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ASDA < TORA?

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ASDA < TORA?

Old 28th Feb 2012, 22:31
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ASDA < TORA?

I was glancing through the KATL AFD and noticed on all rwys the ASDA is less than the TORA.

http://aeronav.faa.gov/pdfs/se_136_9FEB2012.pdf

Can someone explain how this is possible?

While we're on the subject of TORA ASDA, does anyone know off hand which US airport actually has rwys with TORA < ASDA? All the major airports that I'm familiar with have TORA = ASDA (except above example), and typically have blast pads or RSA. Are stopways uncommon in the US?

Last edited by rcav8r; 28th Feb 2012 at 23:08.
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Old 29th Feb 2012, 00:26
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The FAA is no longer issuing waivers for Runway End Safety Areas (RESA). As a result, some airports are having to use as ASDA less than TORA. Jepp & FMS normally do not publish these reduced ASDA numbers at this time. The AFD is the most reliable resource to find proper declared distances.
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Old 29th Feb 2012, 01:07
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Thanks for the reply but can you elaborate on how RSA, which to my understanding is area beyond and not including the SWY, affects ASDA?
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Old 29th Feb 2012, 12:05
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Thanks for the reply but can you elaborate on how RSA, which to my understanding is area beyond and not including the SWY, affects ASDA?
At locations where the area beyond the end of the pavement cannot be used as a runway safety area -- e.g., water, highway, etc. -- the airport management effectively "saws off" the distant end of the runway, designating ("Declaring") that a portion of the pavement is now part of the RSA and cannot be used in calculation of distance for Accelerate Stop.

See FAA AIM 4-3-6-c

and-
Runway safety area - Wikipedia, the free encyclopedia
http://www.faa.gov/airports/airport_...a/cert0905.pdf
http://legacy.icao.int/nacc/meetings...CARDCAip07.pdf
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Old 29th Feb 2012, 14:03
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So what's the justification for allowing an aircraft to have its wheels on the pavement in the RSA when approaching Vr at the end of its take-off run, but not when slowing to a halt at the end of its accelerate-stop?
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Old 29th Feb 2012, 14:50
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So what's the justification for allowing an aircraft to have its wheels on the pavement in the RSA when approaching Vr at the end of its take-off run, but not when slowing to a halt at the end of its accelerate-stop?
I'm not certain that I understand the question, but TORA does not permit that.

Please refer to the cites above.

From the AIM:
(1) Takeoff Run Available (TORA) – The runway length declared available and suitable for the ground run of an airplane taking off.

The TORA is typically the physical length of the runway, but it may be shorter than the runway length if necessary to satisfy runway design standards. For example, the TORA may be shorter than the runway length if a portion of the runway must be used to satisfy runway protection zone requirements.
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Old 29th Feb 2012, 15:56
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I believe what he's trying to ask is why the 'sawed off' part of the pavement that is now part of the RSA, not to be allowed as part of ASDA calcs, but remains available for TORA.
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Old 29th Feb 2012, 16:20
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It is NOT available for TORA.

Please read the last sentence of the definition above.
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Old 29th Feb 2012, 16:23
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If it weren't available for TORA this thread wouldn't exist in the first place.

Going back to the KATL AFD. You can see TORA is greater than ASDA on almost all rwys.

Also, in the second link you provided, the appendix on pg. 3 illustrates such an example where the TORA included 200' of the RSA pavement where as the ASDA did not.

Last edited by rcav8r; 29th Feb 2012 at 17:40.
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Old 29th Feb 2012, 20:35
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rcav8r
If it weren't available for TORA this thread wouldn't exist in the first place.

Going back to the KATL AFD. You can see TORA is greater than ASDA on almost all rwys.

Also, in the second link you provided, the appendix on pg. 3 illustrates such an example where the TORA included 200' of the RSA pavement where as the ASDA did not.
How stupid of me. Next time I'll read the question more carefully prior to posting.

My apologies.

The least I can do is provide the illustration of a TORA > ASDA:



As far as the rational is concerned, I can only speculate...

Wouldn't it seem logical that an airplane requiring the full TORA value would be well beyond V1 as it passes the end of the pavement designated as the ASDA limit?

