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Greenfly07
12th Jun 2007, 11:11
I'm seeking some input on carbon brakes (esp re A320 aircraft). I am aware of the Airbus FCOM 3 recommendations regarding the use of brakes and brake fans, e.g. brake fans on during taxy out if there's an arc above any of the wheels on the ECAM WHEEL page, and delaying the use of fans after landing. I am a TRE currently working in India (DEL OAT approx 48C recently!). The company I am working with has an SOP calling for fans on after landing as soon as an arc appears on any of the wheels (contrary to the Airbus recommendation). I am fairly sure that this SOP is likely to increase brake wear through oxidation of hot spots. I'd appreciate any views on this. Does anyone have any manufacturers' data (we're using Messier Bugatti brakes) on the temperature at which the brakes are most efficient, and the temperature at which max wear occurs ? Thanks in advance for any reply.
P.S. I am new to the forum. If this topic has been covered before, could someone point me to the thread ?

airseb
12th Jun 2007, 12:53
can only give you some info i have from our sop and fcom. carbon brakes efficiency increases with temperature. that's why it shouldn't be a problem to take off with (very) hot brakes. but when the gear is retracted these hot wheels come very near to the hydraulic lines and that's why you've got a temp limit on t/o, ie 300 or 150 with brake fans on (because the temp probe is cooled down by the ventilator).
on landing our sop recommends brake fan on:
-if a wheel is at more than 500 (!)
-5 minutes after landing (to have enough for temp stabilization)
-before entering the stand (because of the carbon particles that are projected around)

typically at max landing weight and full use of brakes and reverse thrust you'll get to 300 about 3 or 4 mins after landing.
also in a 45 minute turnaround the brakes (without brake fan) will be down to 100 (no problem for take off) and with the brake fan on you'll need about 25 minutes to be down to 50.

and a last comment. when taxying the best method is to let the aircrft accelerate to 25-30 kts and then slow it down to about 10 kts, let it accelerate again, etc... your brakes'll stay lower in temp than if braking constantly.

hope it helps.

seb

Dream Land
12th Jun 2007, 13:38
Your views on brake use are in agreement with everything I have been taught, my suggestion might be to contact Airbus Technical support for a written opinion.

PantLoad
12th Jun 2007, 14:00
Gentlemen:

Please refer to the Airbus publication "Summary of Braking Recommendations in the SOP". This was published in 2004 under the "Operational Liason Meeting, Fly-by-Wire aircraft.

There is a lot of misunderstanding about carbon brakes and especially the Airbus SOP. First, let me say that your company's SOP trumps all else. You have to go by your company's SOP, whether you agree with it or not...whether it is in agreement with Airbus or not. Your airline's AOC issuance is predicated upon your company having an SOP. It is therefore a condition of validation of the AOC that the SOPs be complied with. In other words, compliance is legally required.

Now, on to the issue at hand. There are three brake vendors for the single-aisle bus. One is Messier-Bugatti, the second is Honeywell-ALS, and the third is BF Goodrich. I am not an engineer, so I cannot tell you which one is better...or if any one is actually better than the other, etc.

According to the publication cited above, these three designs differ (in one way) by wear rates vs. brake temperature. The BF Goodrich peaks its wear at around 80 degrees c. The Messier-Bugatti peaks its wear rate at around 150 to 160 degrees c. And, the Honeywell ALS peaks its wear rate at around 225 degrees c. (These figures are approximate, as the graph to which I refer is not detailed enough to be more precise.)

Now, having said all that, one thing carbon brakes have in common is that their wear is mainly predicated upon number of applications, not how hard you apply the brakes or at what speed. This is why the FCOM procedure is to allow the airplane to accelerate (if safely feasible) to approximately 30 kts during taxi...then, you apply the brakes to decelerate to approximately ten knots. Repeat the procedure as required. "Technique" (not necessarily procedure) is to plan your taxi (using the above guideline) to minimize your brake applications. For example, you see you have to slow for a turn up ahead...try to plan the deceleration to coincide with the deceleration required to make that turn. (Again, this is technique...not SOP!!! But, you want to minimize brake applications.)

Second point that is important is that of brake efficiency in the event of an RTO. While the max temperature for takeoff is 300 degrees (fans off), the RTO certification for this requires the brake temperatures to be no more than 150 degrees c. As the temperature increases, braking ability decreases. It has no bearing on the brake wear vs. temperature relationship.

The 300 degree limitation is related to the wheel well fire scenario...hydraulic fluid flash points, etc. Airbus does not put wheel well fire warnings in their single-aisle aircraft. Simply, don't get the wheels and brakes too hot, and you don't have to worry about this.

