Difficulties in the aviation sector
Fuel tanks
Currently, fuel tanks are stored in the wings, not needing to sacrifice any useful payload area, and reducing the stress on the wings. This solution is not feasible with hydrogen, due to the large pressures and volume needed.
The current ideas for solutions are to either dedicate a part of the fuselage to this fuel or design a new passenger plane model called the flying wing.
The first might only increase the acquisition cost minimally but will reduce the operating economics, while the second requires large investments, in both the airplane, as well as ground infrastructure.
Supply of these new jets is another question, with it being likely that around 100 - 120 are produced annually, simply securing these jets is likely to be a challenge.
Hydrogen
Airports will need to invest and adjust to the usage of hydrogen, a substance more complicated and potentially dangerous than jet fuel. This can and will be done, but at what cost, and what speed are different questions.
Along with that the supply, emissions, and costs of hydrogen are another question mark. It has been assumed that low-demand hours of electricity will be used to produce the fuel. But other sectors from the fossil fuel consuming industry, electricity storage, and more recently the training of large AI models are also after this type of power. So this assumption largely rests on an inefficiency in the energy market, which even now looks unlikely.
Biofuels
It is also possible that in the shorter term biofuels take on a larger role, as we can already see with mandates in European countries.
However, they also have their issues:
Scaling up of feedstock
Energy losses during the production process
Remaining emissions and increasing carbon emission prices
Adapting jet engines, fuel tanks, and regulatory processes
Unless a low emissions drop in fuel is found, and currently there isn’t a fully available one, even if there were on, there is still the issue of costs. In the long term, biofuels will not be the answer.
Societal challenges
The supply of pilots is already and will continue to be a pain point for the industry. This will increase costs, and if the capacity per plane goes down, this will hurt the unit economics of the sector even more.
Restrictions on airports might further lower capacity at airports, increasing landing costs and so on.
Overall public attitudes are also changing, countries like France are already legislating certain flights away. With the viable alternative of high-speed night trains, and already existing political support. These restrictions are likely to become a major factor.