AviationBanter - View Single Post - Post-Annual Flight

**Ray Andraka** · February 22nd 08, 01:36 AM posted to rec.aviation.piloting,rec.aviation.owning

wrote:

On Feb 21, 4:21 pm, Ray Andraka wrote:

It should tell you if the tank is empty. The fuel gauge is required to
read correctly for an empty tank.

There's an urban legend that the fuel gauge is only required to be
correct for an empty tank. The legend apparently arises from a bizarre
misreading of 23.1337b1. What 23.1337b1 actually says is just
clarifying that the 'empty' reading must correspond to zero USABLE
fuel, as opposed to zero TOTAL fuel. There is nothing whatsoever to
suggest that non-empty readings needn't be correct--that would be
absurd. (If it were true, a gauge that ALWAYS says 'empty' would be
legal! You could just write 'empty' on a piece of paper and call that
your fuel gauge!)

The requirement for indications of a tank's fuel level (not just on
empty) is stated in 91.205b9, 23.1305a1, and 23.1337b.

OK, I was loose with the words. Fact is, if there is only unusable fuel
left in the tank, for all intents it is an empty tank to the pilot while
the plane is flying.

I didn't say that the gauge could be inoperative. All I said was that
there was nothing in the FAR that says it must be calibrated to a
certain tolerance. The only requirement for calibration is that it
indicate empty when there is no usable fuel left in the tank. If the
gauges are operative, indicate empty when on an empty tank, and increase
monotonically when fuel is added, I think the letter of the reg is met.
Of course they have to move far enough to discern an empty (unusable
fuel) tank from one that still has some amount of usable fuel in it I
think the intent is met. I doubt there are many general aviation fuel
gauges that are accurate to better than 5 or 10% of a full tank