Rote use of autobrakes when operationally unnecessary
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Rote use of autobrakes when operationally unnecessary
Training foreign crews from different countries in the 737 simulator it was observed that without exception everyone used the auto-brakes for all landings regardless of runway length. Not one pilot used auto-brake setting 1. Autobrake setting 2 was the favourite even with runways of 10,000 ft length. Others used autobrake 3 with runways of 7000 ft. None considered manual brake landings. Even with 30 knot HW component on a 10,000 ft runway, pilots were still selecting autobrake 2.
The very nature of the brakes coming on at the moment of touch down means heat build up in the brakes. Surely this is undesirable? From ab-initio days it was considered poor airmanship to apply the brakes immediately on touch down (unless stopping distance was critical, of course) because wear and tear is increased and the brakes can get hot.
It is known that spoiler operation and reverse thrust will alleviate the brakes which back off while maintaining a set decelleration level. But why use autobrakes when they are simply not operationally needed? Lazy habits, maybe? - designed to cover careless flying in terms of excess speed and height at the threshold?
The very nature of the brakes coming on at the moment of touch down means heat build up in the brakes. Surely this is undesirable? From ab-initio days it was considered poor airmanship to apply the brakes immediately on touch down (unless stopping distance was critical, of course) because wear and tear is increased and the brakes can get hot.
It is known that spoiler operation and reverse thrust will alleviate the brakes which back off while maintaining a set decelleration level. But why use autobrakes when they are simply not operationally needed? Lazy habits, maybe? - designed to cover careless flying in terms of excess speed and height at the threshold?
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Among other things, reverse thrust and aerodynamic braking from spoilers aren't considered when calculating landing distance. Wheel brakes are.
An autobrake system modulates brakes for a set rate of acceleration (or deceleration, if you will). If reverse thrust is used, the same rate of acceleration will occur, but with less involvement of the brakes. You're out nothing by landing with autobrakes, and you still benefit from reverse with less brake energy when using reverse.
Autobrakes provide a known rate of acceleration, which means that it can be used to calculate stopping distance. In our own calculations, the Landin Data card spits cites the specific stopping distance with each level of braking applied; these distances don't change with or without reverse thrust, but the brake energy and subsequent brake temperature certainly does. If the calculation states that a medium autobrake setting will provide 6,000' of landing distance, then it provides it at the medium setting with or without the reverse thrust. With reverse thrust, the distance remains the same, but the brakes are cooler because the autobrake system uses the brakes less.
Autospoilers and ground spoiler systems are intended not to slow the aircraft, but to disrupt lift and put the weight on the wheels where the brakes can be more effective. This is their primary purpose, and consequently the brakes are the primary device for slowing the aircraft.
Additional braking which may be had from other features such as ground spoilers, reverse and anyother aerodynamic braking, are extra which may be applied to the ground acceleration (slowing) equation...but are not taken into account when calculating the distance...and shouldn't be relied upon given that they aren't permitted when calculating landing distance.
If your students are overusing the brake settings, then this is something to be included in the training. To instruct a student to not use, or disregard the autobrakes is to give away an efficient useful system for no good cause.
The autobrakes will always do a better and more consistent job of applying the brakes than you. Why would you not want to use them?
So far as "landing with the brakes applied," this doesn't happen with autobrakes. The delay applied to the braking system prevents landing with brakes applied, as does the antiskid bypass until the aircraft senses either truck tilt or weight on wheels...and as the autobrakes are part of the antiskid system, the concern of landing with a wheel locked up is eliminated by virtue of the fact that you're using the system to brake which prevents locked brakes.
An autobrake system modulates brakes for a set rate of acceleration (or deceleration, if you will). If reverse thrust is used, the same rate of acceleration will occur, but with less involvement of the brakes. You're out nothing by landing with autobrakes, and you still benefit from reverse with less brake energy when using reverse.
Autobrakes provide a known rate of acceleration, which means that it can be used to calculate stopping distance. In our own calculations, the Landin Data card spits cites the specific stopping distance with each level of braking applied; these distances don't change with or without reverse thrust, but the brake energy and subsequent brake temperature certainly does. If the calculation states that a medium autobrake setting will provide 6,000' of landing distance, then it provides it at the medium setting with or without the reverse thrust. With reverse thrust, the distance remains the same, but the brakes are cooler because the autobrake system uses the brakes less.
