NTSB press briefing on 787-short circuit came first, then fire

The National Transportation Safety Board held its second full media briefing on the investigation of the Boeing 787 battery fire Jan. 9 aboard a Japan Air Lines aircraft at Boston.

Deborah Hersman is chair of the NTSB. Following our usual format for live coverage, we’re synopsizing and paraphrasing her comments.

  • General statement: Safety has been achieved through layers of redundancy and checks.
  • Batteries on the 787 are unique to the 787. Have 8 cells of 4 volts each for 32 total volts.
  • The event battery starts the APU. If it fails, APU won’t start and if it is running APU will shut down.
  • Found thermal runaway, shorts.
  • Trying to find original of fire and reviewing certification procedures.
  • Have disassembled batteries. FDR shows voltage unexpectedly dropped from 32 volts to 28 volts. Consistent with discharge of a single cell.
  • We believe evidence points to single cell initiating event.
  • Cells 5-8 (left side of battery) shows greatest damage. Charred with temp exceeding 500F degrees.
  • The body of evidence probably suggests event initiated in cell #6, with multiple signs of short-circuiting. Started thermal runaway spread to other cells and this started the fire.
  • Now working to determine the cause of short circuiting in #6.
  • Ruled out mechanical impact damage to the battery. All damage occurred after fire.
  • Also ruled out external short-circuiting from battery. Damage occurred inside battery and after significant damage.
  • Still considering: state of charge of each cell and method of delivery of charge; contamination; assembly damage; because battery is really a collection of eight batteries, looking at total design and assembly.
  • Reviewing certification of battery design.
  • Because 787 had novel designs and technology, existing regs didn’t encompass this. So FAA issued special conditions, including for the battery.
  • Special interest to NTSB is how special conditions relate to batteries.
  • We found Boeing determined failures could occur in the battery. Assessed likelihood of failure and affect of failures.
  • Tests performed on batteries. Boeing indicated tests no evidence of cell-to-cell propagation. But our investigation shows that after short circuit, there is propagation and a fire.
  • Boeing assessed that a smoke emission event would occur in less than one in every 10m flight hours. 787 has less than 100,000 flight hours with two battery events and smoke less than two weeks apart.
  • This demonstrates a short circuit in a single cell can result in propagation and smoke events.
  • NTSB still continuing with testing from batteries removed from 787s. Still reviewing certification and testing procedures.
  • Sharing all information with FAA, EASA to get airplanes back into the air. Decision to return 787 to flight will be made by FAA.
  • Will issue interim report within 30 days.

Q&A

  • Certification review by FAA initiated before grounding is a very serious event.
  • The FAA conducts risk assessments for ferry flights and this was an airplane before delivery to a customer (referring to the Boeing ferry flight underway from Ft. Worth to Everett).
  • There are nine special conditions for the battery the FAA issued, based on assumption of no smoke events in 10m hours. We know some assumptions were not met, much less a fire event.
  • This was not unusual for Boeing to work with FAA on testing. It is not unusual for operator (Boeing) to conduct testing. Testing also done by Thales, others.
  • We do have a long road ahead of us. Challenges. Fires consume evidence. But team has been able to identify failures, origin of event and how it cascades and have been able to rule things out.
  • Interim factual report will be comprehensive factual report but no conclusions. Will have additional information. Important to get info out ASAP because the fleet is grounded.
  • Haven’t ruled out other possible external contributors. Still looking at design, certification, manufacturing. Still a lot of work to do.
  • Still working closely with Japanese counterparts. Their event occurred after our event. Our investigation has a little more time on these issues. Not yet in position to compare investigations.
  • The NTSB is working very closely with Boeing, FAA, French and Japanese counterparts. If Boeing is proposing any changes, those will be made to FAA. We don’t determine if 787 returns to flight.
  • We have pinpointed origin of the event to cell #6; had multiple short-circuits. It got into thermal runaway condition and propagated to other sees.
  • We do know short-circuit came first. This does help us identify as we move forward what happened. Obviously certification is over all of these issues.
  • We have not reached conclusions whether it’s OK to continue battery production. As part of investigation, GS Yuasa is part of our investigation.
  • We don’t have information specifically where within Cell 6 the short circuit occurred.
  • We have left a lot of issues on the table we’re looking at. We have not yet identified the cause of the short circuit. We are looking at the design, the manufacturing, the charging and how charging comes into the battery.

