Nicad Battery Thermal Runaway

[sapco2]

A crew taking over a B757 noticed a strong musty smell on arrival at the aircraft. The crew opened the cockpit windows and started the APU for air conditioning. After 30 minutes the smell hadn't dissipated so an engineer was called for. The battery was found to be boiling and fumes were coming from it, so the battery was switched off. The engineers completed their FIM's procedure and the battery was changed.

My question is:

Had that fault occurred whilst airborne, and given that the appropriate QRH Electrical smoke drill would have been completed, what additional measures could sensibly be taken in dealing with battery thermal runaway?

[3 Point]

Don't know about Boeing but my Airbus procedure for smoke and fumes starts with

LAND ASAP!

Happy landings

3 point

[sapco2]

Taken as read 3 points, that's Boeing's drill too.

Thanks all the same for a prompt reply!

[Daysleeper]

Had that fault occurred whilst airborne, and given that the appropriate QRH Electrical smoke drill would have been completed, what additional measures could sensibly be taken in dealing with battery thermal runaway?

Not many....

Theoretically you need to electrically isolate the battery, including stopping it from charging.... problem is how do you positively identify the acrid smell as coming from the battery as opposed to other sources.

And just switching it off might not stop it charging (systems memory a bit rusty). Indeed there is a potential issue there with leaving aircraft unattended and plugged into ground power for extended periods....


Had a similar thing on the ground a couple of years back, battery and charger removed APU bat and charger moved forward to allow dispatch with APU u/s and degraded stby elec power IAW the MEL.

[Hand Shandy]

I`ve seen this happen on a 777 on maintenance , the battery started to boil and the only thing we could do was unplug the battery , [from personal experience not a good idea to wirelock the connector] . One of the contractors decided to be the hero and remove the smoking time bomb from the e/e bay after which it was left to smoulder on the hangar floor .

[JW411]

I had a nicad battery blow up in flight over northern Kenya at night in one Mrs Windsor's HS Argosys just over 40 years ago.

We were going from Aden to Nairobi and had luckily just passed over the Ethiopian mountains when fumes became apparent. The battery box was in an electrical compartment downstairs in the freight bay/passenger compartment at the forward end of the port fuselage.

The F/E went to investigate and came back upstairs to get the asbestos gloves and some tools. He came back to report that the battery was overheating but that he had disconnected both terminals and therefore we should not have a problem until we got on the ground.

About 20 minutes later there was a muffled explosion when the battery blew apart. Fortunately, the damage was contained within the compartment and no one was hurt.

We did an emergency descent (which wasn't very far in an Argosy) and I had complete confidence in the fact that my navigator knew exactly where Mt Kenya was in the dark.

The interesting thing was that the thermal safety strip on the battery did not work as advertised which meant that there was nothing to stop the catalytic reaction once it got started. Needless to say, a lot of aircraft skin had to be replaced.

The funny bit (there is always a funny bit) was that 30 or so of the punters downstairs were going to Nairobi for a religious get together. They started community singing and Land of Hope and Glory could clearly be heard upstairs on the flightdeck!

That was a great help.

[X ONE]

One thing with the above problem is that on A/C such as 757 there is no access into the A/V bay in flight so unless there are other indications then thermal runaway is going to go on unknown to the crew:confused:, and as for the wire locking the coupling, this should only be done thin/weak wire so that the wire can be broken in such instances when A/C is on the ground

[Brizeguy]

Thermal runaway is often not taken seriously. Many times I've been first on an aircraft only to find the Batts flat. Charging in situ is often suggested but not a good idea!
This picture is from a C560XL. Not sure of the cause.

http://www.geocities.com/atalarczyk1/excel_batt

[boredcounter]

Sorry for the thread creep.

I have not heard the phrase 'thermal runaway' for a long while, last heard on Be90/20 where i believe the battery was in the wing root (but please dont quote me) and that was the best part of 20 years ago. At that time, it was a master caution 'battery Charger' or 'battery charging' too long, or similar, that resulted in a diversion.

