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georgeclarke
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Landing Wheel Brake Activation

Thu Oct 29, 2020 11:38 am

Hi All

New to Airliners.net - this is my first topic.

Was wondering if someone can help me understand the common procedure for wheel brake application upon landing. I know that in most cases, runway deceleration is achieved via:

1. Spoiler auto-deploy once sensors detect the wheels spinning on the tarmac
2. Reverse thrust activated between touch down speed till about 80 knots (usually on idle thrust I've heard, unless bad weather or short runway)
3. Wheel brakes deployed.

What I'm not clear on is WHEN during the process wheel brakes are applied. I've read in some forums people saying that from touchdown speed till 80 knots, reversers and spoilers do all the work, and then sub 80 knots reversers go off and the pilots manually apply wheel brakes, as applying them at too high speed knackers them and can risk tyre popping.

But I read as commonly that auto-brake is used in almost all landing situations. I know that autobrake goes from 1-4 (Boeing) or Low-Med-Max (Airbus)..... but I understood that autobrake will apply the brakes as soon as the wheels touch down, not at <=80 knots.

So can anyone shed light on common procedure for when wheel brakes are applied?

Thanks
 
mxaxai
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Re: Landing Wheel Brake Activation

Thu Oct 29, 2020 2:51 pm

On a normal landing, autobrakes engage immediately after touchdown. If the pilot does nothing at all, the autobrake will bring the aircraft to a full stop. Autobrakes disengage once the pilot manually applies the brakes. They do not re-engage if the pilot releases the brakes again.

Autobrakes, along with spoilers, are usually triggered by the transition from air to ground mode during landing. The trigger for that is usually either weight-on-wheels, wheels spinning, radio altimeter measurements, or a combination of these or other sensors. On an Airbus, this transition also changes the flight control laws, i. e. how the control surfaces react to a stick input.


Autobrakes (unless fancy brake-to-vacate variants) will provide a constant deceleration. So if thrust reverse is deployed, the wheel brakes have to work less for the same deceleration and the autobrake system will adjust accordingly. If the runway is slippery, autobrake will apply more brake force to reach the target decelaration, up to the point permitted by anti-slip systems. Only exception is the max / rto setting where the autobrake will always provide the maximum brake force permitted by the anti-slip system.
 
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Starlionblue
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Re: Landing Wheel Brake Activation

Thu Oct 29, 2020 3:21 pm

Welcome to the forums!

1. Spoilers auto-deploy based on weight on wheels, not wheel spin. On Airbus, you get half spoiler deflection with only one main gear on the ground, and full once both are down.

Sde note: Please don't call it "tarmac". That word makes people in the industry twitchy. ;) Surfaces are runway, taxiway, or apron/ramp.

2. Reverse is manually activated by the pilot flying. If you pull full reverse, this should be reduced to idle (just the reverser doors open) by 70-80 knots to avoid reingestion. Once at taxi speed, stow the reversers.

3. The reversers and spoilers don't do all the work above 80 knots. Brakes are involved too. The brakes are activated automatically on touchdown by autobrake. On Airbus, medium autobrake is pretty aggressive and can lead to slamming the nose gear if you don't catch it. As mxaxai says, autobrake targets a deceleration. So if you pull full reverse, reversers do more of the work, and the brakes do less, compared to idle reverse.

The A380 and A350 have Brake to Vacate, meaning activation and deceleration is predicated on the distance to the selected exit. If your exit is far down the runway, you might not have any brake activation for a while.

Once you've slowed to an adequate speed, maybe 80-100 knots, you'd typically disengage autobrake by putting pressure on the pedals. That way you can modulate deceleration to reach the desired exit at an appropriate speed.

Max autobrake is only used for take-off. Never for landing. If you really really need to stop fast on landing, just push the pedals down as far as you can.
 
Lemmy
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Re: Landing Wheel Brake Activation

Thu Oct 29, 2020 3:25 pm

Starlionblue wrote:
On Airbus, medium autobrake is pretty aggressive and can lead to slamming the nose gear if you don't catch it.


Thanks for mentioning this. It's something I've always wondered about. On a bicycle, for example, if you're riding a wheelie and tap the brakes, the front wheel comes down hard.

