Ethiopean 787 fire at Heathrow
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Only needs to be marginally watertight, enough to survive just one hour in (only) one meter of water
DO160F 'Waterproofness' doesn't even have immersion listed as a test method.
If the ELT is specified by the manufacturer as "Permanently Hermetically Sealed and airtight' (I don't know if that is the case, but I doubt it) then DO160 exempts it from further waterproofness testing, if not then the relevent tests for airplane use will be in DO160 Section 10 and will be selected from four test methods, in increasing order of severity:
'Condensing Water Drip'
'Drip Proof'
'Spray Proof'
'Continuous Stream' (this one is fun - think big pressure washer jet aimed at the most vulnerable joints and connectors!)
The choice of test will be made based on equipment type and it's location in the airplane. I don't know which was selected for the ELT in question.
So to say "787 is to wet for electronics" is clearly inaccurate however there may need to be a review of matching test method to equipment type and location if, and only if, there are repeated and multiple examples of random bits of electronics failing due to water ingress. I don't think we have any facts to show that yet?
Don't confuse occasional poor manufacturing quality with design failings - and before I get jumped on, I accept repeated manufacturing errors can indicate poor design of course.
....such as several occurrences of the same wires getting pinched when a battery that is designed to be replaced in service is fitted for instance....... (This example picked entirely at random you understand!)
Last edited by fenland787; 27th Jul 2013 at 10:57.
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Coegie, we've gone away from the "no user serviceable parts inside" , it's a maintenance headache. The older Dukane ULB's (pingers) used to have to go back to the factory for a battery change, the new ones are field replaceable.
What I don't understand is why they are only checking the ones in the '87. Honeywell said there are over 6000 in service. Seems we should be checking them all.
Link to AD http://rgl.faa.gov/Regulatory_and_Gu...2013-15-07.pdf
It does say " This AD is considered to be interim action. Because the fire occurred on a Model 787-8 airplane,required actions in this AD are focused on Honeywell fixed ELTs installed on that model. However,we acknowledge that ELTs are installed on various other aircraft; therefore, continued investigation is required. Once final action has been identified, we might consider further rulemaking. "
ETA: fixed link
What I don't understand is why they are only checking the ones in the '87. Honeywell said there are over 6000 in service. Seems we should be checking them all.
Link to AD http://rgl.faa.gov/Regulatory_and_Gu...2013-15-07.pdf
It does say " This AD is considered to be interim action. Because the fire occurred on a Model 787-8 airplane,required actions in this AD are focused on Honeywell fixed ELTs installed on that model. However,we acknowledge that ELTs are installed on various other aircraft; therefore, continued investigation is required. Once final action has been identified, we might consider further rulemaking. "
ETA: fixed link
Last edited by LASJayhawk; 27th Jul 2013 at 15:58.
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What I don't understand is why they are only checking the ones in the '87. Honeywell said there are over 6000 in service. Seems we should be checking them all.
Link to AD http://rgl.faa.gov/Regulatory_and_Gu...2013-15-07.pdf
Link to AD http://rgl.faa.gov/Regulatory_and_Gu...2013-15-07.pdf
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SLFgeek,
Am very familiar with this issue from Atlas missile days back in the 60's. Looks like Boeing and Honeywell (who installed the batteries??) forgot their basic materials lessons yet again.
Am very familiar with this issue from Atlas missile days back in the 60's. Looks like Boeing and Honeywell (who installed the batteries??) forgot their basic materials lessons yet again.
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It looks that there are two generations of this ELT classic AFN and new (half sized) AFN2:
http://www51.honeywell.com/aero/comm...U_406_AFN2.pdf
I suppose that the AFN2 is used in 787 but is it spread also in older a/c?
http://www51.honeywell.com/aero/comm...U_406_AFN2.pdf
I suppose that the AFN2 is used in 787 but is it spread also in older a/c?
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SFL geek and Amicus are correct about cold flow issues, I am just wondering how/why we think we know Honeywell used "thin teflon insulated wire" in the location where the issue occurred?
