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Captainjc9
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Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 3:13 am

Do Airliners and Turboprops (any commercial aircraft with reverse thrust) always use full thrust? Or only like 80 or 50% reverse thrust? And on top of that do they use full brakes or no brakes?

I've always wanted to know if the pilots, once touched down, do they use the full manual brake or manual braking at all?

Thanks!
JC
 
LH707330
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Re: Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 4:22 am

It's rare that full braking and full reverse are used. What typically happens is that the crew selects an autobrake setting that will get them stopped where they need to be, and then uses that coupled with idle reverse. The computer applies brakes to get to the desired deceleration rate, so if the pilots apply more reverse, then the computer goes softer on the brakes to maintain that desired deceleration output. Going into higher reverse adds engine wear and makes a bunch of noise, so most airlines avoid that whenever possible. A scenario where you might want to use more reverse would be when you're on a short runway, heavy, and have a tight turn. Under such circumstances, you want to put as little possible kinetic energy into your brakes as heat, because that all needs to be dissipated, which can take a while. If the brakes are too warm on takeoff, you're not allowed to go.

Some other scenarios:
Snow/ice: light braking and more reverse
Noise abatement: more brake and little or no reverse
Desired exit near the far end of a long runway: soft braking down to ~80 kts, then coast down to your exit. At SEA, for example, the widebodies usually land on 16L, brake softly with idle reverse, and coast most of the way down the runway to taxiway P to get to the S gates:
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Starlionblue
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Re: Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 5:05 am

As LH707330 mentioned, autobrake targets a specific deceleration rate. So if you pull more reverse you get less braking. This can be advantageous if you're doing a short turn in a hot location, since the brakes will be less hot and thus less likely to impact turnaround time.

Since brakes and reverse are added up, so to speak, to a specific deceleration rate, pulling more reverse doesn't stop you faster on a dry runway. However, if the runway is slippery with snow or something, the brakes might not be able to achieve the desired deceleration rate with idle reverse. So on a slippery runway, normally you'd plan for full reverse.


We mostly plan to use idle reverse as long as the runway is dry. If you land a bit long you can always pull to full anyway. Since you're already at idle reverse the doors are open and there is little delay.

Autobrake is highly recommended since it ensures a symmetric application at high speed. Once you've decelerated under 70 knots or so, tap the brakes to disengage autobrake and modulate with foot pressure. On the A330, normally autobrake LOW is used. On the A350 you have BTV (Brake To Vacate) so you "dial an exit" by selecting it beforehand. The autobrake system then modulates the brakes to minimise runway occupancy time. So if you land long it will automatically apply more brake to make the selected exit, and if you want to roll to the end it might not brake at all initially.

Full manual braking, as in pushing the pedals to the stops, might just send passenger faces into the seatbacks in front of them, breaking their noses in the process. Max braking is brutal and only for emergencies, notably a high speed rejected take-off. The brake discs go red hot and fires are not infrequent.
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mmo
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Re: Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 6:05 am

Just to add a little more to what has been excellently described above. It really depends on the company you work for and what their FCGTM (Flight Crew Training Manual) states. In addition, noise restrictions are often imposed on the amount of reduced thrust that can be used during "normal operations".

The carriers I have worked for all pretty much require auto-brakes to be used on EVERY landing. But, it doesn't state how long it has to be used for. In the example of KSEA 16R, as a TECHNIQUE, it would be acceptable to land with auto-brakes low or 1 and then when you have definitive proof you are slowing down click the auto-brakes off and come out of idle reverse and use manual braking. Carbon brakes work much differently than the old steel brakes and they are very effective. On a widebody, you don't really have to worry about turn times as they are normally at least 90 minutes or longer.