Sounds like the elevators have enough authority to control the rate at which the nose comes down, despite the brakes.
 
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Starlionblue
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Re: Landing Wheel Brake Activation

Thu Oct 29, 2020 3:37 pm

Lemmy wrote:
Starlionblue wrote:
On Airbus, medium autobrake is pretty aggressive and can lead to slamming the nose gear if you don't catch it.


Thanks for mentioning this. It's something I've always wondered about. On a bicycle, for example, if you're riding a wheelie and tap the brakes, the front wheel comes down hard.

Sounds like the elevators have enough authority to control the rate at which the nose comes down, despite the brakes.


There is indeed enough authority in the elevators. The issue, if you will, is that we use low autobrake most of the time, so muscle memory is tuned to it. When using medium, you can get caught a little bit by surprise. No big deal in the grand scheme of things, beyond wounded pride. :D
 
Yikes!
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Re: Landing Wheel Brake Activation

Thu Oct 29, 2020 4:49 pm

Great topic and excellent answers. And welcome to the forum! I don't post much anymore unless something really interesting like this comes along.

To add to the above comments, the most effective way to stop the aircraft is with brakes which is why the first action (after bringing thrust levers to idle) is to have brakes applied. Spoilers and reverse thrust help but it is the brakes that do most of the work.

Airliners generally have two kinds of brakes: steel or carbon. Steel brakes are cheaper to install but with a substantial weight penalty - they're much heavier than carbon brake assemblies.

Carbon brakes are much lighter but, if not used properly, can wear out much faster. Carbon brakes work best when they are hot. They are also "application sensitive" meaning each action, such as "pumping" or multiple applications during a stopping event, wears them down more so than a single application. So, a single constant application of a carbon brake assembly accomplishes two functions: the brakes heat up much faster than with multiple, separate applications, and secondly, reduced wear vs multiple separate brake applications.

Therein lies the bonus of having autobrakes engaged all the way to taxi speed when brake application is usually not required until reaching the ramp. If brake applications are required at the slower taxi speed, carbon brakes don't heat up very much with much less wear than slowing down from landing (or rejected takeoff) speeds.

It's been awhile since I flew the heavy jets - others on this forum may be able to add or correct anything I've written!
 
Max Q
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Re: Landing Wheel Brake Activation

Thu Oct 29, 2020 5:48 pm

Lemmy wrote:
Starlionblue wrote:
On Airbus, medium autobrake is pretty aggressive and can lead to slamming the nose gear if you don't catch it.


Thanks for mentioning this. It's something I've always wondered about. On a bicycle, for example, if you're riding a wheelie and tap the brakes, the front wheel comes down hard.

Sounds like the elevators have enough authority to control the rate at which the nose comes down, despite the brakes.



You raise a good point and it is a consideration, you don’t want too much braking initiated until the nosegear is reasonably close to touching down


The autobrakes on the 757 and 767 will not engage after landing until aircraft pitch is beneath a predetermined value, IIRC it’s 5 degrees


I suspect this system protocol is used on other types as well
 
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Strebav8or
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Re: Landing Wheel Brake Activation

Thu Oct 29, 2020 5:58 pm

Just to add, newer Boeing aircraft have a MAX and an RTO position on the Autobrake switch.
MAX on a 777, with just a test crew is an astonishing thing to experience (you better be buckled in).
RTO is for/during a Rejected Take Off, to reduce the pilot workload under those circumstances.
 
e38
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Re: Landing Wheel Brake Activation

Thu Oct 29, 2020 7:00 pm

georgeclarke, I agree with all the answers above. Just a few additional comments . . .

With regard to your question, "can anyone shed light on common procedure for when wheel brakes are applied?"

At the company at which I work--on the Airbus A-320 series--for a normal landing, it is standard company practice to initiate manual braking as the aircraft decelerates through 80 knots. Remember that autobrakes, if not disengaged, will bring the aircraft to a complete stop on the runway, which is generally not desired! As mentioned above, autobrakes are disengaged by applying pressure to the brake pedals and as the aircraft continues to decelerate, the pressure required to disengage the autobrakes increases. If you wait until the aircraft is fairly slow, i.e., 40 knots or so, the transition can be somewhat abrupt. We have found that the smoothest transition from autobrakes to manual braking occurs around 80 knots. Of course, you can always apply manual braking earlier in the landing roll, if necessary.

