737 Autobrake

[hawk_eye]

I am aware that the different auto brake settings on the 737 target specific deceleration rates. I am wondering though if specific operators can determine what those deceleration rates are, or whether those rates are simply determined and set by Boeing?

My experience on the 737 tells me that it would be nice if there was an auto brake setting between 3 and Max.

Appreciate anyone’s thoughts.

Cheers

[Judd]

it would be nice if there was an auto brake setting between 3 and Max.


The down-side of being addicted to autobrake use (or forced by company SOP) as suggested by your question, is that you soon lose the foot pressure skills required for manual braking where you yourself can vary the brake pedal pressure to what you need.
I understand Boeing never envisaged that autobrakes were to be used on every landing. The 737 FCTM reminds pilots that use of the autobrake system is recommended whenever the runway is limited, when using higher than normal approach speeds, landing on slippery runways, or landing in a crosswind. Common sense would dictate this means a significant crosswind not a gentle breeze. If none of the above then there should be no sweat in applying manual braking.
It is common during simulator training to see eyebrows being raised when pilots are asked to demonstrate their skills at manual braking. Suddenly we see the aircraft swerving all over the runway with centreline tracking non-existent and the aircraft jerking under asymmetric braking. Just another instance where automation dependency inevitably causes degradation of manual skills.

[Chesty Morgan]

Get off your soapbox and answer the question :rolleyes:

[B2N2]

Deceleration rates are set by Boeing.
The amount of braking forces obviously varies with weight in order to achieve said deceleration.
Can’t remember what it was on the 300/400 and don’t know if it was the same in newer 73’s.
We did 60% of our smack downs with manual braking.

[safetypee]

CM #3, Au contraire; Judd addresses a fundamental aspect.
The underlying question is not in the choice of level of automatic braking according to personal preference, but the self questioning and knowledge about automatic systems, and associated skills. Why do we believe that we require this automation.
A simple view is that we don’t; thence it is necessary to consider reasoned arguments for and against such a system, and it’s use.
Questioning and reflection should help us focuses on the underlying, covert assumptions within most automation. What does autobrake assume, what does the pilot know about the operation of the system, purpose, what are the benefits and balances with the continuing need for safe operation.
Given the abysmal overrun safety statistics, such questioning is both justified and necessary.

For the question #1; I don’t know how or why Boeing chooses specific values; but based on other programmes, the deceleration level is a balance between stopping safely and the cost of brake / tyre wear. The stopping distances may well be influenced by operators with large fleets - money talks, so the landing distances - deceleration are tuned for a particular route structure. Other operators suffer the irritation of ‘inappropriate optimisation’. Would your management pay for your wish-list?
As for the choice of deceleration level; there is no particular one which is ‘nice-to-have’, only that which matches the conditions to provide the required level of safety. That requires some thinking, not automation.

The great ‘automation bias’, perhaps for SOPs as well, is in the associated mantras can influence situation assessment. In the extreme pilots are tempted (subconsciously) to chose an aspect of automation (operational procedure) and match the real world situation to that choice. Habit, bad habit.

[Chesty Morgan]

Yes we’re all well aware of the chest beating that goes on when it comes to automation. it doesn’t need to be repeated ad nauseum.

A simple question was asked and ignored in the quest to let everyone know how amazing us old school pilots are because we can press a pedal. What was the term? “Foot skills” :}

It’s tiresome, boring and detracts from someone’s attempt to improve their knowledge.

[maggotdriver]

Not sure about variation from Boeing but I believe the rates are 4,5,7 and 14 feet / second squared correlating to 1,2,3 and max. Hope that helps a little.

[excrab]

Whilst I agree that we should be able to use manual braking, a very good reason for using auto brakes is that if you don't there is (as far as I know) no way of working out the brake cooling times if you use some kind of random manual brake pressure.

[BluSdUp]

Hawk
The answer is no!
It is designed and tested by Boeing and approved by FAA.
Just think of the massive amount of testing required to customize this system for AirlineX!
Have a look at the tables in QRH NNC landing distance!!
If you want a mod on your ride, ask Lufthansa when they got Boeing to reverse the lightswitches and the likes for "fleet standard" due to the fact the Boeing switches works opposite of other aircraft.
Anyway
There is a setting between max and 3: Sett max and gently over-ride when performance ( Stopping distance) assured.
Happy Landings and stopping
PS
Chesty: Take a pill!

[safetypee]

excrab, #8, you appear to be already in the automation rut. Determining brake cooling time, helping the operation, passengers, etc, is not a good reason for autobrake selection, nor a justifiable defence of why you are trying to explain this from the overrun area.
Don’t let the next takeoff determine the level of braking; stop first then think about it.
You and many others may well add caveats and defensive positioning, that safety would come first, that you would not think that way; but once you have had the thought it is very difficult to suppress.

