Pilot taxiing question

[Astro14]

Yes it was. The pilot had said en route thst we were 3rd in line to depart so there wasnt a lot of stop and go on way out there. Taxi speed didnt seem all that fast, pretty normal. My thought at the time, and I told my wife this, if brakes are hot just from taxiing, what about when we actually land this thing? That’s what made me think when we finally landed and got to gate he had to let them cool before trying to park it.

The max temp for brakes is about 600C. I’ll pause while you consider the melting point of lead, which is just over 300C. 300C is the temperature limit (as mentioned previously) for takeoff.

So, yes, you want to take off with brakes that are just a bit cooler than the tip of a soldering iron. And on landing, on some days, they will get quite a bit hotter than 300C. As others have said, 450C is not uncommon if you have to use them hard on landing.

The real reason for that temperature limit on takeoff is the potential for a rejected takeoff at maximum speed.

In the event of a maximum effort stop, at the highest potential speed, those brakes will get heated by the kinetic energy of the airplane. Not just “heated up a bit” - the steel parts will glow red hot.

So, you don’t want to begin that rejected takeoff with brakes that are already too hot - it wouldn’t be good.

 

[97prizm]

Carbon brakes are standard on every aircraft we have, including the 757 and 767, the oldest in our fleet. They’re not that new.

I have had hot brakes in LAS - long story, when I was an FO on the A-320 involving a bleed overheat (that wasn’t a bleed overheat, but a leading edge device sensor that was getting cooked in the sun), 115F on the ramp, a quick return to gate, and brakes that weren’t cooled prior to the next taxi out, and a quick taxi out with a hot airplane.

It was not a good day. Already hot in the back - having to wait for takeoff - all while the packs (the AC compressors) could not keep up with a plane full of people on that hot, hot day.

Apparently the B 757 and 767 had steel or cast iron brakes but carbon was an option. The Dreamliner, according to some articles that I read was the first with electromechanical brakes instead of hydraulic. I would think some type of back up system would be in place as well.

 

[Astro14]

Apparently the B 757 and 767 had steel or cast iron brakes but carbon was an option. The Dreamliner, according to some articles that I read was the first with electromechanical brakes instead of hydraulic. I would think some type of back up system would be in place as well.

I don’t know when we fitted carbon brakes to our 757/767 fleet, or if they were delivered with them (and I suspect it was delivered) but every airplane we operate has carbon brakes. I believe that they were delivered with them, but perhaps they were retrofitted. Some of our 767-300s are nearing 30 years old.

There are a lot of back-ups in the brakes, but there is only one set of friction materials and calipers on each wheel.

The back-ups come from a primary hydraulic system to provide pressure. A back-up hydraulic system to provide pressure. And an accumulator that stores hydraulic pressure in case the first two systems have failed.

 

[kschachn]

A little off topic but one of my favorite videos. I have one of the MD-80 under a similar test:

 

[Just a civilian pilot]

While I haven’t heard of pilots having to wait for the brakes to cool before take off, I have heard of a few cases where pilots took off close to the 300 c limit and receiving a “ brakes hot” caution a few minutes after take off causing them to have to lower the landing gear to cool to 300 c before retracting ( and slowing from 250 knots to 220 knots to not exceed the landing gear door speed limit ). This is to prevent a wheel well fire if any hydraulic fluid leaks.

The “ brakes hot “ amber caution is inhibited on take off from 80 knots until liftoff because Airbus doesn’t want pilots trying to stop just because brakes are above 300 c. Pilots would get the alert right after liftoff in those cases.

 

[Jimmy_Russells]

Very interesting thread

 

[Just a civilian pilot]

The only time the brakes need a LONG time to cool on the Airbus is when one of the brake temperature indicators isn’t working ( rare, but I have seen it , maybe, about 5 times in my career ).

If a crew has an aircraft with this defect on the aircraft, they need to consult the MEL ( minimum equipment list ) and refer to graphs ( landing weight, speed at which pilots applied brakes - not the landing speed - , whether reverse thrust was used, OAT, altitude, runway slope ) to determine how long they will have to wait at the gate before pushing back ( or the next crew will have to check ). The penalty for an inoperative brake temperature indication is very high and can require brake cooling times over 1:15 in some cases. Use of airport brake fans isn’t allowed in the calculations.

This drives me NUTS…..pilots not properly interpreting the MEL. If you ever fly an Airbus as a pilot, please remember that it’s not your approach/landing speed that you check in the graph, it’s the speed on the runway that you first applied brakes ( only when not using auto brake for landing ….if you land with auto brake, then your landing speed is what you enter the chart at ).

A A321 in our fleet was flying around with this MEL this summer and pilots not dealing with this issue caused unnecessary delays landing with auto brake ( talking about an 11,000 runway here ) when they could safely land with no auto brake ( kicks in almost right away ) and apply manual brakes at a much lower speed.

I took this Fin from another crew down south ( airplane swap ) and had to wait 1:30 for the brakes to cool when it could have been as low as 30 minutes ( 11,000 runway ). I landed and gave the same plane to the next crew with only a 30 minute brake cooling required.

Read the MEL carefully.

 

[E365]

No problem on the 737. No brake temp sensors!

 

[Astro14]

The 767-300 is sensitive to getting hot brakes. I think the 767-400 got better brakes - it certainly has bigger main tires. Part of the problem is the engine cool down requirement. It's 2 minutes on the Rolls-Royce RB-211 and 2 minutes on the GE CF-6 but it is 5 minutes on the PW 4056 on the 767-300. So, while I like to shut one down for taxi-in, the 767-300 makes that harder, and takes more braking after landing.

So, 767-300., most days, autobrakes 2 or 3. Cold rainy day in London, or Newark, no worries.

But a hot summer day in Denver? Autobrakes off, max reverse, let it roll for a while, then get on the brakes gently, with one smooth continuous application, to bring it from about 80 knots to taxi speed. Barely warming up the brakes.

Land with auto 2 or 3 on that same day, and you'll have hot brakes by the time you get to the gate.

All a matter of technique, of course, but some techniques work better than others...

 

[Just a civilian pilot]

No problem on the 737. No brake temp sensors!

Hey, we don’t have MCAS so we have to have something to complicate things on the Airbus