Brake Pins
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Brake Pins
Hello guys, I have a stupid question about the brakes indicator pins in Boeing aircraft.
I was skimming the maintainence manual of a B767 airplane and read that brake pins should be checked in normal brake pressure...which is pretty obvious that the brake pressure should be above the red band.
Then I stepped into another paragraph that says:
Two indicator pins on the inboard side of the brake
housing show brake lining wear. When the brakes
operate, the end of the indicator pin must extend
beyond the retaining bracket.
Does that means that we have to check the brakes on the ground always while we have the parking brakes on?
I was skimming the maintainence manual of a B767 airplane and read that brake pins should be checked in normal brake pressure...which is pretty obvious that the brake pressure should be above the red band.
Then I stepped into another paragraph that says:
Two indicator pins on the inboard side of the brake
housing show brake lining wear. When the brakes
operate, the end of the indicator pin must extend
beyond the retaining bracket.
Does that means that we have to check the brakes on the ground always while we have the parking brakes on?
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Hello mayday.call,
All A/C brakes (AIB and Boeing) should be checked with hydraulic pressure applied and the parking brake set or by somebody on the pedals.
I say , by somebody on the pedals just in case that the brake accumulator is not well charged ...
The "length" of the pins , in fact , the measurement will also depends on the brakes temperature ...
They should be checked when the brakes are cold ...
Usually , the brake should be changed when the pin is flushed to the retaining bracket ... some airlines get a company policy where they changed them before to save some money ...
Look carefully to these pins , it is not really an accurate measurement ...
Hope that clarifies.
All A/C brakes (AIB and Boeing) should be checked with hydraulic pressure applied and the parking brake set or by somebody on the pedals.
I say , by somebody on the pedals just in case that the brake accumulator is not well charged ...
The "length" of the pins , in fact , the measurement will also depends on the brakes temperature ...
They should be checked when the brakes are cold ...
Usually , the brake should be changed when the pin is flushed to the retaining bracket ... some airlines get a company policy where they changed them before to save some money ...
Look carefully to these pins , it is not really an accurate measurement ...
Hope that clarifies.
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No probs mayday ...
More infos if interested , as per my own experience , one of the two pins can be missing ...(old 747 , but that depends on brake PN).
The length correspond on the "material" who is left on the discs , as i said , depending on the temperature ...
In some docs , you will even find , the number of cycle remaining depending on this length.
In the worst case , a brake can be de-activated , do you follow me ? but then some operational restrictions as runway length , etc.
More infos if interested , as per my own experience , one of the two pins can be missing ...(old 747 , but that depends on brake PN).
The length correspond on the "material" who is left on the discs , as i said , depending on the temperature ...
In some docs , you will even find , the number of cycle remaining depending on this length.
In the worst case , a brake can be de-activated , do you follow me ? but then some operational restrictions as runway length , etc.
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Just to add to the thread.
The brake wear indicators show the minimum amount of material required for the application of the brakes at 3000 psi on a high energy Rejected Take-off.
Carbon brakes don't expand that much unlike the steel ones of old, even this expansion co-eff would not be the serviceable/unservicable margin. So no point rushing to do your check when the a/c comes on stand to avoid the job! Haha
Bend the brackets like everyone else, NOT! (I have seen it done!!). Usually the limit on ours is 0.060" about 1/16, with park brake set.
The brake wear indicators show the minimum amount of material required for the application of the brakes at 3000 psi on a high energy Rejected Take-off.
Carbon brakes don't expand that much unlike the steel ones of old, even this expansion co-eff would not be the serviceable/unservicable margin. So no point rushing to do your check when the a/c comes on stand to avoid the job! Haha
Bend the brackets like everyone else, NOT! (I have seen it done!!). Usually the limit on ours is 0.060" about 1/16, with park brake set.
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brake pins
Two pins, pin which shows most wear to be used to indicate worn brakes.
Pins had a loose fitting so if indicating worn out could always pull them out and gain a few thousands of an inch, then not worn out.
Or set parking brakes with less than max pressure.
Pins had a loose fitting so if indicating worn out could always pull them out and gain a few thousands of an inch, then not worn out.
Or set parking brakes with less than max pressure.
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I do hope you are not working as an engineer !.
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As Beeline says, the wear pins are set to provide sufficient lining material remaining to absorb a high energy stop such as RTO. Or on carbon brakes, sufficient disk thickness. Letting them go down below-flush or bending/moving the bracket may make the brakes last longer but hazards the aircraft's stopping performance and invalidates its C of A.
Conversely pulling the brakes early, before the pins are flush, can be a very expensive business with heatpacks costing tens of thousands of dollars. The only time you would want to do this is if the aircraft is scheduled to be operating down line for some time with no possibility to routinely change brakes as they reach WTL.
Unless your AMM states hot or cold it's normal to check them cold, if only because they get bloody hot! Parking brake pressure is normal and if you can see different length wear pins that indicates asymmetric brake wear, which is not good - pull these when the shorter wear pin reaches flush.
If you have an over-worn brake and can't change it straight away refer to your MEL procedure and lock it out (if permitted). Over-worn brakes can and do fail spectacularly and you're better off with a known locked-out brake than one about to fail.
Conversely pulling the brakes early, before the pins are flush, can be a very expensive business with heatpacks costing tens of thousands of dollars. The only time you would want to do this is if the aircraft is scheduled to be operating down line for some time with no possibility to routinely change brakes as they reach WTL.
Unless your AMM states hot or cold it's normal to check them cold, if only because they get bloody hot! Parking brake pressure is normal and if you can see different length wear pins that indicates asymmetric brake wear, which is not good - pull these when the shorter wear pin reaches flush.
If you have an over-worn brake and can't change it straight away refer to your MEL procedure and lock it out (if permitted). Over-worn brakes can and do fail spectacularly and you're better off with a known locked-out brake than one about to fail.
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Krystal - not sure if you are having a pop at me or not. Yes I am a Licensed Engineer. Where I work, the approved documents allow me to check brake wear with the brakes hot or cold, only the pin protrusion length differs. This will depend on whether we are doing a daily or a transit check, and that is on 3 widebody types we operate. If you are only permitted to check the wear with the brakes cold, I'm surprised anything flies from your station. PM me if you wish and I'll elucidate further . . . Terry
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Terry,
I was not having a pop at you..my apologies for the misunderstanding as my post followed your own....I should have clarified the comment was directed at the OP...the question he posed being as basic as they come !
I was not having a pop at you..my apologies for the misunderstanding as my post followed your own....I should have clarified the comment was directed at the OP...the question he posed being as basic as they come !
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Brake Pins
FWIW, I agree with Dodo, in that pulling brakes early is expensive. On an old employer's airline (Now defunct!) we got a letter from the manufacturers, saying we were wasting money by cx'ing too early! It was because we often did round robin routes with the A/C away for up to 3 days. Following the letter, our tech services came up with a Company specific guidance letter for route checks. Worked fine 
.
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Company option, performance v/s cost to decide how long the brake pins are over mfgr length limits. Used to love old amm's that had a 2nd option to measure a puck, could move an aircraft this way quite often for many more legs.