To summarize the answer to your question, with Messier-Bugatti brakes, max wear occurs at brake temps approximately 150 to 160 degrees c. Second, the cooler the brakes, the better chance you have of duplicating the RTO stopping capability as per the performance charts. "Cold" is better than "warm"...and "warm" is better than "hot" when it comes to stopping capability. Third, follow your company's SOP.


Hope this answers your questions. I wish I could send you to a URL address to download this publication...I will look to see where I got it.


Fly Safe...


PantLoad

Dream Land
12th Jun 2007, 14:24
Greenfly,
I have a Power Point file that includes some numbers from all three brake manufacturers if you want.

PantLoad
12th Jun 2007, 14:24
Go to http://www.smartcockpit.com

Under "Flight Ops"

"Airbus Braking Recommendations"


That will help....


PantLoad

PantLoad
12th Jun 2007, 14:26
Dream Land,

Great job...

I'd be interested in the PPoint presentation, too!


Ah!!! This is what the Technical Forum here at PPrune is all about!!!:D:D:D


PantLoad

mutley320
12th Jun 2007, 15:37
With reference to your brake issues, your company may insist on their policy and if so just watch out for keen copilots reaching for the fans as you decelerate and selecting MAX instead. It's happened to me, still above 80 knots or so, Not pretty. This happened before Airbus came out with the 5 minute guidance.

Bolty McBolt
13th Jun 2007, 04:28
What ever your SOPs are for using brake fans are..

A request from all the Boys and Girls on the Ramp.

Please switch on the fans before you get to the gate. The huge plume of carbon dust that blows out on application of the fans has a lot to be desired. I would prefer I wasn't using my lungs to filter that air. :ok:

regards

Bolty

Greenfly07
15th Jun 2007, 13:28
Many thanks to all who replied to my request for info. Sorry for the delay in acknowledging - I've been down south fighting with the monsoon for a couple of days.

Pantload - thanks for the link. I have a desperately slow connection here in DEL but will access that site when I get back to Europe.

Dream Land - thanks for the offer of the PP presentation. I have just received a couple of presentations from Airbus by Guy Di Santo. Is your PP by him ? If so, it's probably the same as what I already have.

Bolty Bolt - would I turn on the Brake Fans just as you are peering into the fan guards ? Only if I am at least 75% certain that those fingerprints on the ECAM screen are yours....

Dream Land
15th Jun 2007, 15:24
Is your PP by him ? If so, it's probably the same as what I already have.
Yes, that's the one I have.

Bolty McBolt
18th Jun 2007, 02:11
Greenfly
Only if I am at least 75% certain that those fingerprints on the ECAM screen are yours....
Mate I have no need to touch the screens but I do like to clean brake dust and grease from my hands by wiping them on the inside of the shoulder harness section of the tech crew seat belts :ok:

Mach trim
22nd Oct 2007, 23:57
I still have not read the definitive answer on this.



Interested in hearing more.

Putting the brake fans on just before the gate is too early in my opioion causing hot spots

Personally I prefer to wait and let brakes reach peak temperature let it rise to its peak then put the brake fans on or wait until after my preflight.

most wear occurs between 250 and 70 degrees correct ?
Sorry about the ramp guys but the carbon just comes out initially the initial blast .

Arrowhead
23rd Oct 2007, 01:46
FYI A320 OEB says most brake wear is caused when they are cold - ie on taxi out.

On taxi in, shut one engine down after the required time and you will save many applications and wear, plus some fuel (depending on light A319/heavy A321)

mutt
23rd Oct 2007, 04:23
We have recently ordered A320's and are looking at the " options " list.

For a hot desert environment, would you recommend "brake cooling fans" for operations with 40 min turn arounds.

Do these fans impact on their ease of changing a brake or tire?

Thanks..

Mutt

Dream Land
23rd Oct 2007, 04:42
We operate some A320's and generally use long runways and one hour turns, reaching the takeoff limitation of 300C isn't much of an issue for us, your operation may vary. Brakes may rise to 150C after a normal landing using reverse, if you are heavy and or go for a early turn off, you will have a delay for sure, add to that, taxiing which can really send them high if you have a tailwind or a slow follow me car :}. Don't know the economics myself but we normally use Reverse Idle and Low Auto Brake and all aircraft are equipped with fans.

Mach trim
24th Oct 2007, 00:23
mutt,

Also depends if you will be landing on short runways with heavy weights

I would definitely recommend brake fans.

Although 300C is the limitation.

The brake temperature should not rise above 150 degrees (fans off )to respect the brake energy limitation in a rejected takeoff.

fruitloop
25th Oct 2007, 14:18
Mutt....adds about 15 minutes to the time to change the brake/wheel assy..well worth having !! I would also like ALL crews to turn the fans on BEFORE entering the ramp area !

Mach trim
25th Oct 2007, 16:18
fruit loop,

Interested in hearing more how the carbon is bad for ramp personnel. I understand it is cancerous.