In other words, at the ASDA limit, hasn't the focus of the runway certification switched from stopping safely to achieving a safe flight path?
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Old 29th Feb 2012, 21:23
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How stupid of me.
On the contrary, you've led us to the right documents...

Wouldn't it seem logical that an airplane requiring the full TORA value would be well beyond V1 as it passes the end of the pavement designated as the ASDA limit?

In other words, at the ASDA limit, hasn't the focus of the runway certification switched from stopping safely to achieving a safe flight path?
But isn't that what TODA is all about? Or put another way, in a situation with significant clearway, where TORA, not TODA, is limiting, is it not still about pavement rather than safe flight path.

In practice, is TORA ever limiting?
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Old 29th Feb 2012, 22:05
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Keep in mind that the all the TORA is not going to be used/available for the aircraft roll .. despite what might be inferred from the AIM definition cited.

Depending on the rules in play the use of TORR is that either one third or one half of the airborne distance from liftoff to screen has to be over the TORR .. ie the calculated ground run (which is transparent to the pilot in the AFM) never uses that last bit of the TORR.

ASDR, on the other hand, is serious rubber on pavement stuff.

Can TORR be limiting ? .. depends on the aircraft, runway and ambients. Usually, TOR considerations are hidden in the AFM calculations and, so, tend to be a bit of a mystery for pilots. Some AFMs will provide explicit TOR data .. just depends on OEM practices.
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Old 29th Feb 2012, 23:54
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The RSA came after many runways so in-order to make it fit the ASDA has to be reduced in some places. It's a stopping thing so it doesn't impact the declared going distances of TORA and TODA.
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Old 1st Mar 2012, 05:03
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My head hurt after reading 3 sentences of this thread.

You lot would really be a laugh a minute at the bar in the evening.

Time for a martini.
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Old 3rd Mar 2012, 04:50
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Racv8r,

As stated in these replies and in the AIM, airport design standards may require adjustments to the runway’s declared distances. In the event that the full, standard Runway Safety Area (1000’) cannot be obtain, a portion of the runway may be used to obtain the require RSA length. In this case, ASDA and LDA will be reduced as required to obtain this 1000’. The US is the only country currently applying this method to obtain full RSA; however, other countries and ICAO are considering adopting this practice. Another factor that may affect declared distances is the Runway Protection Zone (RPZ), which is designed to limit undesirable activity immediately beyond the runway. To obtain the required RPZ, the TORA may be reduced below the physical runway length. For example, see Concord, CA (KCCR).

True stopways, where ASDA is > TORA & TODA are rare in the US. Glasgow, MT (KGGW) is one airport that has an honest-to-goodness stopway on three of the runway ends. This is one of the few (only?) airport in the US with fully documented and declared stopway, declared being the operative word for use in accelerate-stop distance calculations. To be declared a stopway, the runway must have the stopway noted in the A/FD remarks and have published declared distances for that runway (ref: AC 150/5300-13).

Unfortunately, there are some aberrations in declared distances at some US runways. Detroit Metro (KDTW) being the latest:

02/451 (A1568/12) - RWY 22L TODA 11300. 28 FEB 17:00 2012 UNTIL 03 MAR 20:00 2012. CREATED: 27 FEB
19:45 2012

Declared Distances
Take Off Run Avbl. (TORA) 12,003/12,003
Take Off Dist. Avbl. (TODA) 12,003/12,003
Actl. Stop Dist. Avbl. (ASDA) 12,003/12,003
Lndg. Dist. Avbl. (LDA) 12,003/12,003

For the purpose of takeoff planning, accelerate-stop distance must be less than ASDA, takeoff distance must be less than TODA, and takeoff run must be less than TORA. Use of declared distances that differ from the full, physical runway length requires takeoff data that can take advantage of an un-balanced V1 speed and unbalanced field length calculation. For those airplane types that provide only balanced field takeoff data based on a balanced field V1 speed (within certification limitations), then the balanced field takeoff distance or runway limited takeoff weight must limited by the most restrictive of the ASDA, TORA, or TODA length.


Rich Boll
Wichita, KS
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Old 3rd Mar 2012, 04:54
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Hold up chaps. There is something not quite right here. I haven't got it fully worked out yet, but thought I'd post my query in the interim.

