Visual determination of fuel on board

[skymstr02]

The only time that a fuel quantity gauge has to be dead nuts accurate is at EMPTY. This is spelled out in other OEM maintenance manuals. I don't care what it says at any other time, but I don't want to be running out when the gauge indicates 1/4 full.
They are all different at any other quantity, and I think that this is in FAR Part 23 (Certification).

[IFLY4YALL]

Under Part 23 the gauge has to be calibrated to zero for the purposes of defining usable fuel from unusable fuel. And there are specifics for determining where usable fuel ends and unusable fuel begins. It has nothing to do whatsoever with gauge accuracy. The gauge is assumed accurate to determine the quantity of usable fuel in the tank at all levels. In order to maintain airworthiness the gauge must indicate the quantity in the tank. Having said this there is a bit of latitude as most light GA gauges are not graduated for dead nuts accuracy. But at half tanks indication you should have half of your usable fuel on board. If not and you decide to fill em up and go fly you would technically be operating an aircraft outside the parameters of airworthiness.

Mark F
Atlanta