Takeoff Field Length = TODA / TORA / ASDA?

[ImperialAero]

Hi all, my first thread so go easy...

When calculating the takeoff length required from a runway at a particular airfield elevation temperature and weather conditions, when considering the Takeoff Field Length available, does the pilot use the TODA, TORA or ASDA of the runway in question.

I ask becasue I am looking at comparing three airfield with varying runway and TORA / TODA / ASDA lengths, and evaluating those with the 'Takeoff Field Lengths' quoted in the manufacturers Airport Planning Manuals. Does this 'Takeoff Field Length' required refer to the required TODA, TORA or ASDA?

I hope this is a simple question with a simple answer, and to avoid any confusion;

TORA is the physical length of the runway available for takeoff including a run-up area if available.

ASDA includes a SWY

TODA includes a CWY and a SWY.

[aviatorhi]

Will vary from region to region (as anything), but for most instances it's TODA from the point of "brake release".

[kwateow]

Using airport planning books is leading you up a wrong path. Take-off field lengths in those manuals refer to a runway without any clearway or stopway. If TORA, TODA & ASDA are different, it is possible (but not simple) to convert these into an equivalent balanced field length so the airport planning charts can be used. But for that you need a proper performance manual or software.

Plus: "TODA includes a CWY and a SWY"....

There is no notion of stopway in the definition of TODA.

Firstly a runway does not necessarily have a stopway beyond the end of the runway.

Secondly imagine a runway which finishes at the top of a cliff, below which is the sea. In this case there is no stopway but an enormous clearway which helps to extend the TODA quite a bit.

[ImperialAero]

Forgive me, for the definitions above, they should all be '...can include...'

[john_tullamarine]

Worth an observation or two, I think.

.. does the pilot use the TODA, TORA or ASDA of the runway in question

Depends. Some AFMs provide individual calculations (although there may be some merging of those calculations for some aircraft) in which case all three considerations must be addressed separately. In some cases, the AFM only provides BFL data and the calculations are simplified.

Generally one can view BFL calculations as being the quick and dirty way to get a quick answer while the detailed calculations generally will get a bit more payload at the expense of more effort expended in the calculations.

I am looking at comparing .... and evaluating those with the 'Takeoff Field Lengths' quoted in the manufacturers Airport Planning Manuals.

Generally the planning manuals are not intended for routine operational use. Rather they provide gross data for the civil engineering airports folks. Suggest you don't try to get too much in the way of other than ROM data from such documents.

If TORA, TODA & ASDA are different, it is possible (but not simple) to convert these into an equivalent balanced field length

An interesting thought. Would you like to elaborate a bit for us ?

There is no notion of stopway in the definition of TODA.

While TODA is not concerned with stopway for stopping, the whole idea of TORA/TODA is that

(i) the former relates to the declared hard bits suitable for routine aircraft rolling over. The calculation of TORR is intended to ensure that the takeoff liftoff point occurs prior to the end of the declared TORA - to make sure that we don't take stuff sited beyond the runway head into the sky with the aircraft. Depending on the rule set, the proportion of the air distance to screen which must be over the declared TORA will be either one third or one half

(ii) while the latter is concerned with getting to screen height. With TORR having fixed concerns with getting off the ground, we can enjoy some latitude in the final part of the takeoff flare to screen and put this beyond the declared TORA. As such we routinely would be flying this last bit over any stopway and part/all of the declared clearway. Thus declared TODA generally will include any stopway.

Firstly a runway does not necessarily have a stopway beyond the end of the runway.

.. but generally does as the routine design standards require a RESA of some sort. This generally also provides for a jet blast area in the opposite direction takeoff.

[CaptainProp]

AR-OPS 1.480
(a)(9) TakeOff Run Available (TORA): The length of runway which is declared available by the appropriate authority and suitable for the ground run of an aeroplane taking off. TORA is either equal to the runway length, or to the distance from the runway entry point (intersecting taxiway) to the end of the runway

JAR-OPS 1.480
(a)(7) Takeoff Distance Available (TODA): The length of the takeoff run available plus the length of the clearway available.

JAR-OPS 1.480
(a)(1) Accelerate-Stop Distance Available (ASDA): The length of the takeoff run available plus the length of the stopway, if such stopway is declared available by the appropriate Authority and is capable of bearing the mass of the aeroplane under the prevailing operating conditions.

Don't forget:

JAR-OPS 1.490
(c)(6) [...] an operator must take account of the loss, if any, of runway length due to alignment of the aeroplane prior to takeoff

When a V1 speed is chosen that gives you equal TODR N-1 (engine failure) and ASDR, you have a balanced field take off.

When the chosen V1 is less than balanced V1, in case of available clearway, wet rwy or contamination, TOD N-1 increases and ASD decreases.

When a stopway is available and a higher than balanced V1 is chosen your TOD N-1 decreases and ASD increases.

To summarize, you have all engine TODR, TODR N-1 and ASDR vs MTOM and climb requirements to consider. You need to find the highest mass calculated to comply with the longest of the above distances on a given runway....and at the same time comply with climb regulations for your specific aircraft (2.4% / 2.7% or 3.0% for 2nd segment depending on 2,3 or 4 ENG) and for the specific airport you are departing from in case of local requirements.

Did I get that right?! :E

[kwateow]

"If TORA, TODA & ASDA are different, it is possible (but not simple) to convert these into an equivalent balanced field length.
An interesting thought. Would you like to elaborate a bit for us?"

Rather than attempt to use my own words, and get it wrong, here is an extract from an (old) manufacturer's performance manual i.e. intended for use by airline planners, not by flight ops.

"In the case of availability of clearway and/or stopway the equivalent balanced field length, EBFL, can be derived from sheets 4 to 9. For each flap setting two charts are provided:

- EBFL as a function of TOD and ASD.
- EBFL as a function of TOR and ASD.

The lower of the two values obtained represents the EBFL to be used to read take-off weight limited by field length."

[john_tullamarine]

Did I get that right?! http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/evil.gif

Putting aside sideline things like brake energy and such, you have a starting generalisation.

However, the TORR is a necessary calculation each time as well as TODR and ASDR. What causes a lot of confusion is that the TORR bit often is hidden in the rest of the calculations and is transparent to the pilot when looking at the AFM. It would be useful if pilot theory training involved an introduction to AFM work using a Type which explicitly addressed all the requirements (eg some of the HS AFMs were good on this point).

here is an extract from an (old) manufacturer's performance manual

Your second post sits better with me than the first. I would be interested in having a looksee at the documents to which you refer to see if my initial thoughts align. Any chance you could scan and either link or email please ?

[BOAC]

Anyone else wondering................................?