Autobrake vs. do-it-yourself
Guest
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Although on Boeing a/c, max autobrake is less deceleration than max manual braking we always start with autbrakes because you just can't beat the system on reaction-time after landing.
On long runways, and when we anticipate on leaving the runway at the end to shorten the taxi-time we sometimes select autobrakes to off. ( Wich, in my company, is non-standard. )
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Track
On long runways, and when we anticipate on leaving the runway at the end to shorten the taxi-time we sometimes select autobrakes to off. ( Wich, in my company, is non-standard. )
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Track
Guest
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Generally, I have developed a preference for using autobrake, just because I find it hard to steer with the pedals in a x-wind AND apply even brake pressure to the brakes, leading to uneven wear, nosewheel scuffing etc. etc.
It is much smoother than manual braking (if I'm driving, anyway!) and seems more reliable.
LO usually, but MED if r/way less than about 2300m or early turn-off reqd etc.
It is a good system, why not use it?
It is much smoother than manual braking (if I'm driving, anyway!) and seems more reliable.
LO usually, but MED if r/way less than about 2300m or early turn-off reqd etc.
It is a good system, why not use it?
Guest
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Auto brakes on Boeings actually are decelleration monitors. I don't have my books at home to give you the percentage of decelleration for each setting, however, they appply wheel brakes in relation to the selected decelleration rate.
In a nutshell they add brakes to normal drag and reversers to give you a preselected rate of slowing. I like to use them because it is the best way to insure you are goin to meet landing perfomance data for a given runway. Most performance calcultions for required braking use the autobrake decelleration rates to creat Min Med and Max as reccommendations for braking.
Lufthansa did a study a few years back with Boeing on AB vs manual braking and found that AB were much better at increasing brake life. Not a cost factor though, most airlines pay per cycle for the brakes under contract. They are much cheaper than vacuuming the runway with the CFM's and damaging the blades at low speeds. The study was published in Airliner mag by Boeing in the early 90's.
In a nutshell they add brakes to normal drag and reversers to give you a preselected rate of slowing. I like to use them because it is the best way to insure you are goin to meet landing perfomance data for a given runway. Most performance calcultions for required braking use the autobrake decelleration rates to creat Min Med and Max as reccommendations for braking.
Lufthansa did a study a few years back with Boeing on AB vs manual braking and found that AB were much better at increasing brake life. Not a cost factor though, most airlines pay per cycle for the brakes under contract. They are much cheaper than vacuuming the runway with the CFM's and damaging the blades at low speeds. The study was published in Airliner mag by Boeing in the early 90's.
Guest
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Airbus TPs did some trials on emergency manual braking vs max auto braking.None of the TPs could beat the AB;partly because most would not apply the unnatural amount of pressure required-those that did initially could not maintain the pressures throughout deceleration.Pilots who were left brain dominant were able to maintain pressure on the right side for longer,vice versa.Some of the max auto brake trials resulted in multiple tyre failure as the a/c came to a stop.
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A certain charter carrier has prescribed that its crews cannot use more than min auto brake due to excessive wear on its A321s. As a result they regularly miss all high speed exits and take forever to get off the runway at a 90 degree exit.
This resulted in a go-around due to an aircraft lined up behind not able to depart before the next arrival.
Nice way to find out about your company's pennypinching - by costing another company substantially more in the go-around!
Please, minumum runway occupancy time - it matters to us all.
This resulted in a go-around due to an aircraft lined up behind not able to depart before the next arrival.
Nice way to find out about your company's pennypinching - by costing another company substantially more in the go-around!
Please, minumum runway occupancy time - it matters to us all.
I suspect that the real reason is that brake wear is directly propotional to application pressure.
For those of us that fly aircraft without auto brake, ther is generally a notice somewhere that reads similar to:
"These brakes operate best at high temperatures, use 600psi per side, unless otherwise warrented"
Now pilots being what they are may or may not follow such a notice - solution: intoduce an automatic system that applies the cheapest amount of pressure (read minimum wear per landing).
For those of us that fly aircraft without auto brake, ther is generally a notice somewhere that reads similar to:
"These brakes operate best at high temperatures, use 600psi per side, unless otherwise warrented"
Now pilots being what they are may or may not follow such a notice - solution: intoduce an automatic system that applies the cheapest amount of pressure (read minimum wear per landing).
Guest
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Using autobrake increases brake wear and brake temperature when operating at high ambient temperatures.However it is reccomended for short rwys, strong crosswinds and contaminated/slippery rwys
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trust your cptn but fasten your seatbelt
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trust your cptn but fasten your seatbelt
Guest
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I hate to throw the cat amoungst the pigeons....... but BF Goodrich did a survey some years back (Carbon disk brakes only) and found the use of auto brake to be very beneficial to the reduction of brake wear. Basically they said it was NOT how hard you applied the brake more so how OFTEN. They also noted that the excessive use of brake fans also increased wear. Our company adopted the policy to reflect same.
