air safety

Feb 17, 2013

Dreamliner woes: Are sweaty passengers to blame?

Is it possible that one of the key benefits of the Boeing 787 Dreamliner, which is denser and more humid cabin air, is the factor that triggered the battery failures that lead to its gr

Ben Sandilands — Editor of Plane Talking

Ben Sandilands

Editor of Plane Talking

Is it possible that one of the key benefits of the Boeing 787 Dreamliner, which is denser and more humid cabin air, is the factor that triggered the battery failures that lead to its grounding?

While the answer may be ‘No’ the question is a good one.

Two people who work for Boeing, one directly, one indirectly through a supplier, have raised the possibility in casual regular conversation.

The common reasoning comes from asking “What was so different in the early passenger service of the 787s, and the test and certification process during which nothing quite like the failure paths of the lithium-ion batteries in the JAL and ANA flights occurred?”

The difference is ‘Passengers’.

One of the highly desirable features of the high composite structure of the Dreamliners is that it is said to facilitate operating the airliner with a lowered cabin altitude, down to 6,500 feet or around 2000 metres instead of  just under 8000 feet (according to Boeing).

Now while Boeing may have been exaggerating the cabin altitude at which modern jets are pressurized or not, to make the differential with the 787 look more than it is, it ought to be pointed out that when the Boeing 707 came along in 1958, it usually operated at 7000 feet cabin pressurization, which was the same as turbo-prop and end-of-era piston engined airliners like the Douglas DC-7C.

Be that as it may, Boeing has the science of better cabin pressurization on its side, in that even a reduction of 1000 feet in effective altitude greatly enhances the retention in the cabin of humidity (or if we want to be direct about this, perspiration and expiration from the skin pores and lungs of those on board.)

And nothing perspires quite like a cabin full of tightly packed passengers, although the JAL and ANA configurations are in their long haul format, generous and comfortable the way an eight across economy cabin in a 787 was always promoted as being.

There may be another clue concerning the issue of high humidity inside 787s in the November 2010 emergency landing of a test fleet Dreamliner at Laredo, Texas, after a fire broke out in the rear under floor electricals near the seat of the JAL fire at Boston airport early in January.

After the Laredo incident, which was said to have most likely involved foreign object damage from something like a bit of metal left lying around which facilitated electrical arcing, Boeing was reported to have decided to install some additional heating to keep the location dry, or, drier.

That particular flight carried dozens of test flight personnel, as did many of them, but not several hundred people seated in the same intimately close confines as found even in a comfortable cabin like those flown by ANA and JAL.

The thought that more now needs to be done not just to contain lithium-ion batteries in the event of similar failures in the future, but to protect them and the electrical system in general from excess humidity, might be on the right track.

Or it could be completely wrong.  Yet the difference between the test experience of the 787s and in-service 787s is the obvious one of lots of people being in a more humid environment.   That might be the critical difference.

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20 thoughts on “Dreamliner woes: Are sweaty passengers to blame?

  1. discus

    Interesting theory. Perhaps the 787 will be the world’s only temperate and arctic zone jet liner 🙂

  2. Roland Delhomme

    The environmental angle was suggested to me by a test pilot with 787 experience. If the 787 does indeed have such an intolerance of environmental variations and is so poorly engineered that it trips off a failure mode in a system that wants to catch fire-which Boeing asserted could not happen, they are condemning themselves of much more than incompetence and a management, executive tendency to obfuscate and mislead. This was expected-and having sat upon the info for nearly a month, the timing’s right; they’re fast running out of time and excuses.

  3. bill mecorney

    Humidity from pax. Hmm, of more concern should be the pressure cycle itself. The eight cells are of prismatic construction, and the electrodes are packed tightly in folded fashion. The electrode stack contains a twenty micron thin separator, made of clear plastic. This separator has a patent failure mode that can be exacerbated by stress within the folds themselves. The NTSB is looking here, as well as for foreign particles in the electrolyte that can trigger malfunction, (thermal runaway).

    The special allowances created for this type battery in the regulations were failed badly by this aircraft.