With regard to another one of your comments, "auto-brake is used in almost all landing situations."

Yes, again, at the company at which I work, it is operations policy that autobrakes--and reverse thrust, as well--be used for EVERY landing. This serves as an operational check of both systems. However, I have ridden in the jumpseat of Airbus aircraft from other airlines where the pilots were not required to use autobrakes for landing--depends on company policy.

P.S. I got a smile out of your comment, "applying them at too high speed knackers them and can risk tyre popping."
I'm not sure I know what "knackering" the brakes is, but I don't think that has ever happened to me!

welcome to A.net

e38
 
Max Q
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Re: Landing Wheel Brake Activation

Thu Oct 29, 2020 9:45 pm

Key to disengaging Autobrakes smoothly on Boeing’s anyway is to slowly increase manual braking pressure through the brake pedals until you’re matching the AB input then apply just a little more.


This should give you a smooth disconnect, another technique is to just slightly retract the speed brakes (system logic immediately disengages autobrakes in case you’ve decided to abandon the landing after touchdown and lift off again)



I’ve even seen pilots on other airlines reach forward and turn off Autobrakes with the selector switch but that’s not in our procedure, they’re difficult to reach with your shoulder harness on and it’s not a good idea on the roll out


As stated you can get a really abrupt ‘lurch’ if you don’t disconnect AB carefully on roll out


Autobrakes are a wonderful thing, as mentioned the RTO function is very powerful, it’s important to allow it to decelerate the aircraft until you’re absolutely sure it will stop in the event of a reject as it provides the absolute maximum braking power available instantly (above 80 knots after reducing power to idle) tripping the brakes off and applying manual braking will not reduce your stopping distance and may well increase it no matter how tempting it is


And of course on landing, especially on a wet / short runway and in strong , gusty crosswinds they’re invaluable, allowing you to concentrate on directional control while they almost immediately, very smoothly and powerfully bring you down to a slow speed
 
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Starlionblue
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 1:36 am

Strebav8or wrote:
Just to add, newer Boeing aircraft have a MAX and an RTO position on the Autobrake switch.
MAX on a 777, with just a test crew is an astonishing thing to experience (you better be buckled in).
RTO is for/during a Rejected Take Off, to reduce the pilot workload under those circumstances.


Why is there MAX and RTO? Wouldn't they both give maximum braking?

On Airbus there's just MAX, which is only used on takeoff.


Max Q wrote:
Key to disengaging Autobrakes smoothly on Boeing’s anyway is to slowly increase manual braking pressure through the brake pedals until you’re matching the AB input then apply just a little more.


Same on the bus. Gingerly increase pressure until you feel the aircraft decelerating in response.

Like many newbies, on the full stop landing in base training, I was a bit too positive on the pedals initially. Practically thrown forward in the harness, followed by "oh, sh*t sorry!". Much laughter was heard from my fellow trainees sitting in business class.

The A350 is particularly light. As one captain joked, if you so much as accidentally breathe too hard in the direction of the pedals on landing, the passengers in economy will hit the seatbacks with their faces.
 
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zeke
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 9:48 am

mxaxai wrote:
On a normal landing, autobrakes engage immediately after touchdown.


Normally a couple of seconds after ground spoilers deploy.
 
trent768
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 11:03 am

Yikes! wrote:
Great topic and excellent answers. And welcome to the forum! I don't post much anymore unless something really interesting like this comes along.

To add to the above comments, the most effective way to stop the aircraft is with brakes which is why the first action (after bringing thrust levers to idle) is to have brakes applied. Spoilers and reverse thrust help but it is the brakes that do most of the work.

Airliners generally have two kinds of brakes: steel or carbon. Steel brakes are cheaper to install but with a substantial weight penalty - they're much heavier than carbon brake assemblies.

