I understand that normal metal brakes experience wear as a function of stopping power. Stopping from high speed causes more wear than normal taxiing. I also understand that carbon brakes experience wear more as a function of number of applications. Every time you engage carbon brakes, you're putting wear into the brakes.

Suppose a plane had both kinds. Then on low speed braking (taxiing), you could use only the metal brakes, but on high speed braking (landing) you could use both. You would get the advantage of light weight from the carbon brakes, and less wear from the metal brakes.

To make things even better, put metal brakes on the nose wheels and carbon brakes on the mains. Now you also have more total stopping power. Since the nose wheel brakes are taking some of the load, the main wheel brakes could be lighter. (I do understand this increases weight/complexity somewhat)

Has any plane ever mixed brake types?

Carbon brakes don't get as hot, and dissipate heat faster and don't pass it on to the wheel assembly nearly as much as steel brakes. Carbon brakes become more effective as they heat up.

There are no nosewheel brakes. Very bad idea.

All brakes wear.

Regardless of braking type, in large aircraft we don't pump or repeatedly apply the brakes; they're applied as needed, released when not.

There are pros and cons of carbon brakes. The pros are lighter weight, longer life and better overall performance. The cons are higher costs, higher overhaul costs. Another issue is heat. Carbon brakes get hotter. Brake fans help, but they add complexity. A short turnaround on a hot day can be a problem. 787s have issues with hot brakes. An issue with steel brakes is they can lock and shatter ( common on a 737 ). The tide has turned towards carbon. I don't think you can steel on a new airliner anymore.

No and it’s needed. The critical brake test is a max TOGW abort and every plane needs all the brakes to absorb energy evenly.


GF

Lpbri wrote:

787s have issues with hot brakes. An issue with steel brakes is they can lock and shatter ( common on a 737 ). The tide has turned towards carbon. I don't think you can steel on a new airliner anymore.

You haven't looked at a 320 with no brake fans. I have had to delay takeoff after a long taxi because the brake temps were out of limits. Takes forever to get the temps down with no fans especially in OMAA

The 717 is notorious for hot brakes on turns less than 50 minutes. We automatically roll out the mobile brake fans whenever they visit our station in BWI during the summer. No other plane in our fleet needs this type of attention.

Interesting idea but not worth the weight and complexity



Incidentally, there are no airliners currently manufactured with nosewheel brakes but they were an option on the 727, we had a few aircraft fitted with them at Continental, they were all operated in the Air Mike division where some of the short, island runways required extra stopping power


These nosewheel brakes were removed when the Air Mike aircraft rotated back to the mainland as they weren’t needed domestically and were quite heavy


I think the Convair 880 and 990 also had nosewheel brakes

mmo wrote:

You haven't looked at a 320 with no brake fans. I have had to delay takeoff after a long taxi because the brake temps were out of limits. Takes forever to get the temps down with no fans especially in OMAA

Yeah, Vegas with no brake fans in the summer. I like to use max reverse and manual brakes and don't touch them until slow and that works, otherwise...ding. Hot brakes on your next departure after the long taxi back out.

If you had both types of brakes wouldn’t you lose the weight advantage of carbon brakes by also having... steel brakes?

Like, you would also lose the health benefits if you ate the veggie burger AND the cheeseburger.

mmo wrote:

You haven't looked at a 320 with no brake fans. I have had to delay takeoff after a long taxi because the brake temps were out of limits. Takes forever to get the temps down with no fans especially in OMAA

The outside air temperature has little to do with rate brakes cool down. The characteristics of how to treat your brakes varies, you need to know if they are Messier-Bugatti, Honeywell-ALS or UTAS brakes.

The main influence of high outside temperature is to increase density height which increases the ground speed during takeoff and landing.

747Whale wrote:

Carbon brakes don't get as hot, ...

Lpbri wrote:

Another issue is heat. Carbon brakes get hotter.

I feel so confused

Zeke2517 wrote:

If you had both types of brakes wouldn’t you lose the weight advantage of carbon brakes by also having... steel brakes?

