How would you fly if your aircraft didn’t have fuel gauges? You’d probably fly the way a flight instructor would want you to. For starters you’d be sure to know just how much fuel you had. Then you’d calculate how much fuel your engine would burn en route. Next, you would ensure that the fuel available, expressed in hours and minutes, exceeded the fuel required—also expressed in hours and minutes—by a generous margin.
This kind of precise knowledge is cumulative, acquired over time if a pilot makes a point during refuelings to fill up and compare actual fuel burns against those calculated before the flight.
Granted you can’t always “top off’ when you get gas, but one of the best reasons for doing so whenever possible is that the fuel-burn information you get might help you avoid running out of fuel some day. And you’d never be tricked by a fuel gauge.
Two accidents that occurred on December 2, 2016, involving single-engine airplanes that ran out of fuel—despite the pilots keeping a recurring watch on fuel gauges—exemplify that problem.
The mishaps also underline why fuel system management remains stubbornly common as an accident cause for general aviation pilots. In both cases, the National Transportation Safety Board determined the probable accident cause as the pilot’s improper planning that “resulted in fuel exhaustion and the total loss of engine power.” The NTSB drew one distinction, faulting one pilot’s improper preflight planning, and the other’s improper in-flight planning.
Improper preflight planning, the NTSB said, probably caused a Piper PA–28-180 single-engine airplane flown by a 605-hour private pilot diverting for low fuel to collide with approach lights after losing power in the traffic pattern at Thomson-McDuffie County Airport in Thomson, Georgia.
The airplane was on the return leg of a round trip from Anderson Regional Airport in South Carolina to Leesburg International Airport in Florida. It had not been refueled in Leesburg.
The pilot described his careful noting of the behavior of fuel gauges at various phases of the flying, and of his method of switching tanks. When switching from the right fuel tank when it was indicating “half of a tank” to the left fuel tank, which had “settled to a little over a quarter on the gage,” that tank “ran dry shortly thereafter.”
Switching back to the right tank when between Anderson and Thomson-McDuffie, the pilot made a 180-degree turn to head for McDuffie. He also reduced power to conserve fuel.
The engine stopped when the flight was in a descending spiral over the airport. Rocking the wings to splash some gas into the lines had momentary effect, but not for long. “Complete engine fuel starvation on base leg, made contact with the ILS landing lights and came to a full-stop landing short of the asphalt runway,” the report said. Neither of the two occupants was injured.
The diversion almost saved the flight. In another case that day, diverting prolonged a flight away from bad weather.
A student pilot was flying a Diamond DA20 from Spanish Fork, Utah, to St. George, Utah, following his flight instructor and another pilot in another aircraft. The student had progressed far down the route when bad weather near Cedar City, Utah, led to a conversation between the two aircraft, and an in-flight change of the student pilot’s plans.
“We decided that it would be better for me to do a touch and go in Cedar City and turn around to head back to Spanish Fork. I remember him asking me how much fuel that I had on board which was three-quarters of a tank,” the student pilot reported to the NTSB.
After the fuel-consuming touch-and-go, the student climbed from the field elevation, 5,622 feet msl, to 9,500 feet bound for Spanish Fork—and into a headwind.
Making a visual check of the fuel gauges when nearing an airport a few miles south of Spanish Fork, “I noticed that I had just under a quarter of a tank of fuel and believed that I had plenty of fuel to complete the flight.”
However, the NTSB noted, “About 10 to 15 nautical miles from the original departure airport, the fuel supply was exhausted, and the student pilot made a forced landing in a field. During the forced landing, the right wing struck a tree and was substantially damaged.”
Fuel gauges notoriously lack checks and balances on their shortcomings. And they are at their worst when they beguile a pilot from safer ways to determine how long the aircraft can remain airborne.
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