decide to self immolate.

More curious to me is why we need a 50+ hour transmit time on a 406 ELT. The Satellites should get a very good position fix in under an hour, even if the ELT isn't reporting last known position. It's not like we're using a loop antenna on 121.5 to find the position anymore. Maybe go back to alkaline batteries and accept an under 12 hour transmit time??

So, should we pull these same units out of the 777's now?

Isn't the presumption that it didn't activate as the first alert would have been from the monitoring system rather than a vigilant ATC seeing smoke from the aircraft?

The AAIB report would also have mentioned if an alert had been generated by the transmitter.

I don't think that's what will end up happening. The three paragraphs in the section Emergency Locator Transmitter (ELT), on page 3, read to me as:

The device is not a new design and has a proven history. The AAIB are looking into the possibility that a short, external to this device, caused the problem with this device, on this plane.

By the way... and just putting it out there... but before everyone got focused on the main battery/apu battery catching fire... I think there were reports of these batteries being flat/failed and having to be replaced...

More than 50 million flight hours without a fire
 

According to the report in today's NY Times:

Either Boeing has extremely bad luck to have this happen on a 787, or there is something else going on here.

re. integration with aircraft wiring.
 

The Honeywell datasheet claims that this unit is connected by 4 x 22AWG wires. This picture shows at least 33 connections as well as the antenna.


http://i1280.photobucket.com/albums/...ps40310599.jpg

Does anyone know what the other 29 or more connections are, and if any of them are likely to be carrying anything other than data/control signals which will most likely be no more than a few milliamps?

Yea, I suspect as much else all these things sitting around on shelves as spares would be popping off right and left.

So what kind of summer sunlight heat load can they take at the top of a composite aircraft ?

Don't think this link has been posted here before, they seem to be eeping a pretty good track of events.

Airchive Blog re 787 Fire incident

Speed of Sound Follow the link in post #477 and it will tell you that it's used for a programming interface.

There are interfaces to remote alarms, switches, aircraft warning systems and the navigation bus for Lat/Long position data.

Hmmm
 

Well, they do but this passage from the log worries me slightly:

...so that's the secret Boeing repair technique then, nice bit of Douglas Fir shuttering ply inside and out, a quick pour of the strongest mix Readymix can deliver and the job's a good'n?

Thanks green granite and ionagh.

So basically data connections then. These will eventually terminate at the pins on an IC inside the unit and if wired incorrectly will most likely 'confuse' the logic of the processor but unlikely to cause a short circuit to the battery pack.

Given the almost faultless history of this device, installation/location of this device may be where the AAIB should be concentrating their efforts.

Folks,
This is NOT what Australian regulations are suggesting. Indeed, Australian regulations require most aircraft, on all but very short flights, (some Ultralights are exempt) to carry an ELT.

What is NOT required is a fixed ELT, for the reasons so comprehensively demonstrated by REAL WORLD results, not theoretical claims about design performance real crash loads, not "designer" crashes.

What is the point of carrying a device that has a failure rate of around 95% (100% in water) AND THIS RESULT INCLUDES LARGE AIRLINE AIRCRAFT not just small GA aircraft.

Quite a number of posters here discuss the merits of a fixed ELT in a way that suggests that the device is actually going to perform some useful function, in the event of a crash. The figures are very clear, the likelihood of any useful broadcast is extremely remote.
In the case of the recent crash at KSFO, I think I am on safe ground in saying that the fixed ELT there in the B-777 (if one was fitted) would not have broadcast a useable signal.

The failure reasons are really quite simple, in the crash sequence, in most cases, either or both the aerial cable or the external aerial are damaged. Although less common, failure of the G switch to activate have been recorded, in circumstance where the calculated G load were such that the system should have worked.

The bottom line here is quite clear, as far as any safety contribution is concerned, fixed ELT are a waste of money and add an extra potential failure mode with on-board fire as a result.

Portable ELTs, on the other hand, have a well established record of producing some quite amazing results, even under the old pre-GPS 121.5/243 COSPAR/SARSAT system, in leading searches straight to the wreck, without even a box search being necessary.

The US Civil Air Patrol, as a result of the Australian research, did a study and found, within the limits of the available data, substantially similar result -- which should surprise no one who has ever spent any time at an aircraft accident site.

None of the airline aircraft I ever flew were fitted with fixed ELT and that never stopped them flying in FAA airspace they were all fitted with with multiple portable ELT, in many cases with a water activated power source, so if it was a survivable land accident, a few blokes were going to have to pee in the plastic bag tied to the ELT for just that purpose. In a ditching, no shortage of "activating fluid".

I have actually had a commercial Li AA size and a 9V NiCad battery have a thermal runaway, in each case the manufacturer said it was impossible. Any exothermic chemical reaction which runs away caused by who knows what ? Impurities acting as an unintended catalyst ? The 9V case was interesting, the multimeter case felt warm, I removed the battery, and it continued to get hotter in my hand until I could no longer hold it so I put it on a bench and watched it finally burnt it all took about 15 minutes from the time the battery was removed from any potential short circuit. A short was unlikely, as the multimeter worked OK when another battery was fitted.

