Plane & Pilot
Tuesday, July 31, 2012

Never Run It Dry

Keeping track of the time/speed/distance equation is only part of fuel management

At 150 knots cruise and perhaps 15% less during the first hour, I expect to fly about 127 nm in the first hour and another 428 nm during the remaining 2.8 hours for a total no-wind range of 555 nm (plus the aforementioned one-hour reserve). Also, remember that I've built in a deliberate three-gallon hedge, at least another 15 minutes of endurance. Add all that to the extra 2.5 gallons in my airplane's strangely enlarged tanks, and there's more like a "free" 30 minutes of additional reserve.

Trying to pin down range precisely assumes you know your airplane well, can count on a given true airspeed and that you'll be flying in calm air with minimum turbulence. It also assumes the winds will be calm (rarely the case).

I could increase range slightly by using a reduced power setting, but Mooneys seem to gain very little range at lower power, so I stick with at least 70% nearly all the time.

I've always used two simple rules to handle the effects of wind. These were taught to me by a highly experienced ferry pilot. Donn flew a little of everything across the Atlantic to Europe in the halcyon days of the '70s and '80s.

Donn's rules were simple: Reduce any forecast tailwind by a third and add 25% to any headwind. The most likely consequence of such a policy is that you'll arrive at your destination a few minutes early and with more fuel than planned. Works for me.

Actual fuel management is usually fairly simple on most general-aviation airplanes with one fuel tank in each wing and a simple selector that has left, right and off positions. I'll generally depart on one tank, usually the left if I'm alone in the airplane, ascend to my chosen altitude, set up the airplane for cruise; then, switch to the opposite tank for an hour and alternate as necessary.

Another peripheral concern if you have two tanks is to make certain the selector works properly. If you run a tank dry, reach down to switch tanks and the selector refuses to move or comes off in your hand, you have a real problem. That's one reason I always switch before any tank gets below about three gallons, providing me a 15-minute hedge to find some place to park.

After my experience in Florida (and a few others before it), I never run a tank dry. I'm not a complete idiot (some parts are missing), but I'm fairly certain Murphy's law will have a tough time catching up with me. I can lose some fuel to overboarding or an air bubble, the wind can become stronger than forecast, consumption can increase, I can suffer rerouting by ATC, the airplane can pick up some ice—slowing my speed—or I can be forced to deviate around weather, and I can still make it to my destination or a reasonable alternate. At least, that's what I keep telling myself.


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