In flight planning for utilizing high speed turnoffs after landing

[Ashatsea 7]

This is not a problem but more of a question I had after listening to a RW Pilot and referencing CH 6 in the FCTM. I had heard a FedEX pilot (MD-11 Pilot) say that after landing on certain runways if it was safe they would either decelerate the plane drastically or use less deceleration in order to get to a pre determined taxiway to make the transit from the runway to the hub or ramp faster. If I want to hit a certain High speed turnoff closer to my terminal at say JFK for example is there a formula or rule of thumb I can use to determine how much flaps, spoilers, autobrakes, and etc I should factor in to my pre arrival brief? I also don't want to throw safety and the FCOM out the door but is the above something RW pilots factor into there landing brief and FMC or is this just real world experience and knowing your aircraft?

[ajpongress 467]

I think it all has to do with the autobrake setting (for FSX, not realworld).Somewhere in the manual, can't remember where, it talks about how much distance each setting of autobrake takes to stop the plane.Any airport chart will show the length of the runway, so you can guesstimate how far down the high speed taxiway you want is, and set the autobrake accordingly.

[Steven_Caffey 23]

Autobrakes actually provide a fixed rate of deceleration, not a fixed stopping distance. Now, under identical circumstances that rate of deceleration will yield the same (or almost same) stopping distance, but to say that "autobrake 2 will always stop you in 1,000 ft" for example would be wrong. "Autobrake 2 on a dry runway at x weight will provide an approximate stopping distance of y" would be more accurate.Looking at the FCOM, there is a chapter starting on page PI.12.1 (PDF page 551) that lists "Normal Configuration Landing Distances" but that is listed as Advisory Information at the top of the page.To the original question, I usually have a look at the Airport Diagram and have an idea where I want to get off. For airports that I fly into often like LAX, I know without even looking that I'm aiming for the forward high speed Z, or the reverse high speed Y if I have time landing on 24R. At JFK landing 31R flying AAL, I want to roll out to V. Normally IRL you'll hear LAX Tower tell pilots "reverse Y approved" if there's room, and on VATSIM I always ask JFK if it's ok to roll to V.

Edited February 24, 2012 by Steven_Caffey

[yos233 1]

Actually since the autobrakes are set at a fixed rate, weight does not factor into it (correct?). The brakes will work harder to slow more weight, but the result is the same.The equation for runway usage is: 0.5 * (Groundspeed * 1.6878)^2 / (Rate of Deceleration in ft/s^2) + 1000.0.5 is like dividing by 2, you are taking your mean speed, and getting time to slow down multiplied by speed to give distance.1.6878 is a conversion from Knots to Feet per second, since we are dealing with feet, multiply by 0.5144 for meters, and use brake rate in meters/second.The addition of 1000 is for having landed 1000 feet down the runway, where deceleration actually begins.------------If you wanted to calculate a high speed exit, you would have to perform the calculation twice, once at landing groundspeed, and another at 40 or so knots. That way you can subtract the distance you 'would' have used for that last 40 knots. It may not be much, but that would be the most accurate calculation. The primary problem would be finding the distance to each high-speed exit to calculate for it.

[Joel 10]

One can use TOPCAT to calculate how much runway space you will be left with and using that, cross reference it to the runway and ultimately the taxiway you would like to use.

[ajpongress 467]

I just guesstimate.If I need a high speed turnoff before the halfway mark I use autobrake 2 or 3, otherwise I'll use 1 if I use the last turnoff where the gates are.

[Airbus Commander 563]

From the real world point of view, the majority of it is experience and guestimation... Remember, that you can calculate your rate of deceleration needed to be at say 20kts by the turn of all day long if you want, but if you land long by say 100ft, then you'll be at 20kts alright, but 100ft past the turn off. That's why you have pilots, we're adaptable and able to decide on the hoof if we're gonna need more of less brake power or reverse thrust throughout the landing roll... You develop the knack for it after a very short while...Rónán.