One thing which has not been mentioned is max breaking and the differences. As has been pointed out, settings below max will give a predetermined rate of deceleration. So if you use more reverse thrust the auto-brakes will provide less of the stopping power. With max or RTO, the pressure applied to the brakes is the full 3000 PSI, and the deceleration rate is not a factor in that. So with max and full reverse, you will leave most of the passengers plastered to the seat in front of them. I have used it several times on acceptance flights and it is a good technique to lock your shoulder harness!!
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Starlionblue
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Re: Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 7:24 am

Most widebody turns worldwide are probably 90+ minutes, but many of our regional ones are 70 minutes. If we are running late we aim to be even quicker than that. Brake temps can become a problem especially if the taxi in and/or out is long.

Autobrake is not 100% mandated by our procedures, but you'd get a really weird look if during the approach brief, you said you'd be using no autobrake. There's no good reason not to use autobrake, so just use it.

If something went sideways and you hadn't used autobrake you would find yourself having tea and biscuits with the chief pilot. Without the biscuits. Or the tea. :D


mmo wrote:
One thing which has not been mentioned is max breaking and the differences. As has been pointed out, settings below max will give a predetermined rate of deceleration. So if you use more reverse thrust the auto-brakes will provide less of the stopping power. With max or RTO, the pressure applied to the brakes is the full 3000 PSI, and the deceleration rate is not a factor in that. So with max and full reverse, you will leave most of the passengers plastered to the seat in front of them. I have used it several times on acceptance flights and it is a good technique to lock your shoulder harness!!


I've never used max, but one of the things that surprised me when moving from the sim to the real aircraft was just how light a touch you need on the brakes on initial application. The sim doesn't seem to do ground handling very well, especially braking. You really want to apply them very gently initially or you'll get quite the jerk. Once you've found the initial "bite", so to speak, you can gradually increase pressure. The A330 isn't so bad but on the A350 you only seem to need to breathe on the brakes to get significant deceleration.
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889091
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Re: Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 10:36 am

Would autobrake be able to detect aquaplaning? If not, how is aquaplaning handled?
 
mmo
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Re: Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 12:10 pm

889091 wrote:
Would autobrake be able to detect aquaplaning? If not, how is aquaplaning handled?


Auto-brakes don't handle the aquaplaning the anti-skid system does. And the auto-brake handles it just fine. It senses the difference in wheel speed and modulates the hydraulics to that respective brake.
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Woodreau
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Re: Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 1:04 pm

As far as turboprops go, beta is fairly effective in getting the aircraft slowed and stopped.

I remember landing on a contaminated runway and being asked by the controller for a braking action report after vacating the runway. I had to respond that I couldn’t give one because I didn’t use any brakes. It was all beta. The controller replied that was the shortest (distance rollout) landing he had seen all day with the contaminated runway.

Braking and reverse can be effective. Landing at KBUR Rwy 8 is one of the few airports where we are required to use a specific configuration of Flaps FULL, MED autobrake and MAX reverse (due to a few airplane overrun incidents over the past few years). At touchdown we override the autobrake and apply manual braking and can get a 320 stopped in less than 3000ft. I found that even that was too much and had to apply thrust to roll to the runway intersection to make the 45 degree right turn to pull into the gate. Because we pulled into the gate less than 30 seconds after vacating the runway and stowing the reversers we had to wait at the gate with both engines running for the remaining 2:30 left for engine cooldown. And then wait for the passengers to complete the deplaning process (via airstair) before we could use brake fans to cool the brakes.
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Starlionblue
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Re: Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 2:15 pm

mmo wrote:
889091 wrote:
Would autobrake be able to detect aquaplaning? If not, how is aquaplaning handled?


Auto-brakes don't handle the aquaplaning the anti-skid system does. And the auto-brake handles it just fine. It senses the difference in wheel speed and modulates the hydraulics to that respective brake.


Expanding on this, anti-skid prevents the wheels locking up and skidding. (Just like in a car, though aircraft had antiskid long before cars.) If the runway is quite slippery and anti-skid has to keep intervening to keep the wheels rolling, you may well not get the targeted deceleration rate, but autobrake will do the best it can.

In modern aircraft, the systems aren't really discrete units. It's all one big redundant magic box with various functions. In the case of the A330, this would be the BSCU (Brake and Steering Control Unit).


Woodreau wrote:
As far as turboprops go, beta is fairly effective in getting the aircraft slowed and stopped.