In aviator, or engineer terms, to the lay ops guy, what is 'thermal runaway' ?

Thanks in advance, would like to try and understand a bit more of the tech stuff.


Bored

[RJ Kanary]

Thermal runaway is a self perpetuating event that often can defy being traced to a single point cause.
Basically, the battery gets hot, due to dendrite growth, charging system fault or just plain end of life.Because it's hot, short circuit paths form inside the battery.Because the short circuit paths have formed inside the battery, it gets hotter.

I think you can see the direction this process is heading in................... :)

[411A]

I think you can see the direction this process is heading in:ooh:...................

Oh yes, and it ain't good, at all.
Had a thermal runaway in an F.27 (battery in the nose wheel well) and when it was done, the battery was a semi-molten gooey mess.
Didn't smell good, either.:(

[johnriketes]

The a/c I fly has a battery temperture gauge displayed in the cockpit that sets off a warning chime and light when the temperature of the battery rises above a certain level. I would be very surprised if Boeing a/c don't have the same. If not why not?

Not that keen on nicads for that very reason and prefer lead acid batteries.

[ssg]

Glad to see this thread come through...can't speak for the airliners...but taking charge of my first corporate aircraft 16 years ago, NICAD installed, two pages of red letter items, hours of sim work, dealing with an inflight battery overheat...had me asking the question..

Why use a NICAD instead of a LEAD ACID

16 years later...no good answer...same cold cranking amps..who cares about he power curve...on and on...

In a Citation, the process of dealing with a thermal runaway is pretty much this...

Battery goes into overheat..you isolate it...Gens off basicaly...since the battery went into overheat, it could still be cooking away...none the less, your supposed to monitor temp, volts, and amps...ofcourse it doesn't cool, they never do...so now you have to totaly isolate the battery from the system itself...the logic being somehow the gens are still give juice to it....

Since I went through this a few years back...due to a bad mechanic who walked away from a regular deep cycle check....

Your basicaly left with hand flying the aircraft, cross cockpit scan, 30 minutes with nothing but com 1, Nav 2, dark aircraft, windshielf bleed air blowing away...and you have to blow the gear down, no flaps...

Do this at night, blowing snow...oh gee the anti skid doesn't work either...it just get's better and better....

Years of arguing with instructors over the lunacy of installing a $5000 NICAD vs a $1000 Lead acid that will never over heat...people are starting to come around.

In a Citation the battery is install right over all the control cables for the elevator and rudder....

So yeah...you get the plane down...if it happens to you...

For the guys that go over the pond, you have to isolate, hope for the best, then try to turn it back on at the last second to get electrical...flaps, gear, ect....and then land....

[Dan Winterland]

The advantage of NiCads is that they give a constant voltage right up to the point that they are discharged whereas Lead Acid batteries give a drop in voltage as they discharge. NiCads are also a bit lighter. However, they have their problems.

One aircraft I flew with NiCads had one battery right above the pilot's feet. in the case of a runaway, you isolated the bat right away and got on the ground asap. We had a "Bat Temp" caption on the CWP.

The 747 classic has it's NiCad batteries on the flight deck!!!!!! And no warnings of an overtemp. The sit behind the flight engineer's panel My company had a nasty incident with a thermal runaway. Luckily, they got the aircraft on the gound in 25 minutes. Could have been a lot nastier if they were half way across an ocean. But the fumes were a rel problem.

[SawThe Light]

Dredged this explanation up from my notes.

"Thermal runaway is a condition in which the current for a fully charged nickel-cadmium battery rises out of proportion to the impressed-voltage level. This condition is caused when heat from oxygen recombination, an inherent property of most rechargeable batteries, causes the battery's voltage to drop as it gets hot.

During thermal runaway, the battery can become dangerously hot, emit excessive amounts of toxic gas, and spew electrolyte. This condition can occur in either the battery workshop or the aircraft.

