Fuel- Top if Off, Please!

Getting back into the General Aviation world has re-opened my eyes with how important fuel is.  Of course we pay attention to it at the airlines and check it a bazillion times before we takeoff and during the flight, but the amount of fuel we need is figured out by dispatchers and then put into our planes from fuelers who are paid to do it.  Fuel is burned evenly from each tank into each engine, so we don't have worry about switching fuel tanks throughout the flight.  And the fuel gauges are very accurate on a commercial airliner!

Many GA airplanes are not quite the same, as far as fuel goes.  Fuel gauges only have to show accurate when they are empty, which is not something I want to test out!  Because of that, we need to visually inspect the tanks to make sure they are full before each flight, and sump it to make sure there are no contaminants (including water), in our fuel tanks.  Water weighs roughly 8 pounds per gallon, whereas fuel weighs only about 6 pounds per gallon; if there is water in your fuel tank, it will separate and sink to the bottom of your sump.  If you see this, continue summing until all of the water is removed from your fuel tank.

While sumping fuel, you have probably noticed that the fuel was either a blue (100LL), red (80), green (100), or clear (Jet-A).  Dyes are added to the fuel to help us identity which grade of fuel is in our tank.  Most of the airplanes I have flown have used 100LL, which is blue.  (As a side note, after you sump the fuel, hold it next to something white so you can verify the color.)

My one exception (minus my airline flying) to that is the Diamond Twinstar, which takes Jet-A fuel.  One important item to note is this: When two grades of fuel are mixed, it will turn clear.  I got asked that question on my commercial checkride and I had absolutely no idea.  The examiner was kind and let me look it up afterwards... whew!

Though many smaller airplanes have only one fuel tank, or two fuel tanks that can be used at the same time, some are not designed that way at all- in fact, you may have to watch your fuel and switch it from one tank to the next every 30 minutes or so.  Make sure you know which type of fuel system you have in your aircraft.  I have heard stories of pilots running out of fuel in one tank, doing an emergency landing, only to remember they still had another tank completely full of fuel.  Don't be that guy (or girl)!

As long as taking full fuel won't put me overweight, I 'top it off' before each flight.  I'd much rather have too much fuel than not enough.  What are your personal minimums regarding fuel?