sunrisevalley
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How Much Of A Runway Is Usable

Fri Jun 07, 2013 1:02 am

The longest runway at JFK is 14511 feet ( and JNB 14500 feet) according to GC Mapper. Do these lengths include overruns etc. ? If so how much of these lengths are allowed to be used for take-off ?
 
Woodreau
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RE: How Much Of A Runway Is Usable

Fri Jun 07, 2013 2:32 am

It depends on the runway.

In the case of JFK, all of it is usable for take-off, however landing only 11,248ft / 31L and 12,468ft / 13R is usable for landing.

The terms used are
TORA
TODA
ASDA
LDA

www.google.com/search?q=tora+toda+asda
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vikkyvik
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RE: How Much Of A Runway Is Usable

Fri Jun 07, 2013 4:29 am

Quoting sunrisevalley (Thread starter):
The longest runway at JFK is 14511 feet ( and JNB 14500 feet) according to GC Mapper. Do these lengths include overruns etc. ? If so how much of these lengths are allowed to be used for take-off ?

Runway lengths do not typically include overruns/stopways/blast pads/clearways.

For JFK's 13R-31L, the runway looks like this:

13R displaced threshold - 2043 ft.
Runway between displaced thresholds - 9205 ft.
31L displaced threshold - 3263 ft.

For takeoff, the whole runway is usually available, so 14511 ft. from either end. That's your TORA (TakeOff Run Available).

TODA (TakeOff Distance Available) is TORA + clearway at the departure end, if it exists (you have to be off the ground in the TORA, but can use the clearway to climb to 30 ft, I believe, per FAA regs).

ASDA is Accelerate-Stop Distance Available, which is TORA + stopway at the departure end, if it exists.

LDA is Landing Distance Available, which is TORA - displaced threshold at approach end.

So for landing, the distances that Woodreau posted are the TORA minus the displaced threshold lengths on each side, respectively. 13R-31L apparently doesn't have stopways/clearways.

Someone else can define overrun/stopway/blast pad/clearway. I always forget.  
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Starlionblue
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RE: How Much Of A Runway Is Usable

Fri Jun 07, 2013 6:28 am

The whole runway is available for takeoff, but if memory serves the aircraft must be at 50ft when crossing the far threshold. So the ground run will always be shorter than the runway.
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vikkyvik
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RE: How Much Of A Runway Is Usable

Fri Jun 07, 2013 3:29 pm

Quoting Starlionblue (Reply 3):
The whole runway is available for takeoff, but if memory serves the aircraft must be at 50ft when crossing the far threshold. So the ground run will always be shorter than the runway.

I believe it's 30 or 35 feet (I forget which). But again, if there's a clearway, I believe that can be used to achieve the 30-or-35-foot height, so you would just need to lift off by the end of the runway.
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sunrisevalley
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RE: How Much Of A Runway Is Usable

Fri Jun 07, 2013 4:51 pm

And another question. Piano X uses the terms for a particular example:
JAR 25 Takeoff Field length : 15284 ft
115% Factored ALL-ENG distance 15026 ft
Balanced field length : 15284 ft.

What do these mean? I believe the actual length needed is 100% of the 115% value. Am I right?
 
daviation
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RE: How Much Of A Runway Is Usable

Sun Jun 09, 2013 4:44 pm

This is probably a stupid question: why do some runways have a displaced threshold? For example, SWF's main runway 9/27 is 11,817 feet, but there is a displaced threshold of 2,000 feet at either end, thereby reducing the available landing runway to 9,817.

I don't see any obstructions at either end; it is mostly level farmland or open field. Is the reason for the displacement because of cost considerations, i.e. the 2,000-foot sections at each end cost much less to build because they don't have to support so much landing weight?

As you know, this runway was used in the past by C-5s and is currently used by C-17s, so the 'undisplaced' portions of the runway are certainly strong enough.

Anyway, I've never quite understood the reason for a displaced threshold - excluding obstructions - other than cost. Can anyone enlighten me?

Thanks.
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citationjet
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RE: How Much Of A Runway Is Usable

Sun Jun 09, 2013 5:16 pm

Quoting vikkyvik (Reply 2):
TODA (TakeOff Distance Available) is TORA + clearway at the departure end, if it exists (you have to be off the ground in the TORA, but can use the clearway to climb to 30 ft,

Russian aircraft seem to use all the available runway.
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Starlionblue
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RE: How Much Of A Runway Is Usable

Sun Jun 09, 2013 7:26 pm

Quoting daviation (Reply 6):
This is probably a stupid question: why do some runways have a displaced threshold?

Obsctruction as you mentioned. Other reasons include noise abatement and concerns about pavement strength.
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Pihero
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RE: How Much Of A Runway Is Usable

Sun Jun 09, 2013 7:58 pm

Quoting sunrisevalley (Reply 5):

And another question. Piano X uses the terms for a particular example:
Quoting sunrisevalley (Reply 5):
JAR 25 Takeoff Field length : 15284 ft

It's the runway length.

Quoting sunrisevalley (Reply 5):
115% Factored ALL-ENG distance 15026 ft

For all the following cases, one has to understand that all computations lead to determine a Max Takeoff Weight for the conditions (temperature / pressure ) of the moment.
Without a clearway and a stopway - the case here - we have
TOR = TOD
TOR is the greater of either TOR n-1 , i.e with an engine failure, or 115 % of TOR n, i.e with all engines operating.
(These figures belong to a particular aircraft, they change with each (sub) type ).

Quoting sunrisevalley (Reply 5):
Balanced field length : 15284 ft.

For performance computations, we deterrmine a V1 that gives TORA n-& = ASDA, in other terms a V1 at which, if we continue the takeoff with a failed engine, we'd stop at exactly the same point we'd be clearing the 35 ft screen height on a continued takeoff.
That distance from the beginning of the takeoff roll is called *Balanced field length* which determine the MTOW.

Quoting daviation (Reply 6):
Anyway, I've never quite understood the reason for a displaced threshold - excluding obstructions -

There is none, really.
A displaced threshold is determined by a 2 % sloped plan from the top of the obstruction intersecting the runway. Then we add 200 ft
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mmedford
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RE: How Much Of A Runway Is Usable

Sun Jun 09, 2013 8:59 pm

Quoting daviation (Reply 6):
I don't see any obstructions at either end; it is mostly level farmland or open field. Is the reason for the displacement because of cost considerations, i.e. the 2,000-foot sections at each end cost much less to build because they don't have to support so much landing weight?

Approach angle and threshold crossing heights
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Starlionblue
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RE: How Much Of A Runway Is Usable

Sun Jun 09, 2013 9:58 pm

Quoting Pihero (Reply 9):
Quoting daviation (Reply 6):
Anyway, I've never quite understood the reason for a displaced threshold - excluding obstructions -

There is none, really.

Learned something new today!
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sunrisevalley
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RE: How Much Of A Runway Is Usable

Sun Jun 09, 2013 11:34 pm

Quoting Pihero (Reply 9):
It's the runway length.

Thank you Pihero for taking the time to explain these various terms.

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