General aviation refers to anything that isn't a military or scheduled commercial flight, but many people think of it as pilots in puddle jumpers or crop dusters spraying fertilizer and pesticides over fields. General aviation's contribution to air pollution is comparatively small and doesn't get much attention. But that doesn't mean it isn't doesn't have an impact.
There are about 225,000 general aircraft in the American fleet and they fly about 26 million hours a year, according to the General Aviation Manufacturing Association. About 90 percent of them are powered by internal combustion piston engines, and they're still burning fuel laced with very toxic tetra ethyl lead. Beginning in the 1970s general aviation pilots started shifting toward a new, lower-lead gas called 100LL, which contains no more than two grams of lead per gallon. Better, but still not lead free.
It's estimated that today about 97% of general aviation planes fly using this fuel, and the remaining 3-percent fly using the same unleaded automobile fuel (known as motor gas or mogas) that you and I use each time we fill up our car.
The feds started phasing out leaded gasoline in the vehicle fleet more than 30 years ago and banned it outright in 1996. If there's a lead-free options for pilots, why aren't they using it?
First off, 60- to 70-percent of the general aviation fleet flies with high-compression piston engines that can't burn unleaded gasoline, so they're stuck with 100LL. For the remaining 30- to 40-percent lower compression engines, it's not as easy as just switching over to mogas. Engines must be modified and then require a Supplemental Type Certificate, an FAA certification ensuring the engines are still airworthy after the mods are made. That take a lot of time, and slows the conversion to unleaded fuel.
Another big problem is distribution. Most general aviation airports have facilities to pump 100LL but not mogas, leaving pilots who make the switch with the annoying and potentially unsafe option of fueling up their planes with gas they've hauled to the airport in jerry cans.
So, general aviation is looking for other ways to get clean. Pilots can conserve fuel by cutting the amount of time that they spend idling on the ground, minimizing fuel going into the cylinders (known as leaning), flying the most direct route and taking advantage of winds. Improved aircraft design and aerodynamics can help, too. Building planes with sturdy composite materials instead of aluminum reduces weight. The airframes and engines of aircraft already in service can be modified to increase speed and reduce fuel consumption.
Operational and design improvements are good, but modifying engines to burn unleaded fuel is the best bet, and the one thing that might hasten the process is the rising cost of L100. It's selling for $6 a gallon in some places, making runaway unleaded gasoline prices seem downright cheap.
*Photo by Flickr user .: sandman. *
