(a)
Then what? What do we do with that density height figure?
Guidance is provided in
CAO 20.7.1.App 1 (2) and App 2 (2). The other Orders provide, variously, permissions to use the protocol.
Your technique is fine and accords with the CAO procedure.
(b)
In the POH you would find the manufacturers charts, but in the flight manual would also be the Australian set, approved for use by the Australian regulator of the time
In the beginning, there were Certificates of Airworthiness, which included limitations and, subsequently performance requirements.
Eventually, the CofA became sufficiently unwieldy to warrant development of an adjunct document, the Flight Manual. For GA aircraft, the Australian Flight Manual was a bit of a perfunctory document and included the bare bones information. Those who flew pre-GAMA format manuals would be familiar with the old style flight manuals.
At some time (long before I came into the game in the 60s) DCA started issuing P-chart performance data. I suspect that the early heavy charts (DC3 etc) were the immediate precursors .. certainly, they were of a similar style. The P-charts were standardised in terms of equations and format and this was promulgated in internal DCA tech memo documents. If anyone is interested I should be able to dig out my copies from the dusty archives so that you can have the actual equations which we used back then. No reason why you can't apply them to the present POH data to provide whatever levels of conservatism you might consider useful.
The bulk of the GA charts you may have seen were done in accordance with a memo which was written by Ian C and Ronnie S in the late 60s/early 70s and was directed at piston aircraft. Due to some problems the Nomad had with the older standards, ANO 101.22 was revised to accommodate turboprop performance and a revised memo was raised by John F. However, due to the latter document's complexity - some big equations - the superseded memo (and ANO) continued to be used for piston aircraft - which made life easier for simple minded chaps like me ...
So far as flight testing was concerned, the OEMs tended to go for comparatively high cost, high accuracy tests for marketing driven reasons.
Typically, tests were recorded by cinetheodolite for analysis. This device was just a fancy combined movie camera with a parallel azimuth (for distance calculations) and elevation (for height calculations) trace recording unit. Analysis consisted of reading off the traces, doing the distance and height sums (the runway/cinetheodolite arrangement was surveyed prior to setup so it was just a bit of trig work), and applying small error corrections from the movie record to allow for camera mistracking of the aircraft during the takeoff or landing. Quite apart from distance data, one could figure out speeds and accelerations to a reasonable level of accuracy from the plotted distance/height against time traces.
This approach was a bit over the top for a C150 and similar ilk so the DCA technique was a very much cut down version involving some fixed cameras to estimate the 50ft distance point. Trust me, analysing a cinetheodolite series of tests was a right time-wasting and expensive pain.
Turned out that the average of several runs gave pretty reliable and repeatable data so it all worked out fine for comparatively little cost. The results were plugged into the memo equations and the usual graphs drawn up. You would have seen examples both of the DCA format and the more common correction carpet presentation .. both gave much the same utility for the pilot.
In the US market, previously, there had existed a range of flight/operations manuals/handbooks published by the various OEMs.
In the mid-70s GAMA (the General Aviation Manufacturers' Association) published a recommended, standardised, GA aircraft operating manual format (GAMA Specification No. 1, first issued 15 Feb 75). When the GAMA POH (which includes the FAA approved flight manual) came into vogue, DCA accepted that document (with some local additions) as a (far more useful) alternative to the old style DCA flight manual and we gradually saw a swing across to the GAMA manuals during the late 70s and into the early 80s.
So far as performance charts were concerned, the older style DCA charts were still required as the US document gave raw data and didn't include any of the ANO required fudge factors.
As an aside, ICAO subsequently published recommended formats for light aircraft and air service operations manuals (Doc 9516-AN/930 - Guidance on the Preparation of a Pilot's Operating Handbook for Light Aeroplanes, 1st edition, 1991 - which was generally similar to the GAMA document - and Doc 9376-AN/914, 1st Edition, 1990). [Having located the three documents in the dusty archives, I'll keep them to hand in case anyone needs to refer to specific words in future].
Generally, use of the GAMA manual removed the need for specific flight tests as the POH data was, itself, so based. DCA accepted selection of a few points from the POH data and those data were then plugged into the equation machine to produce the Australian charts for inclusion in the POH. Nothing to stop anyone doing some tests but I can't recall anyone doing so.
Subsequently, as part of the harmonisation process, the pendulum swing right across ... the GAMA manual was adopted
in toto ... and the old DCA style charts were thrown out with the baby and the bathwater ...
(c)
Among other things, the Australian charts used the same distance factors across all aircraft types
Sort of correct .. the use of these charts generally applied to the ANO 101.22 aircraft (lighties)
(d)
This is where those graphs of declared conditions came in.
Bit off the mark here, I'm afraid. If we go back a long way, Australia was responsible for PNG and, given the poor performance capability of the earlier piston aircraft and the significant terrain in PNG, there arose a classification known as Developmental Air Services. (These predated my time and, while they would have been applicable to mainland activities, my understanding was that the driver was PNG operations). As far as I can see, apart from a legacy definition which somehow hasn't been culled from the CAO, DAS have gone the way of the dodo. Declared conditions were associated with these older operational standards.
(e)
.. and you may use the manufacturers performance charts.
.. but do so with considerable circumspection .. presume that the POH data is barely achievable.