Carbon Brake Dust - Airbus

[sharpshooter41]

Hi all,

I understand that carbon dust coming out of the brakes is cancer causing, and that is why, brake fans are to be switched ON prior to stopping at the gate, so as not to expose ground personnel to its harmful effects.

Can someone give me the reference to this;

[Flare-Idle]

Unable to give you a reference on this.
In general, carbon brakes contain a significant amount of carbon fibers and Silicon Carbide (SiC) , a material which is also used in abrasives. SiC in carbon brakes is formed during the manufacturing process, where a porous carbon fiber and matrix preform is infiltrated with liquid silicon and thereafter "baked" at very high temperatures to form the SiC. The black "dust" you see is a composition of this SiC and other components of the brake (micron size carbon fiber fragments etc.).
Carcinogenic effects of SiC dusts are under investigation with workers in SiC plants. For carbon brakes, I don't know if there is a similar study available.
IMHO, the risks related to carbon brakes are minor since the carbon particle emissions (submicron to angstrom range) of the engines have a much more severe effect on the health of ground personnel.

F.y.i. beryllium brake disks have been used on military aircraft (C-5 Galaxy, F-14 Tomcat) due to their superior energy capacity, yet its dust (beryllium oxide) is severely carcinogenic.

[Beeline]

Ground personnel have the luxuary of the outside environment to minimise the effect of the brake dust being breathed in.

I change these brake packs on a regular basis inside and out, I have always been told it was safe.... eeek!! :eek:

The risk assessment for the task is minimal but does recommend the use of a respiratory mask.

Will be of interest to see if anybody knows more facts on the properties relating to health!

[Dani]

I'm pretty sure that there is no proof that this dust is carcinogenic. If it would be, there would be an avelange of law suites against the manufacturs.

Still I think you better be cautious - as a pilot to hit the fan early and as a ground staff to stay away a bit longer.

Dani

[Dream Land]

We have one hour turns and therefore don't require the use of brake fans, the problem being as soon as the engineer starts playing with the aircraft, they immediately select brake fan on. :ugh:

[PantLoad]

As Dream Land says, the engineers turn the fans 'OFF'...I've seen it the other way.

You have to remember, the wheel and brake temps continue to climb after the landing...with temperatures peaking maybe 25 to 30 minutes after landing.

As always, follow your company's SOP. But, the fans are optional equipment on the Bus...if you have them, use them. That's what they're there for.

PantLoad

[Dani]

completly disagree. Just because you have them doesn't mean that you should use them all the time.

I hate those guys (inclusive the mechanics) who turn it on all the time just to cover their a$$. If you think a little and plan ahead, you hardly ever need them, except for very short turnarounds or heavy braking.

Ideal braking temperature is around 100-200 degrees, so keep it there, don't cool it too low.

Dani

[PantLoad]

Of course, if the fans are not needed, then there is no need to use them. Again, what determines this is your company's SOP.

Just a reminder...and I think you are already aware of this...the certification criteria for an RTO on the SA Airbus limits the brake temps to 150 degrees C. Above this, you may or may not be able to stop in the distance dtermined by the charts.

Fly safe,


PantLoad

[Flare-Idle]

Dust generation is highest when the stator and rotor components of the carbon brakes are cold, i.e. during the initial brake application while on the landing roll and taxi-out. Break wear and correspondingly dust-generation is therefore highest during those phases of operation.
From a friction point of view, in case of carbon brakes the higher the temperature, the better the friction coefficient/deceleration behaviour due to special tribological effects at temperatures exceeding 300°C. However, from a lifetime point of view, temperatures should be kept below 500°C since oxidation effects begin to degrade the structural integrity of the brakes on a long term.

Optimum brake temperatures from an operational point of view depend on the carbon brake pack (i.e. depending on brake manufacturer, e.g. messier-bugatti, Goodrich) in use on the corresponding aircraft.

Fuel, OTP and aircraft utility rate are key factors for most operators, i.e. aiming for the optimum turn-off more often requires firm and continuous brake application to reduce taxi-in time and safe fuel. Brakes consequently get hotter and need to be cooled to enable a 20 to 25 minute turnaround time.

[Dani]

Correct. PantLoad, 150° is valid if the brake fans are turned on. 300 when off.

[sharpshooter41]

Dear All,

Thanks for all the replies.

I saw this Airbus brief on smartcockpit.com regarding use of brakes and let me quote:

Select brake fans

1. Atleast 5 min after the temp check to

Allow thermal equalization and stabilization
Avoid oxidation of brake surface hot spots

2. Just before stopping at the gate, to:

Prevent carbon dust from being blown over ground personnel


Can someone now explain this??????

