CAAO 20.7.1B and Gradients After T/O

[Cost Index]

G'Day,

Here's the scenario. An aircraft of the type listed, turboprop, at MTOW under certain conditions is able to climb in the 1st segment at 1.2% gradient, 2nd, 3.1% and 4th, 2.8%.

The TODR for said conditions is 4500 ft and the runway it'll be going out of has a TODA of 5500 ft necessitating a 4.5% gradient climb after t/o.

The STODA from the ERSA is 5300 ft (3.3%), or 5150 ft (2.5%), or 5100 ft (2.2%) or 5000 ft (1.9%) With all engines operating it'll do 7+% on climb easy.

My question is with the performance data I've extracted is the aircraft able to takeoff at MTOW under these conditions? I think yes, because from what I can understand of the regs the 1st, 2nd, 3rd and 4th segment climb only refer to an aircraft with an engine shutdown.

Therefore because it can perform to the necessary regs requirements over all the segments it doesn't require the aircraft to perform to the 4.5% required obstacle clearance when single engine.

Am I right or will the aircraft have to have it's weight reduced so that the performance given off the flight manual will be able to match the STODA out of the ERSA?

Cheers :D

[DeltaSix]

As far as I know, the climb gadient being referred to ( in the DAPS ) are climb gardients with all engines operating.

You lose an engine and you lose more than 50% climb capability and not unless you work it out on the engine-out graphs under specific conditions ( e.g. temperature, MTOW, others ) that it can do the specified gradient then I can say no, it wont be able to make the climb.

But then again, I dont know exactly what the performance capability of the aircraft that you are referring to.


Just putting my 2 cents in..............


DeltaSix :rolleyes:

[john_tullamarine]

Some comments (which are necessarily general without the particular AFM/runway/aerodrome obstacle data in front of me).

(a) I suggest you don't have enough data to answer the question (I presume that ASDR/TORR are not limiting)

(b) ... what are you proposing to do about obstacle calcs once you are outside the ERSA trapezoid ? A scratch of the chin with the ERSA data suggests that straight ahead obstacles aren't much of a problem .. with some slope data, one can do a simple geometric analysis to work out the approximate distance and height of the critical obstacles.

(c) ... what is the first segment distance ? This may be a show stopper for your simple calculations - keep in mind 20.7.1B.7.2.2. Also, one needs to consider the runway slope geometry

(d) if you can fit the first segment into the spare distance to end STODA, then you can operate to the STODA gradient limit provided obstacles outside the trapezoid are not limiting

(e) 20.7.1B - AEO for the takeoff considerations is largely irrelevant, providing that the aircraft is operated in a manner which keeps it above the presumed OEI flight path. Keep in mind that 20.7.1B RTOW calcs are done for the most restrictive cases .. and that generally is not AEO.

(f) you have, one presumes, done the TOD calcs for all cases and are quoting the most restricted ?

(g) The TODA EOS gradient is of no interest other than for reverse calculating the obstacles from the ERSA data unless you are working on a simple analysis and need the takeoff distance beyond the next STODA value below the TODA EOS gradient .. in which case, that would be the OEI gradient you need to come up with

(h) ERSA/RDS gradients are just that .. simple geometry .. doesn't matter whether the aircraft is AEO, OEI, or on a wing and a prayer .. just don't hit the ground.


Looking to your assessment, consider

(a) the calcs must consider the OEI case

(b) you appear to have ignored first segment obstacle clearance

(c) you appear not to have considered the overall obstacle clearance requirements

[Bula]

Just remember:

the climb gradients in CAO20.1.7B are aircraft requirements. There is no reason why an airport must conform to this.

An aircraft may acheive more then this.

STODA angles (from memory) is taken from that distance to a point 7nm on a splay from the end of the runway. Considering an EFATO situation, why turn if the area ahead is clear and the aircraft is only performing the an obstacle clearance gradient.

JEPP chart gradient will give you the minium gradient to maintain controlled airspace (though on SIDS it will also give the obstacle clearance requirement in most cases)



If you can consider the IAS for each segment on the aircraft type and expected RoC for each segment you can actually plot the climb gradient required for obstacle clearance on your particular aircraft type.


so all in all:

- CAO 20.7.1B is an aircraft requirement
- the 4.5% is techinically an all engine situation, however good airmanship MAY dictate otherwise. (consider instrument approaches and descent to an MDA).
- and like john tullermarine said you can turn left and right the avoid obstacles.
- For the purposes of subparagraph 4.1 (b), the take-off obstacle clearance requirements are met if the net flight path of the aeroplane, following failure of the critical engine at the critical point of the take-off run, would clear by atleast 35 feet vertically all obstacles in the take-off area .....

hope it helps

[john_tullamarine]

A couple of comments on Bula's post, if I may.

