A small population of large (“heavy”) transport and vintage aircraft powered by commensurately large air-cooled radial and liquid-cooled inline piston engines remains active in the U.S. and abroad that cannot be operated on any fuel other than 100/115-octane leaded aviation gasoline. These are aircraft like the Douglas DC-3/C-47, World War II- and post-war era bombers that still earn their living carrying freight and fighting forest fires, some aerial-application aircraft like Stearman biplanes still motivated by Pratt & Whitney R985s, and vintage fighters like North American P-51 Mustangs, Grumman Bearcats and Vought Corsairs often seen performing at air shows.

If the PAFI (Piston Aviation Fuels Initiative) program is able to isolate and certify an unleaded replacement for 100LL avgas, will the aging large engines of these aircraft be able to burn it without performance loss or damage? “We would hope there would be complete equivalence, but if not, there would have to be a ‘balanced’ examination of this,” John McGraw, director, regulatory affairs at the NATA, observed. “If you can cover, say, 95% of piston-powered aircraft with the replacement 100-octane unleaded fuel, but it wouldn’t be suitable for the really big radial engines, there might be an allowance for vintage aircraft to continue to fly on 100LL.”

It’s assumed that the leaded fuel would be more expensive for the relatively small quantities needed to support the dwindling numbers of these aircraft, but at least it could continue to be made available. “We would love to see these historical aircraft allowed to operate for as long as possible,” McGraw concluded. B&CA