Like, you would also lose the health benefits if you ate the veggie burger AND the cheeseburger.

You would lose a small bit of the weigh advantage.

You would have small steel brakes, just enough to stop a taxiing airplane. And you would reduce the size of the carbon brakes a tiny bit, since there are steel brakes to help.

747Whale wrote:

All brakes wear.

Regardless of braking type, in large aircraft we don't pump or repeatedly apply the brakes; they're applied as needed, released when not.

I bet you'll believe that IATA's advice to airline pilots.

The number of brake applications, even at low speeds, is the primary factor that affects
brake life. Aircraft that fly to/from congested airports, that favor multiple brake applications
during taxi, usually have a 20 % to 30 % reduced brake life. Approximately 75 % of brake
wear occurs during taxi operations
...
All recommended braking techniques should mainly aim at reducing the number of brake
applications
https://www.iata.org/whatwedo/ops-infra ... Airbus.pdf

If approximately 75% of brake wear is during taxi, and cheap steel brakes can do the job during taxi, then you could make the expensive carbon brakes last 4x as long!

kitplane01 wrote:

Zeke2517 wrote:

If you had both types of brakes wouldn’t you lose the weight advantage of carbon brakes by also having... steel brakes?

Like, you would also lose the health benefits if you ate the veggie burger AND the cheeseburger.

You would lose a small bit of the weigh advantage.

You would have small steel brakes, just enough to stop a taxiing airplane. And you would reduce the size of the carbon brakes a tiny bit, since there are steel brakes to help.

"Just enough to stop a taxiing airplane" is more than you'd think. It's not a landing or a rejected take-off but on the other hand, we can taxi for up to an hour with numerous brake applications. Lots of heat... Plus now you have another brake system with all the associated hardware.

zeke wrote:

The outside air temperature has little to do with rate brakes cool down. The characteristics of how to treat your brakes varies, you need to know if they are Messier-Bugatti, Honeywell-ALS or UTAS brakes.

The main influence of high outside temperature is to increase density height which increases the ground speed during takeoff and landing.

Zeke, I understand what you are saying but I am talking about a dead aircraft started and taxied out and having to wait. I have experienced this on one more than one occasion. your TAS does not increase significantly during taxi. We were restricted to a 25 Knot taxi speed. OFF THE PFD, that is TAS. A relatively light aircraft having to taxi from the Amiri ramp and having to wait over 30 minutes to have the brakes cool down. The normal one smooth brake application to slow the aircraft down, not riding the brakes were done. Our SOP restricted us from single engine taxi and using the T/R to slow. Why anyone would order the 320 series with no brake fans needs their head examined!

kitplane01 wrote:

747Whale wrote:

Carbon brakes don't get as hot, ...

Lpbri wrote:

Another issue is heat. Carbon brakes get hotter.

I feel so confused

Carbon brakes get hot, like any brake; they don't stay hot like steel brakes; they cool faster, and they don't absorb the heat energy to release it into the wheels nearly like steel does. Carbon is lighter and its more effective the hotter it gets. Steel brakes are the opposite.

Classic 747's in Afghanistan took hours with fans in many cases, to cool enough to take off, and that's after dropping the gear at 18,000 of higher on the arrival to precool it on the way down, leaving it out after takeoff on the hops into Afghanistan, etc. Brakes get hot. At heavier weight, they get particularly hotter. At heavy weights, even with little brake use, the brakes can get so hot during a short taxi just from tire flex and the heat generated that way that a takeoff may need to be delayed, for brake energy. A long three mile taxi at Schipol is a good example.

kitplane01 wrote:

I bet you'll believe that IATA's advice to airline pilots.

Aaah...yeah.

I am an airline pilot.

And an aircraft mechanic with a few decades of experience.

It's always good to be schooled by a private pilot qualified to neither, though. Thanks.

zeke wrote:

mmo wrote:

You haven't looked at a 320 with no brake fans. I have had to delay takeoff after a long taxi because the brake temps were out of limits. Takes forever to get the temps down with no fans especially in OMAA

The outside air temperature has little to do with rate brakes cool down. The characteristics of how to treat your brakes varies, you need to know if they are Messier-Bugatti, Honeywell-ALS or UTAS brakes.