[PantLoad]

No, that's not what I'm saying. What you are referring to is the brake temp limitation for takeoff...300 degrees (or 150 degrees if the fans were running). This limitation exists relative to wheel well fires vis-a'-vis the flash point of Skydrol.

What I'm referring to is the certification for the RTO and brake effectiveness. While carbon brakes wear better when they're warm, they stop better when they're cool (or cold). The RTO certification is based on brake temps no warmer than 150 degrees.

So, in essence, you can legally take off with brakes at 300 degrees, but you may not be able to stop in the runway remaining in the event of an RTO.

Airbus has a publication "Getting to Grips with Aircraft Performance". I think all this is explained in this paper. You've probably already read it, but I think the 150 degree figure for RTOs is discussed in there.

Anyway, this is a great discussion. Thanks, as always, for your thoughtful input.


Regards,



PantLoad

[Dani]

Agreed that the 150°/300° is (also) because of hydraulic fire.

But AI certainly wouldn't certify you for TO with a temperature that is too hot for a RTO. Therefore, if you TO with 300°, AI must have made sure that you can safely absorb all brake energy in case of rejection. There might be one exception: If on your performance computer (runway table) there is a weight limit with the remark "brake energy", you run into this very problem.

As mentioned above by others, wear and efficiency are two different thing, and it is not that easy as you explain it. It depends heavily on the supplier of the brakes.

I was flying in a company where they had a graph of the brake wear in function of temperature: Cold brakes have minimal wear, when temp rises, wear increases to a max to around 300°, then wear goes down again until around 600°. It's a bell curve, or also called Gauss curve.

In other companies we had the information that wear is unimportant as long as you hit the pedals just once: Wear is a function of how many times you apply the brakes. How long or how hot or how strong is neglectable.

When you turn your view towards carbon brakes in Formula 1 car races, there is maximum brake efficiency with very high temperatures. You have certainly seen those pictures of cars driving by with glowing wheel hubs - that's the carbon brakes working.

In aircraft there are slightly different implications, since you have to cover the RTO case. It is better to have (relatively) hot brakes for wear and efficiency, but you don't want to have them too hot, because if they go beyond a certain limit, they get distroyed.

Therefore we have a perfect example for a balance of parameters. We have to make a compromize. Imho it is about 100-200°C. Others weight the danger of hydraulic fire, brake blast in case of RTO higher than efficiency and cost control. Be it as it is. I have made up my mind and stick to it.

Agreed also that this is an interesting topic.

Dani

[Arctaurus]

Dani,

From memory, the rejected take off certification tests are done with brakes that are 90% worn.(10% wear remaining)

Can't put my finger on it, but I think there is a JAR that describes this requirement.

.....The RTO certification is based on brake temps no warmer than 150 degrees.

Does anyone have a written reference to this statement ?

interesting discussion:ok:

[Alber Ratman]

Carbon - Carbon brakes...


A good one because I have been to DABS and have seen how Dunlop make the damm things..

A Rotor / Stator is manufactured by compressed (by a bolted press) layers of carbon fibre weave being subjected in an oven at 1000 deg F (+/- 2) in a hard vacumn, to a supply of methane gas. the gas breaks down, allowing the Hydrogen to combine with any Oxygen (and purify it out as water) and Carbon to cross link the fibres (as the SECOND CARBON!) This process takes four weeks. the stacks are then weighted and reversed back into the same process to equal the process out for all units in that autoclave. The discs are then have a graphite process before they are machine finished.. I also had the free lunch to prove it.

Cancer?? Were did that come from??? :confused: Silicon Carbide? Unless DABS have changed their processes. :ugh:

Flare Idle.. Were did you get your facts from??

Carbon Fibre particles may have the same effect as Asbestos (nobody is sure, but again nobody can say it doesn't!);)

People picking up crashed Harriers, wear respirators to stop inhalating fibre particles contaminated with burnt thermosetting polymer residue (that certainly is cariogenic!:()

Hot Brakes = Blown Fusible plugs = Wheel change, when you want that push back to make that slot time!:)

[25thID]

Here is the link

http://annhyg.oxfordjournals.org/cgi/content/full/47/4/325

The way I read it there is little to worry about. However, it also seems to me it could affect a very few. Good work shop ventilation and perhaps one of those face masks to filter some of it out might be a reasonable precaution.