Concluded.

57 Comments on “NTSB press briefing on 787-short circuit came first, then fire

  1. So, cell #6 short-circuited in the JL battery and began a thermal runway event that could not be stopped? The battery was not damged before the fire? The data recovered from the FDR showed one cell (#6) was discharged before the event.
    I di not know that the APU would shut down if the battery fails, but this does make sense.

    • Wrong interpretation. There was no direct indication that cell #6 lost voltage.
      see:
      “.. FDR shows voltage unexpectedly dropped from 32 volts to 28 volts.
      Consistent with discharge of a single cell.”

      detail inspection shew that the process started with cell #6:
      ” The body of evidence probably suggests event initiated in cell #6, with multiple signs of short-circuiting.”

      derive: with reasonable probability the voltage drop observed was across cell #6.

      • apropos: “unexpected drop of 4Volts”
        what timeframe?
        looks like shorting of cell #6 ( internal/external ).
        if the cell would have been less charged than its neighbours the battery voltage would have been sloping down by less than 2 volts and then shown fast drop by another 2 volts. ( and the. initial battery voltage would have been below 32V due to one cell already having been partly discharged.

    • When you have a short you are discharging the baterry. The electrical energy is mostly transformed into thermal energy. If you have nothing to cool then you are in a situation to potentially start a fire and soon after of a thermal runaway (exponential)

  2. kc135topboom :
    So, cell #6 short-circuited in the JL battery and began a thermal runway event that could not be stopped? The battery was not damged before the fire? The data recovered from the FDR showed one cell (#6) was discharged before the event.
    I di not know that the APU would shut down if the battery fails, but this does make sense.

    Doesn’t this make problems for ETOPS?

  3. * The event battery starts the APU. If it fails, APU won’t start and if it is running APU will shut down.

    Bad. So the battery trips all savety and backup provided by the APU.

    • I think it’s like that on all aircraft. When the APU is up and running the battery will automatically go off-line when the APU takes over.

      • Hmm, you have it reversed? ( or did I misunderstand)

        APU running and the APU-batterie founders will force APU to off.

        apropos:
        Previous information indicated you could fly without the APU battery installed.
        Information from today would indicate the opposite?

      • I have since listened to the original conference and indeed the APU will shut down if the APU battery is not working properly. I suppose the reason behind this is that the APU relies on its own battery power to monitor itself.

        By the way, I did not learn anything new by listening to the live conference, so good and complete was Scotts”s reporting.

    • That is a very bad thing if this happen in flight with shut down engine. I wonder how to resume service iin that situation…

    • Bad? I don’t think so.

      If both engines are out and the APU is not available, you still have the main battery to provide the essentials in case of an emergency. And if that’s not enough you still have the Ram Air Turbine (RAT) to take over.

      Aircraft are allowed to take-off with a disabled APU and they do it all the time. It’s not a big deal really.

      • And now some partial dissent:

        Being able to start the APU during flight at cruise FL was a cert requirement for the APU and is a certification requirement for ETOPS afaik. thus the APU must be required to be operational at least for ETOPS activities? right, wrong?

        • I think the same MEL rule would apply for ETOP. But I am not 100% sure.

      • Nope, if you start the apu to resume the engines but that the apu goes down because the battery that started it is burning, then you can start to pray that the ram provide enough power to resume the apu.
        Yes, this is an unlikely case but recently very remote item have shown more than once…

        • The point I was trying to make is that the APU is not absolutely required for safe flight. There are other alternatives which are part of the overall aircraft safety architecture.

          That’s why aircraft are allowed to take-off with a disabled APU. And if during flight both engines needed to be reignited there is always the possibility of using windmill if the altitude and speed are adequate.

          And in an extreme emergency, the main battery alone will help temporarily to maintain controlled flight and the RAT will take over as soon as it will have been deployed (Gimli).

          To have the APU available is certainly a good thing, but not to have it is not necessarily a “bad” one.