The main influence of high outside temperature is to increase density height which increases the ground speed during takeoff and landing.

Off topic, how would you treat the different manufacturers? Do you adjust the amount of applications or something else? Just curious!

mmo wrote:

Zeke, I understand what you are saying but I am talking about a dead aircraft started and taxied out and having to wait. I have experienced this on one more than one occasion. your TAS does not increase significantly during taxi. We were restricted to a 25 Knot taxi speed. OFF THE PFD, that is TAS. A relatively light aircraft having to taxi from the Amiri ramp and having to wait over 30 minutes to have the brakes cool down. The normal one smooth brake application to slow the aircraft down, not riding the brakes were done. Our SOP restricted us from single engine taxi and using the T/R to slow. Why anyone would order the 320 series with no brake fans needs their head examined!

I don’t understand how you can get to 300 deg with an empty/light aircraft. Especially if as you are saying your letting it accelerate to 25 kts and then one application back to 5 kts.

The limit with fans installed is 150 deg.

TOGA10 wrote:

Off topic, how would you treat the different manufacturers? Do you adjust the amount of applications or something else? Just curious!

The manufacturers have different recommendations for temperatures to operate the brakes at to reduce wear.

zeke wrote:

I don’t understand how you can get to 300 deg with an empty/light aircraft. Especially if as you are saying your letting it accelerate to 25 kts and then one application back to 5 kts.

The limit with fans installed is 150 deg.

Come on Zeke, you've been to AUH. OAT of 50, long taxi from Amiri ramp to 31R. The Amiri, now Presidental ramp is on the NW corner of AUH by the approach end of 13R. It will happen very easy with NO fans installed.

Wouldn’t be much further than a taxi to 15R at RUH. Your taxi at AUH would only be around a 4000 m taxi, not much longer than a normal runway length.

I wonder how much of the heat is brakes, and how much is due to the tyres flexing and heating up?
A couple of years ago we had to tow a B767 from one end of ARN to the other. I was in the flight deck on the brakes (very rare as we usually have TBL with no brakeman) At the start, the aircraft was covered in snow and OAT around M5 degC. When I put the parking brake on at the other end, I remember seeing that the tyre pressures had risen from very low, to normal.

The limit with fans installed is 150 deg.

Isn't the A320 limit 150 deg with the fans running, and 300deg with them turned off?

ps Here at ARN it is very rare to see an A320 with hot brakes, and the fans will reduce them in seconds.

Tristarsteve wrote:

Isn't the A320 limit 150 deg with the fans running, and 300deg with them turned off?

My recollection of the words in limits was 150 deg if fans were used.

For example if taxing and the temps are saying 320 degrees, turn the fans on for a bit and the indicated temp drops to 250 degrees . You are not permitted to turn the fans off and then use the 300 degree limit, you must use the 150 degree limit.

The reason being the temperature pickup is in the airflow of the fans and would underread the actual brake temperature by up to 150 degrees.

Like your towing story, I have also seen temps rise during the takeoff and climb on heavyweight takeoffs, and even increase after gear retraction.

747Whale wrote:

kitplane01 wrote:

747Whale wrote:

Carbon brakes don't get as hot, ...

Lpbri wrote:

Another issue is heat. Carbon brakes get hotter.

I feel so confused

Carbon brakes get hot, like any brake; they don't stay hot like steel brakes; they cool faster, and they don't absorb the heat energy to release it into the wheels nearly like steel does. Carbon is lighter and its more effective the hotter it gets. Steel brakes are the opposite.

Classic 747's in Afghanistan took hours with fans in many cases, to cool enough to take off, and that's after dropping the gear at 18,000 of higher on the arrival to precool it on the way down, leaving it out after takeoff on the hops into Afghanistan, etc. Brakes get hot. At heavier weight, they get particularly hotter. At heavy weights, even with little brake use, the brakes can get so hot during a short taxi just from tire flex and the heat generated that way that a takeoff may need to be delayed, for brake energy. A long three mile taxi at Schipol is a good example.

kitplane01 wrote:

I bet you'll believe that IATA's advice to airline pilots.

