AAIB issues report, recommends rendering “inert” ELT

Here it is. Be sure to also click on the PDF.

37 Comments on “AAIB issues report, recommends rendering “inert” ELT

  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 the crown”

    All in all a very hold back, well written clear report IMO.

    • The question is: did the fire start there?
      The capacity of batteries used within the ELT is according to this source

      14,5 Ah from 3.7 V down to 2 V. About 150 kJ per cell.
      The ELT in question contains 5 cells.

      Total energy: 750 kJ.


      This ELT weights about 3.5 kg. Most of it is aluminium with a heat capacity of about 897 J/(kg · K).

      With just 3 kg of aluminium as capacity temperature rises by 300 Kelvin. Most plastics start burning at temperatures over 350°C.

      Even with 50°C at the crow of the barrel I doubt the ELT as source of the fire. My calculation was even without heat loss to the surrounding environment.

      Maybe there are some materials around with a flash point lower than 250°C in CONTACT with the ELT. – Some lost paperwork?

      • I thought 3.5kg was everything, case, electronics and the battery. Thus when catastrophically shorted the potential was there to get the thing red hot. This should be easy to test though, so we should hear from honeywell soon, I hope. Removing the thing from all aircraft may no be possible, on some this may the only source of location information under some circumstances. Pingers don’t work that well when deep in the oceans.

        But the greater picture is rather troubling, a few notebooks capable of igniting 787’s fuselage skin.

      • 750kJ may be the stored electrical energy of all 5 cells, but that is not the only energy available to a fire. If the cells were to burn, they would release way more heat energy than 750kJ. Plus, there are other combustible materials inside the ELT as well as surrounding it.

        Heck, a 240Cal jelly doughnut contains about 1MJ of chemical energy.

        Notice what the report says and does not say in the excerpt keesje quoted above. There are no other systems that could have initiated the blaze with the aircraft unpowered, but that does not mean there are no other systems in the area that contain combustible materials that could have contributed to the intensity of the blaze.

      • 240 kCal are equivalent to about 1 MJ.

        The ELT case looks more stable to me than Boeing’s battery boom box. The electronic devices inside an ELT are rather small compared to batteries and casing. It’ll be small error to neglect them.

      • No, 240kcal is equivalent to about 1MJ. Notice the difference between small c and large C.

        cal is the thrmochemical calorie: 1cal = 4.184J
        Cal is the nutritional calorie: 1Cal = 1kcal = 4.184kJ

        Neglecting all of the combustible materials both inside the ELT and in close proximity to the ELT will lead to the wrong conclusions, in my humble opinion.

  2. Well if this is the whole story than a few notebooks placed strategically could easily set this thing on fire at any time. And I don’t believe sufficient water would be available to fight it when in flight. Presumably any cabin/ fuselage fire as halon apparently does not work there.

    • I think they are saying the fire damage took place where it did because of the presence of the ELT batteries, but not necessarily that the ELT was the cause of the fire. By “inert”, I assume remove the batteries. This implies, I think, that they reckon it to be a fairly useless piece of equipment.

  3. Why not order it removed from *all* aircraft? They have no idea what caused the fire.

    • The AAIB does recommend that a safety review be done of the Lithium ion powered ELT installations in other aircraft types, and where appropriate, initiate airworthiness action.

  4. Thats going to hurt- no plans for fire abatement inn upper ceiling panels where there is bucu wiring, etc Supposedly the ground power was NOT on but connected ?

  5. Now we know that there was no power on the aircraft. That really surprises me. I can only imagine what the inside temperature was like. On a hot summer day we have a 787 parked outside in the sun for several hours. We know that with a CFRP fuselage acting like a thermos bottle heat would rapidly build up inside, especially in the crown area. Maybe enough to trigger a thermal runaway on the lithium-ion battery of the ELT? Would that heat buildup scenario be enough to explain the one in six thousands (1/6000) battery defect?