    To recertify this battery system will not happen quickly.

  4. comet

    There is no guarantee that Boeing’s Lithium Ion (Li-Ion) battery system will ever be recertified.

    I’m betting that Boeing will eventually be forced to move to Nickel Cadmium batteries for the 787. That in itself will be somewhat disastrous, as the whole electrical architecture of the 787 was designed around the Lithium Ion battery.

    Nickel Cadmium is going to add so much weight to the 787 that it will end up heavier than if Boeing had just used a conventional pneumatic bleed-air system in the first place.

    In some ways it echoes the earlier problem with the composite plastic airframe, when Boeing had to add metal for lightning conductivity (which wasn’t its original plan), taking away the weight advantage they thought the plastic airframe would bring.

  5. Ben Sandilands

    Yeah but! Airlines like blaming everything on passengers!

    Getting back to serious, there is I notice increased noise about there being next to no chance of the 787s returning to service for the peak travel season which is of course how I read your thoughts on this. I just hope the distractions this will cause will not unduly hold up the 777-X.

  6. ltfisher

    Oh dear! I wonder how long it will be before someone ‘discovers’ that all the ‘problems’ with the 747-800 have faded away and that it indeed is a great aircraft, capable of flying with unquestioned reliability.

  7. COTOS

    I think the point maybe that rigorous testing and realistic testing can be two different things, this new cabin environment is perhaps new territory for plane makers. Yeh, sure, DC3’s flew happily at lower altitudes forever but… they were designed for it.
    I know on the 747 for example, and probably all other models, were designed with cabin seat tracks made of corrodible aluminium, and as the same seat track went under galleys and lavs and their ‘wet spots’, fifteen years later we replaced those tracks with hardier material like stainless or titanium because by then the alloy tracks had the structural consistency and the look of weet-bix. BUT that corrosion didnt take 15 years to start there, it started on a small scale around day one of regular airline service after delivery when water, and gravity, was added and flight test engineers were no longer pulling up coverings to see what was happening below, who were also saying ‘no corrosion to worry about down there!’.
    Also i know some operators test new aircraft materials on the ground and again at altitude because of the different environments and different behaviours found there, not that its much different but necessary to completely close out the testing sign off.

  8. Uwe

    some perspective:

    Laredo incident: condensation could be tagged as FOD without this being a lie.

    The A380 cruises another 1000′ lower ( @ ~5000′ )
    ( That is why Boeing advertised as “lowest cabin altitude in a _plastic_ airliner” using wording that insinuated this was a functional requirement. It is not 😉
    The A380 has an intricate arrangement of adding _and_ removing humidity to avoid excessive condensation.

  9. Theoddkiwi

    Err the 787 was not designed around the Lithium Iron Battery, It was designed around 4 x 250kVA engine driven generators, with two 225 kVA APU generators as back up then a Ram Air Turbine to back that up with two batteries to back that up.
    The Batteries will not and never were designed to operate the entire aircraft’s electrical system. No commercial airliner rely on its batteries. They are last resort power and you’ve had a really bad day if your running on batteries. But as long as you’ve got airspeed the RAT will power the essential systems on the plane including hydraulics.
    I doubt humidity has caused the battery problems. Its not like the aircraft are not exposed to much higher humidity sitting at the gate rather than at cruise. Thats why the park the old aircraft in the low humidity desert.

  10. bill mecorney

    Your point is well taken, but the problem is not the power or capacity of the backup system. The issue is to do with the performance and safety expectations of the install relative to its own survival, and damage incurred by surrounding kit if there is a thermal event, or worse.

    At that, the very technology of the emergency power system is in question. The certification of this Lithium Ion chemistry is at risk, and once failed, the road to recertification will not be so easy. So remove them, and replace with a more seasoned type of battery? The integration of the system into the distribution of power throughout the aircraft is deep, and not so easy to alter. And that is before an attempt to satisfy the regulations.. Look for an interim fix, to get flying, and a permanent one for the lasting solution….Depending on a rather embarrassed FAA affixing the yellow tag.

