Parking Brake
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Parking Brake
Fellow PPRUNE Techies,
I am let to believe that a certain " World's Favourite Airline" tells it's 757/767 pilots to keep the brakes set to park, during turnarounds, as this ensures better dissipation of heat. Heat conducted up the U/C legs I suppose. My company and many others, tells pilots to release the parking brake when on stand, as this will allow air to circulate around the brakes and ensure cooling. (Probally an old 707 procedure.)
Do any of you have any views? Which is right/ or is there a right answer?
Regards Lynx
757/767 driver
I am let to believe that a certain " World's Favourite Airline" tells it's 757/767 pilots to keep the brakes set to park, during turnarounds, as this ensures better dissipation of heat. Heat conducted up the U/C legs I suppose. My company and many others, tells pilots to release the parking brake when on stand, as this will allow air to circulate around the brakes and ensure cooling. (Probally an old 707 procedure.)
Do any of you have any views? Which is right/ or is there a right answer?
Regards Lynx
757/767 driver
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Leaving the brakes set to park works fine for me and at least I know the airplane won't roll into a solid object while I write up the tech log.
The only aggravation is frantic waving and ground call bells to tell me chocks are in so that I can release the parking brake.
The brake temp indicators show that the temperature dissipates just fine, but non-Boeing types may be different.
The only aggravation is frantic waving and ground call bells to tell me chocks are in so that I can release the parking brake.
The brake temp indicators show that the temperature dissipates just fine, but non-Boeing types may be different.
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All aircraft I've been on - several different manufacturers - have advised to release the parking brake. Airbus said that it was advisable to release the parking brake as the heat buildup in the brakes caused the hydraulic fluid to break down and become acidic. This contributed to corrosion in the calipers/pistons.
However, at Heathrow some gates have a slope away from the building - presumably for water drainage - and we are required to keep the parking brake set until unloading is complete. Maybe this is a BA procedure for this airport only?
However, at Heathrow some gates have a slope away from the building - presumably for water drainage - and we are required to keep the parking brake set until unloading is complete. Maybe this is a BA procedure for this airport only?
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Allow me to quote the A330/A340 FCOM manual on Supplementary Techniques for Park Brake Use (3.04.32 p.2)
" Releasing of the park brake on the bay will have minimal cooling effect (if any) and could jeopardize the aircraft safety. As a guideline, when brake temperatures are above 400 degrees C, consideration should be given to the use of cooling air when the turnaround time is short. The parking brake is to be left on during normal operations" Note that the 'bus is equipped with carbon brakes. Hope this helps.
" Releasing of the park brake on the bay will have minimal cooling effect (if any) and could jeopardize the aircraft safety. As a guideline, when brake temperatures are above 400 degrees C, consideration should be given to the use of cooling air when the turnaround time is short. The parking brake is to be left on during normal operations" Note that the 'bus is equipped with carbon brakes. Hope this helps.
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Here it's parking brake off most of the time. Terminating for the night, high winds, ice, snow etc. are the exceptions. At least that's the SOP today. You know how often those things change.
The company doesn't even want the parking brake set while the chocks are put in. I was told that it wears out the parking brake valve. So we just hold the brakes while the chocks are put in. Come to think of it, I haven't had a bad parking brake valve for a long time now. It must be working.
The company doesn't even want the parking brake set while the chocks are put in. I was told that it wears out the parking brake valve. So we just hold the brakes while the chocks are put in. Come to think of it, I haven't had a bad parking brake valve for a long time now. It must be working.
The company I fly for now requires the park brake off for better cooling during turn-arounds (carbon brakes), but I don't think that it makes much difference.
The provious jet type I flew mentioned that there was no provision for thermal expansion in the hydraulic circuit past the park brake valve, so the park brake should be off if parking for long periods (overnight), to avoid thermal changes stressing the seals.
The provious jet type I flew mentioned that there was no provision for thermal expansion in the hydraulic circuit past the park brake valve, so the park brake should be off if parking for long periods (overnight), to avoid thermal changes stressing the seals.
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Obviously in the aircraft types mentioned above, the parking brake pressure does not blead off at such a rate to make them ineffectual quickly. On my type, we are recomended to release the brakes, unless there are strong winds. To leave them on for any length of time would be a waist of time unless you are there to continually reboost the pressure. On my previous type, the presuure would remain good all day and night if required.
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Having had a day to mull over the original posting I have two comments.
1 There are old wives' tales about the danger of the brakes welding on.
Obviously they don't.
2 On anything more than short haul have a look at your fuel temperature to see how cold the airframe gets at altitude. Then land in the winter and check the ice on the wings.
Any heat dissipation up the gear into the wings looks like a good thing to me.
1 There are old wives' tales about the danger of the brakes welding on.
Obviously they don't.
2 On anything more than short haul have a look at your fuel temperature to see how cold the airframe gets at altitude. Then land in the winter and check the ice on the wings.
Any heat dissipation up the gear into the wings looks like a good thing to me.
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Well, the old wife is right this time. Don't be fooled by the fact there's carbon brakes down there, they'll seize just as easily as steel brakes will. A hot brake is a dangerous thing, I've witnessed tires cook off the rim 10-15 minutes after arrival and remember that hydraulic fluid is far more flammable than fuel. The average thermal fuse plug on a tire rim is set to 450'c give or take and with the parkbrake set or not the 'only' place the heat can dissipate is into the inner rim area. The contact area to the axles is too small to allow any heat transfer.
