GOT
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Hot Brakes Delays Departure - Preventable?

Mon Aug 08, 2011 5:35 pm

Hi all!

Pardon my ignorance if I missed something obvious, but here goes: I was on AF347 YUL-CDG on the A380 last Friday, August 6th. After being delayed due to late incoming aircraft we finally left gate about an hour late. After taxiing out to runway 24L and waiting for what seemed like a pretty long time, we lined up, waited some more and finally started rolling. However, we never really gained speed and leisurely rolled down the runway, exiting about half way down, then parking somewhere along the crosswind runway. The captain came on the PA, announcing that the brakes were hot from the arrival and hadn't cooled of properly in the heat of Montreal, so we would have to wait another 25 minutes for them to cool off before another attempt. Second time around, all went well and we left around 2 hrs late.

What got me thinking though: How common is this? Would the brakes have been excessively used during landing, or can this result from a 'normal' landing? Why wasn't this noticed earlier? Why did we have to go all the way to the runway and delay planes behind us? Where pilots hoping that they would cool enough on the way? I don't know the exact temperature in Montreal that day, but the plane spent well over 2 hours at gate, wouldn't this usually be enough?

Anything that enlighten the chain of things behind this is appreciated!

Best regards,
Robert
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shamrock137
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Hot Brakes Delays Departure - Preventable?

Mon Aug 08, 2011 10:19 pm

The issue of brake temperature is an important concern to pilots. Hot brakes can severely decrease braking performance in the event of a rejected takeoff. It is quite possible that even though the aircraft was on the ground for 2 hours, the brakes were not able to completely cool off. In addition, a long taxi time as you mentioned could easily heat up the brakes. When the aircraft is taxiing for takeoff, it is at its heaviest, and a long taxi can be tough on the brakes. Sometimes the pilots can request fans to be placed on the landing gear while the aircraft is at the gate to speed up the cooling process. In your case, perhaps the airport did not have the proper equipment for the A380, or other aircraft were already using it.
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contrails15
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Hot Brakes Delays Departure - Preventable?

Mon Aug 08, 2011 10:53 pm

Brake fans being on at the gate wouldn't be enough to decrease the temp of the brakes enough? 2 hour ground time seems like a lot of time.
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Maverick623
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Hot Brakes Delays Departure - Preventable?

Mon Aug 08, 2011 11:59 pm

Quoting GOT (Thread starter):
heat of Montreal

     

Sorry, but being from PHX....  
Quoting GOT (Thread starter):
How common is this?

Not common, but certainly not unheard of.

Quoting GOT (Thread starter):
Would the brakes have been excessively used during landing, or can this result from a 'normal' landing?

Both.

Quoting GOT (Thread starter):
Why wasn't this noticed earlier?

Who says it wasn't?

Quoting GOT (Thread starter):
Why did we have to go all the way to the runway and delay planes behind us?

I'm sure you only delayed the planes behind you a few minutes. Besides, maybe the temp was borderline and the pilots thought they'd cool off during taxi.

Quoting GOT (Thread starter):
the plane spent well over 2 hours at gate, wouldn't this usually be enough?

It depends. It's not just about how hot the brakes are, but how quickly they can dissipate the heat. Being parked in a warm area with little air flow can increase the cool-down time. Maybe they forgot to turn on the brake fans (it happens).

Also, as said, taxiing with a fully loaded plane can be hard on the brakes.
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26point2
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Hot Brakes Delays Departure - Preventable?

Tue Aug 09, 2011 1:52 am

Carbon brakes such as these continue to heat up after brake use is discontinued.

As mentioned hot brakes are not as effective but also putting hot brakes into the wheel-well is not a great idea either.

We are prohibited from taking off if brake temp exceeds 425C on the type I fly.
 
ALTF4
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Hot Brakes Delays Departure - Preventable?

Tue Aug 09, 2011 7:42 pm

Quoting 26point2 (Reply 4):
We are prohibited from taking off if brake temp exceeds 425C on the type I fly.

Thinking about it, it is only logical that the brakes heat up that hot... but... dang that is pretty hot! In cold months, do ramp rats volunteer to do duties in the vicinity of the wheels so they get some radiant heat?  
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contrails15
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Hot Brakes Delays Departure - Preventable?

