Reducing ASDA - effect on operations

[NotaLOT]

Dear All,

I am trying to get my head around the concepts of TORA and ASDA and in particular this one question... (by the way I am not a pilot)

I have a runway where the ASDA is currently greater than TORA/TODA. Now due to some runway works, the ASDA length may be reduced (although it will still be greater than the TORA/TODA by about 10%). TORA/TODA will remain the same as currently.

Does a reduction in ASDA imply that there will be limitations in operations (as in the maximum weight with which one can take off), or is TORA/TODA the main criterion for calculations of weight? In other words, since the TORA/TODA remain the same, there will be no operational limitations even though the ASDA is reduced?

I will be most grateful for your help on this!

[alatriste]

hey!

If ASDA is greater than TORA=TODA that means that the stopway is longer than the clearway.
Taking credit of a stopway allows higher V1 values, that reduces TODR and TORR therefor max operational take off weight is increased.
If stopway lenght is shortened, cause of work in progress, the weight increased will be not that big although it will be higher than when not taking credit of any SWY at all.
The above is true as long as you operated as a non balanced field criteria looking for an optimized take off weight. (most of operators do it).

[BizJetJock]

As most things in life - it depends!!
The majority of aircraft, and all the ones I am familiar with, are unlikely to be affected if the reduced ASDA is still greater than TODA. I can not, however, claim to be an expert on all types and I am sure someone will be able to dig up an example where this is not the case.

Hope that helps!

[FE Hoppy]

hey!

If ASDA is greater than TORA=TODA that means that the stopway is longer than the clearway.
Taking credit of a stopway allows higher V1 values, that reduces TODR and TORR therefor max operational take off weight is increased.
If stopway lenght is shortened, cause of work in progress, the weight increased will be not that big although it will be higher than when not taking credit of any SWY at all.
The above is true as long as you operated as a non balanced field criteria looking for an optimized take off weight. (most of operators do it).

^^^^^^^^^^^^^^^^^THIS^^^^^^^^^^^^^^^^^^^^^^^^^^^

But only in the case when the MTOW is Field Length limited.

[john_tullamarine]

All limitations must be considered separately.

A reduction in ASDA will only become limiting if it results in the separate calculations revealing that the ASDA limited weight is the lowest of all the various limitations (not just the ones you have cited).

Thus, if the original RTOW was

(a) ASDA-limited, it is a fair bet that the ASDA will remain limiting

(b) not ASDA-limited, then one might anticipate that it may, at some stage, become limiting as the value is reduced.

One doesn't often see ASDA > TODA and, generally, one doesn't expect to see TODA = TORA

Not always useful to try and generalise in performance work ...

[Old Smokey]

I've never seen ASDA>TODA, perhaps as J_T suggests, it may exist in rare circumstances. From my point of view, if the ASDA surface is good enough to stop the aircraft upon, then it's certainly good enough to fly over, and TODA should at least equal ASDA.

J_T quoted "All limitations must be considered separately.".
I'm in total agreement, being a very unbalanced individual, but be aware J_T, there's a certain VERY BALANCED individual lurking "out there" in the desert dunes, who will reduce TORA, TODA, and ASDA to ONE figure for his very balanced operations. I can just imagine him right now, at the keyboard, signing in, just got to mu....., standby for incoming

Regards,

Old Smokey

[FE Hoppy]

@JT and OS
Is there a limit to the extent of a stopway? I recall 50% of TORA for Clearway but don't recall a similar limit for stop.

I'm just musing over the idea of ASDA being longer than TODA and somewhere like Edwards AFB springs to mind as there is miles and miles of salt flat which could be declared stopway.

It's purely theoretical of course but I'm a little bored today :-)

[ant1]

FH, The limit for stopway is V1<=Vr.

OS, ASDA>TODA if there is a stopway that does not meet the clearway criteria (500ft wide, etc.) if such a thing exists anywhere on earth.

[john_tullamarine]

Only recall one runway for which ASDA>TODA - in Australia - but, for the life of me, can't bring the location to mind. Never did find out the reason why ..

there's a certain VERY BALANCED individual

he's now flying for a crust so his number crunching is a tad curtailed.

[Old Smokey]

J_T,

I've done about 50% of my airport analyses in Australia, and haven't encountered ASDA>TODA, I'd appreciate your naming the one airport you found if you can recall it, just out of curiosity

ant1,

Thank you, I had not considered the lateral splay in the discussion. It does make sense that a reduced lateral splay could generate a suitable ASDA>TODA.

At least in the Australian environment excessively long CWY and SWY are merely bonuses for a safer operation, as RESA (Runway End Safety Area) comes into play and limits the amount of SWY and CWY which may be used. Frankly, I don't know if the FAR and JAR require the application of RESA, I've always applied the Australian RESA criteria for this consideration when working under these rules. (I love conservatism).

Regards,

Old Smokey

[john_tullamarine]

Is there a limit to the extent of a stopway?

Probably something hidden away in the bowels of the airport design standards. I'll run the question by OverRun who knows about such things.

I'd appreciate your naming the one airport you found

Probably a NSW/QLD country aerodrome as I recall -it was for a third level operator - 30 seat style of aircraft - long time ago now so the recall is a tad faded. I have a picture in my mind of the relevant runway terminating at a cross runway.