      • via http://www.flightglobal.com/news/articles/hamilton-sundstrand-completes-787-apu-etops-testing-340440/

        “The company calls the testing “an important step in providing ETOPS capabilities for 787s upon initial entry into service”.”

        Thus (a working) APU is required for ETOPS?

        “Hamilton Sundstrand adds that the APU starts and operates throughout the aircraft’s flight envelope.”

        You don*t have that just for boasting value, do you?
        ( seems to also apply for most (all) Airbii but not for older B frames )

    • Concur.

      “We have left a lot of issues on the table we’re looking at. We have not yet identified the cause of the short circuit. We are looking at the design, the manufacturing, the charging and how charging comes into the battery”.

  4. Uwe :
    Hmm, you have it reversed? ( or did I misunderstand)

    Indeed one of us has it reversed and I knew this when I replied. It stems from the difficulty I have to understand what DH said exactly. I need to hear the conference or to read the original script.

    In reference to the statement that the aircraft can fly without an APU battery, it would make sense to me because the aircraft can fly without the APU itself. And there is still the main battery which should be available if needed.

    But what might be different on the 787 is the requirement to have battery power for the parking brakes. I don’t know how that would impact operations. For example, if the main battery is disconnected can you still tow the aircraft, provided that the APU is running? Things like that which could be specific to aircraft using electric brakes like the Dreamliner and the CSeries.

    • I believe the brakes and flaps, etc. are hydraulicly operated on the B-787. It just doesn’t have the big multi hydraulic systems of other airplanes.

      • Try starting with

        http://www.boeing.com/commercial/airports/acaps/787electrical.pdf

        for ground power hookups

        http://www.boeing.com/commercial/aeromagazine/articles/qtr_4_07/AERO_Q407_article2.pdf

        for basic electrical system design as it was a few years ago

        It does use electric motors to drive local hydraulic pumps for some feathers, etc

        But on the ground, it uses electric brakes when taxing, and if everything is shut down, then perhaps the battery provides brakes when being towed – a bit unclear

        The hydraulic system in the 787 no-bleed architecture
        is similar to the one in the traditional
        architecture. There are three independent systems
        — left, center, and right — that collectively
        support primary flight control actuators, landing
        gear actuation, nose gear steering, thrust
        reversers, and leading/trailing edge flaps.
        The primary power source for the left and right
        systems are engine-driven pumps mounted on
        the engine gearbox. In addition, the left and right
        systems are each powered by an electric-motordriven
        hydraulic pump for peak demands and for
        ground operations.
        The key difference between the traditional
        and 787 hydraulic system is the power source
        for the center system. In the traditional architecture,
        the center system is powered by two large
        air-turbine-driven hydraulic pumps, which operate
        at approximately 50 gallons per minute (gpm) at
        3,000 pounds per square inch (psi) to meet peak
        hydraulic demands for landing gear actuation,
        high lift actuation and primary flight control during
        takeoff and landing. During the remainder of the
        flight, two small (approximately 6 gpm) electricdriven
        hydraulic pumps power the center system.
        In the 787 no-bleed architecture, the center
        hydraulic system is powered by two large (approximately
        30 gpm at 5,000 psi) electric-motor-driven
        hydraulic pumps. One of the pumps runs throughout
        the entire flight and the other pump runs only
        during takeoff and landing. The higher pressure
        of the 787’s hydraulic system enables the airplane
        to use smaller hydraulic components, saving both
        space and weight. goes on

        • Big or small, you need three systems for safety and redundancy. All three are separate and independent circuits. All aircraft have more or less the same basic hydraulic architecture, regardless of their size.

          What’s new are the locally self contained hydraulic packs that we find on the A380 and A350. Is that the future? Possibly.

  5. …Trying to find original of fire and reviewing certification procedures….

    SAY WHAT ???

    Sounds like a back of the envelope thing- who or how many reviewed and signed off ?

    Or did they disappear after first event ??

  6. What about the November 2010 in-flight 787 fire over Laredo?

    The company said the P100 power panel melted, but battery problems were never mentioned. That’s 3 overheating events: Laredo power panel; Boston JAL aft battery; Takamatsu ANA forward battery. Three different locations but one thing in common – all electrical. Sounds like the recent battery incidents are symptoms of broader problems with the electrical system.