There was a list of approved wire for the 787, I very much doubt that was on it at all, and if it was it would have been for very specific applications, given it is known to have very poor cut-thru resistance, suffers from cold-flow and is heavy! The only real thing going for it is it's high temperature performance.
Assuming we are talking battery leads, I would expect it more likely that a single or double insulated wire with a polymer such as crosslinked ETFE or PDVF/PVF2 outer sheath would be called out?
Amicus, I too was wondering who actually fitted the batteries, given the production delays it is not beyond the bounds of possibility that the early deliveries of ELT were either without batteries or had them removed to be fitted later and given the focus on only units in 787...makes you wonder?
There was a list of approved wire for the 787, I very much doubt that was on it at all, and if it was it would have been for very specific applications, given it is known to have very poor cut-thru resistance, suffers from cold-flow and is heavy! The only real thing going for it is it's high temperature performance.
Assuming we are talking battery leads, I would expect it more likely that a single or double insulated wire with a polymer such as crosslinked ETFE or PDVF/PVF2 outer sheath would be called out?
Amicus, I too was wondering who actually fitted the batteries, given the production delays it is not beyond the bounds of possibility that the early deliveries of ELT were either without batteries or had them removed to be fitted later and given the focus on only units in 787...makes you wonder?
Last edited by fenland787; 27th Jul 2013 at 18:52.
What I don't understand is why they are only checking the ones in the '87. Honeywell said there are over 6000 in service. Seems we should be checking them all.
Normally, I would expect line maintenance to be performed by techs trained and certified to do such work. Including watching for pinched wiring. So the question is: Who did the work on the units stored at Honeywell/Boeing? Perhaps the regulators were already made aware of this maintenance procedure anomaly and decided not to impose additional costs on their other customers.
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They may find a single undertrained tech did the battery work on all suspect units. Or the design could be conducive to wire pinching during cover install, without provision for a visual inspection.
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These people seem to have an eye on the Ethipian fire and its ongoing aftermath. Analysis: Boeing 787 Dreamliner In the Hot Seat Again After Fire at Heathrow Airport
Update 17: Sunday, July 28 11:15AM E.D.T.
ANA and United Airlines have both found problems with the Honeywell ELT beacons. The issues appears to involve a pinched wire in the emergency locator transmitter. United has completed its inspection of its six 787 fleet, where it located one defective transmitter. ANA also found the same issue in its ELT on 1 example of its fleet and on another uninstalled portable beacon. ANA has removed all beacons from the eight 787s used on domestic routes . JAL completed investigations this weekend on its 9 787s. The FAA and Japans transport safety ministry followed suit with the UKs AAIB in recommending removal or inspection of the ELTs, 2 weeks after the Ethiopian issue. European operators LOT, Thomson, Norwegian Air Shuttle, and British Airways (who is set to debut the 787 September 1st) have removed he ELTs from their aircraft but have not reported damage publicly. This far, no airlines other then Ethiopian obviously have suffered service interruptions as result of the ELT issue, though a Qatar 787 has been grounded on Monday due to an unspecified minor technical issue. Boeing has now delivered some 70 787s to its customers, around 20 since the grounding order was lifted in April, including new customers China Southern, Norwegian Air Shuttle, Thomson, and British Airways. These ELT issues are still considered unrelated to the lithium-ion battery defects which caused the worldwide grounding back in January.
Update 17: Sunday, July 28 11:15AM E.D.T.
ANA and United Airlines have both found problems with the Honeywell ELT beacons. The issues appears to involve a pinched wire in the emergency locator transmitter. United has completed its inspection of its six 787 fleet, where it located one defective transmitter. ANA also found the same issue in its ELT on 1 example of its fleet and on another uninstalled portable beacon. ANA has removed all beacons from the eight 787s used on domestic routes . JAL completed investigations this weekend on its 9 787s. The FAA and Japans transport safety ministry followed suit with the UKs AAIB in recommending removal or inspection of the ELTs, 2 weeks after the Ethiopian issue. European operators LOT, Thomson, Norwegian Air Shuttle, and British Airways (who is set to debut the 787 September 1st) have removed he ELTs from their aircraft but have not reported damage publicly. This far, no airlines other then Ethiopian obviously have suffered service interruptions as result of the ELT issue, though a Qatar 787 has been grounded on Monday due to an unspecified minor technical issue. Boeing has now delivered some 70 787s to its customers, around 20 since the grounding order was lifted in April, including new customers China Southern, Norwegian Air Shuttle, Thomson, and British Airways. These ELT issues are still considered unrelated to the lithium-ion battery defects which caused the worldwide grounding back in January.
