Runway slope is a bit of a rubbery animal.
Very few runways will have a uniform (constant) slope. Some have quite variable slope along the runway centreline. There is a number of different ways to define slope - ERSA Intro 21.1 (
www.airservicesaustralia.com/aip/current...ac-1-5_05NOV2020.pdf) provides the Australian definition (maximum elevation difference expressed as a length percentage).
The AIP references (
www.legislation.gov.au/Details/F2014C01367) present some problems as well.
Takeoff requirements are at 4.1(a):
An aeroplane must not take off at a weight in excess of the least of the weights determined in accordance with subparagraphs (a) to (d):
(a) a weight at which the take-off distance required under subsection 6 for the pressure height, temperature, runway slope (if in excess of 1%) and wind component along the runway, is equal to or less than the take-off distance available in the direction of take-off. Approved declared conditions may be used instead of actual pressure height and temperature
Note, though, in respect of slope, this appears to be contradicted by 6.2:
For aeroplanes operated on land, take-off distances are to be determined for a level short dry grass surface.
Landing requirements are at 5.1(a) :
Except in an emergency, an aeroplane must not land at a weight in excess of the least of the weights determined in accordance with subparagraphs (a) and (b):
(a) a weight at which the landing distance required in accordance with subsection 10 for the pressure height, temperature, runway slope (if in excess of 1%), and wind component along the runway at the time of landing, is equal to or less than the landing distance available in the direction of landing. Approved declared conditions may be used instead of actual pressure height and temperature
Note, though, in respect of slope, this appears to be contradicted by 10.2:
For aeroplanes operated on land, landing distances are to be determined for a level short dry grass surface.
Just what the CAO detail might mean at law would be for the legal eagles to establish. Get used to it, folks, this sort of problem crops up here and there in the aviation game and you just need to accommodate it with your strategies. With both engineering and pilot hats on, I read 4.1(a) and 5.1(a) to mean that, while I
may ignore small slopes, there is no compulsion for me to do so - I choose to use whatever slope data I might have available to me on the day.
For practical considerations, I suggest that the pilot should run the sums in a conservative manner. To me, that means, if I have slope information, I will apply it reasonably, regardless of what it may be - that is to say, I will ignore the 1% thing. That will give me useful and practical information. To keep myself sweet with 6.2/10.2, I would also make sure that I had enough runway to suit for no downslope (takeoff) and no upslope (landing).
Is this a bit silly ? Certainly appears so to me.
One of the historical problems is that 20.7 is an operational CAO, not an airworthiness certification document. The latter were in the 101 series but they were unceremoniously dumped in the bin post Ron Yates' report a few years back, now. The origins of 20.7 date back many, many years to the ANOs and were associated with (not always accurate) recasting of the 101 words. Now, we only have 20.7 (and the foreign NAS certification words) with which to confuse ourselves thoroughly, from time to time.
Now, where did this 1% thing come from ? I've never been successful in tracking that down. It dates back forever and a day - certainly before I started out in the Industry in the early 60s. My belief is that it will date back to the days where paddock operations were the rule, rather than the exception, and establishing slope was a bit difficult for the Tiger Moth pilot in the field. Considering the way the numbers usually run, 1% appears to be a reasonable measure below which it is acceptable to ignore the problem. Above 1%, the numbers usually start to become more noticeable and, for that reason, one should make reasonable efforts to establish a slope value for the calculations. Also, keep in mind that, in the old days, a great many aircraft Types had no performance information and operated on declared strip length requirements where the pilot didn't worry about any sums - if the strip length met the AFM requirements, we were good to go.
Until there might be a substantive court case to define what the CAO means, specifically, it just remains one of our little problems around which we have to operate.
) so I’m going to go with the latest advice... include the one percent and over....but please... I’m no whizz... don’t take my decision as the right one... happy study...