Rote use of autobrakes when operationally unnecessary

[A37575]

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?

[SNS3Guppy]

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.

[Dan Winterland]

Carbon or steel brakes? Autobrake generally leads to less wear on carbon brakes.

[Checkboard]

The autobrakes will always do a better and more consistent job of applying the brakes than you.

Rubbish. :hmm:

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.

[SNS3Guppy]

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.

[Checkboard]

*sigh* :rolleyes:

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. :rolleyes:

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).

The antiskid has nothing to do with the autobrake system. :ugh:

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.

[On-MarkBob]

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.

[SNS3Guppy]

The antiskid has nothing to do with the autobrake system.


Actually, it really does.

This, incidentally, is an aviation forum. Not a racecar forum.

You may be in the wrong forum.

[Stan Woolley]

A good pilot can brake better than the autobrake. Fact.


Rubbish :hmm: Sigh :rolleyes:

Not when it's in RTO they can't .Fact.

[SNS3Guppy]

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.

[Kiltie]

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?

[Stan Woolley]

SN3Guppy

Actually, takeoff autobrakes are applied faster than pilot reaction

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?

[thesilversurfer]

Checkboard

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

[FE Hoppy]

SilverSurfer:

That would be a HUD3A. Man machine intergration rather than interface. Don't knock it.

However, checkerboard is talking balls about autobrake.

[GlueBall]

Kiltie: "Autobrake is applied on mainwheel touchdown quicker than my reaction would be to start applying them manually"

Why would you need brake application immediately on mainwheel touchdown?

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.

[BOAC]

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!:ugh:

[CommandB]

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!!! :ok:

"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.... :{

[Kiltie]

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?

[BOAC]

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.....?

[FullWings]

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'.

[Kiltie]

Yes, but always worth dusting off the FCTM (or trawling through the CD with one's magnifying glass) to refresh the memory I suppose. Thanks BOAC.

[A37575]

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)

Ahem! My B737 FCTM has this to say about use of reverse thrust during landing: "Maintain reverse thrust as required 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 full down after the engines have decelerated to idle. Etc.

I can see nothing there that would indicate danger from FOD if the above procedures are used correctly.

With regards to heat dissipation being better at high speed on the ground and that being a factor in the perceived advantage of the autobrake system applying brakes on wheel spin up. In the short period it takes from touch down to taxi speed, the reduction (?) of heat build up due to higher airflow over the brake units at high speed would surely be of no consequence. In any case, the maximum heat attained within the brakes occurs up to 30 minutes after the aircraft has stopped. That is one reason why a brake fire warning can occur well into the climb after take off and not necessarily just as the wheels are tucked away in the wheel-well. The heat build up increases once the landing gear is retracted and cooling airflow is diminished.

[Jimmy Do Little]

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.
Airbus, exactly the same.

Also - reading between the lines of the Airbus QRH - manual braking is only a requirment when "Maximum Performance Braking" is required (QRH 4.04 Notes).


Finally, as "Dan" states... ...Autobrake leads to less wear on carbon brakes...

[stillalbatross]

Other point is multiple failures or distractions in late landing, flare or roll out and without autobrakes there may be an unnecessary delay to you applying manual braking.

Aeroplanes and aviation don't always work perfectly all the time.

[rubik101]

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.

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.

4 to 5 second delay in applying brakes on touch down is better than the Autobrake?

My Flight Manual is the one you want to read, forget Boeing/Airbus...???!!!...



No names mentioned but for goodness sake........Cowboys spring to mind.

[john_tullamarine]

the maximum heat attained within the brakes occurs up to 30 minutes after the aircraft has stopped. That is one reason why a brake fire warning can occur well into the climb after take off

And one of the reasons the FT community likes to dangle the wheels for a while after takeoff to cool the units off following any significant braking effort on test. Indeed, after RTO work, the usual procedure is to turn around and takeoff immediately solely for the purpose of flying around for 5-10 minutes with the wheels down.

I can recall at least one aircraft lost after a overheated tyre burst some time after takeoff ... not a hazard to treat lightly.

[safetypee]

IMHO more frequent use of manual braking would add to safety, particularly in reducing the risk of an overrun. The ‘training’ problem appears to reside with the level of knowledge about the auto-brake systems, and the wider ranging aspects of their use and effect on landing performance.

Re: “Autobrakes provide a known rate of acceleration, which means that it can be used to calculate stopping distance. …” (# 2)

This is only true for a very narrow range of conditions.
The auto-brake deceleration should give a consistent ground distance for the landing weight provided that the touchdown is made at the ‘correct’ speed, on a defined surface (composition and texture), and with known frictional qualities.
The actual landing distance involves an additional airborne distance and a transitional distance for the time taken to deploy spoilers and activate brakes – the total ‘stopping distance’.

For certified performance these additional distances are included in the measured performance landings.
For ‘advisory’ data (unfactored), the total landing distance may assume a fixed airborne distance from the threshold to touch down and a fixed transition time at touchdown speed; it may also assume the use of reverse thrust whereas certification might not.

In normal operation, landings may not match the assumed airborne distance, spoiler/ brake application timing, or achieve the correct touchdown speed (Vref/wind errors). These contribute significant errors in landing distance (ref AC 91-79 (www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/0052f2a2a00d91b28625738e0071e44c/$FILE/AC_91_79.pdf))

If the runway frictional qualities are not as assumed due to a different runway texture or water depth, then the ground distance may vary. The auto-brake brake will apply up to the maximum antiskid brake effort in attempting to achieve the required deceleration, beyond that more distance is required.
In limiting conditions the increased distance may significantly reduce the landing safety margin provided by the LDR, thus there is an increased risk of overrun.

