B737 All Flaps Up landing. Use of Autobrake Setting or not?
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B737 All Flaps Up landing. Use of Autobrake Setting or not?
Discussion arose during a 737 simulator session on autobrake use, where some operators mandate use of autobrakes for every landing.
The example of an all flaps up landing came into the conversation where study of the landing length required indicated it was indeed marginal. The consensus was that it would be wise to have the autobrakes set to Max. In fact, criticism would almost certainly be levelled at the pilot if he chose not to use autobrakes. This would be backed up with reference to the FCTM that says: "Boeing recommends that whenever runway limited, using higher than normal approach speeds, landing on slippery runways or landing in a crosswind, the autobrake system be used."
Then someone pointed out that the QRH (Advisory Information, Non-Normal Configuration Landing Distance Dry Runway) that lists the different landing configurations, also contains a footnote that states the distances assume maximum manual braking and maxiximum reverse thrust when available on the operating engines.
As maximum manual braking gives better deceleration than Max autobraking, it could be argued this footnote implies that autobraking should not be used since deceleration is less than with maximum manual braking. In turn this would suggest the landing distance numbers for Non-Normal Configuration Landing Distance are invalid if autobrakes are used? At first glance, most pilots would indeed select an autobrakes setting for an all flaps up landing on a limiting length runway. Paradoxically, this precaution (some would call it good airmanship) could well lead into the potential for an over-run - since the landing length figures are based upon the much harsher braking available through manual braking, rather than automatic braking. In each case maximum reverse thrust is assumed.
Your thoughts are welcomed.
The example of an all flaps up landing came into the conversation where study of the landing length required indicated it was indeed marginal. The consensus was that it would be wise to have the autobrakes set to Max. In fact, criticism would almost certainly be levelled at the pilot if he chose not to use autobrakes. This would be backed up with reference to the FCTM that says: "Boeing recommends that whenever runway limited, using higher than normal approach speeds, landing on slippery runways or landing in a crosswind, the autobrake system be used."
Then someone pointed out that the QRH (Advisory Information, Non-Normal Configuration Landing Distance Dry Runway) that lists the different landing configurations, also contains a footnote that states the distances assume maximum manual braking and maxiximum reverse thrust when available on the operating engines.
As maximum manual braking gives better deceleration than Max autobraking, it could be argued this footnote implies that autobraking should not be used since deceleration is less than with maximum manual braking. In turn this would suggest the landing distance numbers for Non-Normal Configuration Landing Distance are invalid if autobrakes are used? At first glance, most pilots would indeed select an autobrakes setting for an all flaps up landing on a limiting length runway. Paradoxically, this precaution (some would call it good airmanship) could well lead into the potential for an over-run - since the landing length figures are based upon the much harsher braking available through manual braking, rather than automatic braking. In each case maximum reverse thrust is assumed.
Your thoughts are welcomed.
Land with max autobrakes selected to ensure prompt initiation of braking.
Take over manually as soon as possible with max manual braking for best stopping performance.
Take over manually as soon as possible with max manual braking for best stopping performance.
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Agreed, and to finesse double check the break cooling whilst your there.
All very well piling up on stand looking the hero after dodging the school by wrestling with the controls, only to have a fuse melt, then catch fire and blow half the airport up because your parked right next to a brand new A380 thats just started refuelling
Ie think of parking remote just for a while.
All very well piling up on stand looking the hero after dodging the school by wrestling with the controls, only to have a fuse melt, then catch fire and blow half the airport up because your parked right next to a brand new A380 thats just started refuelling
Ie think of parking remote just for a while.
One thing that is noticeable from the back of the sim is that folk don't get max manual braking, the brake pedal deflection is insufficient. A little coaching and practice sorts that out, the autobrake however is consistent and doesn't need coaching and practice.
My plan in the event is to do as Stilton suggests.
My plan in the event is to do as Stilton suggests.
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One thing that is noticeable from the back of the sim is that folk don't get max manual braking, the brake pedal deflection is insufficient
Slight thread drift but some years ago we were endorsing Asian cadet pilots on the B737-300 simulator. The exercise was high speed rejected take off's. It was observed that while one cadet always did the correct procedure and pulled up where expected, his crash-mate would always over-run despite the engine being failed at the same speed and the student apparently going through the correct procedure.
This had me tossed, until I happened to be watching the instructor screen as this cadet was doing his take-off and noticed the brake chart popping up when this only normally happens on the landing run.
It transpired he was taking off with his feet high on the rudder pedals and unknowingly applied dabs of brake as he moved the rudder pedals. In turn this slowed the acceleration and when he rejected the take off at the correct airspeed he was already further down the runway; hence the over-run.
Faced with this, he vehemently denied dragging the brakes and instead blamed the fidelity of the simulator. Typical culture driven loss of face syndrome. The solution was to have his crash-mate sit on the instructor seat and observe the brake pressure page on the instructor panel. Sure enough, the crash-mate saw the brake pressures bouncing up and down during the next take off run. A rapid discussion took place between the students in their own language and the problem was rectified.