I remember landing on a contaminated runway and being asked by the controller for a braking action report after vacating the runway. I had to respond that I couldn’t give one because I didn’t use any brakes. It was all beta. The controller replied that was the shortest (distance rollout) landing he had seen all day with the contaminated runway.

Braking and reverse can be effective. Landing at KBUR Rwy 8 is one of the few airports where we are required to use a specific configuration of Flaps FULL, MED autobrake and MAX reverse (due to a few airplane overrun incidents over the past few years). At touchdown we override the autobrake and apply manual braking and can get a 320 stopped in less than 3000ft. I found that even that was too much and had to apply thrust to roll to the runway intersection to make the 45 degree right turn to pull into the gate. Because we pulled into the gate less than 30 seconds after vacating the runway and stowing the reversers we had to wait at the gate with both engines running for the remaining 2:30 left for engine cooldown. And then wait for the passengers to complete the deplaning process (via airstair) before we could use brake fans to cool the brakes.



Beta is a whole other story. Like putting out a parachute. :D

Plus turboprops don't have whole reingestion issues, right? On a jet, you have to go to idle reverse at 70 knots (type dependent) at the latest or we risk reingestion of exhaust gases. Except in an emergency where you really want max stopping power, so you keep max reverse and accept that the engine might "cough".
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889091
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Re: Landing - Thrust Reverse and Brake

Tue Jun 09, 2020 8:25 pm

Thanks for the explanations Starlionblue and mmo.

Can the Autobrake setting be changed once the WoW has been triggered? In the recent FedEx overrun in BOM, if the crew didn't expect that much water on the runway/more water accumulation towards the end of the runway, could they have changed the Autobrake setting after touchdown?

In addition, when are the buckets/clamshells/sliding vanes stowed? Automatically below a certain speed, or are they only stowed once the pilot flying flips the lever down?
 
CosmicCruiser
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Re: Landing - Thrust Reverse and Brake

Wed Jun 10, 2020 12:21 am

It's my understanding they had MAX brakes selected. I'm sure they were using max reverse as well. Everyone that flew there knew the problems that existed.
The reversers are only stowed when the reverse levers are stowed.
 
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Starlionblue
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Re: Landing - Thrust Reverse and Brake

Wed Jun 10, 2020 12:31 am

889091 wrote:
Thanks for the explanations Starlionblue and mmo.

Can the Autobrake setting be changed once the WoW has been triggered? In the recent FedEx overrun in BOM, if the crew didn't expect that much water on the runway/more water accumulation towards the end of the runway, could they have changed the Autobrake setting after touchdown?

In addition, when are the buckets/clamshells/sliding vanes stowed? Automatically below a certain speed, or are they only stowed once the pilot flying flips the lever down?


On the A330/A350 autobrake is triggered by ground spoiler extension, so if you select another setting after you've touched down, nothing would happen. And even if you could do it, fiddling with the autobrake pushbuttons during rollout would mean taking attention away from more important things. If you're not getting the desired deceleration from autobrake, use manual braking as needed.

The reverser doors are stowed when you push the levers all the way down. The reverse levers on the A330 and A350 have a detent which corresponds to reverse idle. So if you've used full reverse, you push the levers to the detent, then leave them there until you want to stow the doors. Stowing should be done at taxi speed as per the manual. A good mental trigger is as you exit the runway.
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mxaxai
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Re: Landing - Thrust Reverse and Brake

Wed Jun 10, 2020 11:04 am

mmo wrote:
889091 wrote:
Would autobrake be able to detect aquaplaning? If not, how is aquaplaning handled?


Auto-brakes don't handle the aquaplaning the anti-skid system does. And the auto-brake handles it just fine. It senses the difference in wheel speed and modulates the hydraulics to that respective brake.

