Our flight school is small, consisting of just one very nicely refurbished 1981 Cessna 172. I do most of the instruction, with the owner helping out when he has time. The business is actually a maintenance facility that happens to offer flight instruction; not a true FBO. We don’t have much staff. Fuel is self-serve and owned by the Airport Authority. With only one plane, scheduling is pretty informal. We rent the airplane “wet,” and there is a credit card in the plane so renters don’t have to use their own money to buy fuel.
So it was one Friday in late September. I was waiting for the plane to return from a cross-country so I could give a lesson to an instrument student. The plane returned a little late, needing fuel after the trip. My student and I filled it up and then flew our lesson, which was shorter than originally planned due to our late start. We put 2.3 hours on the Hobbs. The next scheduled usage was at 6:00 p.m. that same evening, an advanced Private student flying locally for about an hour. I told the student to lock the clipboard in the plane, tie it down when he was finished, and put the key in its customary secure location. He is on a fairly tight budget; flew for exactly 1.0 hour.
The next morning one of our regular rental customers, we’ll call him “Jimmy” for this article, took the airplane all day to give rides at a reunion. He brought it back that Saturday afternoon and he and the owner pushed it into the locked maintenance hangar. Nobody flew Sunday, and on Monday I was back with my instrument student. On the preflight my student noted that the fuel gauges looked very low so he taxied it to the pumps to fill it up. I walked over to help out.
My student was doing the honors up on the ladder, and he got 20.1 gallons in the left tank. That got my attention, and I immediately switched the fuel selector away from Both so fuel would not transfer from the full left tank to the low right one. Then we moved the ladder and filled the right tank. When it was all finished we put 39.78 gallons into an airplane with 40-gallon usable tanks. If you figure the 160-hp engine burns about eight gallons an hour, the remaining .22 gallons would power the plane for 1.65 minutes. That’s not enough to go around the pattern. We were lucky it taxied to the pumps.
I know Jimmy because I gave him his first flying lessons some years ago. He didn’t complete his training back then due to money issues, and finally finished up this spring at a different airfield. He came to us when we got our rental plane going in July. The owner checked him out, which went well because Jimmy finished his lessons in a Skyhawk.
Both the owner and I view Jimmy as a conscientious and careful, albeit low-time, pilot. We’re comfortable renting to him. How he managed to all but run out of fuel became a mystery. When I called and told him the circumstances and how much fuel the plane had taken he was aghast. He couldn’t believe it. He said he checked the fuel during his preflight Saturday morning, including using the dipstick (see footnote) we provide with the plane. He said he could touch the fuel with his finger in one tank, and the other one was “nearly full” as well. He put 3.3 Hobbs hours on the plane flying it to the reunion at a nearby airport (no fuel there), giving rides to his friends, and returning to our field. After his initial check of the fuel on the preflight he said he didn’t pay much attention to fuel, thinking that he had plenty for his intended flying. He said there must be some mistake; he could not possibly have come that close to running out of fuel.
That sent me back to analyze the records in more detail. Had the plane been flown on Sunday and the time not recorded on the clipboard? Was some maintenance performed that caused loss of fuel? Could someone have siphoned fuel out of the tanks? My investigation revealed that none of those things happened. When the plane returned from the reunion, the owner happened to be there and they put the plane inside. No chance for fuel theft. Nothing was broken on the plane and neither the owner nor the hired mechanic had worked on it.
Nobody flew it Monday morning before I got there. No blue/green stains appeared on the hangar floor, which would have indicated a leak. There was no time “missing” on the clipboard; it all added up and agreed with the current Hobbs reading.
Jimmy blew it. He and his unwitting friends were very lucky they didn’t end up in a farmer’s field, or worse. Including his 3.3 hours, the plane was flown 6.6 Hobbs hours between fueling. We have been keeping records since we put the plane in service. It burns, on average, very close to seven gallons per Hobbs hour. 7 x 6.6 = 46.2, 6 gallons over 40-gallon usable capacity. Scary!!!
The only reason it continued to run at all is that my student and I did a lot of reduced-power instrument approaches, and Jimmy taxied a lot while giving his reunion friends rides. So the average fuel burn was lower than normal.
That meant I had to have “the talk” with Jimmy. I sat him down and told him essentially what I tell every student I teach to fly. The FARs regarding VFR fuel reserves are too lenient to ensure adequate fuel to complete a flight. Thirty minutes in the daytime and 45 minutes at night just doesn’t get it. I advocate at least an hour of reserve, day or night. That last hour of fuel is to cover for something bad that happens just as you arrive at your destination, not to be consumed enroute. If it appears that you will have less than an hour of fuel when you arrive at your destination, stop and buy more.
It doesn’t make any difference how late that will make you or how angry your spouse or boss will be; do it anyway. You’ll live longer. Many things can conspire to eat up your reserves. Perhaps you or the line service person didn’t really fill the tanks all the way to the top for fear of spilling fuel. Your ground speed didn’t turn out quite as high as expected. Your leaning technique wasn’t all that precise, or worse yet, you didn’t lean at all. (The cruise performance chart specifies “with recommended lean mixture.” If you don’t lean you can throw the Cruise Performance chart away!) The mechanical tachometer was off a 100 RPM or more so you were burning more fuel than you thought.
Then you get where you’re going and can’t find the field. After you sort that out and prepare to land you find out that the field is closed because some unfortunate pilot just landed gear-up on the only available runway. Do you now have enough fuel to get to an alternate airport? Probably not! After this intense discussion, I’m sure Jimmy will check his fuel much more thoroughly in the future.
I can’t leave this subject without talking about leaning. Both Lycoming and Continental recommend leaning their engines anytime the plane is in level flight at cruise power, regardless of altitude. In my capacity as a pilot examiner, I all too often hear that students are still being told to just leave the mixture full-rich below X-altitude; usually 3,000 or 5,000 feet.
This is wrong! It’s not much trouble to teach proper leaning technique. Don’t be too lazy to do it right. You teach the use of the Cruise Performance chart and how to do fuel calculations. Leaning the mixture goes with that. Make your instruction meaningful and safe in a practical way. Take the opportunity to teach and practice leaning technique while on a dual cross-country flight.
*footnote: Dipstick: If your flight school doesn’t provide a fuel dipstick for each airplane I urge you to correct that oversight right now. You can confirm full fuel visually, but once part of it is used you have no idea where you are without a measuring device. Fuel dipsticks are free at Home Depot’s paint department. Go get a handful. Mark the Full line with a Magic Marker. Then your students/renters can visually confirm what the gauges say.
-by Larry Bothe
Larry Bothe is an FAA Designated Pilot Examiner, FAASTeam Representative and Gold Seal Instructor in the Indianapolis, IN FSDO area. He is also a Master Certified Flight Instructor and has over 7000 hours in more than 80 types of aircraft. Larry is part-owner of a 1961 7EC Champ and may be contacted at LBothe@comcast.net.