LS
If it is true that “fixed final reserve may ... not actually be in the tanks” and “you have absolutely no idea of endurance remaining” as a consequence of cumulative errors, despite calculated fuel remaining on landing being 30 minutes, shouldn’t the rule require the declaration of a MAYDAY when calculated FFR on landing falls below 60 minutes? If your actual FOB “might be nothing” at a calculated FOB of 30 minutes, doesn’t the supposed “grave and imminent danger” start 30 minutes earlier?