That only applies to car engines; aviation piston engines evolve much slower and commonly required leaded gasoline til recently - specifically for the lead content, beyond the anti-knock properties. Most common avgas is 100LL, with significant (if reduced) lead content.
Cf. >Lycoming provides a list of engines and fuels that are compatible with them. According to their August 2017 chart, a number of their engines are compatible with unleaded fuel.
>However, all of their engines require that an oil additive be used when unleaded fuel is used: "When using the unleaded fuels identified in Table 1, Lycoming oil additive P/N LW-16702, or an equivalent finished product such as Aeroshell 15W-50, must be used."*