It's interesting that aircraft still use leaded fuel. From what I can tell this is ultimately due to cost concerns.
Only in priston engines, and it’s mostly due to the fact that changing the engines, which are currently reliable and in many cases have been for decades, could introduce new issues. It’s a snails pace industry due to safety and reliability concerns for the most part. It’s super annoying because i always want the best new thing to go with a plane, but when you’re in the cockpit, it’s comforting knowing the plane is 80…
I love/hate flying for all these reasons.