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flyboy80
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General Takeoff Vs Rollout Length?

Thu Nov 19, 2015 5:39 pm

Under general circumstances, and I know there are many variables at hand, do landing rollouts usually use less runway length measured from the touchdown point than takeoffs?

When deadheading at work- I often notice,after touchdown, we exit the runway in 3.0-4K feet with no real violent or aggressive braking apparent. The same aircraft, 737s, tend to not get airborne until at least 4K feet. Again I know several factors at hand here, but is there any general reasoning to note here? I'm sure certain equipment behaves in certain manners based on characteristics- such as a 737-900 using a high final approach speed.
 
vikkyvik
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RE: General Takeoff Vs Rollout Length?

Thu Nov 19, 2015 8:26 pm

Quoting flyboy80 (Thread starter):
Under general circumstances, and I know there are many variables at hand, do landing rollouts usually use less runway length measured from the touchdown point than takeoffs?

I'd say for commercial airliners as a general rule, yes, landings take less distance than takeoffs for the same airplane.

Speeds tend to be a little lower, and you have drag working for you instead of against you.
I'm watching Jeopardy. The category is worst Madonna songs. "This one from 1987 is terrible".
 
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Florianopolis
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RE: General Takeoff Vs Rollout Length?

Thu Nov 19, 2015 8:59 pm

Quoting vikkyvik (Reply 1):
as a general rule, yes, landings take less distance than takeoffs for the same airplane

And you have less mass to decelerate, and your brakes are more effective than your engines (in a fight between engines and brakes, brakes win). And on most landings you're not seeing anything close to the maximum performance of the aircraft. Takeoffs are generally closer to max performance than landings.

An exception to vikkyvik's "general rule" would include contaminated wet/snowy/icy runways with reduced braking action.
 
flyboy80
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RE: General Takeoff Vs Rollout Length?

Thu Nov 19, 2015 9:00 pm

Anyone have the typical landing roll-out length in "standard" conditions, at a "normal" weight, for the type you fly?

Last week I flew on an E175 into LAX- I was surprised at how fast we stopped, albeit with very aggressive breaking. Counting the markers, I estimated our touchdown to runway exit was about 2700-2800'
 
AAR90
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RE: General Takeoff Vs Rollout Length?

Thu Nov 19, 2015 10:12 pm

When I was a young lad, my dad (PAA Capt) explained things this way.....

Takeoff =
Heaviest the plane will be for this flight (max fuel load);
Slowest the plane will be for this flight (starting from zero);
Highest thrust setting the plane will use for this flight (takeoff power).

Landing =
Lightest the plane will be for this flight (min fuel load);
Fastest (near the ground) the plane will be for this flight (already flying);
Lowest thrust setting the plane will use for this flight (idle power).

"Them's are the basics."   
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Starlionblue
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RE: General Takeoff Vs Rollout Length?

Fri Nov 20, 2015 2:30 am

Quoting flyboy80 (Reply 3):
Anyone have the typical landing roll-out length in "standard" conditions, at a "normal" weight, for the type you fly?

A330-300 at 190 tons, sea level, no wind, ISA temp, no slope, manual landing, full flap, autobrake low and both reversers operative gives 6980 feet, but that's from the threshold so the roll out distance should be around 6000ft.

Same conditions with maximum manual braking gives 3930 feet.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
flyboy80
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RE: General Takeoff Vs Rollout Length?

Fri Nov 20, 2015 4:31 pm

Quoting Starlionblue (Reply 5):
A330-300 at 190 tons, sea level, no wind, ISA temp, no slope, manual landing, full flap, autobrake low and both reversers operative gives 6980 feet, but that's from the threshold so the roll out distance should be around 6000ft.

Is auto brake low only relevant to the actual brakes, or does it apply to the entire breaking system, including the TRs?
 
mmo
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RE: General Takeoff Vs Rollout Length?

Fri Nov 20, 2015 5:39 pm

Quoting flyboy80 (Reply 6):
Is auto brake low only relevant to the actual brakes, or does it apply to the entire breaking system, including the TRs?

The autobrakes will be aircraft specific and will not include the T/Rs. Generally speaking, a setting other than max will command a rate of deceleration. So, if you have the T/Rs deployed, the wheel brakes will contribute less braking since there is braking through the T/Rs. As the aircraft slows and the T/Rs become less efficient, the wheel brakes will provide more braking to continue deceleration at the selected rate. When MAX is selected, there is a constant pressure applied to the wheel brakes regardless of the effect of the T/Rs. Generally, the brakes are applied at max hydraulic pressure when MAX is selected.
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vikkyvik
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RE: General Takeoff Vs Rollout Length?