Aaah...yeah.

I am an airline pilot.

And an aircraft mechanic with a few decades of experience.

It's always good to be schooled by a private pilot qualified to neither, though. Thanks.

I get I'm being insulted, but I don't get why. Also, it's not helpful.

No one believes I'm an expert in anything. I don't either. I'm not trying to school anyone. But I understood that the main cause of wear in carbon brakes (unlike steel brakes) is number_of_applications, not total_energy_of_stopping. I believe this because the IATA says so (and lots of other people too). Do you disagree with them? If so, how come? I'm here to be educated.

Also, I like the personal experience stories. But not the insults.

"I get I'm being insulted, but I don't get why. Also, it's not helpful.

No one believes I'm an expert in anything. I don't either. But I understood that the main cause of wear in carbon brakes is number_of_applications, not total_energy_of_stopping. I believe this because the IATA says so (and lots of other people too). Do you disagree with them? If so, how come? I'm here to be educated."

What high school class are you developing this project for?

Brakes are made to stop airplanes. When brakes wear out you replace them.

Any questions? LOL

pikachu wrote:

"I get I'm being insulted, but I don't get why. Also, it's not helpful.

No one believes I'm an expert in anything. I don't either. But I understood that the main cause of wear in carbon brakes is number_of_applications, not total_energy_of_stopping. I believe this because the IATA says so (and lots of other people too). Do you disagree with them? If so, how come? I'm here to be educated."

What high school class are you developing this project for?

Brakes are made to stop airplanes. When brakes wear out you replace them.

Any questions? LOL

No high school project.

It would be better if brakes wore out less often. Or am I confused about that? Don't they cost many much $$$$?

kitplane01 wrote:

pikachu wrote:

"I get I'm being insulted, but I don't get why. Also, it's not helpful.

No one believes I'm an expert in anything. I don't either. But I understood that the main cause of wear in carbon brakes is number_of_applications, not total_energy_of_stopping. I believe this because the IATA says so (and lots of other people too). Do you disagree with them? If so, how come? I'm here to be educated."

What high school class are you developing this project for?

Brakes are made to stop airplanes. When brakes wear out you replace them.

Any questions? LOL

No high school project.

It would be better if brakes wore out less often. Or am I confused about that? Don't they cost many much $$$$?

Take a step back from your research into this issue and reconsider it for a moment. Maybe your high school has a career counsellor you can ask?

You are proposing an additional braking system to reduce brake wear? Adding brakes to save brakes?

Brakes stop airplanes. When they wear out you replace them.

How much weight are you willing to add to an airframe to save brake wear? (Keeping in mind brakes wear out and are expected to do so and are easily replaced)

kitplane01 wrote:

kitplane01 wrote:

I bet you'll believe that IATA's advice to airline pilots.

I get I'm being insulted, but I don't get why. Also, it's not helpful.

No one believes I'm an expert in anything. I don't either. I'm not trying to school anyone. But I understood that the main cause of wear in carbon brakes (unlike steel brakes) is number_of_applications, not total_energy_of_stopping. I believe this because the IATA says so (and lots of other people too). Do you disagree with them? If so, how come? I'm here to be educated.

Also, I like the personal experience stories. But not the insults.

You're not being insulted. You're being insulting. There's a difference.

Do you know what IATA is?

When someone takes the time to explain something to you, and you argue, and then you say "I bet you'll believe it now if XXX tells you," then you're lecturing. Your'e attempting to teach something you know nothing about based on something you read on the internet, and you're attempting to teach it to people who are kind enough to explain it to you, because they do know. It's one thing if you ask a question, another thing if you present it as you have: that's insulting.