Autospoilers and ground spoiler systems are intended not to slow the aircraft, but to disrupt lift and put the weight on the wheels where the brakes can be more effective. This is their primary purpose, and consequently the brakes are the primary device for slowing the aircraft.
Additional braking which may be had from other features such as ground spoilers, reverse and anyother aerodynamic braking, are extra which may be applied to the ground acceleration (slowing) equation...but are not taken into account when calculating the distance...and shouldn't be relied upon given that they aren't permitted when calculating landing distance.
If your students are overusing the brake settings, then this is something to be included in the training. To instruct a student to not use, or disregard the autobrakes is to give away an efficient useful system for no good cause.
The autobrakes will always do a better and more consistent job of applying the brakes than you. Why would you not want to use them?
So far as "landing with the brakes applied," this doesn't happen with autobrakes. The delay applied to the braking system prevents landing with brakes applied, as does the antiskid bypass until the aircraft senses either truck tilt or weight on wheels...and as the autobrakes are part of the antiskid system, the concern of landing with a wheel locked up is eliminated by virtue of the fact that you're using the system to brake which prevents locked brakes.
The autobrakes will always do a better and more consistent job of applying the brakes than you.
For a start, maximum manual braking is stated in the manual as being better than the "MAX" setting on Boeing autobrakes. Any pilot aware of the tendency to favour one foot over the other and who takes a bit of care can do a better, more consistent job of braking than an automatic system. Finally - relying on autobrakes has led to at least one major accident in a 747 at Bangkok.
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You will never be able to establish a consistent, accurate rate of deceleration equal to that established by the autobrake system. Further, when you take it upon yourself to forgo the recommended system (autobrakes), you still use the same system that operates the autobrakes: the antiskid system. (If you're foolish enough to turn that off, too...you get what you deserve).
When in autobrakes, one always has the option of applying manual braking, increasing the autobrake setting, or disconnecting the autobrakes altogether (which happens upon application of manual braking, anyway). Pilot override is always an option.
When in autobrakes, one always has the option of applying manual braking, increasing the autobrake setting, or disconnecting the autobrakes altogether (which happens upon application of manual braking, anyway). Pilot override is always an option.
*sigh* 
www.informaworld.com/index/789570505.pdf - Similar -
The human being is an amazing organism. The human threshold of perception in linear acceleration (including visual and skin perception) is greater than that of the accelerometers fitted to an aircraft.
A good pilot can brake better than the autobrake. Fact.
GOOD pilots - ones who read outside the spoon fed information from a training department are hard to come by.
The antiskid has nothing to do with the autobrake system. 
A GOOD car driver is better than even the best anti skid - it's why racing drivers turn off anti skid systems when they race.
www.informaworld.com/index/789570505.pdf - Similar -
The human being is an amazing organism. The human threshold of perception in linear acceleration (including visual and skin perception) is greater than that of the accelerometers fitted to an aircraft.
A good pilot can brake better than the autobrake. Fact.
GOOD pilots - ones who read outside the spoon fed information from a training department are hard to come by.
you still use the same system that operates the autobrakes: the antiskid system. (If you're foolish enough to turn that off, too...you get what you deserve).
A GOOD car driver is better than even the best anti skid - it's why racing drivers turn off anti skid systems when they race.
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AutoBrake
Some Airlines 'Buy' their brakes in a similar way to how they 'Buy' their engines and other components. You've, no doubt, heard of 'power by the hour' refering to the purchase of engines and APUs and such. A contract from a brake supply company may well specify a charge dependent on the use. To guarentee a high average for that use the agreement might specify the use of 'AutoBrake level 2', for example. To guarentee a high level of Autobrake 1 would suggest that the company would wish to land at airports with only very long runways. Companies using predominently short runways might have to specify normal use of Level 3, and thus pay more.
What we are looking at, at the moment, is the cost of reverse thrust against that of modern brake units. Early days yet, but it would appear that the cost of reverse thrust, including its 'mishandling' by piolts (eg. full reverse at speeds less than 80Kts. and not stowed below 60Kts) causing expensive FOD (damage) that outways the cost of using the brakes. Thus, using 'idle reverse' normally, unless necessary to use more, and better 'knowledge' of Autobrake application, is likely to be a serious option.