[Skyjob]

AUTOBRAKE TECHNICAL INFORMATION
Autobrake Selector / Max Pressure at Brakes (PSI) / Deceleration Rate (ft/sec2)
1 / 1250 PSI / 4 ft/sec2
2 / 1500 PSI / 5 ft/sec2
3 / 2000 PSI / 7.2 ft/sec2
Max / 3000 PSI / 12 ft/sec2 below 80 kts
Max / 3000 PSI / 14 ft/sec2 above 80 kts
RTO / Full Pressure / uncontrolled rate

There is an "on ramp" period where autobrake pressure is applied over a period of time. Approximately 750psi is applied in 1.75 sec, then the pressures above are reached in another 1.25sec for autobrakes 1, 2, or 3 and approx. 1.0 sec for autobrake MAX.

Using high autobrake settings with idle reverse is particularly hard on the brakes as they will be working for the given deceleration rate without the assistance of full reverse thrust. This could lead to the rate not being achieved when the pressure is applied for the selected rate, especially on more slippery runway conditions.

To cancel the autobrake on the landing roll with toe brakes you must apply a brake pressure in excess of 800psi (less than that required for autobrake 1).

[misd-agin]

There is a setting - you.

Select auto brakes 3 and push a little bit harder with your toes to achieve the desired de-acceleration.

[hawk_eye]

Thanks for some of your replies - a couple helpful, others not so much.

Allow me to give some context to the question. I work for an operator of the 737 in Australia - we fly the 738 to a number of ports that have landing distances in the order of 1800m, the shortest one being Hamilton Island with a LDA of 1764m. It is also not uncommon for these places to be wet, and for our landing weight to be fairly close to MLW.

Now, approximately 18 months ago our operator came up with an Operational Landing Solution policy. Essentially this policy REQUIRES us to land with an auto brake selection that ensures that the aircrafts LDR is less than the LDA - which I do not think is an unreasonable policy, given some of the limiting runways we land on.

However the issue arises when landing at Hamilton Island, close to Max Landing Weight on a wet runway. The policy requires us to use auto brake Max - I’m not sure how many of you have landed with Max auto brake in a 738, but it is quite aggressive. Most of the guys will kick the auto brake out fairly soon after touchdown, because if it was left in, you would need to add thrust to roll through to the end of the runway before backtracking, not to mention that all of the passengers are basically thrown forward into the seat in front of them!

So from the research I had done, I was aware that the deceleration rate of AB 3 was in the order of 7 f/s and AB Max was in the order of 14 f/s. The question I posed was to find out whether an operator could request those deceleration rates to be altered - I believe an AB 3 decel of 9-10 f/s and AB 2 decel of 6-7 f/s would be far more suited to my company’s operations.

I’m interested in one posters comments suggesting that changing the deceleration rates would require a heap of flight testing from Boeing. This raises another question I don’t know the answer to, as I would have thought that the landing distances in the QRH would be derived mathematically (but obviously based on a level of flight testing during certification). Am I incorrect in that assumption?

I didn’t mean for this topic to become a debate on levels of automation - I would say at a guess, approximately one third to one half of the Landings I do, I would be overriding the autobrake. It is not uncommon in Sydney when landing on 16R when it’s wet, at high landing weights to override AB 3 in order to make the first high speed taxiway. So I don’t consider myself a ‘child of the magenta line’ - I’m more than happy to over ride AB when needed.

Thanks for all of the replies so far and I appreciate any further detail on the above.

Cheers

[stilton]

Deceleration rates are set by Boeing.
The amount of braking forces obviously varies with weight in order to achieve said deceleration.
Can’t remember what it was on the 300/400 and don’t know if it was the same in newer 73’s.
We did 60% of our smack downs with manual braking.



What does ‘we did 60% of our smack downs with manual braking’ mean ?

[Check Airman]

I remember reading (unverified) that the MD11 cam with a customer option to select a high or low decel schedule for autobrakes. I don't know if Boeing or Airbus offer a similar option.

[sheppey]

It’s tiresome, boring and detracts from someone’s attempt to improve their knowledge.
Chesty. The above quote could well apply to you too. Sarcasm is unpleasant and the lowest form of wit.

Now back to the subject of autobrake use. During the late Sixties or early 70's at a Boeing 727 Symposium held in Seattle, operators from around the world attended. When exchanging views at the symposium, evidence was presented by operators that, contrary to what Boeing had claimed that use of autobrakes would reduce wear and tear on brake units and wheels, autobrake use was causing double the brake changes and same with tyre wear.

Boeing replied by explaining the context of their recommendation. They admitted wear and tear was higher but that it was equal wear and tear so that scheduled servicing periods were more predictable. Boeing also stated that auto brake use was designed for operation where runway conditions were limited such that any delay in applying manual braking could be critical. Boeing further added that where sufficient margin of runway length was available there was no need to use autobrakes.

I doubt at the time that Boeing foresaw pilots using autobrakes as a means to make convenient taxi exit points along a runway; thus converting excess runway available into a considerably shorter landing run. Result - hotter brakes.

[Chesty Morgan]

Chesty. The above quote could well apply to you too. Sarcasm is unpleasant and the lowest form of wit
Except I wasn’t being sarcastic.