[sandpatch 9]

I have not quite understood why aircraft have autobrake? If you drive around a car you do not need a brake assistant to help you stop at perfect distance from a stop sign, neither do you need calculations before exiting at sharp highway exit, it's just normal. The only time I think autobrake is helpful is during an RTO. Do autobrakes even get used in normal operations? My guess is that they are on but manually overridden as soon as everything has settled (about 100 knots).Manfred

[ajpongress 467]

I have not quite understood why aircraft have autobrake? If you drive around a car you do not need a brake assistant to help you stop at perfect distance from a stop sign

A car isn't travelling 150 knots before stopping at the stop sign.Autobrake just helps the pilot lighten the workload. It's enough to watch 20 things on landing to not worry about applying the right amount of pressure of brake to stop too.It also prevents any sudden deceleration. If the pilot's foot slips, or he has a muscle spasm, or he has a heart attack/etc, he could unintentionally put all his weight on the brakes and that kind of deceleration from 150+ knots isn't a good thing for the passengers. Autobrake provides consistant braking until the pilot takes over around 40 knots or so for the turnoff.I don't fly commercial airliners, I'm just guessing here btw. Edited February 27, 2012 by trip7cap

[FLEX1978 373]

Autobrakes are much more efficient then manual braking. Also as mentioned they modulate using the inertial ref system, much more accurate then what a human is capable off. Obviously in certain cases immediate manual braking may be required.Manfred - I drive a pretty big truck, 4x4 although I am used to driving it and braking smoothly I can easily tell a computer would do a better job at preserving brake life. Now imagine a fleet of heavy jets landing everyday with the pilots guessing the decel rate. Bean counters want to save money, autobrake saves them money.I could reel of a whole bunch of boring facts but the bottom line is yes they are and should be used when available. It's not a car or a truck.I will leave you with one boring fact . Max manual braking is stonger the max autobraking.Surprised no one has mentioned 'brake to vacate' on the A380, you just tell it what intersection you want to exit and It will do the rest. Pretty much the future for airliners..Regards

[sandpatch 9]

A car isn't travelling 150 knots before stopping at the stop sign.Autobrake just helps the pilot lighten the workload. It's enough to watch 20 things on landing to not worry about applying the right amount of pressure of brake to stop too.

The thing is that you have to worry even with autobrake, otherwise you end up standing still between 2 exits and need to taxi for 30 seconds on the runway whilst another aircraft is forced to go-around (worst case scenario). But I can definitely understand the safety part where for example a pilot could not "be able" to brake.

Autobrakes are much more efficient then manual braking. Also as mentioned they modulate using the inertial ref system, much more accurate then what a human is capable off. Obviously in certain cases immediate manual braking may be required.Manfred - I drive a pretty big truck, 4x4 although I am used to driving it and braking smoothly I can easily tell a computer would do a better job at preserving brake life. Now imagine a fleet of heavy jets landing everyday with the pilots guessing the decel rate. Bean counters want to save money, autobrake saves them money.Regards

I have driven heavy cars as well, I have a truck driving license and I am currently studying to be a maritime captain for 300m+ ships. I understand the part of braking but for the human feel it just takes a few times of practice and then you can perfectly estimate the braking distance. But on the other part on saving money, I can understand that it saves money to decelerate constantly.__________________________________The reason I brought this up is that I find it a feature not so "important" as other features on aircraft. For example SAS MD80's have no autobrake as far as I know and the landing doesn't feel different from an 737NG landing. But I'd be happy to hear any input from a RW pilot just how you normally do it.EDIT: braking distance, not barking distance :( Edited February 27, 2012 by sandpatch

[aentwis 61]

As I cannot always guarantee having the plane down on the runway at an exact location, I use autobrake according to runway length and conditions (though that has not so much effect in FSX as in real life I guess). 3 - max for higher weights and shorter runways, 2 for most situations and 1 for long runways when I need to go to the very end turnoff...I tend to switch off autobrake by applying brake pressure below 60 knots anyway, so I can usually make one of the turn offs... the NGX stops well enough not to need the whole runway on all but the shorter runways, as long as it is not too heavy anyway...I am sure it is an experience thing... other than that cool technostuff in the A380...Andrew

[BIGSKY 316]

http://en.m.wikipedia.org/wiki/Brake_to_Vacate

[sandpatch 9]

Damm Airbus, one step closer to ILS Cat IIIc

[japascoe 98]

Actually since the autobrakes are set at a fixed rate, weight does not factor into it (correct?). The brakes will work harder to slow more weight, but the result is the same.

Your weight will change your Vref. It won't change the rate at which you decellerate (just as using thrust reverse won't change your decelleration rate if the autobrake is on), but it will change how much you need to decellerate.