Fri Nov 20, 2015 11:50 pm

Quoting flyboy80 (Reply 3):
Last week I flew on an E175 into LAX- I was surprised at how fast we stopped, albeit with very aggressive breaking. Counting the markers, I estimated our touchdown to runway exit was about 2700-2800'

I've actually been paying attention to this on my flights for the last couple years (almost all on B6 A320s). If I remember correctly, the shortest from touchdown to turnoff was around 2700 feet (at BOS, on 22L). Braking felt consistent, but not really aggressive by any means.

Most landings I've been on have been in the range of 3000-5000 feet. But there are plenty of variables, including where they turn off the runway.

And I'm just a lowly passenger, so don't know what's going on in the cockpit.

Quoting Starlionblue (Reply 5):
A330-300 at 190 tons, sea level, no wind, ISA temp, no slope, manual landing, full flap, autobrake low and both reversers operative gives 6980 feet, but that's from the threshold so the roll out distance should be around 6000ft.

Same conditions with maximum manual braking gives 3930 feet.

Is that the regulatory distance (with safety factor of, what is it, 1.5)? Or the actual distance? If it's actual, why would they give it from the threshold?

Quoting mmo (Reply 7):
Quoting flyboy80 (Reply 6):Is auto brake low only relevant to the actual brakes, or does it apply to the entire breaking system, including the TRs?
The autobrakes will be aircraft specific and will not include the T/Rs.

To avoid confusion, I think the answer to his question is that autobrakes will include the T/Rs (by taking their contribution into account).
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Starlionblue
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RE: General Takeoff Vs Rollout Length?

Sat Nov 21, 2015 5:09 am

Quoting vikkyvik (Reply 8):
Quoting Starlionblue (Reply 5):
A330-300 at 190 tons, sea level, no wind, ISA temp, no slope, manual landing, full flap, autobrake low and both reversers operative gives 6980 feet, but that's from the threshold so the roll out distance should be around 6000ft.

Same conditions with maximum manual braking gives 3930 feet.

Is that the regulatory distance (with safety factor of, what is it, 1.5)? Or the actual distance? If it's actual, why would they give it from the threshold?

Actual distance. I'm guessing they used from the threshold since it is a landing distance required (how much runway do you need), not a ground roll distance. If you're at the point where you need to calculate from a table you don't want to add the further complication of deducting the distance from threshold to touchdown from the landing distance available shown on the plate.

[Edited 2015-11-20 21:12:54]
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jetmatt777
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RE: General Takeoff Vs Rollout Length?

Sun Nov 22, 2015 1:38 am

It's also more difficult to get an accurate picture from the passenger perspective. The pilot may know he won't make a certain exit, and use less braking to roll faster towards the next exit a little further down the runway. Or, a pilot may want to make a certain exit and use more braking to get to it.

A flight I was on had a medical emergency, and whether or not it was intentional or not I don't know, but we landed with very heavy braking and made the first high speed turn which leads straight into the gate we were using.

I also notice at PDX, when traffic dictates, occasionally Q400's will land on 10R, and use up about 8,000 feet of it with very little braking. At that point they are right next to the gates they use to park, and they turn off the runway and pull into their spot.
 
Passedv1
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RE: General Takeoff Vs Rollout Length?

Mon Nov 23, 2015 7:42 am

Quoting jetmatt777 (Reply 10):

A flight I was on had a medical emergency, and whether or not it was intentional or not I don't know, but we landed with very heavy braking and made the first high speed turn which leads straight into the gate we were using.

I also notice at PDX, when traffic dictates, occasionally Q400's will land on 10R, and use up about 8,000 feet of it with very little braking. At that point they are right next to the gates they use to park, and they turn off the runway and pull into their spot.

Your intuition is correct...turnoff are planned/dictated by a variety of factors. 10R in PDX is a good example...zip down to the end of 10R at rollout speed instead of having to taxi all the way around the terminal to the south side.

As far as auto-brakes go...I think the responses so far have been overly complicated and I think may be
making the system out to be more sophisticated then it is. The system is very simple, it senses aircraft speed and applies brake pressure to achieve that deceleration rate up to a pre-programmed Max brake PSI. The system does not have any idea what other systems like the reverses are doing. A 737 at a/b 1 will decelerate the airplane at 2.4 kts/sec and apply up to 1285psi to achieve it. At A/B Max you get 8.3 kts/sec or max PSI.

If you do use reverse it will result in less brakes being applied, as will landing with an upslope runway, having a big headwind, deploying the speedbrakes, or landing on lose gravel or dry snow...but to be clear, the a/b system is not "looking" at any of this, it just keeps squeezing harder until it gets its deceleration rate or achieves its max PSI.

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