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Running on fumes – “Those fuel gauges are always showing a little low”

Have you ever heard this from another pilot, or possibly even your instructor? Perhaps he was also told that there is a built-in margin of error, or “that’s just an engineering number”, or perhaps his check is in the mail? It makes me wonder how many pilots are streaking across the sky right now feeling, as industry jargon goes, ‘fat, dumb, and happy’ looking at gauges that tell them the absolute truth, while they’re busy ignoring what they’re seeing?

Here is my own experience with this conundrum of what I will refer to as gauge denial. They say confession is good for the soul. Well, all pilots should be forced, on a regular basis, to confess their sins, the transgressions they have committed in aviation over the last year, and then come forward anonymously for the benefit of all. The following is from my distant past, when I had been a helicopter pilot for a very short time, but I should have known better anyway. It involved a long cross-country flight, over a lot of real estate, no access to a fuel truck, and a fellow pilot who was in deep denial with me.

We had taken off in our UH-1 Huey from home base around nine in the morning with a couple of guys on board, a crew chief, and a bag full of gas. In the UH-1H, a full charge of jet fuel will keep the blades turning and Mr. Engine happy for about two hours and thirty minutes, give or take. After that time things get very quiet. The model ‘H’ Huey’s fuel tank contained 209 gallons. It will be important to remember that figure later.

Takeoff and cruise to our destination were uneventful. It was a glorious fall day, and at ten o’clock we were circling our landing site near the Ohio River. We landed, the generals departed for their designated rounds, and we shut down the Lycoming T53 turbine to await their return. The flight down had been comfortably fast; a tailwind had aided our pace, and the Huey, not known for either her speed or her aerodynamic excellence, had reached a remarkable 115 knots above the ground. In Vietnam, where I had flown for just a year before this incident, that speed was more than enough to get me from one end of our area of ​​operations to the other. In fact, in the war zone, our standard cruising speed in the Huey was 80 knots, or slow enough that the heavily loaded Cobra gunships could keep up with us until they unloaded the ammunition. This factor may have contributed to my complacency about the fuel situation that day. Another factor, about which the god of aviation was remarkably nonchalant, was that I had survived the war, so I may have felt a bit bulletproof. When we landed, the indicator read 740 pounds, or enough for about an hour and fifteen minutes of cruising flight.

The generals returned at eleven and boarded my Huey. Soon the turbine groaned, the blades turned, and we took off into a moderate headwind, heading for home.

Leveling off at 3,000 feet and clearing the cabin, we braced ourselves for what I expected to be a trip north that might be a bit longer than the one south, but not by much. At that point in my career I hadn’t heard the old expression that you never make up in the tailwind for what you lose in the headwind, so I had no idea that the opposite was equally true. A couple of rough calculations on my trusty magic wheel, and I began to see the harsh wisdom in that statement. Checking a second time, then a third time, I turned the wheel on the E6B device, rechecked the settings, blinked once or twice, and shook my head. According to Mister Flight Computer, our ground speed was a glacial 87 knots. In Vietnam that would not have been a concern; there I had never flown more than forty miles in any direction or I would have been received rather rudely. But this was friendly Ohio, where forty miles was only half the way home. I looked at the fuel gauge: 500 pounds, or enough for about 45 minutes of unreserved flight. One more look at the map and my concern grew a little more: our heading line to the base of operations was exactly 80 nautical miles. Given our ground speed, we had another 50 minutes to fly. This was not rocket surgery; we didn’t have enough fuel to get home.

Unless, as many pilots still believe with varying degrees of acceptance, ‘those gauges are always a little low’, in which case we could squeal by.

As new to the game of flight as I was, and so ready to embrace that latest adage, so interested in uneventful flight, and completely dedicated to getting the generals back to their important meeting, I opted to go ahead. The rest is attributed to experience: how it is obtained and at what cost, if we are lucky.

Eighteen miles from home, the low fuel warning light came on for 20 minutes, its brilliant glow flooding the warning panel like the tilt light on a pinball machine. Great, I thought, reaching for the flight computer. To my dismay, our ground speed had dropped a bit, further increasing my pool of aviation experience, teaching me that headwinds always increase as the fuel level decreases.

However, one more spin of the flight computer revealed an ETE of 21 minutes, give or take. By then, the warning light had been casting its fiery yellow glow in my cabin for three minutes. I could have fried an egg in my armpit. Despite the crisp fall day, sweat trickled under my helmet and trickled down my back. I hoped the generals and my team leader wouldn’t notice my discomfort; this was going to be damn close.

Here is the outcome of the story. We landed on the base of operations ramp with the fuel gauge at absolute zero. The 20 minute low fuel warning light had been on for 23 minutes. With utter relief, we twisted the throttle and the blades rolled up. I couldn’t tell with any degree of precision if the engine had stalled due to my input, or if we had simply run out of gas. Watching the fuel truck pull up and stop, I knew the fill that would follow would be very interesting.

The shovels came to a stop, my crew chief tied them down, and the fuel loader began his ritual. The fuel nozzle slid into its port and jet fuel began to spray into the tank, displacing any vapors that remained there. I watched the truck’s fuel supply gauge speed up, reading fifty, a hundred, a hundred and fifty gallons. As it went through 190 gallons and never slowed down, I knew we had come very close to running out of fuel. Finally, at 201 gallons, the auto shutoff kicked in and the tank was full. He had landed the Huey with 8 gallons remaining in the tank, enough for two to three minutes of flight. However, that figure is misleading. Could it have floated along for another two or three minutes? No, and here’s why: According to the operator’s manual, the UH-1 fuel tank holds about five gallons of unusable fuel. Thirty seconds or so would have made the difference that day between a landing and an in-flight blackout.

I learned a lot on that mission. To plan better; finding fuel somewhere, even in a remote location; ignoring a general’s priorities in favor of aviation safety; and stop listening to those tired old aviation maxims that give comfort when what we really need is fuel, and a dose of common sense.

Does the indicator ‘always read a little low’? She did that day, lucky for me. But the unusable fuel factor could have finished me off, regardless. So the next time you hear about a margin of error, or an engineering factor built into the aircraft, believe me. The best way to stay safe and to retire, as I did, with little fanfare and your record intact, is this: build a small margin of error in the other direction. Remember, those fuel gauges are always reading a little high.


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