Yes, we know what carbon brakes are, how they're used, their advantages and disadvantages, and yes, we know the uses and limitations on steel and organic brakes. We work on them, we use them in our daily jobs. We receive training on them. We handle them. In some of our cases, we also buy them, inspect them, etc. We know them. We understand the application. We have brake temperature monitors in the cockpit and can see the results of taxiing, rejecting a takeoff, or landing, and we see it every time and can differentiate between the effects of reverse and no reverse, autobrakes, and varying degrees of manual braking.

I flew a small twin called a Piaggio Avanti; one of the earlier of the small airplanes to get carbon brakes; they were all but useless when cold; it took several brake applications when beginning to taxi to make them effective. Nearly all taxiing is properly done by not riding the brakes, but using them to slow the aircraft, then releasing, and allowing speed to build again before repeating the process. Holding brakes creates friction, increases heat, and ultimately affects stopping distance on a rejected takeoff. The Piaggio had no anti-skid; hot brakes were very effective; so much so that nearly every pilot I knew who flew the aircraft ended up flat-spotting tires. Very, very effective brakes. The braking friction of the brake changes with temperature, and whereas steel brakes lose effectiveness if they get too hot, carbon brakes are the opposite.

Brake applications cause wear. Period. Brakes wear. Period.

I don't have nearly the temperature issues, especially over a long period, in carbon brake equipped aircraft, that I see in steel brakes. The carbon brakes cool faster, don't transfer as much heat. It's not nearly the concern that it is with steel brakes.

When an aircraft is certificated, one of the tests it must do is a high speed rejected takeoff, which frequently results in the brakes getting so hot that they melt, catch fire, etc. You can see for yourself.

Carbon brakes, thermalling tires:

https://www.youtube.com/watch?v=Mr4V680UQ-k

See if you can spot the difference compared to an older brake test:

https://www.youtube.com/watch?v=_G6iFvtzyUo

747Whale wrote:

kitplane01 wrote:

kitplane01 wrote:

I bet you'll believe that IATA's advice to airline pilots.

I get I'm being insulted, but I don't get why. Also, it's not helpful.

No one believes I'm an expert in anything. I don't either. I'm not trying to school anyone. But I understood that the main cause of wear in carbon brakes (unlike steel brakes) is number_of_applications, not total_energy_of_stopping. I believe this because the IATA says so (and lots of other people too). Do you disagree with them? If so, how come? I'm here to be educated.

Also, I like the personal experience stories. But not the insults.

You're not being insulted. You're being insulting. There's a difference.

Nope. You're reading things I never wrote. No insult was written.

Peace

kitplane01 wrote:

747Whale wrote:

kitplane01 wrote:

I get I'm being insulted, but I don't get why. Also, it's not helpful.

No one believes I'm an expert in anything. I don't either. I'm not trying to school anyone. But I understood that the main cause of wear in carbon brakes (unlike steel brakes) is number_of_applications, not total_energy_of_stopping. I believe this because the IATA says so (and lots of other people too). Do you disagree with them? If so, how come? I'm here to be educated.

Also, I like the personal experience stories. But not the insults.

You're not being insulted. You're being insulting. There's a difference.

Nope. You're reading things I never wrote. No insult was written.

Peace

Most forum members come on here to share their enthusiasm for aviation, ask questions, put forward opinions and it’s generally an agreeable back and forth


Your question is an interesting one, it doesn’t matter what experience you have
there’s no reason for it to be treated with disrespect, let alone contempt


Whale is a new member who has endless, long winded opinions on anything and everything, if you dont agree with him or call him out when he’s wrong or makes
things up he will insult and belittle you


It’s classic bully behavior, nothing to do with you, I don’t usually respond to his posts but I see him going after other members all the time, I would suggest ignoring him as I usually do and just interact with the rest of us

Boeing has come with an interesting solution to reduce brake wear on the 787.

If brakes pedals are pressed below certain speed during taxi (30 or 70 Kt depending if it’s -8 or -9), only two out of four brakes on each bogie activate. On a subsequent pedal application they alternate, ie the other two brakes activate, while previous pair remains released.

This way taxi brake wear is reduced by half. In case of harder pedal activation, or at higher speeds, all four brakes activate on each bogie.