Carbon brakes are much lighter but, if not used properly, can wear out much faster. Carbon brakes work best when they are hot. They are also "application sensitive" meaning each action, such as "pumping" or multiple applications during a stopping event, wears them down more so than a single application. So, a single constant application of a carbon brake assembly accomplishes two functions: the brakes heat up much faster than with multiple, separate applications, and secondly, reduced wear vs multiple separate brake applications.

Therein lies the bonus of having autobrakes engaged all the way to taxi speed when brake application is usually not required until reaching the ramp. If brake applications are required at the slower taxi speed, carbon brakes don't heat up very much with much less wear than slowing down from landing (or rejected takeoff) speeds.

It's been awhile since I flew the heavy jets - others on this forum may be able to add or correct anything I've written!

Interesting insights on the carbon brakes!

On a related note, what's the braking procedure on carbon brake equipped aircraft during taxi? I'm no pilot and my only experience is from FS, but I find it quite hard to control the taxi speed without multiple short braking (throttle was already on idle).
 
georgeclarke
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 11:26 am

[list=]Amazing replies everyone thanks for the help![/list]
 
Woodreau
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 11:37 am

They key there is single engine taxi as long as you can.

A 319/320 single engine at idle usually has enough breakaway thrust to start taxiing without having to increase thrust. So having two engines means you’ll be braking a lot.

The key is keeping the taxi speeds low, don’t let your taxi speed get high. 30kts is normally the upper limit for taxi speed.

Braking from 30kts to 20kts will heat the brakes more than braking from 20kts to 10kts.

One thing I do is alternate brakes. Use one brake to slow, then the next time I use the other brake. Cant do that in FS unfortunately... lol
 
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Starlionblue
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 12:18 pm

Woodreau wrote:
They key there is single engine taxi as long as you can.

A 319/320 single engine at idle usually has enough breakaway thrust to start taxiing without having to increase thrust. So having two engines means you’ll be braking a lot.

The key is keeping the taxi speeds low, don’t let your taxi speed get high. 30kts is normally the upper limit for taxi speed.

Braking from 30kts to 20kts will heat the brakes more than braking from 20kts to 10kts.

One thing I do is alternate brakes. Use one brake to slow, then the next time I use the other brake. Cant do that in FS unfortunately... lol


Brake and steer against it?
 
AABusDrvr
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 1:45 pm

On the 737, unless conditions or policy require it, we often land with the autobrakes off, and just use manual brakes. Most will wait until around 100 knots, before getting on the brakes.
 
gloom
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 1:58 pm

Starlionblue wrote:
2. Reverse is manually activated by the pilot flying.


Starlionblue, just to clarify. Isn't that also weight-detect (or wheel-spin-detect) dependant, at least on A planes? I might be wrong, but I guess on Lufthansa that crashed in Warsaw, it was both autobrakes and reversers that failed to activate due to aquaplanning (no wheel spin) and no proper weight on main gear.

Cheers,
Adam
 
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Starlionblue
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 2:56 pm

gloom wrote:
Starlionblue wrote:
2. Reverse is manually activated by the pilot flying.


Starlionblue, just to clarify. Isn't that also weight-detect (or wheel-spin-detect) dependant, at least on A planes? I might be wrong, but I guess on Lufthansa that crashed in Warsaw, it was both autobrakes and reversers that failed to activate due to aquaplanning (no wheel spin) and no proper weight on main gear.

Cheers,
Adam


Reversers cannot be used without weight on wheels. This is a safety feature. However, reverse is pilot controlled. It cannot be automatically activated on Airbus (or on Boeing AFAIK).
 
Lpbri
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 3:09 pm

Not a pilot, but i would think the expected runway exit point may also factor in to brake application. Ive landed at airports with taxi-arounds, and pilots seem to let the airplane coast, so they can get to the taxiway quicker. Unless maybe there is traffic behind.
 
Max Q
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Re: Landing Wheel Brake Activation

Fri Oct 30, 2020 9:27 pm

Starlionblue wrote:
Strebav8or wrote:
Just to add, newer Boeing aircraft have a MAX and an RTO position on the Autobrake switch.
MAX on a 777, with just a test crew is an astonishing thing to experience (you better be buckled in).
RTO is for/during a Rejected Take Off, to reduce the pilot workload under those circumstances.