Tue Aug 09, 2011 8:17 pm

Quoting ALTF4 (Reply 5):
In cold months, do ramp rats volunteer to do duties in the vicinity of the wheels so they get some radiant heat?  

We hang out by the heat exhaust vents under the belly. Brake blowers when the vents aren't pumping out hot air. Great way to dry off too.
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GOT
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Hot Brakes Delays Departure - Preventable?

Wed Aug 10, 2011 3:14 pm

Thanks for all the answers, guess I'll never know exactly what happend...

Quoting Maverick623 (Reply 3):
Quoting GOT (Thread starter):
heat of Montreal



Sorry, but being from PHX....

Pilot's word, not mine  
Quoting Maverick623 (Reply 3):
Quoting GOT (Thread starter):
Why wasn't this noticed earlier?

Who says it wasn't?

Quoting GOT (Thread starter):
Why did we have to go all the way to the runway and delay planes behind us?

I'm sure you only delayed the planes behind you a few minutes. Besides, maybe the temp was borderline and the pilots thought they'd cool off during taxi.

The way I see it, if it was borderline it shouldn't have taken another 25 minutes to cool off. But what do I know really :-P

The point about the plane being heavy during taxi is good though, thanks everyone!

/Robert
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rfields5421
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Hot Brakes Delays Departure - Preventable?

Wed Aug 10, 2011 4:02 pm

Quoting GOT (Reply 7):
The way I see it, if it was borderline it shouldn't have taken another 25 minutes to cool off.

It was probably not over the limit when the taxi started, but the temps increased during the taxi. The pilots thought it would cool off enough when they got into the line for takeoff, but if the temps went up a couple degrees over the limit, the plane could not do a legal takeoff and could not block access to the runway for other aircraft ready to takeoff.

The short taxi down the runway, braking again and turning off would heat the brakes again.

25 minutes was probably needed for the brakes to cool enough below the go/no go temp - so the pilots could be sure the additional braking necessary to get to and lined up on the runway did not raise the temps too high.

They had already tried to go with the temps closer to the borderline and been wrong, so they would probably want the brakes cooler than the last taxi attempt so they did not repeat the failure to takeoff again.
 
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longhauler
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Hot Brakes Delays Departure - Preventable?

Wed Aug 10, 2011 5:13 pm

Quoting Maverick623 (Reply 3):
Sorry, but being from PHX....

I flew a YYZ-PHX-YYZ flight a few weeks ago. The temperature in eastern Canada YYZ/YOW/YUL was hotter at 41C than PHX, which was 36C when we left. It does happen! And trust me, it sure as hell wasn't a "dry heat".

Quoting 26point2 (Reply 4):
Carbon brakes such as these continue to heat up after brake use is discontinued.

As mentioned hot brakes are not as effective but also putting hot brakes into the wheel-well is not a great idea either.

Airbus recently issued some new directives on this issue. As, in fact carbon brakes are MORE effective when they are hot, unlike steel brakes. The bigger issue, is as you state that, you don't really want to put very hot brakes into the wheel well.

While the max brake temp for take-off still stands, it would appear that the issue is not the performance for a rejected take-off. The "hot brake" ECAM warning is inhibited during take-off, so Airbus now suggests if the warning appears after take-off, AND the gear is still down AND if performance requirements permit ... leave the gear down to cool. Then .. they state "retract the gear with an engine failure".

My guess therefore is the max brake temperature for takeoff is a performance restriction after take-off, not for a rejected take-off.
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HAWK21M
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RE: Hot Brakes Delays Departure - Preventable?

Sat Aug 27, 2011 9:23 pm

I've noticed an IL62 heated MLG wheels being sprayed with Steam/water......Is that normal on such a type?.
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qslinger
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RE: Hot Brakes Delays Departure - Preventable?

Sat Sep 03, 2011 11:33 pm

What about hosing the brakes down with cold water for quicker cool down...or even using a fire engine to come to a remote stand to spray water to cool them down? Beats having to go back to the gates for brake cooling?
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roseflyer
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RE: Hot Brakes Delays Departure - Preventable?