Manual / Emergency braking can apparently disable the anti-skid system, see http://avherald.com/h?article=44e3d342&opt=3584 . The BAe 146 skidded across a wet runway with locked wheels and the accident investigation board concluded that regular maximum braking (with anti-skid activated) would have prevented the overrun.
 
mmo
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Re: Landing - Thrust Reverse and Brake

Wed Jun 10, 2020 12:35 pm

True, you can turn off the anti-skid. However, on the aircraft I have flown in the last 20 years, 747-400, 777 and 787 the anti-skid was always left on. On the previous generation, the anti-skid was turned off once you were clear of the runway (747 classic, 727 and DC-10 Can't remember the757). In reality, three would be no reason to turn off the anti-skid. You can hear it cycle when it is working and the anti-skid will attempt to provide maximum braking if you are asking for it.
Emergency braking is something very different. That is used when you have a failure of the normal and secondary brakes. and depending on the aircraft it is protected or not protected by the anti-skid.
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CosmicCruiser
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Re: Landing - Thrust Reverse and Brake

Wed Jun 10, 2020 12:57 pm

True mmo. I, however, don't remember us ever turning off the anti-skid on the DC-10. Maybe some folks did. Wasn't it inhibited below a given speed anyway?
 
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glen
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Re: Landing - Thrust Reverse and Brake

Wed Jun 10, 2020 3:24 pm

889091 wrote:
Can the Autobrake setting be changed once the WoW has been triggered? In the recent FedEx overrun in BOM, if the crew didn't expect that much water on the runway/more water accumulation towards the end of the runway, could they have changed the Autobrake setting after touchdown?


Even if it would be possible to change the Autobrake setting, there is no help in this scenario. If the auto brake does not meet its target deceleration rate due to aquaplaning, it won't meet it at higher Autobrake level neither.
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mmo
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Re: Landing - Thrust Reverse and Brake

Wed Jun 10, 2020 4:34 pm

CosmicCruiser wrote:
True mmo. I, however, don't remember us ever turning off the anti-skid on the DC-10. Maybe some folks did. Wasn't it inhibited below a given speed anyway?


That was a "red tail" procedure for fleet standardization before the introduction of the 744. Up to that time, the anti-skid was turned off and then turned back on during the "Before Takeoff" checklist. The 320 and the 744 changed all of that.

I do remember that being true and I think it was something like 20knots in the 744. But that was lost years ago!!!
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hitower3
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Re: Landing - Thrust Reverse and Brake

Wed Jun 10, 2020 6:20 pm

Fun anecdote regarding autobrake:

Back in 2005, I was traveling aboard a CRJ200 from Austrian, taxiing to the departure runway 34 at VIE.
As it is a rather long way to go, the pilot was throttling up to get the plane to speed. Apparently, he pushed the throttle too much and when he retarded, the brakes kicked in - KaBOOM! Right to a stand still!
I suppose that the autobrake was already set for the takeoff, so the rather high power setting made the system assume that the aircraft was rolling for departure. The closing of the throttles apparently triggered the autobrake for a rejected takeoff...
 
GalaxyFlyer
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Re: Landing - Thrust Reverse and Brake

Wed Jun 10, 2020 9:43 pm

Did the CRJ-200 have auto brakes, in the first place and if it did, did it have RTO? All news to me.
 
Woodreau
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Re: Landing - Thrust Reverse and Brake

Thu Jun 11, 2020 12:12 am

No such animal as auto brakes on a CRJ-200/700/900/1000.

There is anti-skid but no auto brakes. Manual brakes only.
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gloom
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Re: Landing - Thrust Reverse and Brake

Thu Jun 11, 2020 7:11 am

889091 wrote:
Can the Autobrake setting be changed once the WoW has been triggered?


It depends. As people explained normal system, I'll move on to some that do have such capability (even if probably different from what you expect).

New WBs (I think both 350 and 787, I'm sure on 350) have a functions called by Airbus BTV (Brake To Vacate). When activated, it will do its best to decelerate to a given taxiway (many airports have a preferred taxiways for that). Once on ground, using present position in reference to runway, 350 checks distance to taxiway, and starts braking to achieve taxiway with minimum wear and optimum speed. To achieve that, it will:
- apply appropriate braking force
- analyze situation to increase/decrease braking action when required

So I guess, it is pretty close to what effect you wanted.

