Rote use of autobrakes when operationally unnecessary
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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)
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.
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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.
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...
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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.
Aeroplanes and aviation don't always work perfectly all the time.
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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.
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.
Last edited by rubik101; 18th Jul 2009 at 15:05. Reason: Contentious insult deleted.
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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.
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.
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)
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.
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.
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)
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.
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.
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Perhaps the inequality / asymmetric braking problems originate from the lack of manual practice
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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?
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?
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Perhaps the inequality / asymmetric braking problems originate from the lack of manual practice
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.
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Originally Posted by DK FCI
What is it that drives us to operate at the highest level of automation at all times?
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.
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.
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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.
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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.
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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.