Why is there MAX and RTO? Wouldn't they both give maximum braking?

On Airbus there's just MAX, which is only used on takeoff.


Max Q wrote:
Key to disengaging Autobrakes smoothly on Boeing’s anyway is to slowly increase manual braking pressure through the brake pedals until you’re matching the AB input then apply just a little more.


Same on the bus. Gingerly increase pressure until you feel the aircraft decelerating in response.

Like many newbies, on the full stop landing in base training, I was a bit too positive on the pedals initially. Practically thrown forward in the harness, followed by "oh, sh*t sorry!". Much laughter was heard from my fellow trainees sitting in business class.

The A350 is particularly light. As one captain joked, if you so much as accidentally breathe too hard in the direction of the pedals on landing, the passengers in economy will hit the seatbacks with their faces.




On the 757/67 there is a difference between ‘ Max’ and ‘RTO’ Autobrakes


The former is the highest selectable deceleration rate for landing whereas the latter is maximum possible braking, the absolute limit of what the system can provide in the event of a rejected take off
 
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Starlionblue
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Re: Landing Wheel Brake Activation

Sat Oct 31, 2020 4:55 am

Max Q wrote:
Starlionblue wrote:
Strebav8or wrote:
Just to add, newer Boeing aircraft have a MAX and an RTO position on the Autobrake switch.
MAX on a 777, with just a test crew is an astonishing thing to experience (you better be buckled in).
RTO is for/during a Rejected Take Off, to reduce the pilot workload under those circumstances.


Why is there MAX and RTO? Wouldn't they both give maximum braking?

On Airbus there's just MAX, which is only used on takeoff.


Max Q wrote:
Key to disengaging Autobrakes smoothly on Boeing’s anyway is to slowly increase manual braking pressure through the brake pedals until you’re matching the AB input then apply just a little more.


Same on the bus. Gingerly increase pressure until you feel the aircraft decelerating in response.

Like many newbies, on the full stop landing in base training, I was a bit too positive on the pedals initially. Practically thrown forward in the harness, followed by "oh, sh*t sorry!". Much laughter was heard from my fellow trainees sitting in business class.

The A350 is particularly light. As one captain joked, if you so much as accidentally breathe too hard in the direction of the pedals on landing, the passengers in economy will hit the seatbacks with their faces.




On the 757/67 there is a difference between ‘ Max’ and ‘RTO’ Autobrakes


The former is the highest selectable deceleration rate for landing whereas the latter is maximum possible braking, the absolute limit of what the system can provide in the event of a rejected take off


Thanks for info. Very interesting.


Lpbri wrote:
Not a pilot, but i would think the expected runway exit point may also factor in to brake application. Ive landed at airports with taxi-arounds, and pilots seem to let the airplane coast, so they can get to the taxiway quicker. Unless maybe there is traffic behind.


Yes. Definitely the exit is a factor. That's why Brake to Vacate on the A380 and A350 is so handy. Of course, if you don't have BTV you just modulate "manually".

You can also ask to "roll through" if your gate is at the far end. This increases runway occupancy time but unless there's someone close behind you it's fine.
 
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zeke
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Re: Landing Wheel Brake Activation

Sat Oct 31, 2020 5:27 am

Starlionblue wrote:
Thanks for info. Very interesting.


Max autobrake on the 767 is a deceleration rate of 11ft/s^2 similar to medium on a Airbus, like the Airbus the actual brake pressure applied is automatically modulated due to the contribution of spoilers and reverse to meet that rate.

It is less than maximum braking.
 
trent768
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Re: Landing Wheel Brake Activation

Sat Oct 31, 2020 9:16 am

Starlionblue wrote:
Max Q wrote:
Starlionblue wrote:

Why is there MAX and RTO? Wouldn't they both give maximum braking?

On Airbus there's just MAX, which is only used on takeoff.




Same on the bus. Gingerly increase pressure until you feel the aircraft decelerating in response.