Low electrolyte levels, electrolyte contamination, no gas barrier, or a deteriorated gas barrier can cause thermal runaway.

When oxygen recombination occurs, heat is generated, causing the battery temperature to rise and the battery voltage to drop. This process causes the battery to draw a higher charge current. As the temperature of the battery increases, the battery voltage continues to decrease, and the current progressively becomes greater. As this process continues, electrolyte eventually reaches the boiling point. If allowed to continue, the electrolyte level may fall below the top of the plates, causing them to dry out. The cadmium plates may then ignite and burn like steel wool, melting the separator, causing the cell to short circuit, and igniting the hydrogen in the cell. A battery's stored energy can feed a short circuit, allowing it to burn through the entire battery.

In event of a thermal runaway, electrical power should be isolated, and no attempt should be made to handle or move the battery for at least 30 minutes. After this period or when the battery is cool enough, carefully remove the vent caps of the affected cells. Make sure you wear a facemask, gloves and protective apron when doing this work.

Thermal runaway is preventable, but it requires that maintainers rigidly follow servicing procedures at appropriately equipped battery-charging facilities. It is imperative only trained people service and maintain nickel-cadmium batteries. These preventive steps will work in most cases, but a situation occasionally is beyond the control of the battery maintainer. This usually happens when aircraft are required to operate in extremely high temperatures, which is less than ideal for premium battery operation."

It certainly makes one want to go the lead-acid option.

[boredcounter]

Thanks for the explinations guys................

Bloody hell!

Fortunately, this one happened on the deck.

[Blacksheep]

A properly serviced Ni-Cad battery won't suffer thermal runaway and the life of the cell block can be as much as five years, making them much cheaper than lead acid batteries. Unfortunately they seldom receive proper maintenance, as the aircraft manufacturers tend to set the battery life in terms of flight hours in the MSG 2 (or3!) Maintenance Planning Documents. Maintenance Planners (who are much cleverer than Avionics Workshop Foremen) then set ridiculous servicing intervals. The proper way to establish a sensible interval is determined by observed water consumption at regular monthly intervals during the initial introduction into service of a new aircraft type into an operator's fleet.

As an example, when indtroducing the B757 into an operator's fleet, the MPD gave an inspection interval of 2000 flight hours. After not seeing a battery for service in six months, the battery shop called in the batteries for inspection and found low water levels in the cells of both Main and APU batteries. On performing deep cycle/cell balancing, in the APU battery five cells failed to recover capacity - which means a cell block change: 20 cells at $240 per cell! From the water needed to top up the cells, the actual water consumption rate that would guarantee a main battery remaining within tolerance between shop visits was calculated as being three months. (Which just happens to be the interval recommended in the OHM provided by the battery manufacturer. )

The actual interval in use by that operator remains at 2000 flight hours and as far as I'm aware battery cell life for that operator remains no better than 4000 flight hours, representing a cost penalty of about US$1400 per year per battery compared to an estimate of using a service interval of three months. (Discounting the labour savings of not changing the battery more often and extending the 4A check by about twenty minutes... :rolleyes:)

The message is - set a Ni-Cad battery servicing interval based upon observed water consumption rate and perform a deep cycle/capacity check combined with cell balancing at each interval and you'll have no problems and a long life, with a much lower cost of ownership than for lead acids. Let Planners stick to the planning and have specialist engineers do the reliability and performance calculations. :ok:

[ssg]

$5000 NICAD, $300 every 150 hours to service over a three year period = $8600 vs a $1000 Lead acid..no downtime, no servicing. Simple math to me.

There is no powercurve advantage for a NICAD. IF the NICAD dies right as you introduced fuel, you can't cycle the starter to cool it down. You just cooked a million dollar engine. I think 'buggered' is the word they use in the UK.

With a weak lead acid you can see ithe start seqenece get weaker, over weeks...plenty of time to order up a new one, have it waiting at your destination, no special charging equipment, just pop it in.

