As I mentioned in my last entry (/2014/04/11/schedule-route), I knew I would need at least one intermediate fuel stop on this trip. Where to stop for fuel?
In the old old days (I know: there are lots of pilots flying now who were flying long before I was: for them, the old old days are the 50s, 60s, and 70s, not the 80s, and 90s), before the Internet, we had paper charts (VFR—i.e., visual—charts from the FAA, IFR—instrument—charts from the FAA and, in my case and the case of many others, from Capt. Jepp), the Airport and Facilities Directory (A/FD), and various private guides. I used all three for flight planning back then, along with the performance and fuel consumption information from the pilot’s operating handbook for the airplane I was flying. The POH, in conjunction with winds aloft forecasts, told me how fast I’d likely be flying and how much fuel I’d burn each hour. The POH also gave the fuel tank capacity information, and the maximum weight the airplane could safely carry. On a flight across the country in the past, I’ve flown alone or with one person—this time, I expect to be alone—and even with my Mooney’s limited load-carrying capabilities I’ll be able to fill the fuel tanks.
Take the fuel available (in this case, 75 gallons), the fuel burn, the desired fuel reserves (I want at least an hour’s fuel in my tanks when I’m planning to land, even if I have to go to an expected alternate airport for some reason), and I find the time I can fly. Yes, I have to take into account differences in fuel flow under different flight conditions: for example, my Mooney burns about 23 gph while climbing, 11.4 gph in cruise. Include the probable winds at the expected cruise altitude and the true airspeeds in climb and cruise and the result is ground speed; couple expected ground speed with duration and that yields the airplane’s planned range. Oh, airplane can fly six hour legs, let’s say, and your sitzfleisch can only handle four? Use four hours in the planning! But, I’ve always been happy to fly for as long as my airplane will.
(Incidentally, even in these new days, all this information is needed, because I need my airplane’s range to determine the universe of potential fuel stops.)
Now, I can actually start looking for an airport. How many fuel stops would I need? For example, if I’m flying 2,000 nm and I have an 800 nm range, I’ll need two stops; make that range 650 nm, and I’ll need three stops. Going 1,000 nm with an 800 nm range? I can chose any airport starting 200 nm from departure, up to 200 nm from destination. Longer airplane range as a percentage of the leg to be flown means more flexibility—more choices, but more airports to evaluate.
Let’s take the trip at hand: KPAO (Palo Alto) to KGTU (Georgetown, Texas, near Austin): 1,277 nm airport-to-airport along the great circle route. Unfortunately, the great circle route goes through airspace that’s restricted—not available for civilian use when the military is using it. The great circle route from KPAO to KGTU goes right through pieces of the Edwards military complex (R-2508) and the White Sands Missile Range (R-5119 and the parts of the R-5107 complex). The obvious change of dodging Edwards to the north takes me through some of the Nellis-Tonopah areas, also off limits. Some restricted areas in the U.S. are off-limits only some of the time, but Edwards, White Sands, and Tonopah are in use either continuously, or weekdays during, roughly, daylight hours. (I have flown through the Edwards complex—one Sunday, in fact, was able to fly right over Edwards AFB—but I won’t plan on that!)
My working route: KPAO VINCO KENNO DYSSS JUPTR LLO KGTU (Palo Alto airport to the VINCO intersection—a point in space near San José—then on to KENNO and DYSSS intersection to dodge Edwards and Nellis-Tonopah, JUPTR intersection to avoid White Sands, Llano VOR [a radio navigation aid], and in to Georgetown). That jog at LLO is to enter the Austin terminal are from a local point, rather than from some arbitrary point hundreds of miles away. This helps with traffic management and flow.
How does all of this affect fuel stops? The zigs and zags around these restricted areas mean more distance to fly, and decrease effective range. In this case, the distance to be flown increases from 1,277 nm to 1,297 nm, a mere 2% increase. Because of the long distance I’ll be flying and my being able to plan the zigs and zags so they create the longest possible triangle (view this triangle’s other sides as the direct route, and flying right up to the edge of the restricted airspace before turning to avoid it), I can minimize the increase in distance.
