Don't Be Fuelish!


Self-service avgas at my home airport is now $5.65 a gallon. And it promises to go higher with the next delivery from the fuel supplier. Suddenly, the cost of fuel is a much larger portion of my operating costs. I've been running lean of peak so the Lycoming IO-360 in my Cessna Cardinal runs at something under 10 gallons per hour. Doing the math at 10 gallons per hour is simple. It's costing me slightly more than $56 per hour just for fuel. In mid-August, AirNav's Fuel Price Report found that of the 3,530 FBOs it surveyed, the average price was $5.60 (the low price was $3.75 and the high price was $8.70).

One of the indisputable rules of aerodynamics is that things get quiet when fuel no longer reaches the engine, whether from mismanagement of the fuel system or fuel exhaustion. Nevertheless, the accident history is rife with accounts of pilots who crashed or made emergency landings when their engines were starved for fuel. They either didn't know how to manage the fuel system or they were overly optimistic about how long their engines would run with the fuel they had on board.

I worry that the accident record is only going to get worse with the increase in the price of avgas and jet fuel as pilots try to stretch flights to reach their destinations without having to make a fuel stop or to reach an airport with less expensive prices at the pump.

In the past, I've religiously tried to fly at least once a week -- and the engine in the Cardinal seems to be happy with the frequent workouts. It continues to purr along hundreds of hours past TBO. But recently, I've found myself extending my "exercise" flights to a week and a half or two weeks. I'm not sure I'm being cost effective -- particularly as the less frequent use may affect the engine's health. Flying less often may also cause a diminution of my aviating skills.

So, the escalating cost of avgas has a potential influence on safety. Sharing flights with another pilot is one way to maintain proficiency while conserving fuel. I'll probably hear from readers that if I can afford an airplane I can afford the price of avgas, but I bought my 32-year-old airplane with a partner more than two decades ago and it cost less than many cars. Since then the costs for hangar rent, insurance, maintenance and now fuel have all increased much faster than my ability to easily pay them. So conserving fuel is a practical goal.

In order to retain proficiency, Doug Stewart, an instructor and examiner who conducts safety seminars, suggests that pilots use their $100 hamburger flights as an opportunity to practice airwork and procedures to keep their skill sets honed.

There is some confusion about the efficiency of an airplane. Just because one airplane burns 10 gallons an hour and another burns 12 gallons an hour doesn't mean that the second is less efficient. In comparing fuel burns it's important to consider not only how much an airplane burns per hour, but how far it can go in that hour.

As an example, let's say the June Bug burns 10 gallons an hour and the Bumble Bee burns 15 gallons an hour. Before putting pen to paper, it would seem the June Bug is more efficient; but now consider that the June Bug lumbers along at 100 knots while the Bumble Bee buzzes at 200 knots. If they're both making a 600-mile trip in no wind conditions, the Bumble Bee will set down after three hours, the June Bug after six hours. When the two are refueled, the June Bug will take on 60 gallons but the Bumble Bee will only have burned 45 gallons. At $5.00 per gallon, the faster airplane would actually save $75 on a 600-mile flight compared to the slower airplane. So which is more efficient?

What we're talking about here is "specific range" or "specific air range," which is the distance an airplane can travel for every gallon (or pound) of fuel burned. The June Bug at 10 gallons per hour and a speed of 100 knots has a specific range of 10; the Bumble Bee at 15 gallons per hour at 200 knots has a specific range of 13.333.

It seems you don't have to give up speed for efficiency. Of course, if the Bumble Bee burned 20 gallons an hour, the two airplanes would have the same specific range and be equally efficient. And if it burned more than 20 gallons it would be less efficient.

Another consideration in terms of fuel economy is a function of the quantity of fuel an airplane can carry -- often a tradeoff with payload. Obviously, if it's necessary to make a fuel stop on a cross-country flight, that's going to increase the fuel requirement. So specific range as well as the range of an airplane as a factor of its fuel capacity is another consideration.

On the other hand, if you're only using an airplane to enjoy the feeling of freedom an airplane can offer and not for transportation, then you'd be more interested in the time aloft than the distance traveled, and the less fuel an airplane burns per hour would be the deciding factor. The LSA airplanes, with their typically parsimonious fuel burns might have an advantage if your flights keep you close to home.

During their students' introduction to preflighting an airplane all instructors stress the importance of checking that there is sufficient fuel in the tanks to comfortably complete the flight. But after that first lesson, some instructors assure their students there's enough fuel for the lesson and don't require them to verify it. That can create bad habits.