If your still convinced on a NICAD, keep in mind the checklist usualy doesnt work.

If your reading 165 degrees on the guage, pull the batt, and dont see the temp, volts or amps come down: fairly common, then your forced to isolate further. pulling all the gens, dark aircraft..so your on a 30 minute peanut gyro, cross cockpit scan, handflying, one com, one nav, no flaps, handflying, and having to blow the gear down...because in a Citation the hydraulics are electronicaly activated...like many corporate planes....I can't speak for the airlines....

Reason why the temp doesn't come down?...because the battery is in a thermal runaway, and by it's very defination, is that the chemical process is RUNNING AWAY, getting hotter.....I have personaly seen my battery 4 hours later still too hot to handle with bare hands...when they tried to save it, deep cycle, to DRAIN the power first....three times they ran it out the door on a cart, fire extinquisher in tow....

So the checklist many times will force you into turning an abnormal into an emergency situation.

My advice...don't use NICADS...if you have to, then when and if you get a overheat...kill the bat, fly the plane normaly, ingore the flashing red light, land ASAP. If you gotta stay up there for hours...then hand fly like I did, everything off, then before you land turn it all back on at the last second, to get your gear, flaps, ect all back...much safer that way I think....

Food for thought...

[Blacksheep]

Neglect any battery - even a lead acid for three years and it will cost you a lot more than US$1,000! The workload in our lead-acid shop at a 'V' Bomber base 'somewhere in Lincolnshire' was certainly much heavier than the Ni-Cad shops at Changi and Brize Norton. Airworthiness is a serious business and its sad to see anyone involved in aviation who seriously proposes to perform no maintenance on their battery. The worst Lead acid neglect I've seen was on an FAA aircraft that visited Brunei and couldn't start up to depart. The battery had spewed sulphuric acid over the rear pressure bulkhead. We cleaned it up and advised the crew to have a structural inspection upon arrival back at base.

One wonders how much money the FAA saved by not bothering with battery maintenance?

Both Ni-Cads and Lead Acid batteries should be removed for shop maintenance at intervals based upon recorded water consumption figures.

[Dream Land]

Thermal runaway is preventable, but it requires that maintainers rigidly follow servicing procedures at appropriately equipped battery-charging facilities. It is imperative only trained people service and maintain nickel-cadmium batteries. These preventive steps will work in most cases, but a situation occasionally is beyond the control of the battery maintainer. This usually happens when aircraft are required to operate in extremely high temperatures, which is less than ideal for premium battery operationNot an expert here but I was able to see real benefits by the use of Ni Cads, first of all the pilot needs a little education on how to operate, our company engineer taught me not to go on board and check ATIS, get clearance etc., he also taught me that Beech's starting method deep cycled the batteries two times during each start sequence, we used a method (BE-20) of starting the first engine followed by an immediate start of the second engine followed by bringing the first GEN on line. We maintained our battery with a Christy charger and at midlife on the engines, there was no maintenance required, I think that says a lot.

[forget]

The worst Lead acid neglect I've seen was on an FAA aircraft that visited Brunei and couldn't start up to depart.

Hmm. Look something like this?

http://i21.photobucket.com/albums/b270/cumpas/faa.jpg

[Octane]

It happened to me in a hotel room in Jakarta.
Thought I'd be a smartarse and renew the cells in my laptop battery but accidently pierced a cell with my knife when cutting through the battery case....
Problem was, I was in my jocks in my room on the 8th floor with a meltdown happening. The windows were locked shut and with Lithium involved I didn't think dunking them in water was an option. Now I had the high temperature thing happening, as in paint peeling and the other cells going off....
Jumped into shorts and shirt, dropped the steaming batteries in socks and paper bag and raced downstairs. (where are the lifts when u need them?). Slowed to a fast walk, saluted the concierge and raced down the road. Deposited the steaming mess in a drainage ditch...
Wasn't funny at the time, funny how quick u can move when u really need to.

Cheers

Octane