Its not the airlines that burn lead, it is the small piston powered aircraft. Jet and turbine engines are basically diesel burning. However the majority of small aircraft have no choice but to burn leaded fuel. Small aircraft engine manufacturers have been working with petrol companies for more than 20 years now on trying to find an alternative solution to leaded fuel for there engines. The problem is that the engines are high compression. They knock like hell if you try to burn auto gas. The majority are also air cooled. Very inefficient as a whole. Just in the last 4 years has a computer controlled system has come along that adjusts mixer with power and altitude settings. On every small airplane I have flown, you control your mixer, power and manifold pressure settings. Most people think that this should have come along a long time ago, but technology hasn't really changed much in small aircraft since WW2. In the mid 80's an aircraft company named Mooney teamed up with Porsche to build a modern "single lever design" to eliminate pilot controlling 3 throttles. It was a hard learing experience, and had tons of problems. Finally 20 years later, reliable systems are coming to market. Also, Bombardier is building 2 "V6" engines. One is a turbo, the other isn't. They burn auto gas, are liquid cooled, and have a reduction gear box. Instead of having 2500rpm redlines, they are the normal 6k type. So far, these engines haven't come to market yet, but they are in the pipeline. The other is diesel. The biggest problem with a diesel is the wieght of the engine. A 1.7 litre turbo diesel weighs as much as a 320 cubic inch 4 cylinder in the same style plane. It developes 30 less horsepower at sea level, and it is real new to the small aircraft market. Pilots as a whole are very conservative, and like to stick with what they know......magnetos, 2 spark plugs per cylinder, air cooling, and no gear reduction. The also like controlling there mixture and prop angles. Not to worry though. The last company that makes AVGAS will stop producing it in the next 5 years. Simply a matter of math. The total sales of AVGas in a year is less than 2 days sales of Auto Gas. They have already announced it, and small aircraft owners throughout the United States are hoping that a new additive, fuel type or something is stumbled upon. The engine in my fathers plane is a 550 cubic inch turbo 6 cylinder making 310hp. It gets about 12mpg at 201 miles per hour at 13000 feet. If you throttle back to 55% at 6000 feet, you can get over 25mpg at 135mph. Try that in a car. As for the polutants, I've been around airplanes my whole life. A bit of lead ads character, and the decibel level is really not that bad. My father came to visit me here in Washington DC in his bird. With a brisk tailwind he made a 650nm trip in just over 3 hours, and only burned 49 gallons of his 115 gallon fuel supply. I'm waiting to be able to afford a twin engine diesel. It just as fast, and only burns 13 gallons per hour, or 6.5 gallons per side. I'm a firm believer in having 2 engines on a plane whenever you can afford it.