[clark y]

I've always been lead to believe that carbon dust is very bad for one's health, but I think the residual smoke that seeps out of engines on turn arounds is probably just as bad. Jet fuel, turbine oil, hydraulic fliud, sealants, paints used in manufacture and repair are also nasty when contact is allowed.
I occasionally look up at the overhead and see a "high voltage inside " decal wondering how much electro magnetic radiation is being pumped out.
And I haven't even mentioned blue loo or worse- crew meals.

[Gary Lager]

But AI certainly wouldn't certify you for TO with a temperature that is too hot for a RTO. Therefore, if you TO with 300°, AI must have made sure that you can safely absorb all brake energy in case of rejection.

That's an assumption. Pantload is correct - I asked the same Q of our Tech Dept. For performance purposes, a lot of other assumptions are made by AI, some of which we are not informed about. They are not always worst case, since the resulting performance figures would be too conservative to be practical. For an RTO, the brakes are assumed to be 150C.

There are always a great may factors which may affect your ability to RTO safely from close to V1. Taking off with high brake temperatures limits the amount of energy they brakes can absorb. Why introduce another risk factor into an already risky situation?

Brake Fans are there for a reason. Don't like the noise? Buy some ear defenders!

[sharpshooter41]

Dear all

Good to see people using the topic to discuss brake temp limitations.

However my original question is still unanswered.

Is the requirement to switch ON brake fans just prior to stopping at the gate for the reason that the carbon dust is harmful for people around??

The earlier mentioned Airbus brief seems to point to that;

[typhoid]

The Airbus advice could also mean that it's poor form to blow (harmless) black soot over people.

[FlightDetent]

the certification criteria for an RTO on the SA Airbus limits the brake temps to 150 degrees C. I heard this one from someone I am severly inclined to believe, but spent quite some time looking for a reference (FCOM 2, G2G w/TO perf, FCTM, FCOM blue OEBs ...). PL, can you help?

[the rim]

i cannot beleive boofhead pilots .....you sit in the lefthand seat ....oh i will switch on the cooling fans as i have stopped too quickly and i dont give a stuff who i cover with black soot .....where's my allowances tut tut

[PantLoad]

I can't remember where I read this...but, I think it's in the Airbus publication "Getting to Grips with Aircraft Performance".

In any event, it is not correct that the stopping capabilities of the brakes increases with temperature. Airbus also has a publication that explains carbon brakes.

"Wear" is a totally different matter, however. Specific temps for wear rates vary slightly, depending on the vendor (and their engineers, the brake design, etc.), and wear rates improve when the brakes are a little warm.

The 300 degree limitation is for wheel well fires. Airbus design circumvented the need for wheel well fire detection.

It is interesting that Boeing does not believe carbon brakes are appropriate for the 737...but they are looking at using carbon brakes for the new 737 design. (I read this in Aviation Week and Space TEchnology.)

According to Boeing, carbon brakes offer significant advantages...like weight savings...stopping capabilities...etc. But, carbon brakes get hot...and for planes like the A320 or 737, where short ground times are sometimes part of the airline's marketing plan, carbon brakes may not have the cooling times they need for the next takeoff.

Airbus solved this problem with the installation of fans....albeit fans are an option, not standard equipment....most 320's have fans installed. (Buying a 320 without brakes fans is possible, but that's like buying a Cadillac without air conditioning....they normally come with air conditioning.)

So, while the use of fans may be optional (under your airline's SOP), they should be used as per the Airbus SOP or recommendations. And, remember, the temps keep climbing while you're at the gate...peaking around 25 or 30 minutes after the landing.

So, waiting five minutes or so after landing (or just prior to gate arrival) to turn on the fans (as per Airbus recommendation) is a prudent course of action. Depending on the turn time, you still may have the fans running during the next taxi out...turning them off just prior to takeoff.


Fly Safe,

PantLoad

[sharpshooter41]

My own feeling is Airbus would not be putting it in black and white if it was just harmless black soot being blown over the ground personnel. I personally give more credit to the people who made these aircraft.

[alwaysontime]

Look at F1 cars with Carbon Brakes - they need to get some temperature in them for them to work at their best. Airbus brakes regularly exceed 300C on short runways such as ABZ
We turn the fans only if The temps are exceeding 300c and 5 mins have passed - to allow for thermal equalisation across the entire brake assembly. and Avoid oxidation of brake surface hot spots.
OR if the temps are likely to exceed 500C. Again this would be done before pulling onto stand because you can get quite a cloud of brake dust sometimes, which may cover your groundstaff- they would then be crying off to go home and get changed. We routinley turn the fans on in the after starts whenever the temps exceed 100C and off just as we line up. You must have less than 150c fans on or 300C fans off for take off.