Like many newbies, on the full stop landing in base training, I was a bit too positive on the pedals initially. Practically thrown forward in the harness, followed by "oh, sh*t sorry!". Much laughter was heard from my fellow trainees sitting in business class.

The A350 is particularly light. As one captain joked, if you so much as accidentally breathe too hard in the direction of the pedals on landing, the passengers in economy will hit the seatbacks with their faces.




On the 757/67 there is a difference between ‘ Max’ and ‘RTO’ Autobrakes


The former is the highest selectable deceleration rate for landing whereas the latter is maximum possible braking, the absolute limit of what the system can provide in the event of a rejected take off


Thanks for info. Very interesting.


Lpbri wrote:
Not a pilot, but i would think the expected runway exit point may also factor in to brake application. Ive landed at airports with taxi-arounds, and pilots seem to let the airplane coast, so they can get to the taxiway quicker. Unless maybe there is traffic behind.


Yes. Definitely the exit is a factor. That's why Brake to Vacate on the A380 and A350 is so handy. Of course, if you don't have BTV you just modulate "manually".

You can also ask to "roll through" if your gate is at the far end. This increases runway occupancy time but unless there's someone close behind you it's fine.

Based on my experience, on airports that only have turn around areas at the end, the braking can be either very smooth or very hard. The second hardest braking I've ever had was onboard DY 738 at Umeå, the pilot missed the runway exit on the middle of the runway by a bit and decided to slam the brake real hard to avoid unnecessary taxiing. Instead of taxiing for several hundred meters, we only need to taxi by approximately a length of a 738.

The hardest was weirdly on an AY E190 at HEL, again just for the sake of not missing the exit. Turns out, our gate was literally across that runway exit. It was so hard and there was a lot of pale looking Finns wandering around the terminal in shock minutes later :D
 
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Horstroad
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Re: Landing Wheel Brake Activation

Sat Oct 31, 2020 1:35 pm

Starlionblue wrote:
1. Spoilers auto-deploy based on weight on wheels, not wheel spin.

That's not true for all aircraft ;)
The MD11 for example does not have weight on wheels sensors. The Flight Control Computers generate a ground signal when there is wheel speed >80 kt, flaps >31.5° and radio altitude <7 ft. When all these conditions are met, the auto ground spoilers deploy. The FCC also detect an RTO and deploy the Auto Ground Spoilers when the flaps are <31.5°, the aircraft is on ground (NLG compressed), the engines are at idle or reversed and the wheel speed is >80 kt.


Starlionblue wrote:
Strebav8or wrote:
Just to add, newer Boeing aircraft have a MAX and an RTO position on the Autobrake switch.
MAX on a 777, with just a test crew is an astonishing thing to experience (you better be buckled in).
RTO is for/during a Rejected Take Off, to reduce the pilot workload under those circumstances.


Why is there MAX and RTO? Wouldn't they both give maximum braking?

On the 777 MAX AUTO does not give maximum braking. It targets 11.0 ft/sec² with a maximum command pressure of 3,100 psi. RTO gives maximum possible deceleration also with a maximum command pressure of 3,100 psi. There are four more switch positions (1 through 4) which target 4.0 ft/sec² (max 1,385 psi), 5.0 ft/sec² (max 1,600psi), 6.0 ft/sec² (max 1,850 psi) and 7.5 ft/sec² (max 2,150 psi) deceleration. The autobrake system activates 0.1 seconds after a ground signal. RTO is applied immediately when a rejected take off is initiated.

The MD11 also differentiates between landing mode and take off mode for autobrakes. It has MIN, MED, MAX and T.O.. When an RTO is initiated above 100 kt, MAX deceleration level braking will be applied. When an RTO is initiated below 100 kt, MIN deceleration level braking will be applied. MIN targets 6.5 ft/sec² deceleration, MED targets 9.0 ft/sec² and MAX gives maximum possible braking at 3000 psi brake pressure.
 
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Starlionblue
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Re: Landing Wheel Brake Activation

Sun Nov 01, 2020 1:42 am

Horstroad wrote:
Starlionblue wrote:
1. Spoilers auto-deploy based on weight on wheels, not wheel spin.

