TODA Gradients?

[BOK_]

In the Runway Distance Supplement at back of ERSA it will state the TODA and then in brackets next to it the gradient required.

Is that gradient specified required to be mainted up till LSALT/MSA, or some other height - had a quick flick through the perf section in CAO's but to no avail.

Thanks ahead....


BOK

:ok:

[UnderneathTheRadar]

Until you've cleared all obstacles by 35ft (or 50ft) with OEI on the intended flight path up to 400ft or such height as necessary to provide that clearance.

Or at least that's what it seems to me... CAO 20.7.1b section 12.1.

UTR

[Arm out the window]

Stretching the memory banks here, but I think the gradient applies to a splay area from far end of the TODA out to a given distance depending on runway width, among other things.
Basically it gives you a guaranteed obstacle clearance within that splay out to the specified distance (which used to be written in ERSA somewhere as I recall - you can tell I haven't been flying IFR or planks for a while!).
If you're departing IFR and you can make the SID or other departure gradient, well and good, but the TODA gradient and splay area give you possible ways of getting out of trouble if you can't maintain that gradient for some reason.
Happy to be corrected if this is all too vague - must go back to the books again.

[13/31]

The TODA gradient published in ERSA is the obstacle clear surface extending out from the end of the clearway. The runway code number (CN) determines the length of the surface which is surveyed for obstacles. It's all explained in ERSA/Intro-23. The inner edge width of the take off surface is usually the overall runway strip width. Any runway which does not meet the standard dimensions is qualified with a note following the aerodrome details in the RDS section of ERSA.

The actual location of the critical obstacle should be able to be obtained from the aerodrome operator.

[13/31]

Correction to previous post - the approach surface inner edge width is usually the overall runway strip width. The take off inner edge width is 60 metres for code 1, 90 metres for code 2, and 180 metres for codes 3 and 4.

[john_tullamarine]

The surveyed path may not necessarily take you to minimum safe altitude

(While acknowledging your caveats) that's still an understatement. The ONLY time you can (reasonably) rely on the declared data's covering you for the latter stages of the takeoff ... is if you are taking off over water .... and even then be wary of tall masted yachts etc ....

(a) re RDS, the preamble pages define the trapezoid which is relevant to the runway

(b) while the presentation may give you the impression that the data is based on a general inclino survey, usually this is not the case. Normally a baseline survey is done to ID the critical obstacles and then these data are overlaid on a suitable topo to define the EOLs for RDS publication

(c) either the surveyors (and there are only a few who routinely do this work) or the aerodrome owner may provide (gratis, for a beer, or for real money) the survey data. Those of us who practice in this arena have our little lists of who looks after which aerodrome ...

(d) believe dz's statement that the airlines (and consultants) spend a LOT of effort and time sourcing data to complete the takeoff ... and, on occasion, that involves throwing a theodolite over the shoulder and going bush ...

[Victor India]

j_t,

It sounds like you are knowledgeable in this area, but just to keep it simple - are you saying that the gradients in the back of the ERSA aren't a safe way of providing terrain clearance to the end of the splay (usually 15000M/8.1nm)?

We rely on them heavily for engine out departure planning (if we cannot achieve a SID gradient, or where no SID is available). Assuming the net gradient our aircraft can achieve is greater than the OCTG, we consider it usable. We then check the height we can achieve at the end of the splay. Ideally it would be 25nm MSA. If only 10nm MSA achieved, we would then turn at the end of the splay (8.1nm upwind) to remain with 10nm until 25nm MSA is achieved.

In some cases for heavy departures, if 10nm MSA cannot be achieved, we will accept lower. Strictly, in order to just achieve 35' terrain clearance, we can accept 10nm MSA less 965' at the end of the splay. Sometimes, we would consider using the OCTG up to a circling height before turning to climb within circling areas until MSA is achieved.

Is this approach uncommon?

Cheers,

VI

[john_tullamarine]

Caveat - I've been out of routine performance consulting for a few years (got to sleep sometime) so there may well have been the odd change with which I haven't caught up ...

VI - sounds like you are on jets from your profile but probably non-RPT from the post comments ?


(a) check the preamble re splays (ie data relevance)

(b) if you want the maximum information, use Type A charts (available for most of the longer runways) and which are available variously, for a nicely phrased "please", through to a fistfull of money ...

(c) with the exception of the odd runway (CBR 35 comes to mind) the data is straight out .. which doesn't help any if you intend to schedule an early turn. Then it's a case of you're on your own and you need to make sure that you are able to suss out where the bumpy bits are located ..

(d) are you saying that the gradients in the back of the ERSA aren't a safe way of providing terrain clearance to the end of the splay

not at all .. apart from the odd error which sneaks through (and we periodically used to pick these up .. sometimes they were quite outstanding errors). Just be aware of the splay to which the data refers. Also, on 20.7.1B aircraft, be mindful of first segment/second segment deltas and where you are entering the third and fourth .. far too many folk tend to think only in terms of the second.

(e) greater than the OCTG, we consider it usable.

