Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.")

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

Look for our daily Aero-Tips segments, coming each day to you through the Aero-News Network.

Aero-Tips 09.25.06

Should you routinely top off the airplane's fuel tanks after the last flight of the day? Generally the answer is "yes," but it depends on several factors.

The main reason it's a good idea to top off all fuel tanks before the plane sits overnight is to prevent condensation in the fuel. Air inside a fuel tank will cool as the overnight air cools.  If the air is moist and the temperature cools to the dew point, liquid water will condense from the air space in less-than-full tanks and drop into the fuel. Filling the tanks minimizes air space in the fuel system (it will never completely eliminate it), making water accumulation overnight less likely. Of course water in aviation fuel will degrade engine performance and may cause a total engine failure.

Filling up right after landing also ensures you'll be there to supervise fueling, and makes it less tempting to "fire up and fly away" in a low fuel state if time pressures, a line at the fuel pump or a broken-down fuel truck affect your next planned departure.

Top it off?

There are some times, however, when you may not want to fully fuel the airplane before it sits overnight. Most airplanes can carry a full cabin load or a full fuel load, but not both. If you think you may need to carry a full load on the next trip, or you can't predict the cabin load (example: charter flying), you may need to hold off on the final fuel load until just before taking off. In that case, it's best to partially fill the tanks (minimizing air space) and drain the sumps before completing the just-before-takeoff fuel load (to remove overnight condensation before it mixes with the new fuel).

You might also avoid completely filling the tanks if the air is cool and is expected to heat up significantly any time before you fly again. Fuel expands with heating, often enough to flow outward through the tanks' air inlet vent lines. In some designs there is no check valve to prevent fuel from draining overboard through the vents; once started fuel may siphon overboard, partially or even completely draining the tanks.

Aero-tip of the day: Fill the fuel tanks as much as possible before parking the airplane overnight, but fill it completely only if it makes sense to do so.

FMI: Aero-Tips