Rounding, I’m left with a 1,300 nm trip. My Mooney has a bona fide in-flight duration of five and a quarter hours with a reasonable reserve. Planning conservatively eastbound, I’ll have a 200 knot ground speed, and a 1,050 nm range. I won’t be surprised, though, to get a 20 knot tailwind at 25,000′, but I’ll treat that extra 100 nm as reserve (and possibly use it en route to change my planned fuel stop, as I did in 2011 when flying westbound to eliminate a planned fuel stop). Generally, I plan on no tailwind and 25,000′ when eastbound, and a 20 knot headwind and 12,000′ westbound.
Back to planning the fuel stops. With a 1,300 nm flight and a 1,000 nm range, I have an enormous number of possible fuel stops: get me 300 nm from home, and I can start looking for gas, and I can keep looking for gas until I’m 300 nm from Georgetown. Generally, though, I like to split the flight up into roughly even chunks. In this case, 1,300 nm will take about 7 hours, including climbing to altitude (climbing covers ground more slowly than cruising), so I’d really be looking for a fuel stop about 3-4 hours into the flight.
One of the problems flying over the desert southwest is there aren’t many people, so there aren’t many towns, so there aren’t many airports, so there aren’t many fuel stop options. One of the nice things about flying over the desert southwest is there aren’t myriad options for fuel stops, so it’s easier to consider the choices. I like to avoid big-city airliner airports like Las Vegas, Phoenix, and Flagstaff. I need a runway long enough for safe operations: minimum 2,300′ feet at sea level, increasing with altitude (and heat, definitely a factor in the desert in June!). Most of the airports in the desert southwest that have gas will have a long enough airport. Oh, I also want a paved runway: my Mooney doesn’t do well on dirt or gravel, and I’d rather stay off grass.
I’d also like an instrument approach available at my planned fuel stop, in case something comes up and the weather turns a bit bad. Though perhaps unlikely in June along this route, it’s a nice additional safety net, a built-in Plan B.
Reviewing the charts out at 600-800 nm from Palo Alto shows I’ll be around Flagstaff, Winslow, St. Johns, Taylor, and Show Low, Arizona, Santa Fe and Belen, New Mexico, and places like that. In the old days, this is where those airport guides came in: you could find out what FBOs (effectively, in this case, airplane gas stations) were at each airport and phone numbers for those FBOs. You could call the FBOs and ask about their gas prices, whether they had a phone available (no cell phones back then!) so you could call for an update on the weather, and things like that. Back in the old, old days, that’s what I did, too.
I would now have the desired course, dodging all the restricted areas, and the possible fuel stops I’d like to consider (those around mid-flight, in this case). I’d like to find a fuel stop right along my planned flight path, or at least not very far from it. From the compiled list, I’d chose a probable stop, and a couple of alternates.
Today, we have many more tools available. The first one widely available once the Internet came out of the research closet and the Web became a marginally widespread reality, was AirNav. This site, started in 1996, gives pilots a bunch of valuable navigation information, including airports, FBOs, and even pilot comments and reviews! One of the brilliant pieces of AirNav is its fuel stop planner: the Web site’s code logic and database take care of the tedium of checking allll the airports along a route for fuel prices and distance from the direct course. Though it doesn’t allow for route entry—I tell AirNav my departure and destination airports and it assumes a great circle route—it certainly simplifies fuel stop planning. Right there in front of me, with just a little bit of work, I have 10, 20, even 50 possible fuel stops for my trip, along with total distance (again, assuming great circle routes between airports) and fuel prices at each airport. (AirNav gets its fuel information from users, among other sources.)
A few years ago, I wrote about ForeFlight, a flight-planning and in-flight iPad app. That’s another tool I use for flight and fuel stop planning. Ditto Enflight, a flight planning and weather briefing tool on the Web. Enflight gives me better actual operational estimates of things like total fuel burn, duration, and range (ForeFlight uses just one fuel burn rate and speed for a flight, and Enflight uses the actual flight characteristics of my airplane, taking into account the slower speed and higher fuel burn during climb, for example).
Taking all of the information, tools, and techniques into account, I’m currently planning on St. John Industrial Air Park in St. Johns, Arizona—KSJN—for my stop. Here’s AirNav’s info on this flight (KPAO-KSJN-KGTU), complete with a point-to-point great circle route depiction (not the route I’ll be flying, remember).
What about alternatives for the fuel stop, in case something goes wrong? And alternate routes, in case of weather (which can completely derail all the fuel stop planning)? More to come.