Sun Sep 04, 2011 12:06 am

Carbon fiber brakes have an interesting characteristic. They wear faster during taxi and light application then when on hard application during landing. Taxiing will heat them up and cause material to wear. When at high temps the brakes weld particles that flake off back together. Steel brakes are the opposite, but the only new build large jets with steel brakes are 737s for airlines not taking the carbon brake option.

Quoting GOT (Reply 7):
The way I see it, if it was borderline it shouldn't have taken another 25 minutes to cool off. But what do I know really :-P

Airplanes don't operate on borderlines. It's either ok or not. The same is true for visibility, crosswinds, MTOW, etc. Sure there isn't a big change in a few degrees, but if it is certified for a certain temp, then that is the max.
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Max Q
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RE: Hot Brakes Delays Departure - Preventable?

Sun Sep 04, 2011 12:48 am

Quoting longhauler (Reply 9):

Airbus recently issued some new directives on this issue. As, in fact carbon brakes are MORE effective when they are hot, unlike steel brakes. The bigger issue, is as you state that, you don't really want to put very hot brakes into the wheel well.

This is a common misconception about Carbon Brakes.



The reality is that Carbon Brakes WEAR better / less when they are hot. They work just fine at lower temperatures.




This is one of the reasons that the use of idle reverse has been so widely promoted and Pilots have misunderstood why, it is to optimally heat the carbon Brakes so they last longer.




And while we are on the subject of hot brakes, if the A380 in question had four reversers and used max on the previous landing you most likely would not have had that delay !
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rfields5421
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RE: Hot Brakes Delays Departure - Preventable?

Sun Sep 04, 2011 1:25 pm

Quoting qslinger (Reply 11):
What about hosing the brakes down with cold water for quicker cool down...or even using a fire engine to come to a remote stand to spray water to cool them down? Beats having to go back to the gates for brake cooling?

At the temps involved and the way the parts around the brakes and wheels are constructed - spraying cold water on overheated systems can possibly cause fractures of the metal parts due to unequal cooling.

So rather than waiting for a while for the brakes to cool, the passengers could easily have to wait several hours while a wheel is replaced, or a landing gear part is examined for fractures.

Pooring water on hot parts of various different metals and other materials to cool it is a last resort.
 
Viscount724
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RE: Hot Brakes Delays Departure - Preventable?

Sun Sep 04, 2011 7:51 pm

Noted following recent (August 31) "hot brakes" item involving two departing aircraft at YYC, from the Transport Canada daily incident reports. Departing from runway 34 at YYC involves an approximate 2 mile taxi from the terminal.

JZA 316, Air Canada Jazz CRJ-200 was overshot by Calgary Tower at 2 NM final for Runway 34 due to KLM 678, a KLM A330-200, in position unable to depart due to hot brakes. KLM 678 taxied ahead and exited right on Runway 25. Subsequently, the crew of ACA 140, an Air Canada A320, advised on reaching Runway 34 that they were also unable to depart due to hot brakes. WJA 255 and JZA 555 were both caught behind ACA 140 and KLM 678 blocking Taxiway Charlie and were delayed approximately 15 minutes until they could get past ACA 140 and KLM 678 at the holding bay.

[Edited 2011-09-04 12:51:36]
 
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HAWK21M
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RE: Hot Brakes Delays Departure - Preventable?

Sun Sep 04, 2011 7:53 pm

Quoting qslinger (Reply 11):
What about hosing the brakes down with cold water for quicker cool down...or even using a fire engine to come to a remote stand to spray water to cool them down? Beats having to go back to the gates for brake cooling?

Would that not cause a shock cooling to the brake housing & crack it?.
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MD11Engineer
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RE: Hot Brakes Delays Departure - Preventable?

Tue Sep 06, 2011 1:52 pm

Quoting HAWK21M (Reply 16):
Quoting qslinger (Reply 11):
What about hosing the brakes down with cold water for quicker cool down...or even using a fire engine to come to a remote stand to spray water to cool them down? Beats having to go back to the gates for brake cooling?

Would that not cause a shock cooling to the brake housing & crack it?.

Yes. It is the last resort by the firefighters to prevent a tyre fire, but afterwards you can remove the brake and wheel and send it for inspection / overhaul. You´d also have to inspect the axle for damage.