The down side is that pilots can sometimes have too much faith in the autobrake system and do not react fast enough when things start going pear shaped. There has been a number of runway over-runs where the pilots did nothing and then claiming that the autobrake did not do a proper job. I personally think that all pilots should be able to use manual breaking on a regular basis, so that they get a proper 'feel' for the brakes. This is particularly the case for some low houred F/O who often never get a chance to use them at all, except perhaps in the sim!!
Rgs. Bob.
What we are looking at, at the moment, is the cost of reverse thrust against that of modern brake units. Early days yet, but it would appear that the cost of reverse thrust, including its 'mishandling' by piolts (eg. full reverse at speeds less than 80Kts. and not stowed below 60Kts) causing expensive FOD (damage) that outways the cost of using the brakes. Thus, using 'idle reverse' normally, unless necessary to use more, and better 'knowledge' of Autobrake application, is likely to be a serious option.
The down side is that pilots can sometimes have too much faith in the autobrake system and do not react fast enough when things start going pear shaped. There has been a number of runway over-runs where the pilots did nothing and then claiming that the autobrake did not do a proper job. I personally think that all pilots should be able to use manual breaking on a regular basis, so that they get a proper 'feel' for the brakes. This is particularly the case for some low houred F/O who often never get a chance to use them at all, except perhaps in the sim!!
Rgs. Bob.
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The antiskid has nothing to do with the autobrake system.
This, incidentally, is an aviation forum. Not a racecar forum.
You may be in the wrong forum.
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Actually, takeoff autobrakes are applied faster than pilot reaction and at least in our case come on as part of the rejected takeoff as the thrust levers are closed to idle. They operate faster and get the deceleration going sooner than the pilot does.
Taking over from the autobrakes is simple enough, but is there any reason not to arm them? I think not.
Taking over from the autobrakes is simple enough, but is there any reason not to arm them? I think not.
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I am with Guppy on this.
Without having brake temperature gauges fitted to the 737 it is difficult to judge how heavy we are on either foot. I used to be left foot heavy on a jet without autobrake but corrected this because we had temperature indicators.
Autobrake is applied on mainwheel touchdown quicker than my reaction would be to start applying them manually. However, I will usually be manual braking by 90/80kts to modulate enough to find a convenient runway exit.
To apply the brakes early in the landing roll would mean better heat dissipation at speed rather than leaving it late on. I don't understand why you think this would mean excess heat build up?
Beginning braking at the point of touchdown is a method accounted for in the performance calculation. I have yet to see anyone start applying brakes manually at that precise moment. But perhaps that means I am not one of the "good" pilots you refer to. Are you a simulator or line trainer out of interest? What is the opinion of your Head of Training on the subject?
Without having brake temperature gauges fitted to the 737 it is difficult to judge how heavy we are on either foot. I used to be left foot heavy on a jet without autobrake but corrected this because we had temperature indicators.
Autobrake is applied on mainwheel touchdown quicker than my reaction would be to start applying them manually. However, I will usually be manual braking by 90/80kts to modulate enough to find a convenient runway exit.
To apply the brakes early in the landing roll would mean better heat dissipation at speed rather than leaving it late on. I don't understand why you think this would mean excess heat build up?
Beginning braking at the point of touchdown is a method accounted for in the performance calculation. I have yet to see anyone start applying brakes manually at that precise moment. But perhaps that means I am not one of the "good" pilots you refer to. Are you a simulator or line trainer out of interest? What is the opinion of your Head of Training on the subject?
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SN3Guppy
Yes I was agreeing with you as I do in general re autobrake usage.
Checkboard
I wonder if you were in charge what would you do regarding SOP/ Autobrake use in an airline operating say 737-800s ?
Setting autobrake 3 to clear at the end of a 10000' runway is not necessary or wise IMO but that is all about airmanship/training, not autobrakes?
Actually, takeoff autobrakes are applied faster than pilot reaction
Checkboard
I wonder if you were in charge what would you do regarding SOP/ Autobrake use in an airline operating say 737-800s ?
Setting autobrake 3 to clear at the end of a 10000' runway is not necessary or wise IMO but that is all about airmanship/training, not autobrakes?
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Would you rather hand-fly a CAT3 ILS to minimums and attempt a landing since you feel that you are a highly evolved human being and think that you can do a better job than the automation?