What about the thermal equalization or hot spots if you are at the gate 2 minutes after ?

Isn't it better to let the brakes get to their peak temperature before putting brake fans on?

Before you jump I have read the SOP's written by airbus.

Why not wait ( if you can of course, if the brakes are not too hot and you have enouigh taxi out time ) and turn the brake fans on after pushing back. I like to put them on after starting engines (ramp personnel clear ), if I can. You use the brake fans less and make less noise in environmentally sensitive areas


The carbon that comes out as you turn the brake fans on, it seems to me to come out in the initial area.


Interesting with carbon brakes

looseobject
25th Oct 2007, 23:30
As far as i know the brake fans are on optionnal eqpt according to he type of operations(ambiant temperatures, rwy length, ldg weight).
This equipment is very useful during short turnaround (no suffuciant cooling time).
As said in many posts, brakes wear and temperature will depend on many factors ( number of applications, ldg weight, Vapp etc)
So in my opinion, I recommend not to use the brakes fans after lading ( even after the 5 min ), except if the brakes temperature tends to exceed 500C,let the brakes cool ''naturally'' at the gate during turnaround.
After doors closure and just prior to pushback or taxi out, running the fans would be sufficient to reach the rwy with an reasonnable brakes temp (less than 150 fans on)
Totally agree with bolty (post 9), cos running the fans when reaching the gate seems no sens, just imagine the symphony played by many busses parked in the same area,and the carbon dust sprayed into the noses of gnd personnel.
cheers

Right Way Up
25th Oct 2007, 23:46
Ref turning on brake fans during turnround. Its not difficult, just get the PNF to give a thumbs up during the walkround that the no-one is in the vicinity & fire them up.

Dream Land
26th Oct 2007, 06:28
let the brakes cool ''naturally'' at the gate during turnaroundThat's a good one, where I work the first thing the engineers do is push the brake fan PB, lol. :}

Fil
26th Oct 2007, 17:41
We have 9 or so older A320's without brake fans, and a good number of new A319/320/321's all with fans. When the decision was taken to purchase the 31's (last to come) the engineering input was the 320's WITH fans had a lower brake wear than those WITHOUT and that the extra cost of the fans would be reclaimed over time due lower brake wear.

On regular LHR-MAN's during summer time you can find it hard to keep the temps low due short turnarounds.

420
26th Oct 2007, 19:20
i agree that turning on the break fans at the gate will cause lots of unwanted sharp and painful noise (like nails on a chalkboard).But then again, for airlines with short turn arounds throughout the day,i would think that this is a necessary discomfort. after landing with autobrakes low and full reverses,exiting a high speed taxiway followed by taxiing to a bay approx 7 mins away with turns which of course require further gentle break usage,by the time u hit the parking bay,one will have to switch it on. not to mention in hot climates. i would think the temps would be around an average of 250++ by then. so if we were to leave the fans off during quick turnarounds,it should go down to (if the temp DOES reduce in the first place) to about 220? and after pushing back and the ramp guys clear out you switch on the break fans,sure there would be ample time for the brakes to cool....but u still got to taxi to the runway...with the same 7 minute taxi with the extra load and fuel now and with the same OAT and not to mention...a 220 C on the brakes. so yeah the fans are on...., but its being used at the same time. i doubt it'll reduce to 100 C or below before T/O. and i know the limitations for airbus is 150 with fans off...but hey,dont think id risk it with an RTO:=.

dont know about u guys.:hmm:

Mach trim
26th Oct 2007, 19:27
Good point I like to get the temp down to at least 60 degrees ( my target ) before turning brake fans off in case of RTO

PantLoad
27th Oct 2007, 17:01
The Airbus FCOM SOP for all of this is correct, proper, minimizes environmental problems, maximizes brake wear and efficiency, etc., etc.

My advice is to simply follow the Airbus FCOM...unless your company's SOP differs...then, of course, you are obligated to follow that, instead.

PantLoad

fruitloop
28th Oct 2007, 00:07
Mach trim
The reason that "I" would prefer to have crews turn the fans on BEFORE entering the ramp area is as you mentioned that on Initial start up a "mist" of brake-dust which can be seen(carbon which isn't really healthy for any-one being of a cumulative nature)and the "gassing" from the Lithium grease when it reaches a "certain" temperature (invisible but smelt)(wheel bearings) that always seems to happen to me when setting up the fuel panel.Added to this any lubricants that have made their way (gravity with assistance from condensation)to the brake area (including landing gear grease,spilt strut fluid,corrosion inhibitors etc etc)which all add up to "interesting smells" being blown around.

slf911
28th Oct 2007, 11:53
As a non pilot and a watcher of formula one racing, I have seen discs on cars get red hot and wondered what is the temperature at which carbon brakes start to fail? Appreciate you would not want to get anywhere near this other than in RTO.