      • I’m afraid an “arc” is “related to current”.

        Yes, I understand what the company disclosed of it’s investigation (notably, the NTSB did not investigate). And I don’t doubt that they undertook the investigation in good faith. But with three electrical incidents involving heat and smoke (I understand Boeing is very sensitive to the terms “Flame” and “Fire”) I think the Laredo event is work reconsidering.

      • “metallic” FOD was a guess, wasn’t it?

        Think about what could connect all three together!

        Potential common cause : FOD in the form of condensation ?
        Traditionally condensation and electronics don’t go all that well together.
        2/3 blogs back I explained the mechanics for largescale arcing triggered by (even small amounts of) water incursion.

      • I believe Uwe is correct. Metallic Foreign Object Debris was Boeing’s best guess for what caused the fire on approach at Laredo, but the debris was never recovered.

        This entire electrical system seems incredibly sensitive if FOD and condensation cause fires. Keep in mind, there has NEVER been an electrical fire in the fuselage of a 777 with 18 years of service and over 1000 units delivered.

        Theory: exploding batteries, melting power panels, inflight temporary loss of power; all symptoms of an electrical system that is carrying too much load.

      • I stand corrected (by myself). There was a 777 fire at LHR in 2007 involving a power panel. With apologies.

    • There is that Egyt Air 777 with a cockpit fire ( afaik a write off ).
      Also cockpit window heater “hot events” seem to be a Boeing specialty.
      ( IMU with the FAA for a decade or more in the process of making this an issue )

      Nonetheless electrical problems are not prevalent in non 787 aircraft.
      But note nothing much has changed in how Boeing did electrics from the 707 to the 777.

      Then one very big “wide spectrum” step with limited historic experience.

      Airbus seems to have a much more evolving history in that ( and most other ) area.

  7. Normand Hamel :
    I think it’s like that on all aircraft. When the APU is up and running the battery will automatically go off-line when the APU takes over.

    </blockquote

    I have worked in the automotive industry for years and maybe I might be wrong, but when a car is started, the battery is no longer providing power, the alternator takes over in supplying power to run all the electrical systems and keeping the battery charged and the voltage regulator keeps the voltage in a narrow range to prevent the alternator from self destructing due to voltage climbing too high and melting the stator connections.
    Again, I do not suppose that the same principle applies,but it seems the batteries have a very limited time frame when powering up the APU.
    I await some ones reply with a greater knowledge in this area.

    • Well historically you could operate a car with an old style DC generator without a battery.
      With the advent of AC 2/3 phase alternators with rectifiers the battery was needed as a buffer. The inductive properties of the generator (voltage spike on load shedding ) required it . I haven’t looked at really modern car electrics though I feel certain that the battery still is a required element to buffer system voltage under varying loads.

      My personal guess is that on the 787 the same happens. The battery is “not used” in the sense of no net current being drawn. But the battery might be heavily involved in stabilising the bus voltage. ( High inrush and outrush currents, would explain why the battery ages fast. on the third hand this would heat the battery and prohibit condensation killing some other explanation ).
      So this is just a very wild guess.

  8. I’m not as optimistic as Scott about all of that. It could take more than a few weeks to find out what happened. There’s nothing which could make think that the end of the nightmare is closer now after reading what NTSB has said. I don’t say it’s impossible that they fix the battery in a few weeks but months or weeks it’s like gambling in Las Vegas (I’ve some work to do these days in Nellis AFB, that’s why !).
    I’m more and more convinced that the A350 architecture is much more comforting and safer.
    Even if the battery problem is fixed tomorrow, big questions about the 787 electrical architecture reliabilty will remain above this airplane like a sword of Damocles. It will be very difficult and very long to restore confidence in the 787 design. I’m even not convinced that it’s possible (I mean without destroying its reputation like it has been the case for the DC10).

    Sorry for this very pessimistic post, you can burn it after reading. It was just my 2 cents (in a slot machine).

      • Wikipedia shows 183 “deliveries” inclusive of 1979 to the end of the program. I assume the 40 deliveries in 1980 were from pre-1979 orders – deliveries dropped to 11 two years later.