Autobrake is very much a part of the automation system,its there to make life easier i-e monitoring vs manipulation. If you dont like what its doing,disengage and takeover.
SS
Would you rather hand-fly a CAT3 ILS to minimums and attempt a landing since you feel that you are a highly evolved human being and think that you can do a better job than the automation?
Autobrake is very much a part of the automation system,its there to make life easier i-e monitoring vs manipulation. If you dont like what its doing,disengage and takeover.
SS
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Kiltie: "Autobrake is applied on mainwheel touchdown quicker than my reaction would be to start applying them manually"
There is no need for that unless you're a cadet pilot who is scared to run off the pavement long before you reach the end. All you're doing is heating up and using up the brakes early for no reason and only minimal braking effect.
Let reverse thrust and the spoilers do their job of initial deceleration before stomping on the brakes. Or you can select auto brakes after landing . . .when you're half way down the pavement if you're so apprensive of using your feet on the pedals.
Except for the RTO function, auto brakes are not ideal in all situations, especially not on long runways where reverse and spoilers alone will slow you to virtual taxi speed.
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Once again we are off, arguing about 'autobrake' v 'feet' and how it works. Let's not lose sight of the original post which was about INAPPROPRIATE settings of a/b. A great bit of kit, it works, and it is predictable. APPROPRIATE use is a good idea. For CALCULATED runway exit points it is unbeatable - and smooth.
NB A37575 NEVER MENTIONED RTO!
NB A37575 NEVER MENTIONED RTO!
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Attempting to answer some questions A37575 actually asked;
"The very nature of the brakes coming on at the moment of touch down means heat build up in the brakes. Surely this is undesirable?"
Yes heat will build up in the brakes of course, however this is always going to happen when you apply the brakes manual or automatic and is planned for in the manufacturing process. Most airlines will have some sort of SOP regarding the use of A/B in conjunction with brake cooling times. I land the majority of the time with a/b 3, FL40 as I tend to land on short runways. With this set-up brake cooling is not an issue for our 25 min turn-around. Obviously a/b setting can be altered if needed and that is pilots discretion so long as you prove you can stop before the end of the runway!!!
"But why use autobrakes when they are simply not operationally needed? Lazy habits, maybe?"
Autobrakes can be disconnected at anytime by pilot input and so if after touchdown you so desire to do so - then fair enough. I find I tend to d/c them around 90kts (as another poster has already said) to modulate for the best exit. However I personally feel it is prudent to have them armed. If they are there and can/do help - why not use them!? Better to have them armed to MAX and d/c them on touchdown than not have them armed and forget to brake manually....
"The very nature of the brakes coming on at the moment of touch down means heat build up in the brakes. Surely this is undesirable?"
Yes heat will build up in the brakes of course, however this is always going to happen when you apply the brakes manual or automatic and is planned for in the manufacturing process. Most airlines will have some sort of SOP regarding the use of A/B in conjunction with brake cooling times. I land the majority of the time with a/b 3, FL40 as I tend to land on short runways. With this set-up brake cooling is not an issue for our 25 min turn-around. Obviously a/b setting can be altered if needed and that is pilots discretion so long as you prove you can stop before the end of the runway!!!
"But why use autobrakes when they are simply not operationally needed? Lazy habits, maybe?"
Autobrakes can be disconnected at anytime by pilot input and so if after touchdown you so desire to do so - then fair enough. I find I tend to d/c them around 90kts (as another poster has already said) to modulate for the best exit. However I personally feel it is prudent to have them armed. If they are there and can/do help - why not use them!? Better to have them armed to MAX and d/c them on touchdown than not have them armed and forget to brake manually....
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Glueball -
There's every need for applying brakes as soon as possible on a runway where field length is an issue, and you don't need to be a cadet pilot to practice that. Rightly or wrongly, or naively if you like, my technique is always to use an autobrake setting appropriate to the stopping distance available in the QRH; which is usually Autobrake 1 on "long" runways but Autobrake 3 at my base airport (less than 2000m LDA). The initial autobrake application is a damned sight more balanced than I could muster, and I prefer to disarm it using manual braking during the rollout.
Incidentally, manipulating the autobrake selector during the landing roll is a no-no now for us. This is to recognise the manufacturer's Bulletin which addressed some problems experienced by other operators where their pilots were attempting to deselect the autobrake to OFF but inadvertently rotated the switch to RTO with some rather abrupt results.
