Folks,
Most of you just don't "get it", including CASA.
The history of the concept of "fixed final reserve" is all about the history of aircraft running out, or almost running out of fuel, when gauges and/or howgoesit all indicated sufficient fuel.
Can you use "it" --- and all the legalisms are nonsense, because you do not know, FOR CERTAIN, if you even have it to use ---- regardless of the situation.
If you are in a situation where you will land with less than 30m, indicated or calculated, it is an emergency, you are as dumb as a box of hammers if you think you can do otherwise --- not all that uncommon in the aviation field. This is quite independent of any other non-normal situation that might be attracting your attention.
All measuring systems are subject to error, or more correctly, order of accuracy. Light aircraft fuel contents gauges are notoriously inaccurate and unreliable, flowmeter systems not much better, until you get into heavy iron, and there it is still around +/- 3% order of accuracy.
You always start out NOT knowing EXACTLY how much ENERGY you have, you only ever have an approximation of how much you have consumed, and therefor, you only have an approximation of what you have left, and only an approximation of how fast you are burning said remaining.
The whole idea of FIXED FINAL RESERVE is so that, on the day when all the +/-'s stack up against you, your engines are still running at touchdown.
Look up the history of the near misses, the very near misses, and the losses, and ask yourself (sorry Dirty Harry)
do I feel lucky today , because you will need luck on your side, not an acceptable way of flight management --- or perhaps, is it not your pax. lucky day.
Forget whether it is "required under CASR XXX but not CASR YYY", it is needed so you engines will ALWAYS have motion lotion at touchdown.
The engineering physics don't vary with the flight category, it all goes 'orribly quiet when you run out.
Tootle pip!!