  9. Normand Hamel :
    Bad? I don’t think so.
    If both engines are out and the APU is not available, you still have the main battery to provide the essentials in case of an emergency. And if that’s not enough you still have the Ram Air Turbine (RAT) to take over.
    Aircraft are allowed to take-off with a disabled APU and they do it all the time. It’s not a big deal really.

    AFIK the battery needs only to power things for a minute or so until the RAT deploys

    Of course with both engines out- it allows one to maintain control until landing/splashdown

    Suggest you search on GIMLI Glider to read about an actual case on 767 early on

    • GEEZE ! Talk about ( cheap electronics design/fabrication of measuring instrumentation for permanent use )

      Looks like

      a) some sort of circuit board INSIDE the case
      b) open backplate connection to multipin passthru
      c) casual mix of ground and positive instrument leads alongside each other in same bundle
      prone to chafing under vibration for example
      d) no real cooling provisions between cells and outside of case

      e) no shock mounts in evidence

      f – no high temp ( silicone?? ) covers over positive terminals- drop a wrench on battery with cover removed and watch the fireworks – EVEN my auto has battery covers !!

      g) NO ** obvious ** consideration for negative g loads keeping cells in place

      But it looks neat !

      definitely not man rated- or passenger rated !!

      meets the faster and cheaper criteria – which is all that matters to the top !!

  10. Don Shuper :

    Looks like
    a) some sort of circuit board INSIDE the case
    yes, actually two and i would have decided on having them outside the core containment
    b) open backplate connection to multipin passthru
    c) casual mix of ground and positive instrument leads alongside each other in same bundle
    prone to chafing under vibration for example
    reduced interference on signal leads, this is OK and the finishing is done nicely

    d) no real cooling provisions between cells and outside of case
    yes, no cooling, no(t enough) separation, burst plates evcuate into/over the cell array

    e) no shock mounts in evidence
    imho one would attach shockmounts from battery case to rack ( if needed)
    f – no high temp ( silicone?? ) covers over positive terminals- drop a wrench on battery with cover removed and watch the fireworks – EVEN my auto has battery covers !!intact specimen have a conformal cover ( nylon?) on top of all connections, see NormH’s ref
    from the “pre” images it looks like the cells have a separating plastic mask covering the upper rim of all cells ( below the interconnects, black material
    b>tentatively I would expect a similar holder cupping the bottom, this also answers one question I had: the cell “cases” are not in contact with the battery box
    g) NO ** obvious ** consideration for negative g loads keeping cells in place
    But it looks neat !
    definitely not man rated- or passenger rated !!
    meets the faster and cheaper criteria – which is all that matters to the top !!
    In my interpretation cell were assumed to be 100% no burst or therm. runaway, the design follows from there also going low cost “low cost”.

    IMHO the detailing would indicate that the designer(s) were US educated engineers.
    This would fit in with the GS-Yuasa Lithium people sitting in the US
    http://www.gsyuasa-lp.com/contact

  11. Uwe :
    “metallic” FOD was a guess, wasn’t it?
    Think about what could connect all three together!
    Potential common cause : FOD in the form of condensation ?
    Traditionally condensation and electronics don’t go all that well together.
    2/3 blogs back I explained the mechanics for largescale arcing triggered by (even small amounts of) water incursion.

    Well that’s what I reckoned here a couple of days ago…

    • The development, testing and certification of the electrical system is part of the review. The handling of the Laredo incident will no doubt be part of that.

  12. Supposedly ONE of the advantages of LI-ion is ability to accept a rapid recharge, which seems to be mentioned in reasons why LI-ion was picked over other. But it makes me wonder just WHY a rapid recharge is needed ( compared to slower charge rates ).

    Could it be cuz of fast turnaround issues in commercial service ?

    Use battery for actuating brakes when towing, cockpit indications when fueling door open, etc.

    Then charging so as to start APU ?? instead of ground power to start apu to then start engine one, etc ??

    Or fast charge on takeoff for some reason ?

    I would assume ( probably wrong ) that APU would be running on takeoff until say 10K feet just in case of other failures during takeoff – or landing ??