[de facto]

Dear JT,Old Smokey,

Apologies for the drift but could you please tell me the Minimum LEGAL flaps retraction altitude for ICAO?
I know FAA and JAA is 400ft.
If you have a document with your answer thatd be great

[NotaLOT]

Dear All,

Thank you for the replies, the picture is becoming a little clearer. So in essence, it all depends on whether TOW is currently ASDA limited.

As far as I understand it, for this particular runway, the TODA=TORA because of lack of a clearway (due to obstacles), although there is plenty of concrete to ensure an ASDA that is greater than TORA/TODA.

Thanks again!

[Old Smokey]

Hello NotaLOT,

Be careful, your remark it all depends on whether TOW is currently ASDA limited had me a bit worried.

ASDA is a purely physical dimension of the Runway characteristics. It is not related to aircraft performance.

ASDR (Accelerate-Stop Distance REQUIRED) is an aircraft performance limitation and "fits" your worrying statement. If ASDR=ASDA, then the aircraft is performance limited.

By the way, I fly over your part of the world quite often, which airport are you talking about where ASDA>TODA?

Regards,

Old Smokey

[OverRun]

I'm of the same mind as Old Smokey: "I've never seen ASDA>TODA, perhaps as J_T suggests, it may exist in rare circumstances."

I've had a good re-read of ICAO Annex 14 on stopways, and there is no airport induced limit in length for the stopway. The concept of TORA=TODA, and a longer ASDA is clearly contemplated in ICAO Annex 14. The picture from it should appear below (see example C):


This example is not usually seen in Australia because usually TODA is the full length of the runway plus the length of any clearway. What we do, where there is no designated clearway, is that the part of the runway strip between the end of the runway and the runway strip end is included as part of the TODA. In Australia, this distance is usually 60m, and so the TODA is usually 60m longer than the TORA. This Australian practice has been registered with ICAO. Any stopway is not involved.

I guess some other States do not include this part of the runway strip between the end of the runway and the runway strip end as part of the TODA; hence the ICAO example C in the picture above. This may be the case for NotaLOT.

Please note my frequent use of the word 'usually' in the above. As JT said

Not always useful to try and generalise in performance work ...

The stopway concept in ICAO seems to be that:
a) it can be of lesser strength than the runway
b) it has to be as wide as the runway
c) it must be included in the runway strip.
d) the stringent gradient limits for the first/last quarter of the runway need not be applied.

I can see an advantage using a stopway where the ground is rather uneven (saves on earthworks and levelling), and I can see an advantage where the subgrade is soft and the runway pavement is very thick (reduced thickness). I have looked professionally at some Greek airports recently where it could be of real use. The savings could be worthwhile – certainly it would repay a bit more effort at design stage.

But it is rarely seen in modern airport engineering practice. I speculate that this may be a consequence of de-skilling in the design office, or perhaps it is a consequence of airports outsourcing their engineering to design firms who enjoy getting their design fees paid as a percentage of total construction cost. If they do less work for their fees and don’t refine the design by including stopways, and they reluctantly increase the total construction cost by spending more on earthworks and pavement, well . . . . .

Turning back to NotaLOT's case, I've got a thought for a gentle check. ICAO requires the stopway to be within the runway strip – which means that the obstacles might mean that the runway strip is limited in length and thus preclude a long stopway . . . .

[NotaLOT]

Hi Old Smokey,

I take your point about ASDA v ASDR, it is what I meant, but perhaps not expressed precisely enough.

The runway concerned is Rwy 11 at Warsaw Airport, where, according to the AIP, the following declared distances are listed:

TORA = TODA = 2300m
ASDA = 2597m

There is no stopway or clearway for this runway.

Regards

[mutt]

There is no stopway or clearway for this runway.

2597-2300 = 297 meters, what is this distance called?

O_S with the fleet replacement of the Classic and MD90, we are getting dragged kicking and screaming into the optimum world But at least we still have the MD11 which doesn't account for a Stopway or Clearway

Our logic on the older aircraft was that they didn't have any allowance for line up nor did they have the ability to stop! Remember that these are aircraft were certified with NEW BRAKES and TIRES!

FE_Hoppy. The performance limit for the stopway is half the takeoff flare distance.

As for airports with ASDA > TODA, look at Peshawar in Pakistan, it has a stopway but the trees surrounding the runway prevent it being used as a clearway.... (Unless they chopped the trees down recently ) Its also a novel runway in that it has a train track crossing it!

Mutt

[NotaLOT]

It's called about 300 meters Mutt

But seriously, there is no clearway or stopway declared in the AIP for that runway, so I am not sure what you would call it!

[john_tullamarine]

The performance limit for the stopway is half the takeoff flare distance.

Some clarification for those who might be confused by this statement.

Distance to liftoff must be such that at least half of the distance from liftoff to screen (takeoff flare distance) is over the TORA. Hence one can only schedule half of the flare distance beyond the TORA and into the TODA which provides the practical limit on clearway.

The BCAR rules used 1/3 rather than 1/2 but that is probably of little interest to anyone these days.

Generally we would cite clearway rather than stopway for the second part of the takeoff flare .. but, no matter.

we still have the MD11 which doesn't account for a Stopway or Clearway

I always had a suspicion that no-one at Long Beach had any concept of stopway or clearway.

[ant1]

mutt: I guess you meant "the performance limit for the clearway is half the takeoff flare distance".

Stopway can reach to the infinite and beyond but remember, as I previously posted, that you gotta have V1<=Vr