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Dont forget you wont be leaving empty handed!
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Dont forget you wont be leaving empty handed!
Guest
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Agree with Boxer on this.
On the 777 with carbon brakes we were told that the same amount of wear was inflicted on each application regardless of the pressure applied. (Not sure about duration of application, but I believe the inference was that this factor was irrelevant also)
Because of this 'fact' the training section encouraged the use of either left or right brake application only to effect retardation during taxi operations. This, they maintained, would reduce brake wear costs.
With conventional brakes none of the above is a factor.
Regards
Exeng
On the 777 with carbon brakes we were told that the same amount of wear was inflicted on each application regardless of the pressure applied. (Not sure about duration of application, but I believe the inference was that this factor was irrelevant also)
Because of this 'fact' the training section encouraged the use of either left or right brake application only to effect retardation during taxi operations. This, they maintained, would reduce brake wear costs.
With conventional brakes none of the above is a factor.
Regards
Exeng
Guest
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One stupid question more...
When does the Auto Brake actually activate? At the moment the both main gears are down or not until the nose is down? I guess the nose has to be pushed down before activation in order to prevent the slam effect of maximal braking.
Yeah, I know, this is a silly question...
Thanks anyway...
Samuli
When does the Auto Brake actually activate? At the moment the both main gears are down or not until the nose is down? I guess the nose has to be pushed down before activation in order to prevent the slam effect of maximal braking.
Yeah, I know, this is a silly question...
Thanks anyway...
Samuli
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Far from a silly question....
Auto brake is armed on gound for take off and is only in the active range above 72 knots on take off role, it is activated on retardin of the Thrust levers to idle which induces spoiler deflection in turn activates autobrake MAX. Now for landing it is very simular in that on the deflection of spoliers there is a timed delay on fixed decel rates for MED and LOW. Med is 3 meters per second squared after a 2 second delay at touch down whereas LOW is 1.7 mps sq. with a 4 second delay (if my memory serves me correctly). They are activated on SPOLIER deflection or if spoliers were not armed then on the selection of reverse.
We also see DECEL in green on the autobrake selectore when 80% of the selcted braking required is achived.
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Gravity always wins....
Auto brake is armed on gound for take off and is only in the active range above 72 knots on take off role, it is activated on retardin of the Thrust levers to idle which induces spoiler deflection in turn activates autobrake MAX. Now for landing it is very simular in that on the deflection of spoliers there is a timed delay on fixed decel rates for MED and LOW. Med is 3 meters per second squared after a 2 second delay at touch down whereas LOW is 1.7 mps sq. with a 4 second delay (if my memory serves me correctly). They are activated on SPOLIER deflection or if spoliers were not armed then on the selection of reverse.
We also see DECEL in green on the autobrake selectore when 80% of the selcted braking required is achived.
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Gravity always wins....
Guest
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Anyone knows how much more or less prone carbon vrs steel brakes are to bind together if parking brake is set with extreme high brake temps ?
Airbus has a pretty good bulletin regarding carbon brakes but I would be interested to read that BF Grch. study , where can I find it ?
BF G. was not helpfull when I contacted them some time ago
Thanks , Manuel
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From the BF GOODRICH guide: CARBON BRAKE LIFE IMPROVEMENT Recommendations:
1)Minimize number of taxi brake applications, especially prior to takeoff.
-Anticipate engine spool up and spool down characteristics to avoid overshooting desired taxi speed.
-Combine several short taxi applications into fewer, longer taxi applications.
2)Apply brakes sooner during landing stop.
-Utilize lower levels of thrust reverse.
-Utilize higher autobrake settings or manual braking.
When the BF Goodrich rep came and talked to our group, he said that the majority of the wear was done on the first flight of the day, when the brakes were cold. 300 degrees was about optimun for the least amount of wear.
1)Minimize number of taxi brake applications, especially prior to takeoff.
-Anticipate engine spool up and spool down characteristics to avoid overshooting desired taxi speed.
-Combine several short taxi applications into fewer, longer taxi applications.
2)Apply brakes sooner during landing stop.
-Utilize lower levels of thrust reverse.
-Utilize higher autobrake settings or manual braking.
When the BF Goodrich rep came and talked to our group, he said that the majority of the wear was done on the first flight of the day, when the brakes were cold. 300 degrees was about optimun for the least amount of wear.
