Fuel is one of those absolutes in aviation, like altitude and airspeed, that positively must be maintained and managed until the aircraft is parked. It would seem simple enough to keep sufficient fuel in the tanks to enable a planned landing. But, several times a year, some pilot somewhere tries to fly with his tanks contaminated by air, with a less-than-successful outcome. It’s embarrassing to run out of gas in a car, but it’s more than embarrassing in an airplane, when you can’t just coast over to the side and flag down a passerby. Rather than preach to the choir about checking for fuel quantity before departure and keeping plenty of reserves, let’s examine why people run dry and see how it can be prevented.
Three methods persist in bringing us to earth, when it comes to running out of fuel. The first, fuel exhaustion, is simply using up every drop of gas on board; there are no options, the airplane is now a glider and it must be steered to a landing of some sort. The second error, fuel starvation, means the pilot mismanaged the fuel supply, running empty on one tank and allowing himself to be forced down while there’s still fuel available somewhere onboard. Lastly, a fuel system failure is more rare, but it can happen, such as when a pump fails, a valve won’t function or a leak develops, rendering all or some of the fuel unavailable.
Amazingly, some pilots just don’t have a clue as to how their engines are supplied with the necessary fuel. Understanding one’s fuel system is crucial to longevity in this business, meaning that you need to know how many tanks there are, how they feed, and what it takes to get the fuel to the engines–lines, vents, pumps, valves and drains. Easy fuel management is a great asset for an airplane, but it’s important for pilots to know that not every airplane is as friendly as others they’ve flown. Moreover, the system behind the perceived simplicity is often quite complicated.
Most modern transport-category aircraft utilize automated, simplified fuel manage-ment procedures. This does not mean the fuel supply and delivery system is simple, just that it normally does not require pilot interaction. You must still understand its inner workings and how to recognize faults. You were given an overview of your plane’s plumbing during initial or differences training; review the layout periodically to maintain your knowledge.
As an example of how important it is to understand the plumbing, Cessna’s older tip-tanked piston-powered twins had a convoluted fuel system that grew more complex over the years of production. Fuel is contained in as many as six tanks, which must be used in an exact order, with pumps on the engines, in the tanks and in the lines, some of which are activated on their own and some by pilot-actuated switches. The valving and gauging takes some study, and I guarantee you that running a tank dry once in a while is a given. Not studying a diagram of an old twin Cessna’s fuel system before flying it is a big mistake.
Another case of ignorance that leads to running out of fuel is guessing at the consumption rate. I never cease to be amazed at the pilots who actually base their decisions on simple rules of thumb, instead of the numbers derived by test pilots and placed in the airplane’s operations manual. Even those latter figures, however, need to be verified in your own operation. Yes, a fuel computer works off a super-accurate transducer in the line, but even it can be fooled by incorrect inputs from the crew, or erratic refueling, perhaps caused by a sloping ramp or an unfamiliar fueler.
The intense desire to get home even if the fuel is running low, or to finish the flight without making an inconvenient stop, or neglecting to refuel because you don’t have the correct credit card with you, has put more than one airplane down a few miles short of its intended arrival.
We can all succumb to pressure to complete a mission. Once upon a time, I nearly had to glide in with a turbocharged executive twin in the dark, because I was returning after midnight and it would have been difficult to find fuel at that hour, and because my passengers were anxious to get to bed. Whatever the reasons, once committed, I wound up staring at the seductive airport beacon light, inching closer as the gauges settled more solidly on the empty mark, mixtures leaned to the edge of roughness. The approach was straight-in, since the wind was in our face (as it always is when you’re pushing fuel) and we parked at the pumps, feeling quite full of ourselves for completing the trip. The next morning I signed a fuel receipt that showed five gallons were left in each side of the system, hardly enough for a good go-around. That’s what comes of letting a desire to complete the mission override your judgment.
Sometimes you start a mission with a barely-adequate fuel load and then everything changes, leaving you with an unexpected marginal fuel state. In the foregoing scenario, an unplanned drop-off stop earlier in the evening had eaten up some of our fuel reserves with an extra climb back to altitude. Increasing headwinds or passengers who can’t make up their mind are simply actions that have to be dealt with; it’s your responsibility to pick the best fuel stop and eliminate the pressure to press on. If you’re coming back later than expected, take on extra fuel; refueling options become more limited in the wee hours. Remember, you’re the one acting as pilot in command and the pressure of the mission can’t be allowed to make you abdicate your responsibility.
Wishing and trusting doesn’t add fuel to the tanks. A fatalistic acceptance of a situation has often led to a pilot proceeding until dry-tanks, ignoring all the signs because of his assumption that all will turn out right. I once had to take fuel out to one of my airplanes that was sitting in a wheat field, its tanks dry because the pilot kept on going with the gauges on empty, hoping the airplane would make it home.
I suppose one reaches a point at which there’s no sense in worrying, because there’s nothing more you can do. However, such acceptance should be a last-ditch condition. As long as you have flight controls and flying speed, you have the power to improve your situation, even if it’s just steering to stay over landable terrain. You must, however, plan to never reach such an untenable point.
When you plan the flight, base your expectations on worst-case scenarios. Add extra time to a headwind calculation and don’t count on every bit of tailwind that’s forecast. Move to the more-pessimistic line on the cruise chart if you’re between altitudes or power settings. Don’t pin your hopes on fueling at only one airport along your route. That may be the one that’s closed for construction, blocked for traffic or out of fuel. Every planned stop needs an alternate and that alternate needs an alternate.
In August, 2001, an Airbus A330 exhausted its fuel supply over the Atlantic, because an unknown leak was dumping Jet-A overboard at many gallons per minute. Miraculously, an airport 65 n.mi. away in the Azores was reached with altitude to spare and all 306 persons aboard survived the dead-stick landing. Had the crew known the source of the excessive consumption, steps could have been taken to isolate the leak.
Most fuel incidents happen because no one manages the fuel, not because the gauges fail or a filler cap comes off or headwinds pick up. Start by checking the tanks during preflight. If you want full tanks, make sure you have full tanks, and that doesn’t mean fuel is simply visible in the filler neck. Most flat wing tanks can hold several gallons more if topped off slowly and you had better believe that placarded amount painted beside the fuel filler port was based on squeezing in every drop.
Computational errors have brought about some famous fuel-exhaustion incidents, the most notable being the “Gimli Glider”, a Canadian Boeing 767-233 that was mistakenly short-fueled by employing the wrong metric-conversion factor. Fuel gauging and fueling systems can be calibrated in gallons, liters, kilos and pounds, but the aircraft’s engines know only time. Make absolutely certain you are working with the correct units when computing your fuel load, both to avoid an erroneous over-weight takeoff and the other extreme of a serious shortage of fuel in the cruise and arrival segments. Bush-country pilots, tasked with bringing out anything that can be stuffed aboard, frequently quip “fuel doesn’t weigh anything”, preferring to have extra endurance when crossing the jungle. However, excessive tankering limits performance and it costs fuel to lift the added weight to altitude.
Pilots run out of fuel because they ignore the obvious and refuse to make piloting decisions. Taking an upbeat, optimistic view of life may you a joy to be around, but it won’t extend the time left in your tanks. Learn your airplane’s fuel system, then use that knowledge to make good fuel decisions.