Dave Butler wrote in message ...

If you're paying attention and know your fuel burn you can predict the moment of
running out within plus/minus a few minutes. When the fuel pressure gauge drops
to zero, you still have some time while the engine continues to run smoothly.
Switch tanks when the fuel pressure drops, the pax will never know.

Of course, you've run some on the other tank previously, so you know the fuel in
the other tank is sweet.

Bingo! Dave's right on the money. My plane's flight manual
cautions against running a tank dry (I believe there's an outside
possibility of fuel pump cavitation). Using fuel pressure method
works great. I do this on long cross-country flights where maximizing
my range is important. In my Cherokee, the fuel pressure will begin
to drop with about 1.5 gallons usable in the tank (close enough for
me). At this point, assuming no unusual fuel burn, I have 1.5 hrs of
fuel left in the other tank, which in the real world means I have 1/2
hr. to be on the ground.


This old pilot thinks everyone should do this at least once so that they know
how their plane behaves in this situation. It also provides a chance to make a
direct measurement of exactly what your tank capacity is.

Agreed. I do this on every flight where I'll be flying at maximum
range. By running a fuel tank almost dry, I know if my fuel burn is
normal and can complete the flight as planned. If the tank runs out
before the clock says it should, I still have a bunch of gas to make
it to an alternate (assuming I'm not flying in some of the more remote
parts of the Northern Territories of Canada :-).

By using this method, I can usually guess the fuel burn on a long
cross-country flight to within 1 gallon. This kind of knowledge makes
flying in sparsely populated areas a lot more comfortable and allows
me to get better utilization of the amount of fuel my plane is able to
carry.

Note : Do not take the above to mean that I fly my tanks to
dangerously low levels. My personal limit is to land with a minimum
of 1 hr. in the tanks. In 16 yrs. I've never landed with less, but by
gauging my fuel burn precisely, I can often reach my destination with
1.2 hrs. remaining, thereby maximizing my range, yet minimizing my
risks.

John Galban=====N4BQ (PA28-180)