On 2005-08-22, Ron Rosenfeld wrote:
As a matter of fact, I believe that the fuel quantity indicators are only
required to be accurate at zero fuel in level flight (for a/c certified
under Part 23).

Close, but no cigar. That one is a bit of an OWT. The fuel quantity
indicator must be calibrated to read zero when there is no usable fuel
left, but:

23.1337:

b) Fuel quantity indication. There must be a means to indicate to the
flightcrew members the quantity of usable fuel in each tank during
flight. An indicator calibrated in appropriate units and clearly marked
to indicate those units must be used. In addition:

(1) Each fuel quantity indicator must be calibrated to read
zero during level flight when the quantity of fuel remaining
in the tank is equal to the unusable fuel supply determined under
§23.959(a);

--
Dylan Smith, Castletown, Isle of Man
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"Maintain thine airspeed, lest the ground come up and smite thee"