.. but check the first segment (if appropriate) and be conscious of the third/fourth unless the rocks are all low down ..

(f) height we can achieve at the end of the splay.

.. you're obviously flying a pocket rocket .. that's not the normal expectation for heavies ..

(g) .. we will accept lower.

I see .. and, depending on the numbers, then what do you do ? apart from trust in the Almighty's benevolence ?

(h) Is this approach uncommon?

Probably not in some circles .. but generally tightened up a bit in the reputable RPT arena

This sort of topic set has been discussed on numerous occasions in PPRuNe .. you might like to run a search on usernames Old Smokey, Mutt, and me to dig them out ..

[Victor India]

j_t,

thanks for the reply. in response to your point (e) below...

we generally plan extended second segments to reach MSA. It is simple from a planning point of view, easily calculated with the FMS and the aircraft can achieve it in most cases within time limitations of TakeOff thrust. So 3rd/4th segments are normally irrelevant for us as they occur above MSA.

regarding (g) ... you asked how low? As I stated, generally we aim to achieve an MSA (1000' terrain clearance) by the end of the splay, but can accept lower. As 35' is the required terrain clearance (scary minimum, but legal), we could in theory accept MSA less 965'. In practice though, when planning a departure, I would want substantially more terrain clearance at the end of the splay. If I expected less than 500' I would plan a turn within the circling areas until MSA is achieved.

All very blunt analysis when the obstacle limiting the MSA may be miles off the centreline, but with operations to many airfields for the first time at short notice, it is a safe method.

You're guess re non RPT is correct, hence the lack of airline designed (commercially available!) escape procedures. Regarding (h)... I take your point that the "reputable RPT" arena wouldn't use these methods. Of course they are aiming to allow maximum uplift. The methods we use are generally far more conservative for simplicity, but at the extreme would limit our capability where a well designed escape procedure (eg RNP departure) would not.

All comes down to dollars, but I believe we have a safe approach...

VI

[john_tullamarine]

(a) extended second segments to reach MSA.

.. the simplest and often best option when available .. providing that the first segment (if existing .. which normally is the case for higher performance aircraft) doesn't become more limiting than the second for the runway in question ...

(b) .. we could in theory accept MSA less 965'.

.. so long as you are still considering nett rather than gross

(c) .. less than 500' I would plan a turn within the circling areas

ditto and providing that the plate data is suitable for your gameplan .. the procedures designers are a good source of plate data for the normal glass or two payment arrangements ...

(d) .. but I believe we have a safe approach...

the only thing which counts at the end of the day is that you have a plausible and marketable story at the enquiry in the event that it turns to custard for whatever reason ...

If you have too much time off on a MEL RON .. do give me a call .. always happy to have an ale with performance motivated flight crew folks ... we could always grab Centaurus to make a threesome over coffee .. he, certainly, is a pilot who fits that description ...

[Victor India]

ah yes... Centaurus... I believe I've had the pleasure somewhere here on similar issues before :)

VI

[john_tullamarine]

Centaurus' opinions are those of a very experienced flyer and one who is quite knowledgeable regarding performance work .. one would be ill-advised to discount his views without good reason.

[Victor India]

j_t,

No disrespect of Centaurus intended... quite the opposite actually. My last post was poorly phrased in that it was open to interpretation as sarcasm (although I certainly have used that poor form of wit in the past, but not this time).

Cheers,

VI

[john_tullamarine]

VI,

Please .. I did not, in any way, read your post to be other than very fondly disposed toward the good Centaurus.

I was only emphasising that his views are those of a venerable greybeard veteran and, as such, worth heeding... immediately, I can hear his admonition .. "enough of the greybeard stuff there, JT" ..

Perhaps I need to be more careful in my own wordiology to avoid misunderstanding ....

Peace, brother ...

[Kiwiguy]

Could I tip toe in here and ask something please ?

If only 10nm MSA achieved, we would then turn at the end of the splay (8.1nm upwind) to remain with 10nm until 25nm MSA is achieved.

I read your concept Victor India of turning to stay within the safe radius but I thought (in NZ at least) that one was only allowed to deviate 15 degrees from projected runway centreline on SID ?

I'm not an instrument flyer so maybe I am confusing different concepts ?

[Arm out the window]

The concept there would be to turn within the splay area near the outer end, where it's widest, of course, and then fly back towards the airfield climbing at whatever rate you could get. You would either get to 10 nm MSA and set up for an approach or whatever, or at least reach the circling minimum, climb in the circling area until reaching MSA and go from there - instrument approach, diversion etc.
15 deg of splay at 8 nm would give you about 2 nm laterally each side of the runway width, hopefully enough to do a reversal and stay in the area.

SIDs are good if you can maintain the design gradient with an engine out
(3.3% or whatever) but not much use when you can't, as is the case for a lot of non-RPT people.

[john_tullamarine]

The concept there would be to turn within the splay area near the outer end

For a 20.7.1b bird ... unfortunately you need to continue the splays during the turn ..... and, if OEI .. you are looking at a large radius anyway ?