That's not true for all aircraft ;)
The MD11 for example does not have weight on wheels sensors. The Flight Control Computers generate a ground signal when there is wheel speed >80 kt, flaps >31.5° and radio altitude <7 ft. When all these conditions are met, the auto ground spoilers deploy. The FCC also detect an RTO and deploy the Auto Ground Spoilers when the flaps are <31.5°, the aircraft is on ground (NLG compressed), the engines are at idle or reversed and the wheel speed is >80 kt.

.


Well, of course, McD went their own way. :D
 
GSOtoIND
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Re: Landing Wheel Brake Activation

Sun Nov 01, 2020 5:39 am

Starlionblue wrote:
Horstroad wrote:
Starlionblue wrote:
1. Spoilers auto-deploy based on weight on wheels, not wheel spin.

That's not true for all aircraft ;)
The MD11 for example does not have weight on wheels sensors. The Flight Control Computers generate a ground signal when there is wheel speed >80 kt, flaps >31.5° and radio altitude <7 ft. When all these conditions are met, the auto ground spoilers deploy. The FCC also detect an RTO and deploy the Auto Ground Spoilers when the flaps are <31.5°, the aircraft is on ground (NLG compressed), the engines are at idle or reversed and the wheel speed is >80 kt.

.


Well, of course, McD went their own way. :D

I'd love to hear what the reasoning was behind such a convoluted solution. This smells of engineers creating a problem in order to solve it. Bastiat's Broken Window Fallacy, anyone?
 
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Strebav8or
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Re: Landing Wheel Brake Activation

Sun Nov 01, 2020 3:46 pm

Starlionblue wrote:
Strebav8or wrote:
Just to add, newer Boeing aircraft have a MAX and an RTO position on the Autobrake switch.
MAX on a 777, with just a test crew is an astonishing thing to experience (you better be buckled in).
RTO is for/during a Rejected Take Off, to reduce the pilot workload under those circumstances.


Why is there MAX and RTO? Wouldn't they both give maximum braking?

On Airbus there's just MAX, which is only used on takeoff.


Not sure of why the two settings. As an A&P, we test both positions during maintenance activities that require us to do so. From the flight crews I spoke with RTO is much more harsh than MAX braking.
Of course, only a few flight crews have experiences of RTO..
 
GalaxyFlyer
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Re: Landing Wheel Brake Activation

Sun Nov 01, 2020 5:03 pm

An RTO initiated at V1 is much dicier operation that a landing touching down despite wet or contamination. RTO is max braking available, the other modes target a G loading less than maximum brakes.
 
VMCA787
Posts: 255
Joined: Fri Sep 04, 2020 9:31 pm

Re: Landing Wheel Brake Activation

Sun Nov 01, 2020 7:45 pm

RTO provides max braking with 3000psi applied to the brakes. While MAX provides a rate of deceleration. RTO is more braking than the MAX function.
 
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zeke
Posts: 16358
Joined: Thu Dec 14, 2006 1:42 pm

Re: Landing Wheel Brake Activation

Sun Nov 01, 2020 8:11 pm

Strebav8or wrote:
Not sure of why the two settings. As an A&P, we test both positions during maintenance activities that require us to do so. From the flight crews I spoke with RTO is much more harsh than MAX braking.
Of course, only a few flight crews have experiences of RTO..


On a Boeing, the MAX setting when landing on a dry runway results in a deceleration rate that is less than that from full pedal (full hydraulic pressure) braking, the amount of brake pressure applied automatically changes with how much reverse and spoilers are assisting the deceleration. On a wet runway, MAX will generally result in application of maximum hydraulic pressure in order to achieve the desired deceleration rate, which may be the same as that produced by maximum pedal braking. In general, a higher setting provides greater deceleration. However, on a wet or slippery runway, maximum deceleration capability may be achieved at one of the lower settings, and deceleration may not be improved by selecting a higher setting, it depends on how slippery the runway is. The RTO setting uses maximum braking, i.e., maximum system hydraulic pressure.

MAX autobrake on the Boeing is like MED or HI on the Airbus (A380 auto brake settings are BTV, LO, 2, 3, HI), it is the highest automatic deceleration rate available.

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