(a) agreed .. the prescribed limits are the WAT limits one sees bandied about in discussion and represent the Design Standard's endeavour to make sure that, in the event of a failure, there is a marginal chance that the aircraft might actually not head downhill OEI. Be aware that 20.7.1B is an operational document, a bit like Parts 91 and 121 while the actual design requirement is in the Design Standard, eg Part 25

(b) splay distances vary according to the runway code and may not go out very far at all. Operator/pilot is expected to know which applies to what .....

(c) why turn ? .. the splay may contain very uneconomic obstacles and the payload may be considerably better with a turn .. or, as an alternative, the straight ahead path, if over severe tiger country, might be a pretty silly alternative to a turn towards benign terrain

(d) SID gradient required often involves uneconomic RTOW for an airliner if one plans the OEI escape path via the SID

(e) monitoring the instruments is a good means of guarding against unexpected poor performance .. but I would not like to base obstacle escape paths on that alone .. better to do the sums back in the office

(f) net flight path .. that's what the whole thing is about .. and that needs to be done back in the office .. although newer types have the availability of onboard widgets to do the sums. However, the accuracy always will depend on the quality of the obstacle data used ... GIGO applies here, bigtime.

[Cost Index]

John, pardon my ignorance :D but what is AEO, GIGO and EOS? Also check you PM's.

All I really want to know is, does the a/c need to be able to perform in the OEI case to the stated 4.5% through all segments? Or is it only one particular segment that need concern me, or none at all (on paper that is)?

I can't find anywhere where this 4.5% splay is measured from or how far it extends.

I did this Performance type thing when studying for such a/c many moons ago and since then I have never used the knowledge practically or theoretically so the basics fail to come to me now . So bear with me.

Cheers

[john_tullamarine]

Apologies .. and don't lose sleep over ignorance .. we all have lots of that stuff .. do what you are doing and rectify it ...

AEO all engines operating
OEI one engine inoperative
GIGO garbage in .. garbage out
EOS end of strip (superseded terminology)
RDS runway distances supplement to the ERSA

Got your PM and answered .. let me know if it doesn't turn up.

(a) you need to have whatever OEI climb capability is necessary to avoid hitting the ground. Complicated if the obstacle is beyond the end of the second segment ... how are you going to include the geometry of the acceleration segment ?

(b) splay geometries in the RDS preamble. Distance related to the runway category

(c) TODA splay commences at the end of the TODA

... like all things .. if you don't play in the mud a lot .. you stay clean .. which is rather boring.

best regards,

John

[Woomera]

and eeerm is the DER still around old chap.?:ok: in the long a go, stumped the guy doing my renewal with it.:E I'd only found out about it, with some difficulty, including a call to the CAA during the prep in the days before:p

[john_tullamarine]

... err ... mate ... my memory is flawed ? what is the DER ? ... presumably not the FAA's Designated Engineering Representative ... or even CASA's CASR 146 version to be ?

[Dehavillanddriver]

Departure End of the Runway - DER

The ERSA gradients can be misleading.

Case in point was Canberra, the ERSA gradient was generated by reducing the distance that they used to look at the obstacles because to use the full distance applicable to the runway would have generated a gradient that looked too big. (Bad explanation but there you go!)

The old Ansett method of "stay within 10 nm and avoid obstacles visually" always amused me - it just means that you can see the hills as you fly into them!

[john_tullamarine]

Departure End of the Runway - DER

I've been in the game (not THAT game .. this game) for nearly 40 years and have not come across this other than as the term. I'm assuming that Woomera is referring to an Australian thing which is similar to the RDS in that it gives obstacle data ? .. in which case could I ask what it was and what data it gave ? Could be that I know it by a different description, perhaps ? .. or maybe I have missed the point, once more ?

Case in point was Canberra

How so ? So long as one knows what the RDS data is based on, there is no problem .. and, in any case, one can generally get the obstacle data from the survey on which the RDS is based without too much angst.. not many, if any, ERSA entries are based on inclino surveys. Then again, CBR is a bit of a mongrel dog of an airport .. I have an extremely detailed area obstacle library for that place and have done several tedious longhand analyses involving local countryside tours in getting to a safe height.