Another oft neglected instructional procedure is how and when to properly control the mixture. Since most flight training takes place at relatively low altitudes and students are admonished not to lean below 5,000 feet (where engines can develop more than 75 percent power), they don't learn to lean the mixture. And if they do, they're leery about pulling the red knob and tempting fate since they know that's how they kill the engine at shutdown.

Scenario-based training, during which the instructor presents real-life situations (a closed runway at the destination, higher than forecast head winds, deviations to avoid weather, active MOAs, forgetting to lean the mixture, etc.), can go a long way to ingraining the proper respect for monitoring howgozit on the fuel front.

There's an old pilot's tale that says that the fuel gauges are only required to be accurate when they indicate that the tanks have exhausted the useable fuel. FAR 23.1337(b)(1) does seem to indicate that limitation, when it states, "Each fuel quantity indicator must be calibrated to read 'zero' during level flight when the quantity of fuel remaining in the tank is equal to the unusable fuel supply."

But contrary to conventional wisdom, the gauges aren't required only to be accurate at empty. FAR 23.1227 (b) (Powerplant instruments installation) states, "There must be a means to indicate to the flight crew members the quantity of usable fuel in each tank during flight." In other words, if the fuel gauges are functioning properly they should give an indication of the fuel remaining throughout a flight, not just when the tanks are down to unusable fuel.

Nevertheless, it's probably better that students learn not to trust the gauges but to determine for themselves whether there's sufficient fuel in the tanks to complete the flight with sufficient reserves. Visually checking the fuel amount is relatively simple on a low-wing airplane, but requires a bit more effort when the wings act as shade providers. My Cessna 150 had foot rests on the strut to make it relatively easy to peer into the fuel tanks; my Cardinal has no struts, so I carry a small aluminum stepstool to let me eyeball the tanks.

Looking in, it can be easy to tell if a tank is full. But if you haven't topped it off you'll need some sort of calibrated dipstick to determine how much go gas is really resident in the tank. Sporty's and other pilot supply shops sell aircraft-model-specific calibrated fuel gauges as well as generic gauges that can be calibrated for any fuel tank. Knowing how much fuel feeds your engine by time -- not distance -- is important in order to keep track of the fuel remaining.

Fuel totalizers that meter the flow of fuel from the tanks to the engine have the potential to be very accurate in presenting the fuel being used and the fuel remaining. Unfortunately, their accuracy in terms of fuel remaining is dependent on the pilot accurately updating the fuel quantity when the tanks are topped.

The fuel requirements for VFR flights, detailed in FAR 91.151, have to be considered a bare minimum. The official rule says that no person may begin a flight in an airplane under VFR conditions unless (considering wind and forecast weather conditions) there is enough fuel to fly to the first point of intended landing and, assuming normal cruising speed, during the day to fly after that for at least 30 minutes; or at night to fly for at least 45 minutes.

For IFR operations, the rules require enough fuel to reach the first airport of intended landing, to fly from that airport to the alternate airport (if one is required); and to fly after that for 45 minutes at normal cruising speed.

If pilots were good about continually assessing and updating the status of their flight -- and fuel reserves -- the requirements might be reasonable, but pilots aren't always good about changing their minds after a flight is underway. They'll bull ahead even when it becomes prudent -- and obvious -- that things aren't working out the way the flight plan had predicted.

There are ways to conserve fuel. George Braly of GAMI (General Aviation Modifications, Inc.), which makes balanced fuel injectors, presents a compelling argument for the efficacy of operating engines lean of peak, even if specific range suffers from a decrease in airspeed. Certainly proper leaning, whether lean or rich of peak, is important and will conserve fuel.

Selecting an altitude with more favorable winds is another way to stretch your fuel. Some of the in-cockpit weather programs display the winds aloft at different altitudes, and controllers will often approve a request for a change in altitude. But you'll have to be proactive and ask. If your flight is westward it will likely be against headwinds that will often be less robust at lower altitudes. If your schedule allows, the winds also tend to be less vigorous early in the morning or late in the afternoon.

If your flight permits, you can take a page from the glider pilot's manual and fly along the upwind side of ridges that parallel your course. You can also save by negotiating a gradual descent to your destination rather than staying high and diving.

Running out of fuel is, at the least, embarrassing, and at the worst, fatal. Get in the habit of constantly -- and frequently -- recomputing your reserves during a flight. Establish a "hard" minimum time remaining at which you'll make a precautionary fuel stop. Whatever you do, don't be fuelish and get caught with your tanks down!