Last edited by A37575; 9th Jan 2013 at 11:44.
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If runway limited, Auto brake MAX and immediately after touch down max manual braking.
The autobrake applies braking quicker than any one would.
The Autobrake at MAX will give you MAX hydraulic pressure(3000psi) at touchdown,ONLY when the first deceleration is sensed(speedbrakes/reversers) take effect will the autobrake reduce the braking force,therefore it is reasonable I think to expect full manual braking by at least the initiation of the other deceleration devices.
The reason why the distance is less with manual braking is that the Reversers deceleration force is ADDED to the the braking force rather than possibly reducing it.
Going to a limited runway with flaps up is asking for trouble obviously...
The autobrake applies braking quicker than any one would.
The Autobrake at MAX will give you MAX hydraulic pressure(3000psi) at touchdown,ONLY when the first deceleration is sensed(speedbrakes/reversers) take effect will the autobrake reduce the braking force,therefore it is reasonable I think to expect full manual braking by at least the initiation of the other deceleration devices.
The reason why the distance is less with manual braking is that the Reversers deceleration force is ADDED to the the braking force rather than possibly reducing it.
Going to a limited runway with flaps up is asking for trouble obviously...
Last edited by de facto; 9th Jan 2013 at 12:43.
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I am thinking that the only way to land with the brakes on would be with the parking brake set which of course we try to avoid. If you touchdown under normal circumstances with the brake pedals APPLIED, you actually don't have any brakes on at touchdown due to locked wheel protection although I think that once the wheels spin up, then the brakes will be applied just a moment later resulting in the near equivalent as having landed with brakes on but without blown tires.
Is this correct?
Is this correct?
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The locked wheel and the touchdown protections are a function of the antiskid.
So yes with Autobrakes OFF and feet on brakes at landing,if the antiskid is quick enough and you dont burst a tire then the touchdown protection will quick in and release brake pressure until the tire speeds are within 50 kts i think of your groundspeed so you will lose braking that way anyways...and field limited or not ill never do such a thing as landing with brakes on..
So yes with Autobrakes OFF and feet on brakes at landing,if the antiskid is quick enough and you dont burst a tire then the touchdown protection will quick in and release brake pressure until the tire speeds are within 50 kts i think of your groundspeed so you will lose braking that way anyways...and field limited or not ill never do such a thing as landing with brakes on..
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All very well piling up on stand looking the hero after dodging the school by wrestling with the controls, only to have a fuse melt, then catch fire and blow half the airport up because your parked right next to a brand new A380 thats just started refuelling 
Ie think of parking remote just for a while.
Ie think of parking remote just for a while.
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I normally landed on Runway 9 at MIA. 13,000 feet long. I would be a fool landing no flaps in a 757 with max brakes. Obviously we would have a brake fire for no reason. I wouldn't even touch the brakes to around 80 knots because you only need half the runway to stop. Use common sense in situations like this. The book is there for reference but common sense should prevail.
The best possible deceleration – minimum landing distance, is with max manual braking and reverse thrust.
With autobrake and reverse the landing distance may be longer. This is because reverse may meet much of the selected value of autobrake deceleration, resulting in a reduced brake pressure.
With max manual braking and reverse, the effect of reverse is additive to manual brake (with autobrake it may only complement it - as #6).
This is shown diagrammatically on slides 10 – 14 in the Boeing presentation ‘Landing on Slippery Runways’.
Depending on the brake system design, the touchdown wheel-lock protection should work irrespective of autobrake / manual selection, although in some types it may be associated with antiskid, but each may be separate, independent, functions.
Check the small print on advisory landing data charts whether the distance data assumes manual or autobrake ; e.g. third bullet on side 14, Boeing gives both for normal ops (slides 6/8) – but check again for abnormal configurations.
An old copy of a 737 QRH for flapless landing states “Assumes maximum manual braking and maximum reverse thrust when available on operating engines”. Also that the assumed air distance from TCH to touchdown is 1000ft; this is unlikely to be achieved, even more so if a shallow/flat approach is flown.
With autobrake and reverse the landing distance may be longer. This is because reverse may meet much of the selected value of autobrake deceleration, resulting in a reduced brake pressure.
With max manual braking and reverse, the effect of reverse is additive to manual brake (with autobrake it may only complement it - as #6).
This is shown diagrammatically on slides 10 – 14 in the Boeing presentation ‘Landing on Slippery Runways’.
Depending on the brake system design, the touchdown wheel-lock protection should work irrespective of autobrake / manual selection, although in some types it may be associated with antiskid, but each may be separate, independent, functions.
Check the small print on advisory landing data charts whether the distance data assumes manual or autobrake ; e.g. third bullet on side 14, Boeing gives both for normal ops (slides 6/8) – but check again for abnormal configurations.
