Post-Annual Flight

Jay Maynard wrote:

Why is it so remarkable that the fuel gauges in the new aircraft I'm looking
at are actually considered reliable? I've hear dlots of comments to that
effect. "Hey, fuel gauges you can believe! Wow!"

Exactly. G

I know what the regs say, but I also fly actual aircraft, not
theoretical or paper versions.

In rec.aviation.owning 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.


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...

23.1337(b)(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...

91.205 Powered civil aircraft with standard category
U.S. airworthiness certificates: Instrument and equipment
requirements.

(a) General. Except as provided in paragraphs (c)(3) and (e) of this
section, no person may operate a powered civil aircraft with a
standard category U.S. airworthiness certificate in any operation
described in paragraphs (b) through (f) of this section unless that
aircraft contains the instruments and equipment specified in those
paragraphs (or FAA-approved equivalents) for that type of operation,
and those instruments and items of equipment are in operable
condition.

(b) Visual-flight rules (day). For VFR flight during the day, the
following instruments and equipment are required:
...
(9) Fuel gauge indicating the quantity of fuel in each tank.

If "you can't trust it to within a quarter tank", you should probably
get it fixed.

Yeah, I know, it is common and nobody seems to care, but that isn't
what the regs say.


--
Jim Pennino

Remove .spam.sux to reply.

On Feb 21, 4:15*pm, wrote:
* *(9) Fuel gauge indicating the quantity of fuel in each tank.

If "you can't trust it to within a quarter tank", you should probably
get it fixed.

Yeah, I know, it is common and nobody seems to care, but that isn't
what the regs say.

The regs are kind of vague about how precise and accurate the
indication has to be, so there's some leeway. But a gauge that's flat-
out broken is obviously beyond the pale.

wrote:

If "you can't trust it to within a quarter tank", you should probably
get it fixed.

Yeah, I know, it is common and nobody seems to care, but that isn't
what the regs say.



BTW, if your gauges don't show repeatable indications, it is time to
overhaul the gauges, the senders or both. While the gauges may not be
calibrated to show the actual quantity remaining, the FARs do require
them to indicate accurately at zero (and they generally do if they are
working at all). Regardless, you shouldn't be getting a 1/4 tank
variation from day to day with the same amount of fuel in there. While
the markings on mine don't correspond too well to the actual fuel
quantity, the position of the needle for a given amount of fuel is
fairly constant unless the electrical system is off and the battery
running down (don't ask me how I know that).

Tha FARs basically require the gauge be operating (which means it
increases when you add fuel and decreases when you burn fuel), and that
it is accurate when the tank is empty. There is nothing there about
calibration otherwise, and I'd bet that most of the airplanes out there
have gauges that meet the rules (the exception being those that don't
indicate at all).

wrote:
In rec.aviation.owning 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.


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...

23.1337(b)(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...

91.205 Powered civil aircraft with standard category
U.S. airworthiness certificates: Instrument and equipment
requirements.

(a) General. Except as provided in paragraphs (c)(3) and (e) of this
section, no person may operate a powered civil aircraft with a
standard category U.S. airworthiness certificate in any operation
described in paragraphs (b) through (f) of this section unless that
aircraft contains the instruments and equipment specified in those
paragraphs (or FAA-approved equivalents) for that type of operation,
and those instruments and items of equipment are in operable
condition.

(b) Visual-flight rules (day). For VFR flight during the day, the
following instruments and equipment are required:
...
(9) Fuel gauge indicating the quantity of fuel in each tank.

If "you can't trust it to within a quarter tank", you should probably
get it fixed.

Yeah, I know, it is common and nobody seems to care, but that isn't
what the regs say.

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.

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.