Brakes

[chinny]

Question-if you have a brake temp gauge in the cockpit-and you have a brake cooling page in your QRH-what are the rules on following the advice given-forget all the mumbo jumbo of the legal issues of the QRH and the implictions-just,what would you do:bored::confused:

Thanks

VTSP
chinny

[Pugilistic Animus]

If you have a brake temperature gauge use that in accordance with the published QRH limitations---if it becomes a MEL item then you use the QRH item follow the Guidance WRT to Brake cooling times


PA

[chinny]

PA

so you advise to wait for the prescribed cooling period then proceed.

What about the school of thought that says that brake cooling period is to gauge the total amount of energy that can be absorbed by the brakes in the event of an abort.:hmm: Dont shoot the messanger-i know what i think and what i would do!!!

VTSP
chinny

[Capt Claret]

Use the QRH advice to determine how long it might/should take for the brakes to cool. Go when brake temp gauge indicated required temp is/will be met.

My question. Say the limiting brake temp is 120C, and one has 2 wheels at 90, 1 at 120 and one at 130. Does one average the temps or wait until they're all at/below 120?

[SNS3Guppy]

Brake cooling charts aren't suggestions or guesses. They're technical data to which you should adhere. Les, ther are certainly legal implications; fail to adhere to the data provided and you haven't a leg to stand upon. But the same platform which stipulates you must be legal demands also that you be safe. Be safe by paying close attention to your brake energy and cooling data.

I'm not sure I understand the question. The data is there, use it. Period. It is NOT a suggestion in passing; it's put there to be used and followed.

You don't average the wheel assemblies. If the brake limit is 120, and you have a brake at 130, you have a brake over the limit. Do what must be done; put fan on it, delay the flight, depart with the gear down for the prescribed time period if applicable, etc.

If you start your taxi with a brake that's already borderline, the taxi could put it over. You may have inadequate or assymetrical braking in the event of a rejected takeoff. You may find that you end up with a brake fire, or that the airplane won't stop at the next turn in the taxiway. You may end up with brake damage; an hour delay might save forty thousand dollars in replacement parts. You really don't want a wheel assembly to explode or blow out fuse plugs. You have the data before you; use it.

[Pugilistic Animus]

Chinny:

I'm not 100% sure [like 98%]---that if you have brake temp. gauges then it you don't have to defer to the time limit guidance specified in the AFM---as the temperature is the limiting factor in BE absorption---not time---

However if you have no gauges fitted or it's a MEL'd Item---then you must adhere to the brake cooling times in order to assure that a RTO {especially if actually limited in the RTOW by BE}


Capt Claret---
If I were the skipper I'd wait until All the Brake temps are below limits;)



PA:)

[chinny]

Ok....so a bit more clarrification then.

On Chocks- Brakes temp gauge says 150.BC page says cooling period 35 mins.

which is correct option?

a) brakes off wait 35 mins before taxing.

b) wait til brakes cool to normal operating temp and then taxi.

c) ignore brake cool temps altogether.

All i'm trying to get is the general feeling out there about the right way.As i said before I know what i think but that doesnt make me right!

VTSP
chinny

[Capt Claret]

I don't know how departing with the gear down helps if a brake is over the recommended temp, as opposed to over-temp (too hot). The temp limit in most cases is to ensure sufficient energy absorption in the event of a rejected take-off, so leaving the gear down after take-off won't help unless the brakes are over temp.

For my money, I wouldn't decline to taxi as I've seen brake temps drop 20 degrees or so during taxi on occasions.

Pugilistic Animus, you're probably correct. It'd be nice to have a definitive answer though.

In the Douglas Boeing 717 QRH, the relevant pages are entitled; Takeoff Brake Advisory Information, and, ESTIMATED Brake Cooling Time

From this I take the estimated cooling time chart to be a guide as to how long it should take for the brakes to cool to the required temp, not a mandated time to wait. If there's a temp gauge, surely the point is to use it.

[SNS3Guppy]

The effects of a long taxi vary, but generally increase brake temperatures. Brake use during taxi, and wheel temperature increase from the taxi process don't usually cool the gear.

In my operation, the result of a three mile taxi alone can put brake temps into the red.

Leaving the gear down after takeoff obviously isn't done to prevent taxiing or taking off with high brake temps. It's done when a prolonged taxi has left high temps and when the leg will be short. Likewise, early extention prior to arrival is a useful and often recommended technique for cooling brakes and gear before landing.

Brake temperature is not only a function of remaining stopping power. Clearly the amount energy the brakes can absorb and transform to thermal energy (heat) is limited, and therefore the capability of the brake has it's limit. However, simply because the brake gets hot doesn't mean it quits working. Carbon brakes improve in performance with an increase in temp, up to a point. Organic and semi-metalic experience a decrease in the coefficient of friction as temperature rises, again, up to a point. Each type of brake material has a temperature range at which it's most effective; increase the temp above that point and the brakes effectivess will "fade" or decrease. Extend a little beyond that, brake damage can occur.

It's not just the brake damage. High temperatures damage wheel assemblies and tires. Internally, tires gas at high temperatures, creating flammable mixtures inside the tire, which can explode. Rubber deteriorates in the presence of heat. Fuse plugs melt. Hydraulic fluid boils, drastically reducing it's ability to deliver uniform effective pressure.

A brake cooling chart gives you a guideline. Simply because the chart says an hour doesn't mean in an hour you can disregard the temp indicators and go fly. It means one can expect an hour for the brakes to cool. This can be decreased by the use of fans, or it may take longer. It's guideline.

which is correct option?

a) brakes off wait 35 mins before taxing.

b) wait til brakes cool to normal operating temp and then taxi.

c) ignore brake cool temps altogether.


Obviously one doesn't ignore brake temperatures. The cooling times are advisory, indicating what you can expect. Any limitations prescribed are just that; limitations.

You may have data describing what to anticipate for taxi, or you may not. You may be able to plan your cooling for the additional temp rise of a long taxi, or you may be taxiing at light weights with an engine shut down and have little brake use or temperature rise.

Wait the 35 minutes, monitoring temperatures and evaluate. Look for temperatures in an acceptable range for your aircraft and intended operation, then decide. If you happen to be using cooling fans, don't simply note the temperature and go. When the fans are removed, you may very well see a temperature increase as the temperature normalizes, or becomes more uniform again, throughout the brake and gear assembly.

Don't ignore those temperatures.