More common sense really.
I'm leaving xxx and the ops spec requires that I arrive in yyy with an hour's reserve.
Each engine sucks 30 galons per hour, but returns 10 gph to the main tanks (fuel injection), so we'll burn 20 (30 - 10) gph a side. If the journey takes an hour and a half, how much will I need?
The answer of course is: ((1.5 + 1) * 20) = 50 gallons a side. Which is coincidentally the capacity of the main (tip) tanks.
I can therefore ask the fbo to top off the tips and I'll be alright - and better still, I can show planning that followed the letter of the ops spec.
Simple stuff really and again if you do it all the time, you don't need the calculation, just "top of the tips" will do.
And for extra points...what kind of airplane is this?
Hope I don't seem too