BTW, we had a lot of issues with carbon brakes due to catalytic oxydation, materials like anti-icing fluid (both for runways and aircraft) seem to interact with the hot carbon brakes that the brake discs go soft and literally crumble apart. We had to change a lot of brakes due to this on our airline alone and the brake overhaul shop we are working with had issues getting enough new brake discs from the manufacturers, because other airlines had the same issues.

Jan

[Edited 2011-09-06 06:54:24]
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HAWK21M
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RE: Hot Brakes Delays Departure - Preventable?

Tue Sep 06, 2011 5:14 pm

Quoting MD11Engineer (Reply 17):
Yes. It is the last resort by the firefighters to prevent a tyre fire, but afterwards you can remove the brake and wheel and send it for inspection / overhaul. You´d also have to inspect the axle for damage.

Water on the hot tire could be more serious than on a hot brake for obvious reasons.....
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MD11Engineer
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RE: Hot Brakes Delays Departure - Preventable?

Tue Sep 06, 2011 6:48 pm

Quoting HAWK21M (Reply 18):
Quoting MD11Engineer (Reply 17):
Yes. It is the last resort by the firefighters to prevent a tyre fire, but afterwards you can remove the brake and wheel and send it for inspection / overhaul. You´d also have to inspect the axle for damage.

Water on the hot tire could be more serious than on a hot brake for obvious reasons.....

The firefighters will approach the overheated wheel from either front or back, never from the side and will use a spray nozzle, not a sharp jet of water.

Jan
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buckfifty
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RE: Hot Brakes Delays Departure - Preventable?

Wed Sep 07, 2011 9:53 am

The other solution is to install brake fans. Wonderful devices these are, and are great for aircraft that are constantly doing short turnarounds. Not sure how much they weigh, but they are especially useful going to ports where they don't have any (or have poor) brake cooling equipment.

Which reminds me, sometimes when we go to India, they use ground air conditioning carts to cool the brakes for us.
 
shnoob940
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RE: Hot Brakes Delays Departure - Preventable?

Wed Sep 07, 2011 10:34 am

Quoting Viscount724 (Reply 15):
unable to depart due to hot brakes

Excuse me for being stupid, but couldn't they just leave the gear down for a minute or two after takeoff, and the wind rushing past would cool down the brakes?
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zeke
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RE: Hot Brakes Delays Departure - Preventable?

Wed Sep 07, 2011 10:54 am

Quoting GOT (Thread starter):
What got me thinking though: How common is this?

Very, almost every landing I will have hot brakes, i.e. indicating above 300 deg C after I get to the gate. That is the limit for us to takeoff.

Quoting GOT (Thread starter):
Would the brakes have been excessively used during landing, or can this result from a 'normal' landing?

Normal.

Quoting GOT (Thread starter):
Why wasn't this noticed earlier? Why did we have to go all the way to the runway and delay planes behind us?

As a rule of thumb, the brakes will cool in excess of 1 degree per minute, if I see the brakes at 400 deg C and 40 minutes to pushback I know in most cases I will be okay.

Quoting GOT (Thread starter):
I don't know the exact temperature in Montreal that day, but the plane spent well over 2 hours at gate, wouldn't this usually be enough?

If you have a downhill taxi to takeoff, or need numerous brake applications while taxiing, the temps will go up. For departure the aircraft is at a higher weight than landing.

Quoting buckfifty (Reply 20):
The other solution is to install brake fans.

Not practical on a long haul aircraft, the fuel cost would be too high.

Quoting Shnoob940 (Reply 21):
Excuse me for being stupid, but couldn't they just leave the gear down for a minute or two after takeoff, and the wind rushing past would cool down the brakes?

Need the brake temps to be low enough to meet the performance requirements on takeoff.
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rfields5421
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RE: Hot Brakes Delays Departure - Preventable?

Wed Sep 07, 2011 2:01 pm

Quoting Shnoob940 (Reply 21):
Excuse me for being stupid, but couldn't they just leave the gear down for a minute or two after takeoff, and the wind rushing past would cool down the brakes?

