April 2012
Last year, I was appointed to the Modesto City-County Airport Advisory Committee, a group chartered jointly by the city and county to give advice to the airport manager. We have monthly meetings, the topic of which, I suspect, is probably the same as that for most other General Aviation airports: how to increase revenue, which fell dramatically in the 2008 recession, and has yet to recover to anything like pre-recession levels.
A common complaint in those meetings is the high cost of 100 low lead (100LL) aviation gas. I’ve been told multiple times by different people something along the lines of “five-dollar Avgas is killing General Aviation.” (If that sounds cheap where you live, bear with me).
That set me to thinking… Granted that all pilots would like to see it priced lower, just how important is the price of 100LL, really?
I’m one of five pilots in a partnership with a fixed-gear single engine piston airplane. Each partner pays $140 per month for fixed costs (hangar, insurance, annual inspection), and $50 per hour for variable costs (unscheduled maintenance and engine reserve), dry. Our fuel burn is about 13 gph. As a group we average about 500 hours per year, or 100 hours per partner, so the per-hour cost for each of us averages:
140 x 12/100 = $16.80 hourly share of fixed costs
+ $50.00 per hour maintenance/engine reserve
+ 68.77 (13 gallons 100LL @ $5.29/gallon)
= $135.57/hour
Now suppose the cost of 100LL goes up (or down) by a full $1 per gallon. Multiply by 13 gallons per hour, and you’re looking at a $13 dollar per hour difference… just slightly less than 10 percent. That’s not nearly enough to affect how much flying I will or won’t do.
This result will of course vary some depending on how much you fly, but there’s an old rule of thumb that operating costs for a fixed-gear piston single run about double the cost of gas, which is pretty accurate for us. In twins and retracts, the operating cost is typically more like three times fuel cost or higher, which would mean that the change in fuel cost would have an even smaller impact. So I really don’t think the cost of Avgas is the limiting factor for General Aviation.
If it’s not Avgas, what keeps so many of us on the ground? I think the overall poor state of the economy is a major factor. I’d fly more if I could, but that depends a lot more on how much money I can bring in from my writing than on whether the cost of gas rises or falls by a dollar. To some extent I can affect that by trying to drum up more business, but the economy really limits that. Retired pilots don’t even have my option—they’re limited by fixed or investment incomes. And all GA pilots are dealing with a lot of uncertainty.
And the cost of fuel generally—not just Avgas—is also a factor, in a couple of ways. For most of us, use of our airplanes is somewhat optional, while using a car is a necessity. Here in California, the cost of auto fuel is now pushing $4 per gallon, and for someone with a long daily commute, that fuel eats into the budget for nonessential things like weekend flying.
Indirectly, we see increased fuel costs reflected in the way other costs are going up. Our partnership increased the maintenance fee from $40 to $50 per hour last year because the old rate simply wasn’t covering our costs. I suspect that fuel costs underlay some of that—it costs more for the maintenance shop to keep their lights on, and it costs more to get parts shipped in.
The situation is certainly different for commercial operators, which put a lot more than 100 hours a year on their airplanes. A few years ago, I spent a week flying right seat in a light twin operated by a medical group in South Texas. I was told that they typically flew their airplanes enough to overhaul the engines every two years—1,000 hours per year— and nearly always met their 2,000-hour TBO. Their variable costs (fuel, engine reserve and nonscheduled maintenance) must be much higher than fixed costs, and fuel probably is the largest single factor.
Airlines are feeling the fuel pinch to an even greater extent. According to American Airlines, the cost of Jet-A went up about 300 percent between 2003 and 2011, and it’s continuing to rise. This has caused American and other airlines to look at ways to save money, one of which is to cut less profitable flights, especially those flown on older (and less fuel efficient) turboprops… which brings me back to serving on Modesto’s airport advisory council.
One of the first things I was asked to vote on was a long-range strategic plan to lengthen our main runway so that KMOD can accommodate larger jets. Currently, airline service here is on old Embraer turboprops. In the long run, that’s going to move to regional jets, or we’ll see the service go elsewhere.
But back to GA for a minute. I have a tip that may save money for readers who, like me, are still flying airplanes with steam gauge panels. Before sending your directional gyro (DG) or horizontal situation indicator (HSI) out for an expensive overhaul, check your magnetic compass.
Mechanical DGs and HSIs always precess to some extent—and eventually that precession gets bad enough that the gyro must be overhauled or replaced—but how do you know the DG or HSI is precessing? That’s usually done by checking it against the magnetic compass. Pilots may not realize that magnetic compasses require periodic calibration. Checking these instruments against an uncalibrated compass will show errors that look like precession even with a brand-new, perfectly good DG or HSI!
If you have an official compass rose at your airport, you can check your compass (and DG/HSI) against it fairly easily. Start your engine, taxi to the compass rose, turn on everything you normally use while flying (radios, lights, strobes) and note any effect on the compass reading.
Then taxi off the rose, turn back and taxi into position facing north according to the rose and note any deviation. If that looks okay, set the DG or HSI to match the compass, taxi away and return lining up with the other cardinal directions (east, south and west) and finally back
to north.
You should wind up with the magnetic compass within three degrees of north. If it’s off by more than three degrees on any of the cardinal directions, it needs to be swung. On the other hand, if the compass is fine but the DG/HSI differs by more than three degrees, it’s probably due for an overhaul.
I got this hint from Edward Maher’s book “Avionics Troubleshooting and Repair” (McGraw-Hill Professional), which I found well worth the $39.95 cover price. I’ll add an extra recommendation based on my own experience: if you find yourself suspicious that the compass may be misleading you in-flight, try setting your DG or HSI against GPS track. Barring a strong crosswind at your altitude, GPS track should be very close to magnetic bearing, and if you find the HSI or DG precessing compared to both the GPS track and magnetic compass, it’s a sure bet you need a gyro overhaul. If the GPS and gyro agree, better check the compass! –JDR
John D. Ruley is an instrument-rated pilot, freelance writer, and recent graduate of the University of North Dakota Space Studies graduate program (www.space.edu). He is also a volunteer pilot with www.ligainternational.org, which operates medical missions in northwest Mexico, and a member of the board of directors of Mission Doctors Association (www.missiondoctors.org). Send questions or comments to editor@www.piperflyer.com.
