Going the Distance

Consider all the VFR options

May 1, 1998

According to the DUATS flight planner, the distance from Boulder, Colorado, to Memphis is 779 nautical miles — a bit of a stretch for my Cessna 185 Skywagon; without help from the wind gods, we would need a stop somewhere between central Kansas and northwest Arkansas to replenish the fuel tanks.

On the morning of the flight, with high ceilings and excellent visibility, I decided to go VFR. Strong 50- to 60-knot tailwinds were forecast all the way to Tennessee. This would allow me to make the flight nonstop in four hours and 12 minutes, using 59 gallons, with more than an hour's reserve.

When planning for a long flight, I start with a big weather picture and work toward the details. I watched The Weather Channel for an overview, then downloaded the forecast, radar, and winds aloft charts from AOPA Online ( www.aopa.org/members/wx/). Finally, I dialed DUATS on my computer for a thorough briefing.

Flight planning is often thought of as the activity done just before takeoff — but in truth, it should be a continuous, ongoing process that stops only upon reaching the chocks at the destination. In flight, I always look for information that doesn't fit into the model I have created, based on previous information. Flexibility is a key ingredient in this type of flying; I don't ever get stuck on "have tos" (e.g., I "have to" land at such-and-such a place). Another destination may be a wiser choice.

Airborne and climbing eastbound from Boulder, I found the winds at low altitudes out of the east and calm; once clear of the Denver Class B airspace, I began a slow climb to a planned cruise altitude of 9,500 feet to take advantage of winds forecast to be from 260 degrees at 62 knots. But when the aircraft was passing through 7,500 feet, the groundspeed dropped off, indicating that the winds were not as predicted. I punched the numbers into my Garmin GPS 90 and arrived at a true airspeed of 147 kt — but a groundspeed of only 168. The tailwind wasn't as strong as it was supposed to be — but then, it often isn't.

So what do you do when the winds are not as forecast? Make new plans! A blown forecast should be a bell-ringer for pilots, signaling a need to rethink your whole flight plan; it's probably time to look for possible new destinations and explore new possibilities. When winds-aloft forecasts are blown, I also immediately want to know what else is not going to go according to the forecaster's plan. Forecasts are based on a computer-model prediction of winds aloft over six, 12, or 24 hours; if the actual winds do not fit the model, terminal and area forecasts based on those winds will almost certainly need revision, too.

When the winds aloft are not as forecast, I figure a worst-case scenario like this: to make it to my destination, Memphis, I need to average at least 150 knots groundspeed. If the groundspeed sinks below this "drop-dead" number, it's time to pay close attention; I may need a new plan. I start thinking then about where I can safely go, considering the weather in the area of possible destinations and the capabilities and range of the airplane. I may have to drop into some destination well short of my original one, just for the better weather.

When the groundspeed stays below my drop-dead number for a while (unless I know that it will pick up down the road), I get out AOPA's Airport Directory and plan a fuel stop. When VFR, as on this trip, the change in destination also means a call to flight service to change my VFR flight plan.

It's important to begin this "How goes it?" process early in the flight. Start by verifying the planning you did previously with real-world numbers. Is my flight plan still valid, or is it beginning to look like another scheme to reinvent our government? How's the destination weather holding up? Begin making contingency plans early if there is a widening chasm between reality and your earlier plans.

Did you know that the federal aviation regulations do not specifically require a pilot to check the weather while en route under VFR? The requirement for being familiar with the weather and forecast is a preflight requirement only. Of course, you can't cover everything with a regulation; that's where good judgment takes over.

The FARs also say that I cannot begin this VFR flight unless I have enough fuel to go to the destination plus 30 minutes; at night, 45 minutes is required. No alternate is ever required for VFR, although it is a good idea. Once I'm airborne, the FARs do not require me to land with any fuel at all, a curious omission — common sense and good judgment are my only guides after leaving the ground. My personal rule is to require the same minimum 30- or 45-minute fuel reserve throughout the flight, although I shoot for an hour.

As I cruised in smooth air at 9,500 feet over eastern Colorado, I wondered if there was anything else I could do to maximize my disappointing groundspeed. Should I climb? Descend? Change my routing? I tried 7,500 feet, hoping for a counterclockwise change in wind direction at lower altitude, but the tailwind began to wane after level-off there. So I climbed back to 9,500 and took the slightly higher groundspeed. The 185 burns about 18 gallons per hour in the climb, one third of a gallon per minute; so if it takes four minutes to make that climb back to a higher altitude, the fuel burn amounts to only a little more than one gallon. If fuel is that scarce, you're already in trouble.

Flight watch (122.0 MHz) is a good resource while in cruise. You can often eavesdrop on this frequency and pick up just the info you need; or, call and let the specialists help you shop for options. They might even have actual winds-aloft figures. Be sure to give back to the system with a good pilot report, especially if you encounter something (winds, ice, turbulence, thunderstorms, etc.) that was not forecast. Give estimated winds aloft, temperature, sky condition, and a ride report. It might help the next pilot to make crucial plans.

Should you slow to long-range cruise to extend the endurance when the wind gods are not smiling on you? It depends. The Skywagon is like most single-engine airplanes: By setting maximum power available at 9,500 feet, 65 percent, the book says, we should see 140 knots true airspeed; the 650 miles remaining would take four hours, four minutes. Fuel burn would be 13.7 gph for a total of 56.2 gallons. Slowing to 55- percent power reduces true airspeed to 129 knots with a fuel flow of 11.7 gallons per hour; the 650 miles would take 4.4 hours and a total fuel burn of 51.5 gallons. Thus, it would take 20 minutes (9.2 percent) longer to complete the flight to save 4.7 gallons (8.3 percent).

Would that make a difference? Maybe, if I were 4.7 gallons short. Of course, that extra 20 minutes will seem like forever with fuel gauges bobbing at the critical "E" mark, especially when you normally use time as your fuel gauge.

Is it OK to lean the engine more aggressively? Will I save anything? Look to the engine manufacturer for guidance; Teledyne Continental Motors says that I can lean the IO-520 to peak with no problems, but they prefer that it run richer. The numbers in the operating manual reflect 50 degrees richer than peak; I can save a couple of gallons by operating at peak, although the true airspeed will drop, too.

I pay close attention to fuel gauges when they are telling me that I have less fuel than calculated. This makes it important to intimately know the fuel gauges in your airplane if you don't have a sophisticated fuel totalizer. Do they read high or low? When they say "E," does that mean that you have a half hour left or that you're going to log more time toward your glider rating?

When I was crossing southwestern Missouri into Arkansas, the groundspeed increased to 174 knots and gave me the comfort to press on for Memphis. By my calculations, I would have about an hour's fuel aboard when I landed. I checked the weather with flight watch again; the ceiling in Memphis was still better than 5,000 feet with five miles' visibility.

On the ramp, it took 68 gallons to fill the tanks — I still had 16 usable gallons left. That's a little more than an hour at high cruise with this airplane, comfortable reserves in day VFR weather. If the weather had been marginal, or the arrival after sundown, I would have stopped back in Wichita, eaten a late lunch, and planned a second leg to Memphis.

Particularly when making long trips, the planning for a VFR journey becomes just as critical — and perhaps more so — as when flying IFR.