Never Run It Dry

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

It was the Christmas holiday, and I was on my way back from the Bahamas to Venice, Fla. Joe Ponte of Piper had graciously loaned me a Cherokee Six 300 in conjunction with a pilot report, and I had elected to take my mom and stepfather on a quick, four-day trek to Freeport and Nassau.

On the trip back, we made a stop in Fort Lauderdale to clear customs, turn in our survival gear and close our international flight plan, then relaunched for the short hop diagonally across the state to Venice on the Gulf Coast.
My parents were luxuriating in the back of the big Six as we cruised 6,500 feet above the swamp when the engine suddenly quit cold.

The immediate silence got everyone's attention, especially mine. I was the number-one son, and mom trusted me implicitly in any airplane. I didn't want to dispel that trust by doing something stupid, though it seemed I already had.

Of course, I had let one of the Cherokee Six's four tanks run dry, and the engine had shut down in a heartbeat, without a telltale tick of the fuel flow or any other forewarning. As calmly as I could, I turned on the fuel pump, then, feigning a casual motion, reached down and switched to a tank with some fuel in it. I turned to Mom and Bob in the back seat, summoned what I hoped would be a reassuring smile and said, "Sorry about that. It's no big problem. I just ran a tank dry. The engine will pick up in a few seconds."

I turned back forward, expecting power to return at any moment. I waited and waited. Nothing happened. We were gliding down toward Lake Okeechobee, and I was beginning to wonder if we were about to discover firsthand that the lake was only five feet deep as I had read.

Finally, after perhaps 20 seconds that seemed more like 20 minutes, I heard some expectant coughs from the Lycoming before it came slowly back online. We continued to Venice, and Mom's only comment after we landed was, "Does that happen often?"

Fortunately, if you're smart enough to plan ahead, it need never happen even once. I obviously wasn't and didn't, so it did

Fuel Management
The AOPA Air Safety Foundation reports that fuel exhaustion or mismanagement are all-too-common causes of accidents, generally fourth behind landing accidents, takeoff incidents and maneuvering flight at low altitude. Fuel exhaustion is exactly what it sounds like—running the tanks dry. Fuel mismanagement relates to landing with fuel still on board but inaccessible because of a system problem, because the pilot didn't know he had it available or simply forgot to change tanks.

Fuel management isn't really that tough these days, considering that totalizers keep almost perfect track of fuel burned and remaining. Even modern aircraft fuel gauges are more reliable than they used to be. In fact, managing fuel use was never that difficult to begin with, provided you knew how much you had on board, how much you were burning and when you departed. Assuming there were no leaks, the answer was a simple problem in elementary math. The difficulties arise when you don't know all three of the items above. Trouble is, many pilots are convinced they do know how much fuel is in the tanks when, in fact, they have only a vague idea.

Let's consider fuel capacity. According to the book, I can carry 64 gallons in my Mooney…or can I? I bought my airplane in 1987 and knew it had never been wrecked, so it was reasonable to assume the tanks were not deformed and still in the original shape. Fortunately, I had my Mooney's tanks resealed a few years ago, so I had the perfect opportunity to determine true capacity. Every ounce of fuel had to be drained in order to reseal the tanks, and that meant I was starting from true empty.

Accordingly, I pushed the airplane out to a level ramp, with no apparent list left or right. It was mid-morning, and the temperature was about 60 degrees F, pretty close to standard, so fuel density wasn't a concern. (Some long-distance flyers, in search of maximum range, have their fuel supercooled and pumped aboard at the last possible minute, then climb quickly to high altitude and burn the top off each tank before the avgas can expand and overflow.)

When the fuel truck arrived, I asked the fueler to pump the 100LL slowly so there would be less chance of an air bubble. While he pumped, I shook the wing at the tip to help any air escape. Then, I watched carefully to make certain the level came to the exact bottom of the filler neck.

When the fueler was done, the meter suggested I had taken aboard 33.1 gallons in the left tank and 33.4 gallons in the right, a total of 66.5 gallons, 2.5 more than maximum. According to Mooney, that's all usable, so I could assume that figure for flight planning. I don't. I use the standard 64-gallon capacity instead.

A deformed tank can be more common than you might imagine, and any deformation will almost always rob you of fuel capacity. After a friend with a Comanche 260 died of a heart attack many years ago, his widow asked me to maintain his airplane for her, taking it out for a walk every two months or so. She swore she'd never sell it, as it had been her late husband's beloved toy. Finally, reality intervened, and she asked me to sell it for her.

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