Please release the brakes if the brakes are hot and save my kind from having to do unnessesary brake and tire changes.
A side note, some of you may remember a Nationair DC-8 on contract to the Haaj a few years back. For the lack of a nitrogen bottle one of the mains was about 40psi low for a number of cycles. Fiction from the tire plys rubbing against each other caused a heat build-up sufficient to blow the tire apart in the wheel-well ultimately bringing the aircraft down. It's the little things.....
Please release the brakes if the brakes are hot and save my kind from having to do unnessesary brake and tire changes.
A side note, some of you may remember a Nationair DC-8 on contract to the Haaj a few years back. For the lack of a nitrogen bottle one of the mains was about 40psi low for a number of cycles. Fiction from the tire plys rubbing against each other caused a heat build-up sufficient to blow the tire apart in the wheel-well ultimately bringing the aircraft down. It's the little things.....
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Not strictly to do with issue of setting the parking brake or not with respect to brake cooling but I did have a fright a few years ago in the A320 when the aicraft rolled backwards on the stand circa one metre, despite the fact that the chocks were in!
Investigation revealed that the stand area was very slippery due grease, oil deposits and the chocks actually slipped on the surface.
Neither myself nor the First Officer were aware that the aircraft had moved as we were attending to post flight paperwork duties until a cabin crew member came to ask whether we had moved as there was misaligment between the aircraft and the jetty!
Fortunately there was no damage or injury to personnel but I learned quite a lot from this incident - not the best way to end the working day so be warned!
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Investigation revealed that the stand area was very slippery due grease, oil deposits and the chocks actually slipped on the surface.
Neither myself nor the First Officer were aware that the aircraft had moved as we were attending to post flight paperwork duties until a cabin crew member came to ask whether we had moved as there was misaligment between the aircraft and the jetty!
Fortunately there was no damage or injury to personnel but I learned quite a lot from this incident - not the best way to end the working day so be warned!
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So far none of these horrible things has happened to me, apart from a 1-11 rolling backwards after I mis-interpreted a hand signal, so I conclude that setting the parking brake works fine although there may be highly unusual circumstances when the brakes are dangerously hot. But then, by definition, they are unusual.
I was a bystander as a crewmember taking over a 747 which had just made a rejected take-off, for reported vibration.
Something was lost in the translation because of nationality differences but,regardless, the ground engineers decided to take the beast for a high speed run down the runway.
Remember that it had already done one abort.
They charged off as fast as they dared and stood on the brakes.
At that stage I pointed to the brake temperatures but they were on a mission and ignored them and when they decided to do it all over again I left the cockpit in order to disassociate myself from what I thought might happen next.
This high speed run was followed by a taxy to the apron with the engineers saying they had found no sign of vibration.
It was not long before every single tyre fusible plug blew, bar the nosewheel.
Count them (on a 747) - I can't remember.
Needless to say there were insufficient replacements and even if there had been, the brakes and wheels would have been seriously hot for hours.
The flight was cancelled.
This was not in the UK.
I was a bystander as a crewmember taking over a 747 which had just made a rejected take-off, for reported vibration.
Something was lost in the translation because of nationality differences but,regardless, the ground engineers decided to take the beast for a high speed run down the runway.
Remember that it had already done one abort.
They charged off as fast as they dared and stood on the brakes.
At that stage I pointed to the brake temperatures but they were on a mission and ignored them and when they decided to do it all over again I left the cockpit in order to disassociate myself from what I thought might happen next.
This high speed run was followed by a taxy to the apron with the engineers saying they had found no sign of vibration.
It was not long before every single tyre fusible plug blew, bar the nosewheel.
Count them (on a 747) - I can't remember.
Needless to say there were insufficient replacements and even if there had been, the brakes and wheels would have been seriously hot for hours.
The flight was cancelled.
This was not in the UK.
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On the A320, whenever there are high brake temperatures, we usually release the parking brake. Reason behind this is that when the parking brake is left engaged, the hydraulic fluid heats up in the adjacent lines, which may lead to early degradation of the fluid.
[This message has been edited by MFALK (edited 31 May 1999).]
[This message has been edited by MFALK (edited 31 May 1999).]
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Your right about that, the fluid is always there, but when the brakes are left on the pistons are in contact with the brake disc backing plate and theoretically the heat can transfer more easily to the fluid.
Although on all the tech training courses I've been on overheated fluid has never been brought up. The synthetic fluid nowadays is designed to handle high heat as is the engine oil and remember there's no dedicated brake fluid in an airliner, it's all circulated at some point or another.
Although on all the tech training courses I've been on overheated fluid has never been brought up. The synthetic fluid nowadays is designed to handle high heat as is the engine oil and remember there's no dedicated brake fluid in an airliner, it's all circulated at some point or another.
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Are the brakes hot? Flick some spit at the brake and note the sizzle factor. If it sizzles like a frying egg all is ok. If it evaporates as soon as it touches its hot! After a while youll have you own personal sizzle scale and can grade the heat in the brakes accordingly. Saves burnt hands too.
NOTE: Dont use snot! Thick green snot absorbes heat and will not give you a true indication of brake temperature. Also snot charcoals easily.
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Slasher. President, Boeing Brake Temp Research Labs.
NOTE: Dont use snot! Thick green snot absorbes heat and will not give you a true indication of brake temperature. Also snot charcoals easily.
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Slasher. President, Boeing Brake Temp Research Labs.