Even if the safety issues could be resolved, the cooling requirements and high volume make liquid hydrogen impractical for commercial aviation.

The most likely carbon neutral solutions for aviation fuel are either algae produced bio fuels, or synthetic hydrocarbons manufactured using renewable energy.

*Manufacturer using low-carbon energy.

At the moment, biofuels are renewable but high-carbon and nuclear is low-carbon but not (considered) renewable.

I know nothing about the topic, but there seems to be a nice Wikipedia article that your question prompted me to find: https://en.wikipedia.org/wiki/Hydrogen-powered_aircraft

I'm suddenly imagining a hydrogen balloon-plane at take off that uses up the hydrogen in the balloon as it flies, until the balloon has been fully reeled back into the plane and it lands on a runway like a normal plane, with reserve hydrogen in its wing-tanks.

If you time it right, it just slowly drifts to the ground and lands vertically with a slight jolt.

Depends on your definition of aeroplane: https://en.wikipedia.org/wiki/Skylon_%28spacecraft%29#SABRE_...