Originally Posted by
andrewr
That'a an interesting interpretation. Can you cite a reference? You are saying that when they say 30 minutes, they don't actually mean being sure you have enough fuel for 30 minutes?
If you burn 15 litres/h, and can gauge fuel level in 2 tanks with +/- 5 litres accuracy your margin of error is 40 minutes... 30 minutes doesn't help much. 30 minutes plus whatever uncertainty is in the reading seems like a much more likely interpretation.
Andrewr, I believe what he is referring to is that your FFR is meant to cover a few things such as Accuracy, Potential Fuel Contamination (Water), Mis-Reading (Not the same as accuracy) and a host of other potentials. If we did not have this then anytime someone slightly misreads their gauge, splashes it up the dipstick a bit high, has a bubble in their tank, puts the dipstick in on a bit of an angle by accident etc...etc... you're opening yourself up to getting overhead thinking you have 5-10mins spare (enough time to land) but actually not, or worse yet getting to that situation 5-10mins before arriving rather than in the circuit. I was always taught FFR is meant to be a final guard against a variety of potential mistakes/issues that could be easily made/missed. In other words you think you have that 30mins in the tank but you've should never assume you actually do.