Why Pushing the Limits on Reserves is Never a Good Idea | Flying Magazine

Why Pushing the Limits on Reserves is Never a Good Idea

It's just fuel-ishness.

Frisch’s Big Boy

Frisch’s Big Boy Mainliner restaurant has been serving burgers since 1939.


The original Cincinnati Frisch’s Big Boy restaurant, which opened in the 1930s, even today sports a somewhat modified but still charming version of the original retro airplane on its large outdoor sign. This popular hamburger joint (and much more) is on a busy street, about 2 miles north and slightly right of Lunken Airport’s southwest parallel runways.

Last week, having lunch with my sister and half listening to her prattle on about her spoiled mutt, Ben (named for aviator Carl Ben Eielson), I was munching on a Big Boy and thinking about an aircraft accident that happened some years ago — very nearly in this restaurant’s parking lot. It was back in my misspent days working on the dark side, posing as an FAA operations inspector while surreptitiously trying — whenever possible — to advocate for the pilot. In this case, while the screw-up may have been understandable, advocacy was simply impossible.

A young private pilot had left Lunken in a rented Cessna 150 to pick up his father at an airport on the south side of Dayton, Ohio. Then, probably over gross with two guys and fishing gear, they launched for an airport in central Michigan. After a day on the river, the fishermen headed home into the wind and landed at KMGY (Dayton Wright Brothers Airport) to drop off the pilot’s dad. By this time, it was dark, and the solo flight to Cincinnati would be in the black of night.

In those days before self-serve fuel, it seems strange that the pilot didn’t check to see if the FBO at Wright Brothers would be open. And when his dad asked if he was OK on fuel for the 50-mile flight to Lunken, he said it was no problem, maybe since the only alternative would have been an inconvenient diversion back 15 miles northwest to Dayton’s Cox Field. Well, as it turned out, there was a problem — a big one, especially at night — because the engine quit several miles out on final for the runway at Lunken. The pilot made a rather “inelegant” forced landing on the road next to Frisch’s restaurant. Thankfully, he survived, but suffered pretty severe injuries and had already been taken to the hospital by the time I arrived with another airworthiness (maintenance) inspector.

The National Transportation Safety Board “owns” all accidents, but it delegated this investigation to our FSDO — not uncommon when an event isn’t particularly newsworthy, there are no fatalities and it involves a small airplane not being flown by a John Denver or John Kennedy. Anyway, determining the cause on this one was a no-brainer since there was no fire, no fuel spillage and my airworthiness counterpart found the tanks, lines and carburetor devoid of fuel.

An FAA investigation is geared toward potential pilot violation(s), while the NTSB focuses on all causes that contribute to an accident. A subtle difference, but in short, the FAA is looking for whom to blame, even if some “findings” (an expired medical, transponder check or so on) have nothing to do with the event. But accidents involving fuel violations are difficult to prove; as Mac McClellan wrote in a 2002 Flying article, “FAA fuel requirements are based on planning, not the actual amount in the tanks when you land.”

So, the next day, I began by calculating if 22.5 gallons (full tanks less the unusable 3.5 gallons) was enough for this flight, factoring in mileage, fuel consumption in climb and cruise, wind and groundspeed, the stop in Dayton and the extra 45 minutes at cruise power required at night. Then I called the FBO at the Michigan airport to determine if they did, in fact, take off with full tanks.

The lady who ran the FBO answered the phone. She hadn’t yet heard about the accident, but when I asked if she remembered an airplane with that N-number landing the previous day, she said, “Yes, I remember — I won’t forget that Cessna. And you can bet I’d never rent one of our airplanes to that guy.”

“Really? Why?”

“Because when we fueled the airplane after he taxied in yesterday morning it took 23 gallons.”

I could tell you more stories of airplanes running out of fuel within miles of a destination airport, but I suspect you already know plenty and, if you’re honest with yourself, you understand the “logic.” I don’t always agree with my more famous and skilled confreres John and Martha King, but

I value one of Martha’s admonitions. If you’re planning a flight that’s anywhere near the maximum range (in time, not miles) of your destination, decide beforehand on someplace about midway to land for fuel. Never choose a fuel stop that’s near your destination because, as you get closer, it’s too easy to convince yourself that there’s enough fuel and “I’ll save a lot of time and hassle by going on.” If you haven’t experienced that temptation, you will. So just take it out of the equation and commit to stopping about midway en route before taking off. And then hope you encounter the Mother of All Tailwinds.

My mind’s been on fuel events (and I’ve had a few, as you know if you read this column) because of my Cessna 180’s rather robust consumption: 14 gph. To get 130 ktas, I’ve always used 24 inches Hg and 2,400 rpm. This 1956 model holds 56 gallons, which is usually more than enough, but a concern for lengthy flights, or in weather, at night or in areas with few airports. My friend — and guru of all things aeronautical — Barry Schiff, suggested a closer look at the charts in the Continental 0-470-J engine manual might show how to get the same speed at a lower fuel consumption by using some “over square” settings.

Another friend, engine guru Bill Schmidt, who owns Signature Engines, agreed and said as a rule of thumb on flat engines, adding one inch of manifold pressure and reducing 100 rpm will give you about the same power. What they were saying is at these over-square settings, the reduction in engine friction lowers fuel consumption, which, Schiff reminded me, is what Lindberg taught P-38 pilots who needed more range in the South Pacific during World War II.

Guess what! At 25 inches Hg and 2,300 rpm (flying at 3,500 feet msl), the fuel burn is down to 13 gph, and at 26 inches Hg and 2,200 rpm, it’s only 12.2 gph — same power, and same 130 ktas.

Please don’t try this with your flying machine without consulting your POH or talking to your mechanic; if you don’t already realize this, I’m a rather superb pilot but possibly the world’s worst mechanic.


More Stories