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.

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Aero-Tips 12.26.06

It's depressing how many airplanes run out of fuel just short of the pilot's intended destination. Part of the reason for fuel starvation and fuel exhaustion mishaps may be that fuel gauges are notoriously inaccurate.

Most lightplane fuel gauges are electrical-mechanical devices. A common installation will have float sensors in the fuel tanks, sometimes multiple sensors within a singe tank. As fuel level decreases the float descends in the tank. Pivoting on an arm, this drives the other end of the arm upward as the float drops. This other end of the arm makes contact with a wire or strip of metal; a small amount of electricity flows through this part of the sensor and, the farther up the arm rises (as the float drops), the greater amount of wire or metal electricity must flow through in the system.

The senor measures the drop in electrical power on the other end of this wire or metal strip. The amount of electricity sensed is directly proportional to the resistance encountered by electricity through the sensor, which in turn is a direct function of the distance the electricity must flow. Hence, as the float drops and the other end of the arm rises, there's more electricity lost in the system. Circuits in the cockpit change this electrical reading to an indicated fuel level.

Anything that affects the system-fuel sloshing in turbulence, uncoordinated flight, low electrical power, old wiring, stuck floats or bad circuit boards-results in an inaccurate fuel indication.

In fact, fuel gauges in our aircraft are required to real accurately only when the tank is empty... like they do us a lot of good at that point. Fuel gauges are a good trend instrument, to see if the fuel load is about what you expect, and is burning off an a predictable rate, but they need to be verified by visually checking fuel level in the tanks, comparison to other fuel indicators like totalizers, and cross-checking against known amounts of fuel put into the tanks before flight, indicated fuel burn, and a good old clock.

Aero-tip of the day: Understand the use and limitations of cockpit fuel indicators.

FMI: Aero-Tips