All the known issues relating to the entire electrical and battery system worry me, especially as the wiring is apparently not covered in the usual type of insulation, but an ultra thin coating of Teflon. Teflon is an amazing material, but not good at resisting abrasion. A problem on the coating over aluminium wire in a damp un-insulated area of the plane near the skin could be part of the problem. I will not be surprised if the wiring eventually has to be replaced.

around 5 hours ?

Yes data but not brought out into airplane wiring I would think, these will be for the 'through the skin' programming/upgrade/testing of the ELT. I think the only wires that are connected will be the four wires which I suspect may well be a CAN interface running to the RDC(s)

As an engineer in a completely different industry, I often refer to air crash investigations as an example of how to learn from mistakes and improve the product.

One thing that has always impressed me is that AAIB reports are written in clear English with any jargon and acronyms explained, so those not involved in the aviation industry can understand them.

It's a bit of a surprise then, that the first recommendation of the report is ....initiate action for making inert.....

This has been reported in the media as 'switching off' which is plainly the wrong interpretation.

As it is unknown if the fault was internal or external to the battery pack, would it not have been better to recommend removal of the ELT or the ELT battery?

Does 'making inert' offer other options, like encasing the battery pack in a metal box, and surrounding it with a flame suppressant material?

No, or at least not unless that modification had already been approved. I think 'make inert' means just that - remove any source of energy or other hazard

Inert:
See Chernobyl - I think the inside of the tail section has to be encased in concrete

Seriously I think the investigators know that wrongly calling "Lithium Battery" as the problem would be a PR disaster so they are careful to call it as an internal OR external issue. Not least as they are probably still uncertain of precisely what DID happen. Remember they spent months not finding conclusive evidence of what caused the main batteries to self destruct even with several to examine

I suspect the "Inert" wording is intended to convey "Make harmless" and thereby encourage the fullest practical set of Battery removal, Cable disconnection and removal/isolation actions

Were already there - see my post #520

Absolutely no comparison to the JAL flight although a rapid descent knowing that the composite roof section was burning through just in front of the tail, would worry me a bit. :)

I remember watching the TV documentary about the 777, ("21st Century Jet"?) and was surprised that the plane and engines were to be fully designed on computer and not need testing.

One older engineer insisted that an engine SHOULD be tested for real on a plane and possibly, because of the presence of cameras, the then boss Mullally finally agreed to test fly an engine on an existing plane. As it banked slightly just after take-off there was a compressor stall, and it transpired that the programmers had forgotten to consider Gravity!

I have now learned that rather than strengthen ties between management and engineering, Boeing has separated the two even further by moving management to Chicago, hundreds of miles away.

This division of management from production, then issuing unrealistic demands and deadlines to the "dirty end of the company" is sadly all too common in industry and commerce these days and I feel it is a deeply flawed business model, and one which may be partly responsible for delays and problems with the 787.

We saw this so clearly in UK when companies such as the railways and Water Boards were privatised: engineering staff were rapidly chucked off the management team and side-lined. They were replaced by Business studies graduates with little or no understanding of the dirty end, who soon cut back on maintenance staff and procedures, and a string of serious and fatal accidents soon started.

ELT removal consequences
 

There is one aspect which, to my knowledge hasn't been mentioned so far.

The AAIB appear to be recommending that the ELT is removed or disabled, at least on the other 787s. But in the AF447 disaster the ELT might have allowed the aircraft to be found sooner, had the batteries lasted longer. In fact IIRC there was a recommendation in the BEA final report that ELTs be fitted with batteries of longer endurance to give searching teams more time to locate an aircraft (worst case at the bottom of the ocean).

I appreciate that it was a different aircraft type, but surely the principle is the same. I imagine that if AF447 had never happened no one would be particularly concerned whether or not the ELT was fitted or working, but of course this isn't the case now.

Sadly, because AF447 sank and salt water virtually prevents any RF transmission (other than VLF or ELF as used to communicate with submarines), it would not have helped.
I think the FDRs have a sonar type transducer 'pinging' away to allow location underwater but I don't thing the standard ELT does?

lightning strike.

An aluminum body would have safely grounded the energy around the skin.

the composite body allowed it through and into the ELT, setting it on fire.

ELT
 

ELT like the one fitted on the ET B787 is an option. Many airlines do not have it. In my airline none of the B777 or early Airbus have it. So it makes little difference if you remove all the units fitted to B787. Mind you there are more portable units on aircraft located in the cabin that can be manually deployed. There are also a couple of units on the door slide raft. These are cylindrical in shape. I think the ones fitted to AF flight was one of these units. These are accessible to cabin crew in case they have a run away battery.

Another question if some one can answer. We hear that the fuselage skin of this ET aircraft is not holed as most of us concluded from the video grab. This is as per the AAIB. They have mentioned severe damage to about 8 feet of the skin. The smoke was first noticed by ATC who initiated the emergency action. If all the doors were closed, how did they notice the smoke? From a vent?

Yeah, it would be a tough call - stay at 40,000' so the flames go out but pax turn blue, descend to 10,000 and the pax turn rosy pink and so do the flames...