Post-Annual Flight

Jay Maynard wrote:

On 2008-02-21, wrote:

I never use the fuel gauges for anything other than
passing reference, since we do everything by visual inspection and the timer
in our Garmin GTX-327 transponder.

How do visual inspection or your timer tell you if you've got an in-
flight fuel leak? That's an important reason for the fuel-gauge
requirement.


How does a fuel gauge that's so unreliable that you can't trust it to within
a quarter tank tell you whether you've got a fuel leak? That description
applies to every aircraft I flew during my primary training, late 1970s
vintage Cessna and Piper and Grumman products (this was in the late 1980s).
I was taught to verify the tank's level on preflight, and use time and
consumption per hour to figure usage.


It should tell you if the tank is empty. The fuel gauge is required to
read correctly for an empty tank. I use a timer and visual inspection
as my primary, but I also use the fuel gauges to verify that my fuel
burn is approximately what I expected it to be.

Jay's flight manual tells him to position the fuel selector on the
fullest tank (he's got four of them) in his pre-landing check list. If
I were in his shoes, I would plan my flight so that the tank with the
inop gauge was used early in the flight so that one of the others is the
fullest tank on landing. For take-off the same advice is in the AFM.
In that case, you have presumably just visually checked the fuel level,
so you can safely take off on the tank with the inop gauge. Still, as
the inboards are the "main" tanks and are supposed to be filled last and
used first (at least on a Six, which has the same fuel system), I'd be
getting that gauge fixed sooner than later.

I did have one of my tip tank gauges stop working about a decade ago for
the same reason (float fell off), and like Jay I put that off until the
annual, but I also didn't use the tip tank during that time the gauge
was broken and placarded it as tank unusable.

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.

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

On Feb 21, 8:36*pm, Ray Andraka wrote:
I didn't say that the gauge could be inoperative. *

Sorry, I didn't mean to suggest that you yourself were promulgating
the full-blown legend.

All I said was that there was nothing in the FAR that says it
must be calibrated to a certain tolerance. *

Yup, that's certainly true.

The only requirement for calibration is that it
indicate empty when there is no usable fuel left in the tank. *

But the tolerance for THAT isn't specified, either! Whether the fuel
quantity is zero or nonzero, the only requirement is for an
"indication" of that quantity. By common sense, the indication has to
be CORRECT, within some reasonable (but unspecified) tolerance.
There's nothing in the regs to suggest that the indication for an
empty tank has a more stringent accuracy requirement than the
indication for any other level has.

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.

I disagree. I don't see why you substitute an implicit monotonicity
requirement for an implicit accuracy requirement. Surely it's fine to
have a gauge that is highly accurate, but has regions of negligible
nonmonotonicity; and surely it's not ok to have a gauge that's wildly
inaccurate (say, reporting 50 gallons when there are really just 5)
but monotonic without exception.

Speaking of urgan legends, it's a not true that FAR 23 applies to aircraft certified under CAR 3. CAR 3 requiremnets are not as stringent regarding the accuracy of the gauges (or a lot of other stuff). FAR part 23 does not apply to Jays aircraft. However FAR part 91 does. Technically, he was illegel, but he did use a lot of common sense dealing with the issue. The FAA would probably hang him out to dry if he crashed due to a fuel issue, and placarding the tank really didn't make the flights legal.

FAA regs are written to cover any plane that could be flown by any rated pilot. They don't make exceptions to the situations where an owner is aware of a issue and takes steps to fly safely inspite of the issue. So even if the owner took sensible steps to fly safely under the circumstances, he is still illegal, but then again, so am I when I drive 60 in a 55 mph speed zone.

His biggest mistake was bringing it up in a public forum where every one could fuss at him. If he flew with the tank empty and didn't have it placarded, the gage would be right, and the FAA wouldn't know there was a violation - as long as he didn't fess up to knowing it didn't work when there was fuel in the tank.

While sensible, the placard is incriminating and if he is keeping fuel in the tank, then he is using it and the gauge should work. However this isn't really a terrible crime for a person using his own aircraft and sensibly dealing with the issue. He is probably aware that the FAA might make a point out of it if he crashed. But he made a descision to keep flying based on what he considered an exceptable risk.

Originally Posted by

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.

Ray Andraka wrote:


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

Actually, the FAR makes no statement of accuracy for fuel gauges.
The misunderstanding that people interpret as the "must be correct
at empty" is merely a statement that the Empty mark is supposed
to be the end of USABLE fuel rather than bone dry.