The old Ansett method of "stay within 10 nm and avoid obstacles visually"

.. long time since I've read AN publications. Only relevant to below 50,000 lb (or, as it is now, 20t) .. never relevant to the jets or heavy turboprops as these require an IMC analysis. The general concern, though, if valid .. far too many airlines leave a lot to the person least equipped to do the sums ...

[Dehavillanddriver]

The Canberra problem was that the ERSA gradients, based on the runway classification, should have accounted for obstacles to x distance (can't remember and couldn't be bothered to look it up - sorry - lazy I know!)

However if you looked out to that distance the gradient was very high, so in order to make the gradient look better, they stopped looking at about 3500m - ------hey presto - gradient looks better!, from memory the survey went to 15000m and the gradients were calculated using the obstacles in the 1st 3500m

I never used the ERSA stuff anyway when doing an analysis - as you mentioned I just used the surveys and topos.

Can't remember the specifics, not even thought about it for a few years, but the stink was that for people who decided that they would use the ERSA gradients it was deceptive.

The AN pubs that I have even for 737's etc talk about staying within 10 miles - they had an escape but it kept them within 10 nm - I'll try and find them, they are hiding in a box in a lockup somewhere and give you a quote - but essentially the implication was that they didn't look beyond 10nm for obstacles - I may have gotten the wrong impression but don't think so.

[Woomera]

Well there you go, it used to be on the DAP ?? (DhD help me out here) and referred to the earliest point at which you should execute a departure requirement and/or from which a SID was referenced .??

It was hidden in amongst all of the other letters, numbers and generally incomprehensible debris you couldn't read without a magnifying glass and halogen spotlight in the cockpit at night.

Especially after a night on the port, still I spose that's why GOD invented SO's :} :ok:

[john_tullamarine]

DHD,

Knowing the AN ops engineers of old quite well, I think I am safe in suggesting that there were three categories of analysis

(a) those runways which were commercially important or technically difficult and warranted detailed analysis ... I still have a copy of John W's original F27 longhand analysis report for CBR .. talk about being a bower bird ...

(b) routine Type A based analyses for wherever they could get the charts

(c) all the rest where an aircraft might bolt to .. based on ERSA (and its precedent documents) along with whatever else was able to be scrounged. These generally had some words about staying within a radius and heading back to the aid after the recommended turn ... makes very good sense in most cases. However, the boys and girls had a great big wad of topos and other data sources .. the recommendations were based on consideration of what was out there. By the way, if you want a garage full of enhanced OPMs for various airports around the traps .. I'm your man ... collected quite a few over the years.

Then again, John G, as I recall ... discovered on RDS entry for a country strip which showed a ginormous obstacle .. which, of course, was an artefact and didn't exist - this sort of thing occurred from time to time. Most people aren't aware that the RDS has more than the odd error and that the good folk at AirServices do appreciate an email highlighting errors which crop up ... some of the aerodrome owners likewise .... picked up a few myself over the years.

Main thing is ... user beware ... one needs to treat the fine print seriously with any of these documents.

Re the 737 manuals .. I have the AN 732 and 733 manuals tucked away in the dust somewhere ... I'll dig them out sometime and refresh my deteriorating memory bits and pieces.


Ah, THAT Woomera ... all OK, now ... I have the DER in view. Talking about lights and such, I can recall my first foray into lookovers ... was doing a job in BNE and using a mate's vehicle .. which had dreadful cabin lights ... couldn't read the street directory the first night (in fact, it looked all sort of .. black) and, having bought a $2 special set of lookovers a day or so earlier so that I could read the little lines in the takeoff carpets .. gave them a go ... 'twas like turning on a spotlight ... gone downhill progressively ever since.

Of course, now .. like you ... my kids shake their heads and wander off muttering things like "silly old bugga" every time I complain about not being able to see the things that they have no difficulty reading at night ... their time will come and I will have the last laugh ..

[Arm out the window]

DER is still alive and well, as it has been for a good number of years, look at CS Radar Dep for example.
Never heard of EOS though!

[john_tullamarine]

EOS - end of strip .. old terminology in ancient versions of the AIP

[Arm out the window]

I think it must be a requirement to change acronyms a minimum of every 5 years in order to ensure the maximum amount of confusion; can't have everything staying simple - that would never do!

[john_tullamarine]

.. easy on there a bit, mate ... we consultant chappies derive a fair living from acronymous obfuscation .. just don't ask me to say the foregoing rapidly ten times late in the evening ....