Lycoming Engines announced this week it has launched development of its TIO-360-EXP "Thunderbolt" engine-with the ultimate goal of operating the engine on unleaded fuel. But the company carefully notes a long pathway of research and approvals necessary before that goal can be reached. The turbonormalized, intercooled engine is nominally rated at 180 horsepower up to 20,000 feet. It is currently approved without performance restrictions for use with ASTM D910 100LL (low lead) aviation gasoline; but it is also approved for unleaded 91/96UL rated fuel that has been approved by Lycoming under its Service Instruction 1070. Translation: the engine can run on certain unleaded gas, but during the trial phase, Lycoming is being very careful about quality control and specific fuel-content parameters that are acceptable. Following further evaluation, Lycoming expects ultimate approval for use with EN228 and ASTM D4814 "automotive-based" fuel as long as it meets the engine manufacturer's "specifications for safe operation in aviation applications."