    I would consider it bizarre if Boeing had no plan “B”, in reserve, since the technologogy is new in aircraft, and the possibility of just such a problem as this one will have been anticipated? Airbus have announced they will remove their own version of Lithium Ion battery power from their new venture, the A350.

  11. comet

    I said the 787 electrical architecture was built around the Li-ion battery, because without Li-ion, the whole architecture would have been a daft idea.

    There would be no point removing the engine bleed air and its ducting to save weight, only to add more weight with huge NiCad batteries. The 787’s electrical architecture only makes sense when used with Li-ion batteries. Now, it’s looking very much like it was a daft idea.

  12. Theoddkiwi

    I am pretty sure the much lower maintenance requirements of a bleedless system and the restrictive nature of flying with a degraded bleed system far out way the extra weight of a couple of extra nicads. Aircraft get grounded often due to failed or degraded bleed systems. Electrical power systems are generally the most reliable. Its incredibly rare for an aircraft to be flying on the RAT and standby power with the most common cause being fuel starvation rather than some significant electrical failure. Flying on Standby Power is nearly an impossibility on most modern aircraft. But Flying with limited or no bleed air is far for common place and more regular event.
    I still maintain that this Battery issue while dramatic with these two events, in the long term will not be as hard as people are making it out to overcome.

  13. AngMoh

    Theoddkiwi & Comet:
    I am of the same viewpoint as Theoddkiwi: switching to a NiCad battery should be trivial from a electrical standpoint – the 4 generators, APU and RAT should fly the plane under almost all conditions.
    However, looking at how stubborn Boeing is with insisting on LiIon, I am starting to wonder why this insistence. I am also puzzled about the statement from Boeing that LiIon is the only battery which can charge from 10% to 90% capacity in 75 minutes (this is from memory so the details could be different). Why is there a need to charge so much so fast?
    I am coming to the conclusion that the LiIon batteries are integral to ensuring the power stability on the 787. The 4 generators have sufficient capacity, but their dynamic response is relatively slow (its probably 100s of milliseconds when microseconds are needed). For example, when an electrical power system activates, there is an instantaneous increase in load, potentially made worse if it is an electric motor with a large inrush current. However, the requirement for stability of the electrical power bus might be very strict. If you have a microgrid (and the 787 is a 2MW microgrid), stability is always a challenge and the easiest way to make a microgrid more stable is to add fast energy storage. Main candidates today are flywheels, supercapacitors or batteries. If the LiIon batteries are really used in this way, substituting them will be a major issue – a NiCad battery has a completely different dynamic response – but fixing the problem could also be a huge headache. It also explains why test flights are needed and why the electrical system as a whole is under scrutiny.
    For reference, I found another article promoting supercapacitors, but one of the examples stated is that Airbus rejected an DLR electrical nosewheel design due to the fact that the design required a LiIon battery to manage load variations.
    Now coming back to sweaty passengers: This would also explain why sweaty passengers induce a problem. The aircon system as well as other electrical systems like entertainment, lighting, toilets etc must work harder and based on patterns of people. If they introduce more variation while testing was done under more static conditions, the power system would be less stable and the LiIon battery would need to work much harder in its power stability role, potentially triggering the problems seen now.
    This is just my hypothesis, but I think it is a pretty educated guess. I have been involved in projects where LiIon batteries are used to stabilise the power systems involving renewable resources and the battery size requirement to meet grid specifications was much larger than what I expected at the start of the project.

  14. Damo

    The battery power and generator power are 2 different systems. The generators power the AC busses,which then in turn power TRs (transformer/rectifiers) which power the DC busses.
    The power from a battery is only ever DC. The large power users are normally AC powered. In an emergency if you lose all generators the batteries will power a static inverter to provide momentary limited AC power for instruments until the RAT (ram air turbine) has had time to deploy and spin up to speed and produce AC power.

    What does this mean?
    The batteries aren’t normally subjected to large current draw in normal operation unless a TR fails or you start the APU on the ground with no external power. The batteries also provide a no break power transfer for the DC power supply. This means when power supply changes from one bus to another the battery keeps the bus powered while the switching happens.

