Yeah I have wondered about this option as well. Hydrogen fuel cell cars make very little practical sense for a lot of reasons, but most of those reasons don't seem to apply so much when you're dealing with air travel:

- It'll be a long time before fuel cells are cost competitive with gas or electric cars, but for planes the cost of fuel and operation is much more significant than with a car, so the upfront cost for building the plane seems less significant in comparison

- Refueling infrastructure is much easier to implement at a (relatively) small number of airports than it is to build many small consumer refueling stations everywhere

- Space is more important than weight in a car, but the opposite may be true for a plane

- Crash safety is a much bigger problem for cars than planes - plane crashes are rare, and if a plane crashes there's a good chance everyone dies anyway, but if you're designing a car you're going to have to be really careful to make sure every other fender bender doesn't result in a hydrogen explosion

Of course there's the issue that most hydrogen today is created from fossil fuels, but perhaps there are ways to generate it sustainably and still remain competitive with the cost of jet fuel?

Electric cars can be a very competitive alternative to gasoline cars, but electric batteries are not yet energy-dense enough to make long-distance air travel viable, so it feels like hydrogen planes might be the least bad solution if we want to get off of fossil fuels.