B737 All Flaps Up landing. Use of Autobrake Setting or not?
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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.
de facto, parabellum, 
A major problem for the industry is interpreting the assumptions made in certification and operational regulations. Thus what might be clear in theory is not so easy to apply in practice, but this should not result in out-thinking the intent of regulation or recommendation in maintaining safety.
Thus any interpretation which does not minimise landing distance when required might be judged with hindsight as inappropriate.
From the Boeing ref @#13, max manual braking provides better deceleration than max auto in dry conditions, but there is equivalence for wet or contaminated runways. From this, an argument citing the physical human factors problems of brake application might be justifiable, particularly for normal operations.
However, for an abnormal flapless-landing where a pre-landing distance check could suggest the need for a dry runway, the use of autobrake from SOP (or habit) may be more difficult to justify, yet the source of the difference also involves ‘human factors’, either judgement in determining SOPs, or operating habit.
For the judgement aspect, consider the “without undue force or exceptional skill’ phrase often used in certification – max manual brake is certificated which implies suitable ease of use.
Guidance comes from the Boeing QRH in that there are no landing distance data using autobrake with abnormal flap on either ‘good’, ‘medium’, or ‘poor’ runway surfaces; implying the use of max manual brake in these circumstances – confirmed by the small print assumption quoted in #13. Thus perhaps the human factors aspect should be more orientated at reminding crews to change ‘habit’ / SOP for abnormal landings.
Re certification of antiskid for max landing weight #19. For those aircraft with antiskid, the certification performance landings are flown with antiskid operating, the best performance / acceptable control and safety may depend on it.
A major problem for the industry is interpreting the assumptions made in certification and operational regulations. Thus what might be clear in theory is not so easy to apply in practice, but this should not result in out-thinking the intent of regulation or recommendation in maintaining safety.
Thus any interpretation which does not minimise landing distance when required might be judged with hindsight as inappropriate.
From the Boeing ref @#13, max manual braking provides better deceleration than max auto in dry conditions, but there is equivalence for wet or contaminated runways. From this, an argument citing the physical human factors problems of brake application might be justifiable, particularly for normal operations.
However, for an abnormal flapless-landing where a pre-landing distance check could suggest the need for a dry runway, the use of autobrake from SOP (or habit) may be more difficult to justify, yet the source of the difference also involves ‘human factors’, either judgement in determining SOPs, or operating habit.
For the judgement aspect, consider the “without undue force or exceptional skill’ phrase often used in certification – max manual brake is certificated which implies suitable ease of use.
Guidance comes from the Boeing QRH in that there are no landing distance data using autobrake with abnormal flap on either ‘good’, ‘medium’, or ‘poor’ runway surfaces; implying the use of max manual brake in these circumstances – confirmed by the small print assumption quoted in #13. Thus perhaps the human factors aspect should be more orientated at reminding crews to change ‘habit’ / SOP for abnormal landings.
Re certification of antiskid for max landing weight #19. For those aircraft with antiskid, the certification performance landings are flown with antiskid operating, the best performance / acceptable control and safety may depend on it.
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A major problem for the industry is interpreting the assumptions made in certification and operational regulations
Now if Beoing misenterpreted 'assumptions' made in certification,i think it is becoming quite hard for a pilot to make a perfect judgement...
Most pilots use data and recomendations from their aircraft to the best of their knowledge,a knowledge that is given to them by Boeing in that case.
Boeing does not do test of non normal distance with autobrake system on,does it mean it cant be done? i think not.
For the judgement aspect, consider the “without undue force or exceptional skill’ phrase often used in certification – max manual brake is certificated which implies suitable ease of use.
Guidance comes from the Boeing QRH in that there are no landing distance data using autobrake with abnormal flap on either ‘good’, ‘medium’, or ‘poor’ runway surfaces; implying the use of max manual brake in these circumstances – confirmed by the small print assumption quoted in #13. Thus perhaps the human factors aspect should be more orientated at reminding crews to change ‘habit’ / SOP for abnormal landings
Many pilots in the SIM when having to perform a landing above the MAX landing weight will go directly for the MAX manual braking,now this HABIT along with a 13000 feet dry runway should be discouraged or?
A flaps assymetry with the lowest flap at 15 deg and one at 25 will lead you to a landing (NON NORMAL landing distance) using flaps 15 speeds and max manual braking..should a pilot do that too?(a speed that would be equivalent to an faa approved 2 engine approach speed,where Auto brake landing data are published..)
The non normal checklists do include for non normal situations the choice of Autobrakes..otherwise in the descent defferred items,the autobrake ____ would show OFF? Or not appear.
I believe pilots have the choice,i chose to use it.
Wouldnt you think that having the autobrake set at MAX and then brief and reminded to go max manual braking is on the safer side than land with no autobrake selected with a chance of a distraction and much more distance lost due to delayed manual braking?
Re certification of antiskid for max landing weight #19. For those aircraft with antiskid, the certification performance landings are flown with antiskid operating, the best performance / acceptable control and safety may depend on it.
Last edited by de facto; 11th Jan 2013 at 02:45.
de facto, as with many operational aspects in aviation there may be no clear answer – a solution depends on the situation. Pilots will have a choice, but the process of choosing should consider the differences between published ‘fact’ and what might be believed (myth, bias, false interpretation).
In choosing a course of action, a pilot must be able to justify the chosen option as being based on a sound understanding of the situation and knowledge of contributing factors, with the objective of minimising risk.
For the flapless landing case, my choice would be biased by the lack of max autobrake distance to compare with max manual brake distance; and to use max brake until a safe stop was assured, irrespective of runway available.
Alternatively, if autobrake data were available, then using autobrake might be justified with suitable mitigation such as a dry surface or longer runway, but even these have to be judged against the many other sources of variability in landing.
Re autobrake testing, worn tyres, etc, the relevant sections of FAR/CS 25 and AC 25-7 provide a good knowledge base.
In choosing a course of action, a pilot must be able to justify the chosen option as being based on a sound understanding of the situation and knowledge of contributing factors, with the objective of minimising risk.
For the flapless landing case, my choice would be biased by the lack of max autobrake distance to compare with max manual brake distance; and to use max brake until a safe stop was assured, irrespective of runway available.
Alternatively, if autobrake data were available, then using autobrake might be justified with suitable mitigation such as a dry surface or longer runway, but even these have to be judged against the many other sources of variability in landing.
Re autobrake testing, worn tyres, etc, the relevant sections of FAR/CS 25 and AC 25-7 provide a good knowledge base.
Last edited by safetypee; 11th Jan 2013 at 20:20. Reason: typo