Cheers,
Adam
 
mmo
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Re: Landing - Thrust Reverse and Brake

Thu Jun 11, 2020 11:46 am

gloom wrote:

New WBs (I think both 350 and 787, I'm sure on 350) have a functions called by Airbus BTV (Brake To Vacate).


There is no BTV on the 787.
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Starlionblue
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 1:28 am

gloom wrote:
889091 wrote:
Can the Autobrake setting be changed once the WoW has been triggered?


It depends. As people explained normal system, I'll move on to some that do have such capability (even if probably different from what you expect).

New WBs (I think both 350 and 787, I'm sure on 350) have a functions called by Airbus BTV (Brake To Vacate). When activated, it will do its best to decelerate to a given taxiway (many airports have a preferred taxiways for that). Once on ground, using present position in reference to runway, 350 checks distance to taxiway, and starts braking to achieve taxiway with minimum wear and optimum speed. To achieve that, it will:
- apply appropriate braking force
- analyze situation to increase/decrease braking action when required

So I guess, it is pretty close to what effect you wanted.

Cheers,
Adam


The A380 and A350 have BTV. Not, as mentioned, the 787.

BTV doesn't decrease brake wear since carbon brake wear is related to the number of applications, not the braking force.

The purpose of BTV is largely to decrease runway occupancy time. For example, by delaying braking later if your exit is far down the runway, the average rollout speed is higher and the runway occupancy time lower.

You have to pre-select the braking action for BTV. For example on a long runway, if you've selected "wet" it will start braking earlier than if you've selected "dry", as worse braking action is expected.

If you land a bit long, BTV will apply the brakes harder to make the designated exit.
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gloom
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 5:29 am

Starlionblue wrote:
The A380 and A350 have BTV. Not, as mentioned, the 787.


OK, passed by someone who was a pilot, I assumed he knew what he talked about.

Starlionblue wrote:
BTV doesn't decrease brake wear since carbon brake wear is related to the number of applications, not the braking force.

The purpose of BTV is largely to decrease runway occupancy time. For example, by delaying braking later if your exit is far down the runway, the average rollout speed is higher and the runway occupancy time lower.


OK, it doesn't in terms of maintenance. However, what I had in mind was that comparing to other options (simple low/med switch, or manual braking), and due to computer constantly calculating distances, it will use brakes (or, to say exactly: remaining distance) as efficient as possible. This should result in reaching taxi speed just before leaving the runway to speedway/taxiway, and less heat in the brakes at this moment. And also, it could increase/decrease forces on brakes as asked by previous poster.

Anyways, thanks for corrections.

Cheers,
Adam
 
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Starlionblue
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 6:40 am

gloom wrote:
Starlionblue wrote:
The A380 and A350 have BTV. Not, as mentioned, the 787.


OK, passed by someone who was a pilot, I assumed he knew what he talked about.

Starlionblue wrote:
BTV doesn't decrease brake wear since carbon brake wear is related to the number of applications, not the braking force.

The purpose of BTV is largely to decrease runway occupancy time. For example, by delaying braking later if your exit is far down the runway, the average rollout speed is higher and the runway occupancy time lower.


OK, it doesn't in terms of maintenance. However, what I had in mind was that comparing to other options (simple low/med switch, or manual braking), and due to computer constantly calculating distances, it will use brakes (or, to say exactly: remaining distance) as efficient as possible. This should result in reaching taxi speed just before leaving the runway to speedway/taxiway, and less heat in the brakes at this moment. And also, it could increase/decrease forces on brakes as asked by previous poster.

Anyways, thanks for corrections.

Cheers,
Adam


I might be wrong, but I don't think heat would be reduced very much. The energy you need to transfer from the forward speed of the aircraft to the brakes remains the same. Granted, the "peak pressure" might be lower than with just a fixed setting, so that might make a difference.

Force on brakes is not really a problem. They can take much more than what they do in normal operation. We're barely touching them in most cases.