An old copy of a 737 QRH for flapless landing states “Assumes maximum manual braking and maximum reverse thrust when available on operating engines”. Also that the assumed air distance from TCH to touchdown is 1000ft; this is unlikely to be achieved, even more so if a shallow/flat approach is flown.
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Bubbers,
The OP question was mentionning the runway lengh being critical...of course if the runway is 13000 feet long,no needto usemax braking..i would go with 2 initially....
The OP question was mentionning the runway lengh being critical...of course if the runway is 13000 feet long,no needto usemax braking..i would go with 2 initially....
de facto, the choice of a lower autobrake setting may involve many assumptions, e.g. condition of the runway surface, brake/tyre condition, thrust reverse contribution to deceleration, or any additional safety margin for flying inaccuracies.
How and when is it possible to realise that the lower setting might be insufficient?
Then what, and will any change be sufficient at a late stage of the rollout.
.
How and when is it possible to realise that the lower setting might be insufficient?
Then what, and will any change be sufficient at a late stage of the rollout.
.
Last edited by safetypee; 9th Jan 2013 at 22:41. Reason: typo
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de facto, the choice of a lower autobrake setting may involve many assumptions, e.g. condition of the runway surface, brake/tyre condition, thrust reverse contribution to deceleration, or any additional safety margin for flying inaccuracies.
How and when is it possible to realise that the lower setting might be insufficient?
Then what, and will any change be sufficient at a late stage of the rollout.
.
How and when is it possible to realise that the lower setting might be insufficient?
Then what, and will any change be sufficient at a late stage of the rollout.
.
In the case of a DRY runway,no wind,and a 13000 feet runway,the use of AB 2 would me more than sufficient for stopping distance at Max landing weight flaps up and with a sufficient margin from brake temp limits...have a look at the QRH for NORMAL landing distance with Flaps 40 and add approach speed adjustment of 55 kts,it will give you a good idea of runway you will need if other parameters such as wind,runway condition,touchdown point,reversers ....stay the same.
Have a look at brake cooling temp at a speed of vref40 max landing weight plus speed adjustement at touchdown.
By the way the AFM landing distances include a ONE second delay to account for Max manual braking application,not the case when using autobrakes,so to answer the OP,if after all calculations for landing distance with max braking and factors such rwy condition,wind,weight.....and you find out there is not One meter to spare at the end and you cant divert,well the Setting of MAX autobrake will give you a second of MAX auto brake lead on the AFM over going directly to Max manual braking.
In the case of dry and wet,the AFM distances account for normally worn out tires,however the Fully modulated Antiskid system does NOT need to be checked at Max landing weight for certification....so you are on your own there and hope the antiskid perform properly.
Last edited by de facto; 10th Jan 2013 at 06:55.
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This subject came up when I did my 737-200 course in Seattle in 1977.
It is correct to say that full manual breaking is greater than Max auto brake but it would be quite wrong to say that it must, therefore, be used in preference to Max autobrake as it completely misses the human factor.
With due respect Safety Pee, your statement:
is true in theory only.
If we think the flapless landing process through, using Max auto brake, the brakes will activate as soon as the system agrees the aircraft is on the ground. At this same point, should Max auto brake not have be selected, the pilot is lowering the nose, selecting reverse, keeping straight and trying to apply max braking through the pedals, an unfamiliar exercise in coordination that is something we don't normally get the chance to do very much, (try it in your chair whilst reading this!). More importantly try it in the SIM the next time, you will be very hard pressed to beat the initial braking achievements of Max Auto brake, even after several practices.
The consensus at Boeing was, let the Max Auto brake do it's job ASAP whilst the pilot completes the touch down then, by all means, go for max manual breaking, when the pilot is not trying to do a few other things at the same time. Do remember that the Boeing numbers and procedures are based on the average line pilot, not the TRE/SIM instructor.
It is correct to say that full manual breaking is greater than Max auto brake but it would be quite wrong to say that it must, therefore, be used in preference to Max autobrake as it completely misses the human factor.
With due respect Safety Pee, your statement:
The best possible deceleration – minimum landing distance, is with max manual braking and reverse thrust.
If we think the flapless landing process through, using Max auto brake, the brakes will activate as soon as the system agrees the aircraft is on the ground. At this same point, should Max auto brake not have be selected, the pilot is lowering the nose, selecting reverse, keeping straight and trying to apply max braking through the pedals, an unfamiliar exercise in coordination that is something we don't normally get the chance to do very much, (try it in your chair whilst reading this!). More importantly try it in the SIM the next time, you will be very hard pressed to beat the initial braking achievements of Max Auto brake, even after several practices.
The consensus at Boeing was, let the Max Auto brake do it's job ASAP whilst the pilot completes the touch down then, by all means, go for max manual breaking, when the pilot is not trying to do a few other things at the same time. Do remember that the Boeing numbers and procedures are based on the average line pilot, not the TRE/SIM instructor.