There may be something in the difference between RESA and RSA. RESA in its ICAO implementation is from the strip end. RSA in the FAA implementation is from the runway end. So with the RSA, it is easy to fiddle with the runway length independently of the strip, and so it is possible to have the ASDA less than the TORA.

But with the ICAO RESA, this starts from the strip end which is at least 60m (200') beyond the TORA. So under ICAO rules, if RESA is needed and cannot be built, the TODA (and thus the TORA) have to be artificially reduced to provide the RESA length. This also probably means that some stopway has been created consisting of the now-redundant pavement/strip. The stopway is not included on the TORA or TODA, but can be included in the ASDA calculation. So the ASDA can be longer than the TORA and TODA, but never in the ICAO system can it be < TORA.

I'm welcoming constructive comments here, because this rather mirrors an intractable runway problem in Oz that some of us have got at present.
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Old 3rd Mar 2012, 12:44
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OveRun,

In FAA parlance, the RSA encompasses the entire runway. The RSA width limits may be identified by the runway hold short signs as the must be located no closer to the runway than the RSA limit. There’s a takeoff RSA that extends beyond the departure end of the runway and a landing RSA that extends out before the approach end of the runway. However, if the runway is operationally bi-directional the takeoff RSA for both runway ends establishes the RSA length beyond each runway end. The illustration shown in the CARDAip07.pdf ICAO document linked earlier in this thread depicts this concept.

In the US, the RSA is intended to contain the aircraft in the event of runway excursion, laterally or off the ends. It must be graded and constructed (does not need to be pavement) to support the aircraft without undue risk of damage to the aircraft in the event of such an excursion. When the airport geography does not allow the airport operator to obtain the full RSA length beyond the runway end, then FAA allows the operator to declare a reduced ASDA and LDA to obtain the required length (or obtain as much as practical while not adversely impacting the runway’s usability).

In the US, ASDA may be less than TORA or TODA as necessary to obtain the required RSA length. My understanding is that in ICAO Annex 14, ASDA may not be less than TORA or TODA.

On another note, I failed to mention in my previous post that TODA may be reduced to less than the full, physical runway length (and less than TORA) if by doing so the airport operator can obtain a clear 40:1 OCS as defined in AC 150/5300-13, Airport Design (not TERPS…closely related, but different 40:1 surface). The allows the airport operator to establish a runway length that the FAA TERPS procedure designers will use in evaluating obstacles in the TERPS takeoff Initial Climb Area (ICA) and may result in the elimination of 40:1 TERPS OCS penetrations that would result in non-standard takeoff minimums and/or use of a takeoff climb gradient on a SID. There are some airports (I believe that one example may be found at Memphis, KMEM) where this technique is applied.

Rich
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Old 3rd Mar 2012, 14:13
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richjb,

If I'm understanding it correctly, RSA compliance, at least in the US, is implemented by the FAA on a case by case basis?

Take KDCA for example, its rwys are all within 1000' of either the river or a highway, yet is able to retain rwy length declared distances.
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Old 3rd Mar 2012, 16:49
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In the UK the CAA publish CAP 168 Aerodrome Licensing. In there is a section about RESA which follows the ICAO regs.

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Old 4th Mar 2012, 03:10
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richjb,

Thanks for the explanation. The FAA RSA is rather like the ICAO runway strip (or more accurately the graded strip). Both are similar dimensions, but different names. The dimensions of both vary with aircraft class (i.e. size).

ICAO matches FAA using a combination of runway strip and RESA. The ICAO runway strip for a medium airline jet is typically 150m (500 feet) or more wide and runs the full length of the runway to extend 60m (200 feet) beyond the end of the runway at each end. The RESA starts beyond the runway strip at each end and extends at least another 90m (300’) or the recommended 240m (800 feet). It sort of matches the FAA’s RSA which I show below using the image from the useful 9CCARDCAip07.pdf reference you mentioned.


FAA runway safety area



ICAO runway end safety area

BTW I say typical because there are many ICAO runway strips for airline aircraft which are 300m (1000 feet) wide, and some which are 300m (1000 feet) wide but only the central 150m (500 feet) is graded and constructed for the passage of an aircraft without undue risk.

However there are still a number of subtle differences between FAA and ICAO here, and it is important not to blindly copy from one to the other (i.e. RSA is much wider beyond the end of the ICAO strip; RESA is stronger pavement).
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