Efficiency. When it comes to runway occupancy time reduction, sure. But again, BTV will not reduce wear. One brake application is one brake application.
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mxaxai
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 10:19 am

Starlionblue wrote:
If you land a bit long, BTV will apply the brakes harder to make the designated exit.

What happens if you can't make the designated exit, e. g. due to landing too long? Does it try to still make it with some hard braking, maybe call for more thrust reverse? Or does it switch to the next exit, assuming there is one?
 
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Starlionblue
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 10:58 am

mxaxai wrote:
Starlionblue wrote:
If you land a bit long, BTV will apply the brakes harder to make the designated exit.

What happens if you can't make the designated exit, e. g. due to landing too long? Does it try to still make it with some hard braking, maybe call for more thrust reverse? Or does it switch to the next exit, assuming there is one?


Yes and yes.

Land long after planning idle reverse? Full reverse is an option.

Manual braking with more pressure than programmed autobrake? Also an option.

If your plan isn't working, make tactical decisions to fix it.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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dennypayne
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 4:00 pm

Starlionblue wrote:
Land long after planning idle reverse? Full reverse is an option.

Manual braking with more pressure than programmed autobrake? Also an option.

If your plan isn't working, make tactical decisions to fix it.


Just out of curiosity, what happens if your plan is unworkable from the beginning, e.g. you inadvertently select an exit that is at the wrong end of the runway so that it is a physical impossibility to make that? How does the system respond to that input?
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BravoOne
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 4:32 pm

mmo wrote:
gloom wrote:

New WBs (I think both 350 and 787, I'm sure on 350) have a functions called by Airbus BTV (Brake To Vacate).


There is no BTV on the 787.



The 777X will have a "Brake to Exit" selection when it enters service. It may become available on the 787 as well but nothing definitive at this time.
 
889091
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 10:26 pm

Back to the FedEx incident in BOM. Assuming either one of the reversers on Engine 1 or Engine 3 (disregard Engine 2 as it is mounted on the centreline) was INOP and with a runway that contaminated with water, would they have landed with full reverse, or brakes only?
 
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Starlionblue
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 11:10 pm

dennypayne wrote:
Starlionblue wrote:
Land long after planning idle reverse? Full reverse is an option.

Manual braking with more pressure than programmed autobrake? Also an option.

If your plan isn't working, make tactical decisions to fix it.


Just out of curiosity, what happens if your plan is unworkable from the beginning, e.g. you inadvertently select an exit that is at the wrong end of the runway so that it is a physical impossibility to make that? How does the system respond to that input?


When you select a runway, the ANF (Airport Navigation Function) map shows markings along the runway for "wet" and "dry". These represent the minimum rollout distance in those conditions.

If you select an exit before the markings the system will display the exit in amber instead of green.
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Starlionblue
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Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 11:11 pm

889091 wrote:
Back to the FedEx incident in BOM. Assuming either one of the reversers on Engine 1 or Engine 3 (disregard Engine 2 as it is mounted on the centreline) was INOP and with a runway that contaminated with water, would they have landed with full reverse, or brakes only?


You can land with full reverse on one engine and inop on the other. Use the rudder to compensate. So most likely they planned for full reverse given the contaminated runway.
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CosmicCruiser
Posts: 2452
Joined: Tue Feb 22, 2005 3:01 am

Re: Landing - Thrust Reverse and Brake

Fri Jun 12, 2020 11:12 pm

Just using your assumption, they would most likely still used reverse, less on the outboard, more on No. 2 unless directional control was a problem then just two,
 
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Starlionblue
Posts: 20183
Joined: Fri Feb 27, 2004 9:54 pm

Re: Landing - Thrust Reverse and Brake

Sat Jun 13, 2020 7:03 am

CosmicCruiser wrote:
Just using your assumption, they would most likely still used reverse, less on the outboard, more on No. 2 unless directional control was a problem then just two,


Indeed.

Either way, the procedure for loss of directional control on landing, which could happen on a contaminated runway, is back to reverse idle, regain control with rudder/steering, then full reverse again.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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