Check this article out, lots of cool info in there: http://code7700.com/carbon-carbon_brakes.htm

thepinkmachine wrote:

Boeing has come with an interesting solution to reduce brake wear on the 787.

If brakes pedals are pressed below certain speed during taxi (30 or 70 Kt depending if it’s -8 or -9), only two out of four brakes on each bogie activate. On a subsequent pedal application they alternate, ie the other two brakes activate, while previous pair remains released.

This way taxi brake wear is reduced by half. In case of harder pedal activation, or at higher speeds, all four brakes activate on each bogie.

Thanks for posting this. I was about to ask, "has anyone thought of alternating the brakes applied?"

LH707330 wrote:

Thanks for posting this. I was about to ask, "has anyone thought of alternating the brakes applied?"

Yup, it’s a pretty neat solution and a relatively simple one. Mind you, 787 brakes are all electric. I wonder if alternating brakes could easily be introduced on a traditional hydraulic brake assembly.

In addition to the link above on how carbon brakes work, there’s a pretty good video on the subject on YouTube:
https://youtu.be/SG4Aw5BujEU

thepinkmachine wrote:

LH707330 wrote:

Thanks for posting this. I was about to ask, "has anyone thought of alternating the brakes applied?"

Yup, it’s a pretty neat solution and a relatively simple one. Mind you, 787 brakes are all electric. I wonder if alternating brakes could easily be introduced on a traditional hydraulic brake assembly.

In addition to the link above on how carbon brakes work, there’s a pretty good video on the subject on YouTube:
https://youtu.be/SG4Aw5BujEU

I was thinking about that too, I'm not sure how easy it would be to make the hydraulic brake designs only apply pressure to one pair of wheels.

thepinkmachine wrote:

Boeing has come with an interesting solution to reduce brake wear on the 787.

If brakes pedals are pressed below certain speed during taxi (30 or 70 Kt depending if it’s -8 or -9), only two out of four brakes on each bogie activate. On a subsequent pedal application they alternate, ie the other two brakes activate, while previous pair remains released.

This way taxi brake wear is reduced by half. In case of harder pedal activation, or at higher speeds, all four brakes activate on each bogie.

I think the 777 has a similar system

kitplane01 wrote:

I understand that normal metal brakes experience wear as a function of stopping power. Stopping from high speed causes more wear than normal taxiing. I also understand that carbon brakes experience wear more as a function of number of applications. Every time you engage carbon brakes, you're putting wear into the brakes.

Suppose a plane had both kinds. Then on low speed braking (taxiing), you could use only the metal brakes, but on high speed braking (landing) you could use both. You would get the advantage of light weight from the carbon brakes, and less wear from the metal brakes.

To make things even better, put metal brakes on the nose wheels and carbon brakes on the mains. Now you also have more total stopping power. Since the nose wheel brakes are taking some of the load, the main wheel brakes could be lighter. (I do understand this increases weight/complexity somewhat)

Has any plane ever mixed brake types?

Carbon Brakes weigh 30% less than steel brakes and get twice as many landings!! Why would you want to use a heavier Brake and carry more Zero Fuel Weight?
If that makes sense to you? Then see how many guys agree with you because I for one Do NOT! Many airlines are dumping Steel brakes of they can.

thepinkmachine wrote:

Boeing has come with an interesting solution to reduce brake wear on the 787.

If brakes pedals are pressed below certain speed during taxi (30 or 70 Kt depending if it’s -8 or -9), only two out of four brakes on each bogie activate. On a subsequent pedal application they alternate, ie the other two brakes activate, while previous pair remains released.

This way taxi brake wear is reduced by half. In case of harder pedal activation, or at higher speeds, all four brakes activate on each bogie.

That's a clever idea. Thanks for posting. Taught me something new.

strfyr51 wrote:

kitplane01 wrote:

I understand that normal metal brakes experience wear as a function of stopping power. Stopping from high speed causes more wear than normal taxiing. I also understand that carbon brakes experience wear more as a function of number of applications. Every time you engage carbon brakes, you're putting wear into the brakes.

