It varies significantly by airline, route and aircraft type. There is some open data on this from Form 41 filings sent to the FAA (here's a piece of analysis ba

It varies significantly by airline, route and aircraft type. There is some open data on this from Form 41 filings sent to the FAA (here's a piece of analysis based on it https://www.faa.gov/sites/faa.gov/files/regulations_policies/policy_guidance/benefit_cost/econ-value-section-4-op-costs.pdf https://www.faa.gov/sites/faa.gov/files/regulations_policies...) Fuel and maintenance tends to cost more than the aircraft lease or financing/depreciation costs, so yes they'd have to justify it economically based on the fuel being affordable (and possibly lower maintenance)? In the near term, I think proponents of hydrogen aviation are expecting increases in taxes on jet fuel to do some of the work on operating economics, whilst they build out their own infrastructure.