But well done for the rest of your post.

[Skyjob]

So from the research I had done, I was aware that the deceleration rate of AB 3 was in the order of 7 f/s and AB Max was in the order of 14 f/s. The question I posed was to find out whether an operator could request those deceleration rates to be altered - I believe an AB 3 decel of 9-10 f/s and AB 2 decel of 6-7 f/s would be far more suited to my company’s operations.

I’m interested in one posters comments suggesting that changing the deceleration rates would require a heap of flight testing from Boeing. This raises another question I don’t know the answer to, as I would have thought that the landing distances in the QRH would be derived mathematically (but obviously based on a level of flight testing during certification). Am I incorrect in that assumption?


1) There is no option to alter the rates set by the manufacturer. There IS an option for ordering the SFP variant, which enables less LDR effectively. Hopefully, your company already has the latest Boeing Performance Improvement Packages installed, which helps a little bit as well, other options are available, fleet weight reductions for one...
2) QRH distances are mathematically derived, but mathematically derived from flight test data in the first place. So new flight tests would be required to validate any new settings, from which then new QRH distances can be calculated...

[hawk_eye]

1) There is no option to alter the rates set by the manufacturer. There IS an option for ordering the SFP variant, which enables less LDR effectively. Hopefully, your company already has the latest Boeing Performance Improvement Packages installed, which helps a little bit as well, other options are available, felt weight reductions for one...
2) QRH distances are mathematically derived, but mathematically derived from flight test data in the first place. So new flight tests would be required to validate any new settings, from which then new QRH distances can be calculated...


Thanks Skyjob :ok:

[BluSdUp]

Thanks for elaborating on your question.
Got to love the -800 at MLW, she is fast.
Having started o TPs on 1000m rwy and the odd 800m I love short fields.
PAX comfort is by definition when they can hug the waiting family and wave goodbye to the nutter that made it happen!
As they say in WF : A good landing is a hard landing ( Boeing calls it firm!??)

Q/A
1 Do you have the Short Field Kit, Helps a wee bit.
2 Were do you go ( ICAO/ IATA code?)
3 Is it grooved?
4 Does it have displaced treshold and or overrun?
5 Does it ever snow there?

My big thing has always been max effort after touhdown on restricted field, as I have had multiple optimistic and wrong BA reported.
Never mind rubber deposits when damp and wet.
It is not an exact science, me thinks!
Most of my FOs have never seen AB MAX.
I think that it is important when flying the 738 to be ever so conservative with regards to landing.
Had it slide a couple of times, BOY did I wish I had a TP then.
Anyway.
AutoBrake MAX, gently over ride, when stopping assured, works for me and my PAX!
Remember the goal of the exercise : 1 No CNN 2 No HQ for tea/ biscuit 3 No report !
Not so technical, be practical!
Happy Landings
Regards
Cpt B
Happy landing, and stopping

[Derfred]

I think the OP’s point will be familiar to many NG operators.

Autobrake 3 is often not quite sufficient, and Autobrake MAX is around DOUBLE Autobrake 3 and is quite unfriendly to the pax if not needed.

It would be nice if Boeing had implemented an Autobrake 4 on the 737NG.

But they couldn’t. For the same reason they couldn’t implement a lot of other nice things. Ask the FAA.

[Sig229]

At my company (SWA) we are not authorized to use AB1, not sure why. Also if we're using AB we have to use at least the minimum that provides a positive stopping margin based on landing performance data. So in some cases, KMDW in the summer for example, even dry the numbers will require AB Max which discourages most people from using them. I would think it would be prudent to use 3 or even 2 so there's no delay in applying brakes but without the aggressiveness of Max. Since 1 is so tame why not just make 1 equal to what 2 is now, same for 2 equal to current 3, have 3 be somewhere between current 3 and Max, and keep Max where it is now?

[excrab]

At my company (SWA) we are not authorized to use AB1, not sure why. Also if we're using AB we have to use at least the minimum that provides a positive stopping margin based on landing performance data. So in some cases, KMDW in the summer for example, even dry the numbers will require AB Max which discourages most people from using them. I would think it would be prudent to use 3 or even 2 so there's no delay in applying brakes but without the aggressiveness of Max. Since 1 is so tame why not just make 1 equal to what 2 is now, same for 2 equal to current 3, have 3 be somewhere between current 3 and Max, and keep Max where it is now?

Auto brake one is such a low retardation that it is achieved by cycling the brakes on and off, which reduces the life of carbon brakes. Probably the reason they don’t want you to use it.

Despite my having unnecessarily being accused of some sort of “automation dependency” or similar rubbish by an earlier poster, if you only need auto rake one you may as well go with manual braking, or even no braking and reverse and just roll to a halt if the runway is long enough. Apparently, according to the same previous poster their is no need for professional pilots to refer to the brake cooling schedules, even if you have short turn arounds, as long as you have massaged your ego by turning the automatics off, so that should be no problem.

[Centaurus]

as long as you have massaged your ego by turning the automatics off, so that should be no problem.
Puerile attempt at humour..