"Bob Martin" wrote in message
...
With regards to fuel tanks in a C172, why does the takeoff and landing
checklists both call for the fuel selector handle to be in the "both
tanks" position?

The only time that fuel is set to one particular tank is on the
ground. I've never used fuel from only one tank in flight. Why would
someone do that?

Not really related to 172's, but our RV-6 has no "both" position... either
left, right, or off. You just have to remember to switch them
occasionally.

Also, IIRC the 150 has just "on" and "off".
There is a significant difference here between low wing, and high wing
designs. If you have a low wing aircraft, and have a 'both' selector, if one
goes empty, air is sucked into the system by the fuel pump, and fuel
delivery stops. Hence low wing aircraft with a 'both' position, have to have
a central 'sump' from which the fuel is drawn. On high wing aircraft, where
the fuel is delivered by gravity, if one tank goes dry in the both position,
fuel will still feed from the other. Hence 'both', is relatively unusual on
low wing designs, but more common on high wing planes. This is why your RV6,
doesn't have a 'both'.

Best Wishes