    From an outsiders view- some of the reasons re fast charge do NOT seem to make sense

    BWDIK ??

    • The mains reason, and the only valuable one in my opinion, is to save weight and space. Like you, I can’t see why fast recharge would be a desirable feature on an aircraft.

      The APU battery is independent of the MAIN battery. On the 787 they are interchangeable for maintenance purposes, since they are identical. So if the MAIN battery is dead you can substitute the APU battery and kill the APU until a new battery is installed.

      But system wise the APU battery takes care of the APU plus minor tasks like powering navigational lights when towing the aircraft. The MAIN battery is an MEL item. The aircraft cannot take-off without a serviceable battery.

      If all the electric power goes out in flight the MAIN battery will keep the Captain’s instruments operational. On the 787 the MAIN battery is also required to power the electric brakes when there are no other electrical sources available.

      Normally the APU is used only when the engines are not running or when there is no external power available. It wastes fuel to run the APU when it is not absolutely required, and airlines avoid using it as much as possible. But during a hot summer the APU can supplement the engines, which then run at idle power, to cool the cabin when the aircraft is taxiing.

      • Airlines use the APU regularly at the gate to cool or heat the cabin, depending on the outside weather. This is done on all airplanes with operational APUs, not just the B-787.

        • Actually many airlines, if not most, try to avoid doing this unless there is no ground air conditioning available at the gate. In the past it made little difference because the price of fuel was much lower. The use of the APU has almost become anathema. Practices have evolved over the years.

          But sometimes they don’t have the choice because either ground power is not available, or ground air conditioning, or both. The turn-around time is also a factor. Southwest comes to mind. They operate in the hottest parts of United-States and they never stay on the ground for very long. So I can imagine they would use the APU more often than some other airlines. For Alaska Airlines it might be different. The “best practices” vary among airlines and between countries. And also from one era to another.

          One day airplanes will not even taxi on their own power. Airbus is working on a nose wheel electric drive for taxiing the aircraft. They have actually installed a prototype on an A320.

  13. kc135topboom :
    Airlines use the APU regularly at the gate to cool or heat the cabin, depending on the outside weather. This is done on all airplanes with operational APUs, not just the B-787.</p

    OK- then would they use them to start main engines on a short turnaround ? or would they shut them off during refueling during ” normal ‘ weather ?

    Still gets back to my question – WHY need a rapid recharge capability for other tnan an unusual situation ??

    • Yeah the APU can and is used during refueling operations.

      But, I agree with you, I see no need for a rapid recharge capability. Southwest is famous for their 20 minute turn around between flights, they use the APU, and ‘old’ Ni-Cad batteries to start the APU, yet they don’t seem to have any problem maintaning a good recharge rate.

      In the KC-135A/E/Q our APU also had a seperate Ni-Cad battery. It would recharge when the APU was running and the generator was ‘on-line’. But we could also recharge the APU battery with the aircraft electrical system by simply pushing in 2 circuit breakers.

      • In the days of the DC-8 and 707 there was no APU on most aircraft. But what about the KC-135? Was it a feature that was added on later models, or a retrofit kit, or simply a military requirement?

        • The APU has been ‘standard’ equipment on the KC-135 since 1955. But it only provided electrical power and heat, no bleed air to start the engines. We used a slow burn cartrage for that, or ground power carts that provided bleed air.

          The B-707 and DC-8 had no APU option, so they used ground power carts.

  14. Did I miss the taste fo the briefing here or does D.Gates express it in stronger words:
    “In a blunt briefing Thursday, the chief of the National Transportation Safety Board (NTSB) said the government and Boeing badly underestimated the possibilities for failure of the 787’s lithium-ion batteries.”
    ref: http://seattletimes.com/html/businesstechnology/2020307773_ntsb787xml.html

    on charging:
    taking high charging currents would be of interest if the battery has to buffer a DC bus
    to limit overvoltage ( charge of death for Li-Ion, much more benign for LeadAcid and NiCd ).

    also if a significant part of available battery charge is required for an emergency breaking
    ( ground, low speed, no/low RAT power available) the battery as to be topped of ASAP.

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