In any case, my company SOP is to use autobrake when serviceable, so it's a no-brainer. To step outside this SOP would require a valid safety reason which rarely presents itself. Reading between the lines, I can't help thinking there have been some posts on this thread inferring that to use autobrake shows a lack of initiative, or one that is being unnecessarily harsh to the braking system. The argument of reversers vs brakes on non-limiting runways is an old one, and I am sure every company has an opinion of which to manipulate moreso than the other.
To digress, one poster mentions he stows the reversers at 60kts. After 80kts, I tend to reduce them to idle until a lower speed than 60kts, not least to avoid hydraulic lock in the sleeves of the NGs to meet the "at least ten seconds of use" rule of thumb. Perhaps this is my bad habit? When do the rest of you stow them, out of interest?
There's every need for applying brakes as soon as possible on a runway where field length is an issue, and you don't need to be a cadet pilot to practice that. Rightly or wrongly, or naively if you like, my technique is always to use an autobrake setting appropriate to the stopping distance available in the QRH; which is usually Autobrake 1 on "long" runways but Autobrake 3 at my base airport (less than 2000m LDA). The initial autobrake application is a damned sight more balanced than I could muster, and I prefer to disarm it using manual braking during the rollout.
Incidentally, manipulating the autobrake selector during the landing roll is a no-no now for us. This is to recognise the manufacturer's Bulletin which addressed some problems experienced by other operators where their pilots were attempting to deselect the autobrake to OFF but inadvertently rotated the switch to RTO with some rather abrupt results.
In any case, my company SOP is to use autobrake when serviceable, so it's a no-brainer. To step outside this SOP would require a valid safety reason which rarely presents itself. Reading between the lines, I can't help thinking there have been some posts on this thread inferring that to use autobrake shows a lack of initiative, or one that is being unnecessarily harsh to the braking system. The argument of reversers vs brakes on non-limiting runways is an old one, and I am sure every company has an opinion of which to manipulate moreso than the other.
To digress, one poster mentions he stows the reversers at 60kts. After 80kts, I tend to reduce them to idle until a lower speed than 60kts, not least to avoid hydraulic lock in the sleeves of the NGs to meet the "at least ten seconds of use" rule of thumb. Perhaps this is my bad habit? When do the rest of you stow them, out of interest?
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Since the question was about 737, most people follow the Boeing rec of
"Maintain reverse thrust as required, up to maximum, until the airspeed approaches 60 knots. At this point start reducing the reverse thrust so that the reverse thrust levers are moving down at a rate commensurate with the deceleration rate of the airplane. The thrust levers should be positioned to reverse idle by taxi speed, then to full down after the engines have decelerated to idle."
Simple, really.....?
"Maintain reverse thrust as required, up to maximum, until the airspeed approaches 60 knots. At this point start reducing the reverse thrust so that the reverse thrust levers are moving down at a rate commensurate with the deceleration rate of the airplane. The thrust levers should be positioned to reverse idle by taxi speed, then to full down after the engines have decelerated to idle."
Simple, really.....?
Autobrakes are great but brilliant in crosswinds/asymmetric landings. I don't know about others but I'd find it very hard to get consistent manual braking with large rudder inputs using toe brakes... You're trying to produce two identical and steady forces on your toes combined with two different and changing ones on each leg - no mean feat! With the autobrake you just have to steer.
Reversers (B777): We have carbon brakes so unless it's going to impact the turnaround, idle only. 'Reverse', i.e. full is close to the deceleration of the autobrake 1 setting, so we try to avoid that combination as it increases brake wear by coming on-and-off. I tend to keep them in down to taxi speed as it gives a smoother transition when stowed and the manual says they're OK to use to a full stop. If we have used reverse above idle, I try and let the engine wind down before going into forward thrust as this can lead to quite a 'thump'.
Reversers (B777): We have carbon brakes so unless it's going to impact the turnaround, idle only. 'Reverse', i.e. full is close to the deceleration of the autobrake 1 setting, so we try to avoid that combination as it increases brake wear by coming on-and-off. I tend to keep them in down to taxi speed as it gives a smoother transition when stowed and the manual says they're OK to use to a full stop. If we have used reverse above idle, I try and let the engine wind down before going into forward thrust as this can lead to quite a 'thump'.