Every pilot has his own tolerance for risk, but most of us who fly ferry across the oceans on a semi-regular basis have developed our own set of guidelines for when we will or won’t fly. We like to hope that those guidelines make perfect sense, but they often don’t. They’re just our way of doing things, they work, and that’s all that matters as long as they keep us alive.
This comes to mind because of a recent experience with a Grand Commander 680FL from Van Nuys, Calif., to Melbourne, Australia. The airplane was old, but in generally good condition. It came fitted with a standard 156-gallon center tank that feeds both engines, plus a pair of 33.5-gallon wing auxiliary tanks dedicated to their respective engine. That’s 223 gallons of internal fuel.
The ferry system included a pair of interconnected tanks in the aft cabin with 330 gallons of total capacity and a 137-gallon tank at the center cabin. That means a total capacity of 690 gallons. If that sounds like a lot, consider that the airplane was fitted with a pair of eight-cylinder TIO-720 Lycoming engines, which were rated for 400 hp per side.
If the little O-320 and IO-360 Lycoming engines are among general aviation’s most efficient powerplants, the big Lycomings have always been among the least efficient, and the TIO-720 is about as big as they come. Specific fuel consumption is roughly 0.45 pounds per hp per hour on the largest Lycoming. Do the math, and the total burn at 75% power works out to 22.5 gph per engine or 45 gph total. Of course, that’s using best power rather than best economy, and you could certainly expect to do better running slightly leaner, probably 21 gph or so. You obviously could save yourself some fuel by throttling back to 65% power.
In seeming contradiction to the math, fuel flows on this airplane were reading unusually low, 16 gph on the left and 18 gph on the right, and I was fairly certain that wasn’t correct either. To get a better handle on fuel burn, I climbed out of Long Beach, Calif., on the short positioning flight to Oakland, Calif., using the center tank, leaned both engines to the proper level, switched to the auxiliary tanks and ran for exactly one hour, then switched back to the mains. I was hoping for a burn of 20 gallons per engine per hour, so I might have expected to see the gauges for the 33-gallon auxiliary tanks reading about 13 gallons on landing.
Instead, they read slightly below 10 gallons. When I refueled in Oakland, the auxiliary tanks took 23 gallons each, suggesting that burn was much higher than normal, rather than lower as indicated by the fuel flows. If the burn really was 15 to 16 gph, my 690-gallon capacity meant that I had about 15 hours of fuel to exhaustion.
The following day, I calculated the winds for each of the eight zones over the 2,100 nm between Oakland and Honolulu. In contrast to the surprisingly wet winter we had in Southern California this year, the second wettest in history, and the accompanying strong headwinds going to Hawaii, the overall component was slightly favorable plus three (a three-knot tailwind), but even with that miniscule help, the time en route came out to 13 hours and 42 minutes. In theory, that number would give me only one hour and 18 minutes of reserve.
No-go, not even close. If you’re flying a four-hour cross country over land with dozens of airports within easy divert range, you may be able to justify flying with an hour of reserve. If you’re only in the air for four hours, any unforecast headwind or nasty weather has little time to develop, and its impact on your time en route is minimal. When the flight leg stretches to 13 hours or more, any change in the wind is obviously magnified.
My buddy Jeff Kopps of the National Weather Service in Monterey, Calif., is one of those folks whose forecasts of wind and weather are almost eerily accurate. (Don’t call him unless you’re going across the pond. He doesn’t do local forecasts.) I have sometimes come within two minutes of the flight plan on a 13-hour flight to Hawaii with the benefit of Jeff’s almost “Twilight Zone” accurate forecasts. That’s not a function of my brilliant navigating or flight-planning skills, by the way. I merely punch the numbers into the electronic E6B and copy down the results.
Still, even the best weather computer models miss the mark sometimes. Back in the mid-1990s, fellow pilot Jon Egaas and I launched from Santa Barbara, Calif., John in a huge, yellow, turbine-powered Ayres Thrush crop-duster (he called it his “kerosene school bus”) and me in a new Mooney MSE, both headed for Hawaii and on to Australia. Loaded heavy, we were about evenly matched at an initial 150 knots.
Right out in the middle, 1,000 miles from any place with a name, we ran into weather that beat us all over the sky. John diverted to Hilo, Hawaii, and landed on fumes in a near zero-zero rainstorm, and I struggled into Honolulu in better weather with eight gallons remaining, about 45 minutes of reserve. Even in an MSE, that’s too close.
Most pilots who ferry piston singles and twins across the Pacific wouldn’t consider making the trip from California to Hawaii with less than a two-hour reserve, and three hours is preferable. The problem on the Commander was I had no way of gauging how much fuel I was burning or how much I had remaining. In other words, I could fly out 1,000 nm from land and not have any idea if I had enough fuel to complete the flight.
The only answer was to install a fuel totalizer to give me a proper measure of fuel burned and fuel remaining. Totalizers are generally accurate to a few tenths of a gallon, and with a Shadin on the panel, I would know exactly how much I had burned and how long I could continue to fly at the current consumption or if I needed to consider throttling back to a more efficient power setting.
The rest of the story is anticlimactic. The Australian owner was predictably unhappy with the delay, but reasonable about the problem and agreed to have a totalizer installed. I’m currently waiting for the work to be completed as this is written. Once the totalizer is installed, I’ll be launching once more for trip number 184 across a big pond.
Bill Cox is entering his third decade as a senior contributor to Plane & Pilot® and provides consulting for media, entertainment and aviation concerns worldwide.
E-mail him at firstname.lastname@example.org.