Piston-engined aircraft, which are basically just light general aviation aircraft, can and have used ethanol.
Most commercial aircraft use jet engines. Other biofuels that are chemically closer to kerosene can be used in most existing jet engines in blends; use of 100% biofuels for hasn't been extensively tested-- but it has been tested![0] This is also the highest-hanging fruit and I wouldn't worry about it in 2019.