‘The use of autobrake LOW for normal operations helps to reduce brake wear by reducing the number of brake applications to one, and by increasing the brake temperature to moderate levels. The use of autobrake MED is recommended to reduce runway occupancy, when landing on a short or contaminated runway and when operating in LVPs.’Carbon brake wear is related to the number of brake applications and to the temperature. hence getting the fans on

[cwatters]

I know carbon nano tubes aren't the same as carbon fibers but...

Carbon nanotubes may be as harmful as asbestos (http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2008/05/20/BUDG10P518.DTL)

Carbon nanotubes may be as harmful as asbestos
Ann Fernholm, Chronicle Staff Writer

Wednesday, May 21, 2008

PDT SAN FRANCISCO -- One of the most promising materials for the future of technology, carbon nanotubes, might be as harmful as asbestos if inhaled, according to a new study published Tuesday in the scientific journal Nature Nanotechnology.

Animal studies indicate that these long and very thin carbon molecules could cause a cancer called mesothelioma, which occurs in the lining of the lungs.

"The problem of asbestos was caused when it was released into the air, if it was handled inappropriately or incorrectly. Carbon nanotubes could do the same," said Andrew Maynard, chief science adviser to the Project on Emerging Nanotechnologies in Washington and one of the authors of the study.

"With this information, we should assume the worst, we should think of them as asbestos. But more research might relax that point of view."

Carbon nanotubes, 10,000 times thinner than a human hair, are among the materials many scientists believe will be used to build tiny electronics.

In 2001, IBM made an array of transistors out of carbon nanotubes. In 2004, General Electric created a carbon nanotube diode, and last year, UC Berkeley scientists used single carbon nanotubes to make the world's smallest radio.

Today, the most widespread application is in plastic materials reinforced by carbon nanotubes. Stronger than steel but light as plastic, carbon nanotubes are highly attractive to manufacturers of everything from sporting goods to airplanes. They can be found, for example, in some tennis rackets, baseball bats and bicycle frames.

"I would be very surprised if it is dangerous to use, let us say, a tennis racket or baseball bat containing carbon nanotubes," Maynard said. "But I do not think it is OK to tell people that we think it is safe - we've got to have evidence."

Such products, he said, should go through a number of tests investigating, for instance, what happens when they break or when the surface is rubbed against the ground. He also wonders what happens when the products are disposed of.

"Is there a chance that the nanotubes will enter the environment?" Maynard said.

The main concern, however, is the effect on people processing carbon nanotubes and manufacturing the materials containing them.

At Unidym, a Menlo Park company exploring the possibilities of using carbon nanotubes in such items as touch screens, precautions already have been taken.

"This is what we expected. It fits with the paradigm that long and skinny fibers can cause asbestosis. It does not really matter if they are made of carbon or asbestos. The key is not getting them into the body," said Ken McElrath, vice president for product development materials at Unidym's facility in Houston, which manufactures the carbon nanotubes.

To protect employees from breathing nanotubes, the manufacturing is conducted in closed ventilated systems. People working with the nanotubes also are protected by dust masks with respiratory filters.

McElrath said he found the study to contain some positive news: Shorter carbon nanotubes might not be harmful.

"We are using these kinds of findings in our product design," he said. "We try to stay away from things that potentially cause problems."

The research presented in Nature Nanotechnology used an animal model developed in the 1980s to study the development of mesothelioma, which can be caused by asbestos exposure.

Using this model, the nanotubes were injected into the abdominal cavity of mice, which is lined by tissue similar to the human lung and is a sensitive predictor of mesothelioma. After one week, there was an inflammatory response to longer versions of the nanotubes.

"This is a very important study; it is very well done. It shows that you do get an inflammation that is similar to asbestosis. What is not known yet is the long-term effect," said Vincent Castranova, involved in the nanotoxicology research at the National Institute for Occupational Safety and Health.

Also unclear is how this experimental model for mesothelioma translates into reality. Scientists do not know under which circumstances these long carbon nanotubes will form a breathable dust, or whether this dust will work its way into the lung.

"Here we run out of information," Maynard said.

Meanwhile, Castranova recommends people working with carbon nanotubes follow National Institute for Occupational Safety and Health guidelines for working with engineered nanomaterials, which involve the use of respirators and special filters to clean the air.