On 2007-04-02, Maxwell wrote:
If you are planing a flight with so little reserve, which is obviously
considered both legal and acceptable

A one hour reserve is hardly "little reserve". It's quarter of the
duration of a 1960 Cessna 182 (which has relatively small tanks,
especially compared to later models of Cessna 182). A one hour reserve
is double the day VFR minimum requirement.

(My current aircraft carries only 2.5 hours of fuel! Although its fuel
gauge is a much simpler purely mechanical indicator which does work
properly and gives a reasonable indication of fuel remaining.)

gage, and physically _stick_ the tanks on preflight. My personal experience
with fuel gages has been that they can cause more problems than they solve,
if you try to rely heavily on them.

So does any instrument if you don't have a cross check. Fuel gauges in
particular ARE the cross check to your preflight visual check, and fuel
burn calculations. If you re-read my message, you'll see in the
particular example I gave that the fuel was visually inspected twice,
and calculations had been performed, and a landing short of the
destination was chosen because the fuel gauge showed less fuel than the
fuel calculations predicted. The error turned out to be in the fuel
level inspection, an easy mistake to make in an unfamiliar aircraft.

The only means of fuel cross check once in flight are the fuel gauges -
you can hardly stick the tanks in flight. Gauges that actually work and
reasonably indicate the fuel level remaining can provide a cross check
which can prevent the following situations:

- lack of experience with a particular aircraft type
- error in fuel burn calculations
- error in engine management (mixture too rich)
- mechanical failure (fuel leak)
- error in preflight (forgetting to do a visual check, or being fooled
because the aircraft was parked on a slope)

....from a normal landing at an airport short of your destination, into a
fuel exhaustion accident. Indeed, some years ago, a poster to this
newsgroup ran out of fuel due to a fuel leak. Perhaps the pilot had been
conditioned to believe that fuel gauges were utterly useless and did not
include them in a cross check, instead relying on a single source of
data (fuel calculations and time in flight).

Cross checks in aviation are a _good thing_. Failing to maintain a
basic instrument that can provide a useful cross check means there's one
less tool at your disposal to prevent an accident.

(In particular, never trust a fuel gauge if it says you have more fuel
than you think you have. However, ALWAYS trust a fuel gauge if it says
you have less fuel than you think you have! Landing to find out why is a
lot cheaper than pressing on, believing your fuel inspection and fuel
burn calculations - only to end up upside down in a field half an hour
later because your fuel was being pumped overboard. How are you going to
detect mechanical problems with the fuel system if the gauge isn't
working? This is why broken fuel gauges should be fixed).

We expect to have to do cross checks for everything else - navigational
cross checks (we never rely on a single source for navigation, whether
this be only using a single road to positively identify a ground feature
instead of the road and two other features), or for our instruments (we
don't just bore holes IFR looking only at the attitude indicator for
attitude information - we scan the other instruments to make sure that
the AI is telling the truth), and we fly approaches not only with the
ILS tuned in, but a timer running, or some other kind of cross check
like a crossing radial.

Why is it therefore deemed not only acceptable but entirely normal
that there is no in-flight fuel cross check in the form of a gauge that
at least gives a reasonable indication of how much fuel you have left?

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