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Karel_x
It looks that there are two generations of this ELT classic AFN and new (half sized) AFN2:
Less than half the weight and less than half the batteries needed to power it.
So both units have a 50 hour operating time and a ten year battery life and yet both generate the same 150mW/5W RF output. If the new unit (the 406AFN2) is doing this using only two cells instead of five, then either the circuit losses in the new ELT are more than halved or the battery chemistry in the AFN2 is producing more than twice as much power!
Do we know that the new unit is also using Lithium-Manganese chemistry or are we just assuming it?
Could this fire have been caused by a trapped wire AND a damaged battery with a much higher energy density than its predecessor? We keep hearing that 6000 of these units have been used without incident but how many of the Mark 2 version are in service?
This may not be solely a 787 thing, it may be a problem with the new version of the beacon.
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Speed of Sound
We keep hearing that 6000 of these units have been used without incident but how many of the Mark 2 version are in service?
Last edited by fenland787; 28th Jul 2013 at 13:01.
The AAIB Special Bulletin specifically identifies the ELT in question as the RESCU406 AFN (see Safety Recommendation). If the model would be AFN2, donīt you think the AAIB would have said so?
Air Accidents Investigation: Download PDF document
Air Accidents Investigation: Download PDF document
Question from non-engineer SLF:
What would it cost to design in a supply-rail fuse for the ELT battery? Or failing that, a length of fusible PCB track.
With the glorious benefit of hindsight, a pinched wire seems a rather simple and thus probable error.
What would it cost to design in a supply-rail fuse for the ELT battery? Or failing that, a length of fusible PCB track.
With the glorious benefit of hindsight, a pinched wire seems a rather simple and thus probable error.
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John Marsh
What would it cost to design in a supply-rail fuse for the ELT battery? Or failing that, a length of fusible PCB track.
However, as I said in earlier posts Honeywell have been at this game a very long time, I really can't believe they didn't think of that and the need to protect the cells from shorts 'upstream' of the PCB(s), so the question we are left with is:
What failure mode did the box and it's installation manage to come up with that meant it didn't work?
Last edited by fenland787; 28th Jul 2013 at 15:23.
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I wondered the same, so last week I contacted Honeywell on exactly that point. Honeywell confirmed it was AFN2.
I can see the AAIB possibly just referring the unit as its base model name RESCU406AFN but it also refers to it containing a 'set' of batteries rather than a 'pair' and makes reference to '6000 units' which clearly must be the original model.
The first safety recommendation (2013-16) refers specifically to the RESCU406AFN model but the second recommendation (2013-17) refers to "installations of
Lithium-powered Emergency Locator Transmitter systems" which I assume means both mark 1 and mark 2.
For some reason the mark 2 model has the wording RESCU406AFN on the case, which may be the cause of the confusion.
Very strange!
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The pinched wires, I would suppose, are on the wiring between the battery and the connector to the PCB, which could be subject to being moved and not fixed in location and routing. More like the design of a portable phone battery than a cell phone. Only fuses right at the place where the wiring enters the battery, or inside the battery casing, would be total protection.
However, they add another layer of risk in the failure flowchart, and engineers could have decided the cost outweighed the benefit.
Of course, this is all guessing, that could be halted by one decent picture of an open unit.
However, they add another layer of risk in the failure flowchart, and engineers could have decided the cost outweighed the benefit.
Of course, this is all guessing, that could be halted by one decent picture of an open unit.
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I don't know if it is any help, but here is the company product brochure for the Honeywell RESCU406AFN2
http://www51.honeywell.com/aero/comm...U_406_AFN2.pdf
http://www51.honeywell.com/aero/comm...U_406_AFN2.pdf