Excessively hot brakes won't stop the aircraft in normal distances if the takeoff has to be aborted. If the brakes exceed the maximum operating temp, then all the takeoff distance and speed calculations are wrong. The aircraft probably would not be legal for takeoff at all on many airports, or near maximum weights.
 
citationjet
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RE: Hot Brakes Delays Departure - Preventable?

Wed Sep 07, 2011 7:05 pm

Quoting Shnoob940 (Reply 21):
Excuse me for being stupid, but couldn't they just leave the gear down for a minute or two after takeoff, and the wind rushing past would cool down the brakes?

You will need the brakes to work in case you DON'T takeoff; in other words if the takeoff is aborted.
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RE: Hot Brakes Delays Departure - Preventable?

Thu Sep 08, 2011 8:33 am

Quoting zeke (Reply 22):
Need the brake temps to be low enough to meet the performance requirements on takeoff.
Quoting rfields5421 (Reply 23):
Quoting CitationJet (Reply 24):

Ok, I see now.
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HAWK21M
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RE: Hot Brakes Delays Departure - Preventable?

Thu Sep 08, 2011 9:54 am

Quoting MD11Engineer (Reply 19):

The firefighters will approach the overheated wheel from either front or back, never from the side and will use a spray nozzle, not a sharp jet of water.

Wouldn't Wheel shattering create uneeded FOD & Aircraft damage.
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c172akula
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RE: Hot Brakes Delays Departure - Preventable?

Thu Sep 08, 2011 6:54 pm

Quoting HAWK21M (Reply 16):
Noted following recent (August 31) "hot brakes" item involving two departing aircraft at YYC, from the Transport Canada daily incident reports. Departing from runway 34 at YYC involves an approximate 2 mile taxi from the terminal.

I was looking over the CADOR reports today and that one caught my eye, then I come across this thread and new the answer right away. That long taxi combined with the hot weather (for YYC) that we have been having had to have caused that.
 
bonusonus
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RE: Hot Brakes Delays Departure - Preventable?

Thu Sep 08, 2011 9:55 pm

Quoting HAWK21M (Reply 16):

Would that not cause a shock cooling to the brake housing & crack it?.

Yes, this would definitely be bad for the components, and likely risk damaging them.
However, spraying a fine mist of water along with the cooling air would probably be more effective without running the risk of cooling the components fast enough to cause fracture.

Brakes have to be able to tolerate some water at hot temps, considering they are used in an all-weather environment.
 
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HAWK21M
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RE: Hot Brakes Delays Departure - Preventable?

Fri Sep 09, 2011 9:55 am

On the B737/757s the use of water is def not permitted for cooling purposes......
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Ward86IND
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RE: Hot Brakes Delays Departure - Preventable?

Fri Sep 09, 2011 9:57 am

Earlier this summer I was on a DAL A320 out of IND and we actually extended the gear in the middle of the climb for about 2 minutes to cool the brakes down. The captain said hot brakes are very common this time of year. I wonder why we didn't just leave the gear down on departure instead of waiting a good 10 minutes after gear retraction. Outside temp was 96 degrees in IND.
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Starlionblue
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RE: Hot Brakes Delays Departure - Preventable?

Fri Sep 09, 2011 10:16 am

Quoting Ward86IND (Reply 30):
I wonder why we didn't just leave the gear down on departure instead of waiting a good 10 minutes after gear retraction.

Performance reasons?
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tdscanuck
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RE: Hot Brakes Delays Departure - Preventable?

Fri Sep 09, 2011 1:59 pm

Quoting Ward86IND (Reply 30):
I wonder why we didn't just leave the gear down on departure instead of waiting a good 10 minutes after gear retraction.

The climb calculations for the takeoff assume gear up shortly after liftoff. If you leave the gear down there is no guarantee that you can achieve the FAR-required climb gradient if an engine fails. Once you're up and away that requirement goes away and the crew can drop the gear back down.

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RE: Hot Brakes Delays Departure - Preventable?

Fri Sep 16, 2011 8:24 pm

There's been a lot of taxiway work at YUL over the summer, with various taxiways closed at one time or another, sometimes with serious consequences on ground traffic. I've sat in an A330 just off the runway for 20 minutes because there was only one way to/from the apron that day and we needed to wait for outbound traffic to clear before proceeding to the terminal. The wait off the gate on the way out an hour later was well over 60 minutes.