    Whilst the batteries are always connected to a DC bus in normal operation when things are normal, they are only being charged using a trickle system. If the aircraft has an electrical emergency then the batteries are will be used. So for the batteries to fail in normal operation whilst not under an emergency load then that is a problem.

    Not being able to extinguish a LiPo battery if it is on fire, that is an even bigger problem.

  15. Geoff

    Thanks everyone – this chain has got to be one of the best and most informative this electrical-neandrathal has ever read! You’ve got some clever readers Ben

  16. AngMoh

    Everything is connected. Power flow in TRs can go both ways. My guess is that the rectifiers are active devices and not only control power flow in both directions, but also manage active vs reactive power at the AC side and performs the voltage conversion. The same way as a motor can become a generator and reverse.

    You state:
    “The batteries aren’t normally subjected to large current draw in normal operation unless a TR fails or you start the APU on the ground with no external power.”
    My point is that I don’t believe this is correct in the 787. I believe the battery is used as an energy sink to keep the electrical system stable.

    “Whilst the batteries are always connected to a DC bus in normal operation when things are normal, they are only being charged using a trickle system”
    My point is that it seems that they are NOT being charged using a trickle system. Why would Boeing insist that charging from 0% to 90% in 75 minutes is a requirement (or at least a distinct advantage) for the 787 electrical system?

    There are supposedly 100+ battery changes in a fleet of less than 50 while each battery is USD$16000-18000. And supposedly because the battery discharged to 15% capacity and then being locked up as a “safety measure”. If the LiIon batteries were used in a traditional config / use, then the locking condition should never occur. Even modern cars have a simple monitoring system that if you leave lights and the radio on while the car is parked overnight, they will be switched off once the charge (voltage) of the battery drops to a critical level to ensure the car can be restarted the next morning. And during flight the batteries are supposedly trickle charged. Here a 16000 USD battery goes in self-destruct mode “for safety”? My assumption is that the LiIon is used in a critical function in flight until it no longer can perform this function.

    For me, the information which is coming out does not line up with the traditional operation of batteries. I am speculating at the moment but I just can not see that 787 batteries are used the way batteries were used in the past.

    BTW: this is one of the best resource I have found describing the 787 electrical system:

  17. Uwe

    Even before FirstFlight Boeing knew that their L-Ion batteries would die early. ( FlightBlogger : 2008 : )
    If your service life appears to underperform you are abusing your technology. i.e. too much current ( in, out ) voltage too low, high temperature too low or too high.

    Lange Aviation ( Antares 20 e-plane ) expects 3000 SAE cycles or ~20 years servicelife from their Saft Li-Ion cells ( the same Airbus uses on the A380 an in various military and space applications )

    The 787 appears to be infested with cross connecting power converters.
    I would go with other posters assumption that the Battery has low net load ( Boeing : “not used” ) but is heavily used for buffering supplies ( Boeing : “complex” and “heavily integrated” ).

    Boeing seems to have succumbed to “exessively brilliant” design decissions completely ignoring KISS principles.

  18. Uwe

    just for the fun of it:
    Power requirement for _engine_ start ( GEnx-1B ): p57
    max 350kW ( ~700A draw from +-270VDC bus) , average ~200kW for ~50s

  19. bill mecorney

    “For me, the information which is coming out does not line up with the traditional operation of batteries.”

    But it does. The use is traditional, the Batteries are not. Why load a battery in, and not use it except in an emrgency? The LiIon battery is a good candidate for long and dependable SOC to start the APU. What it does not do well, and we see proof here, is fold in with a traditonal demand to be distributed in an integrated system…..

    That was the dilemma. In hindsight, the Li system for back up, with a superb dispatch rate, A NICd system for switching power and POSITION lights, towing, and FUEL instrumentation, etc.

    The Lithum scheme works well. If it is not ‘used’…….

  20. Damo

    Uwe, just to remove the confusion about the A380 and Li-Ion batteries, the A380 uses for standard Nicad batteries for the normal power system.
    It only would use Li-Ion for emergency light power packs and other smaller systems, not for the main or emergency power.

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