Suppose a plane had both kinds. Then on low speed braking (taxiing), you could use only the metal brakes, but on high speed braking (landing) you could use both. You would get the advantage of light weight from the carbon brakes, and less wear from the metal brakes.

To make things even better, put metal brakes on the nose wheels and carbon brakes on the mains. Now you also have more total stopping power. Since the nose wheel brakes are taking some of the load, the main wheel brakes could be lighter. (I do understand this increases weight/complexity somewhat)

Has any plane ever mixed brake types?

Carbon Brakes weigh 30% less than steel brakes and get twice as many landings!! Why would you want to use a heavier Brake and carry more Zero Fuel Weight?
If that makes sense to you? Then see how many guys agree with you because I for one Do NOT! Many airlines are dumping Steel brakes of they can.

My idea was that since steel and carbon brakes have different wear causes, and since brakes are expensive, one might optimize costs by using both. But the alternate brake application idea also reduces the same problem, and for electric brakes needs only software and not additional hardware/weight, so ....

Basically, I asked about my idea and found out someone already had a better solution. Cool .. I get to learn.

what a common time for cooling brakes? i understand its very depends on temp and alt

Just some thoughts having gone through the steel brake vs. carbon brake change over in the 1980's:

1. Any weight loss/gain on an aircraft is negligible unless the flight is at cruise level for more than 3 hours. Good for widebodies but most US narrowbody flights are less than 3 hours at cruise though this is changing with the MAX and NEO's. Climb/Descent portion of the flight doesn't see a noticeable fuel savings with changes in weight.

2. With carbon brakes, there is usually a 2x increase in landings/heat pack before replacement but the cost was over 4x higher than a steel brake heat pack replacement. The carbon disks now have a refurbishment process but its only good for one run so then you are installing new carbon rotor and stator disks. Fabrication of the carbon-carbon matrix disks is an extremely expensive and time consuming process. Repair costs are closer to a steel brake but is still more than 2x.

3. Early carbon brakes were notorious for low speed grabbing at the gate. As you came up to the stop point at the gate, the brakes were applied but without an immediate feedback of slowing down. More brake pressure was applied and then the brakes abruptly stopped the airplane. Changes were made to the brake metering valve pressure application at slow speed. Carbon brakes are more prone to freezing but operational changes have fixed this issue.

4. Changing from steel to carbon or in reverse requires the re-certification of the aircraft type. Extremely expensive - it was over $1M US some 30 years ago for which the ROI was too long.

5. Carbon brakes operate at a higher temperature for efficiency and there are limits to the high strength steel (HSS) used in the landing gear that must be maintained. HSS loses the surface compressive layer affect of shot peening around 500 deg. F. which reduces the fatigue life of the part. Also, the coatings on the axle have to change as cadmium plating will also melt at this temperature and liquid metal diffusion of the cadmium into the steel causes the part to crack. Sermatel and Zinc-Nickel plating are ways to protect the axle and have the cadmium plating removed from the high temperature areas. The use of stainless steel sleeves with baffling reduces the temperatures to the axle. The CRJ series and A380 use temp indicators on the axle to visually check if the temperature limit has been exceeded.

6. A mix of carbon and steel disks would not be effective as currently there is only a single set of pistons and you would need to build effectively 2 brakes into one with 2 sets of hydraulic pistons - too expensive and possibly more required maintenance costs associated.

7. The newer technology 'brake-by-wire' electric brakes seem to be the way the industry is moving. Lightweight, including no hydraulic lines on the landing gear and a small piston head that contains electric actuators which eliminates the large hydraulic brake crown which lessens the NDT requirements at overhaul so the cost per landing will come down over time.

Future braking will be electric at low speeds. Taxi under your own power, no pushback, delayed engine starts, fuel savings and regenerative braking similar to your Tesla. No way steel brakes will return.

https://www.safran-landing-systems.com/ ... -taxiing-0
https://www.flightglobal.com/news/artic ... co-324327/