    Now the question is can the Dreamliner fly safely without an ELT device? Personally I don’t think it is a wise thing to do because the 787 has a bad safety record, even if it has never crashed before. The thing is that I view this aircraft more and more like a disaster waiting to happen. And if it was to crash it would be left without an ELT to quickly locate it. If ELT devices are useless devices, like many people seem to suggest, why not remove them from ALL aircraft? The logic behind this decision is that the ELT is a potentially dangerous device on the Dreamliner. So on the balance the ELT has to go. But I hope they will find an alternative soon.

  6. I remember, there were problems with 787 connected to groundpower. Paris Airshow 2012? Correct?

    • Yes, but those aircraft were probably powered on, this one was not. It was only connected.

      • Would be interesting to know, if the “power situation” of the a/c is monitored (and recorded) while aircraft is parked.

  7. I find it interesting that the only external damage the report mentions is blackened and peeling paint and damage to the composite structure, but not actual holes in the fuselage. I wonder if the smoke observed from the tower was just the paint and matrix material cooking off. In my experience, paint and similar coatings can give off a lot of smoke when exposed to just heat without an open flame. No holes is also consistent with the fact that the fire was not brought under control until fought from the interior of the aircraft. Upon additional examination of the photos available, it is not clear to me that actual holes are present.

    • Coincidence? But I don’t buy it. “Something’s happening here, but we don’t know what it is …”

      • I’m not sure what you are saying here. I was merely pointing out that what looked like holes in the available photos, may in fact not be holes at all.

        Of course this distinction probably makes little difference as far as structural integrity is concerned. Severely heat damaged CFRP may not be much different than a void in terms of supporting shear or compression, or even tension for that matter.

  8. Did it strike anyone that less than two months before the aircraft were returned to service after being grounded several months because of lithium-ion battery runaways we are yet again facing another lithium-ion battery runaway? The irony is that it has apparently nothing to do with the previous ones. Or does it?

  9. An interesting excerpt from the report:

    “Detailed examination of the ELT has shown some indications of disruption to the battery cells. It is not clear however, whether the combustion in the area of the ELT was initiated by a release of energy within the batteries or by an external mechanism such as an electrical short. In the case of an electrical short, the same batteries could provide the energy for an ignition and suffer damage in the subsequent fire.”

    Perhaps an external electrical short in a miswired or defective external connector to the ELT? According to the report, it sounds like right now it’s either that or a thermal runaway induced by excessive crown temperatures caused by a hot day.

    Boeing should probably put out a bulletin for airlines to check the connectors on the ELT, similar to the checks already performed by ANA and JAL.

  10. On a lighter note, the first 787-9 was moved from the FAL to the paint hangar Wednesday evening under the cover of darkness.



    Short piece:

    I guess Boeing must have done all this work on the 787-9 to distract our attention from the hopelessly faulty and fire prone 787 electrical system;)

  11. Maybe if it was a hot day they moved it under the cover of darkness to ensure it wouldn’t burst into flames!

  12. I still vote for sneak circuits and ground loops – but until more info available its only speculation

    I don’t know what photos some are viewing when they say they can see no holes- in the fuselage otther than looking at the right side rear- left side rear shows major holes and exposed stringers ,etc

    • Hey Don,

      I’m not claiming there are definitely no holes in the fuselage, but in light of the AAIB report, I went back and looked at the best shots of the left side I could find and all I can be absolutely sure of is that there are dark spots with lighter spots between in the pattern of stringers and longerons. There is some detail at the edges of the dark spots that give the impression of depth (thru hole), but that detail could also be flaked paint. The lighter spots could represent a lack of baked paint because the skin over the stringers and longerons would have taken longer to get to temp due to the increased effective thickness. The fact that some longerons are hollow would have also aided this effect.

      If the skin was completely burned away, the exposed stringers and longerons would not be white. They would either be the natural color of the CFRP, or charred black. The fact that the damaged areas are dark does not necessarily mean a hole because of dark natural color of the material. The dark spots could just indicate a lack of paint.

      This is just my speculative 2 cents based on viewing the photos in light of new info.

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