Let’s keep this discussion simple for now – and just a discussion as I haven’t finished my reading and analysis.
CAO 20.7.4 has performance limitations for small aeroplanes regarding takeoff, landing and climb. Let’s just consider takeoff distance and takeoff climb in a Super Decathlon for this discussion in the context of a day where the temperature is just over 40 deg C.
We must determine the takeoff distance required to ensure that it is less than the takeoff distance available. We may use approved declared conditions instead of actual pressure height and temperature – the CAO simply states that without stating its applicability.
Performance information for the Super Decathlon is not in the Approved Airplane Flight Manual as it was certified to an early version of FAR 23 so refer to the manufacturer’s Operating Manual.
i.e. one of the premises of CASA’s statement above does not apply – there is no relevant limitation in the AFM. The only performance item which suggests a limit is the service ceiling of 16,000 ft.
Takeoff distance is provided for temperatures from 0 deg C to 40 deg C and pressure altitudes from zero to 6000 ft. Could we use the declared density altitude chart? Not too hard to derive takeoff distance as a function of density altitude but quite some time is required to do it.
The takeoff distance table has a simple statement for the effect of wind. Data is for a level hard runway. It specifically states that it is not applicable for grass fields however what if we are operating from a sloping grass field?
The UK CAA has a very sensible Safety Sense Leaflet 7C on aeroplane performance at https://publicapps.caa.co.uk/docs/33/20130121SSL07.pdf
It has good advice about the effect of such things as grass and slope but can we use it? The same information was published in the Sept-Oct 2002 issue of CASA’s Flight Safety Magazine – can we use it?
Let’s move on to takeoff climb performance per CAO 20.7.4. In the takeoff configuration at takeoff safety speed the aeroplane must have an ability to achieve a climb gradient of 6%. Absolutely nil data on this in the Super Decathlon manuals.
There is some information on en-route climb performance but only at the speed for maximum rate of climb and only at the standard temperature.
A note in the Exposure Draft of Part 91 (MOS for 91.1035 Aircraft Performance): “It is the intention that CAOs 20.7.4. …. will be subject of a project to review them and provide guidance material in the form of an AC in the future. Much of the content of the CAOs contain either certification standards or outdated information. CASA expects pilots to operate in accordance with the aircraft flight manual (AFM). All performance information in the AFM is produced and complies with the aeroplane certification standards.”