Folks,
In the original consultation, the fixed final reserve was 30 minutes at "normal fuel flow", it was pointed out that there was no such thing as "normal fuel flow".
Hence the long time convention of using "holding fuel flow", which can be defined, but the ICAO 30 minutes has been increased to 45 for piston engine aircraft.
The question is why? What was wrong with complying with ICAO, why is a piston engine a reason for greater reserves??
"In the day" the "45 minutes plus 15%" was all legally usable fuel, the minimum fuel on landing was nil, not a good idea. I hope by now that we all understand the rational of "fixed final reserve", but there is not even an attempt to justify 45 minutes.
Tootle pip!!