The flight school where I rent from has all late-model Cessnas, and there
is no doubt that they do not drain evenly.

I've heard several "urban-legend" style explanations for the uneven
drainage issue, and I don't claim to know which one is accurate. However,
they don't generally seem to drain unevenly enough to have any significant
impact on weight and balance...

Now I actually did all my PPL training in a low-wing Tampico that did not
have a "both" option. And a year or so later, when I started flying
Cessnas, I saw the "both" selector as a major convenience, and I took
advantage of it. But a while ago, I flew in a friend's Bonanza, a low-
winger, and we were talking about fuel management. And he reminded me of an
EXCELLENT reason to switch tanks during flight even if there is a Both
selector. I think someone on this thread mentioned briefly...

Basically, let's say your flying West, into a headwind. It's a little
stronger than expected, and so you're all ****ed off, and gunning the
engine up a bit to try to make up some of the ground speed. Maybe you're at
a different altitude than planned, and for whatever reason you're not
leaned out as well as you could be. Based on your "optimum" calculations,
you think you have 5 hours of fuel. But between the headwind, and not
flying optimally as planned, you use 10% more fuel than expected, and you
are going to use 10% more time than expected...

Bottom line, you now need a fuel stop, but you don't know it...

If your fuel selector is on Both, you get one shot. Your right tank may run
dry first, but you won't have any idea until your completely dry in both
tanks. You get to glide to the nearest golf course and call for help.

If you are switching tanks every 1/2 hour, and your right tank runs dry,
it's like an alarm. Your engine fails, and you do your ABC checklist,
switch tanks, and get your power back. You can take a moment to calm down,
figure out what happened, and find the nearest airport with services and
fuel up. You get a "second chance". Of course, it's not guaranteed - you
might only have a drop of fuel in the other tank. But flying on both
guarantees you to be a glider on empty...

Ever since that conversation, I fly "low-wing" style once airborne, and
switch tanks to both on taxi, takeoff, and landing only...



Peter R. wrote in
:

Koopas Ly ) wrote:

Is the procedure of only using one tank only applicable to certain
C172 year/models? I've flown a variety of 172's from late 60's models
to brand new 2002's, and have always used "both" tanks during
flight...just wondering...

Switching tanks is not in the '02 172 CRUISE checklist, but it is
something that I do to maintain an even balance across both tanks.
This is because the difference (at least in the '02 172SP I fly)
between the two after a long flight can be substantial.