Well in the USA the time planning is based on the OEI or depressurized still air flying time ..
but fuel planning takes into account wind with different increases for both forecast or actual winds that reduce tailwind and increase HW. fuel for deterioration of the engine, fuel for general errors but the flying TIME is based on the still air condition
but fuel must be carried for the actual conditions with extra fat,..that but may be greater than the still air time for a TW back does not entirely erase the effects of the HW out and vice versa...I think that section is can be a little confusing
and the AC is also a bit wordy,..but I learned it best to read the FARS very 'face value' likewise the advisory circulars should be read in conjuction with the FARS
PA