There's a lot more taxiing and sitting on the brakes going on than usual, that certainly can't help brake temperature.
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Kaiarahi
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RE: Hot Brakes Delays Departure - Preventable?

Sat Sep 17, 2011 3:31 pm

Quoting Max Q (Reply 13):
if the A380 in question had four reversers and used max on the previous landing you most likely would not have had that delay

1. I know from other threads that you think T/Rs are the answer to everything, including a maiden's prayer, but I'm wondering if you have the landing performance numbers for the A380 plus calculation of the additional numbers for additional reversers to back that up?

2. One of the reasons, often repeated on these threads, that the A380 does not have outboard T/Rs is the risk of FOD damage at many airports because of the span.
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HAWK21M
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RE: Hot Brakes Delays Departure - Preventable?

Sun Sep 18, 2011 12:33 pm

Quoting blueflyer (Reply 33):
There's a lot more taxiing and sitting on the brakes going on than usual, that certainly can't help brake temperature.

Another contributer is those hurrying Crew that taxi way beyond the required speeds.
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DrEsteban
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RE: Hot Brakes Delays Departure - Preventable?

Sun Sep 18, 2011 11:40 pm

Interesting fact; one brake application on an A320 equals approx $80 in brake wear. Hence the importance of correct braking technique, ie don't 'ride' the brakes!!!
 
rfields5421
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RE: Hot Brakes Delays Departure - Preventable?

Mon Sep 19, 2011 4:17 pm

Quoting Max Q (Reply 13):
if the A380 in question had four reversers and used max on the previous landing you most likely would not have had that delay !

Uh?

This was a delay at takeoff.

If the aircraft had excessively hot brakes from the previous landing - it would not have left the gate. The issue in this case was the hot brakes caused by taxi, not landing.
 
don
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RE: Hot Brakes Delays Departure - Preventable?

Tue Sep 20, 2011 4:16 pm



JAL uses these external brake cooling fans, especially on the freighters on which you always land with heavy landing weights.
 
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HAWK21M
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RE: Hot Brakes Delays Departure - Preventable?

Wed Sep 21, 2011 11:21 am

Quoting don (Reply 38):

JAL uses these external brake cooling fans, especially on the freighters on which you always land with heavy landing weights.

Some types have cooling fans as a customer option built into the Wheel.
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longhauler
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RE: Hot Brakes Delays Departure - Preventable?

Wed Sep 21, 2011 12:27 pm

Quoting don (Reply 38):
JAL uses these external brake cooling fans, especially on the freighters on which you always land with heavy landing weights.

Wow, that is a great rig. I have copied the picture and forwarded it to our Flight Ops managers. I could see that being very useful.

Quoting HAWK21M (Reply 39):
Some types have cooling fans as a customer option built into the Wheel.

We had cooling fans on our A321s. But some non-flying manager decided the cost of maintaining them, and the cost of carrying them was too high .... Doh! (A321s are often delayed on fast turns due to hot breaks)

Quoting rfields5421 (Reply 37):
This was a delay at takeoff.

If the aircraft had excessively hot brakes from the previous landing - it would not have left the gate. The issue in this case was the hot brakes caused by taxi, not landing.

It depends where you start. If it is a cold airplane, with brakes at say 25C, they might be 100C by the time you take off. However, if the brakes are hot from the previous landing, and current conditions do not cause a fast cool down, you might be starting your taxi at say 200C. Then with a short taxi, they would be under the maximum of 300C. But add a hot day and a long taxi and they may well be above 300C .... caused by the previous landing.
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HAWK21M
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RE: Hot Brakes Delays Departure - Preventable?

Wed Sep 21, 2011 8:58 pm

Quoting longhauler (Reply 40):
We had cooling fans on our A321s. But some non-flying manager decided the cost of maintaining them, and the cost of carrying them was too high .... Doh! (A321s are often delayed on fast turns due to hot breaks)

Exactly the reason....Reliability of the fans & costs due to the added weight.
I may not win often, but I damn well never lose!!! ;)

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