There is the original version 1 (PS2) where the RC fuel depletes no matter what you are doing, while in version 2 (PS2, PC, Xbox) it only depletes when you are actually pressing gas and are flying. The famed difficulty comes from people playing on the original PS2 version, where the fuel acts as a timer and you only have like 3-4 minutes to beat the entire thing before it runs out. This combined with the controls made it super fucking tough to beat. You had to memorize everything and sort of speedrun it.
"Follow the damn train" got nothing on that one, I cleared that on my 2nd try while the Zero mission needed a lot longer.