Some thrust reverse use is normal during landing. Any deceleration provided by reverse enables the auto-brake to reduce the brake effort while still meeting the required deceleration; operators who buy brake time and use reverse may have a poor deal – are you paying for brakes that you don’t use.
Thus reverse might be considered to add a safety margin, minimizing the risk of overrun. However, this could be a false argument where the additional safety margin from reverse becomes a norm for operations and crews may become dependent on the ‘expected’ availability of reverse i.e. they use of lower than required auto-brake settings because previous landings (with reverse) ‘were OK’.
The use of higher power reverse with auto-brake could mask occurrence of some risky landings due to errors in the factors above.

This suggests that where landing conditions are good, a long non limiting runway, and reverse is to be used, then auto-brake provides few operational or technical benefits - except providing a smooth feel due to the constant deceleration. If pilots are equally capable, then why not let them use the brakes and add to their experience; brake for safety, not for comfort.

During a manually braked landings, pilots can relate to the deceleration from the applied brake effort via foot force (pedal deflection). During auto-brake operations pilots do not have this feedback which is an important cue aiding ability in judging the actual stopping distance in relationship to the runway conditions and speed at touchdown – opportunity for more experience.
This again is a safety argument for manual braked landings in suitable conditions.

In adverse conditions or on limiting runways (and RTOs) there is a more balanced safety case for using auto-brake at the higher settings. However, without manual braking experience, the problems of ‘masking’ the applied brake level from the crew might appear ‘surprising’ when cancelling reverse in marginal operations.
Furthermore, some auto-brake/landing SOPs might unintentionally rely on reverse to provide a consistent safe landing distance; if so, then in conditions where certificated performance might assume reverse use (EU/JAA contaminated perf) then there could be some nasty surprises.

Re: “… brakes coming on at the moment of touch down …”
Not in some auto-brake systems, which at lower settings delay or ramp-up the brake pressure to give priority to thrust reverse deceleration at high speed.
See: Chap 8.4, page 2. (www.flightsafety.org/alar_resources.html)

Re: “...Autobrake leads to less wear on carbon brakes...”
Is this fact or myth? Decelerating to a stop requires the dissipation of energy – the same level from identical touchdown speeds, same wt, etc; the variable is the rate of dissipation of energy. If the manual braking level is the same as the auto-brake, then brake temps/wear should be equal.
Perhaps the inequality / asymmetric braking problems originate from the lack of manual practice.

[A37575]

Perhaps the inequality / asymmetric braking problems originate from the lack of manual practice

As a frequent observer in the simulator, I can attest to that...

[DK_FCI]

Lol - I dont even have autobrake as I fly the CRJ - so to me this seems like a "theoretical" discussion.

The CRJ200 is a runway intensive little plane, cat D approaches into short runways - all with manual braking and manual throttle btw. We do it safely and consistently day in and day out, in sunshine, in rain, in snow.

Surely that can be safely and consistently done in a B737 too - if not I think the problem lies elsewhere.

So from that perspective I dont really see what all this fuss is about.

What is it that drives us to operate at the highest level of automation at all times?

[Stan Woolley]

Perhaps the inequality / asymmetric braking problems originate from the lack of manual practice

What manual practise are we talking about here, Maximum effort stopping or everyday landings?

At my home base I use Autobrake 3 for the vast majority of landings but I still get lots of practise at manual braking to make the preferred turnoff (avoiding backtrack and distressing the guy behind).In my airline the FO would not get much practise because only the Captain has a tiller and generally takes over as we get below 60kts.

As for max effort well I can't practise that with pax and in the sim we want to encourage leaving RTO engaged.

This discussion is of course very type dependent but for modern Boeings/Airbus types Autobrake is a great piece of kit. There are many areas where practising would improve (occasionally required)performance but in reality it's not possible or not sensible.

[BOAC]

What is it that drives us to operate at the highest level of automation at all times? - it is called 'SOP' - written largely by those who's understanding of flying is now a bit tarnished, and often driven by insurers and accountants.

[safetypee]

JT Re # 26 “… the FT community likes to dangle the wheels for a while after takeoff to cool the units off following any significant braking effort on test. Indeed, after RTO work, the usual procedure is to turn around and takeoff immediately solely for the purpose of flying around …”

Generally true for high brake useage, except for RTOs, which tend to have greater energy levels than landing (TO wt above max landing wt).
However, considering that although the initial brake temps were low, the landing energy in stopping has gone somewhere, but not through the brake fans that quickly. Thus the debate is that although the energy was in the brake heat pack, because it did not indicate on the temp gauges then the tyres were not in danger of heat soak. Thus in-flight cooling helped cool both the brake pack and tyres. (I’m not entirely convinced, but it worked).
For RTOs the higher energy levels did not permit the choice, often as did the presence of the fire truck!

Don’t try this at home – and don’t forget to look after the tyres.

[john_tullamarine]

oh dear .. once again my casual comment's lack of caveat gets me into trouble .. concur ... anything approaching a performance RTO energy level attracts an F-Troop pre-positioned response rather than a quick re-launch.

[muduckace]

Tower Air used to allow auto brakes at discretion. 99 deg in Miami 13k foot dry runway and the result of usage of max auto brakes would usually be 5 or 6 thermally discharged tires. Brake wear is also un necessary just to attempt the first turnoff.

[Rananim]

Autobrakes on landing should be optional.Let the pilot decide.RTO is a different matter.However,I would say that until the pilot has learned to use manual braking as smoothly and evenly as autobrakes,he/she should be discouraged from using autobrakes.Avoids automation reliance.Some FO's when asked say theyve never touched the brakes in anger which is not right.Get comfortable with manual and then use auto at your discretion(short rwys x-wind etc).An airline that makes AB usage mandatory is not correct.