Retrofitted long-range hydrogen aircraft: A viable path to sustainable aviation?

The aviation industry faces increasing pressure to decarbonize, yet long-range flights have limited alternatives due to the need for high-energy–density fuels. Hydrogen is a promising candidate, but its feasibility depends on selecting the optimal production pathway, addressing nitrogen oxides (NO_x) emissions, and managing hydrogen leakage. This study comprehensively evaluates six hydrogen production pathways for retrofitted long-range hydrogen aircraft, assessing their emissions, operating costs, and environmental-cost trade-offs. The results show that without NO_x mitigation, hydrogen-powered aircraft emit 8.6% to 58.6% more equivalent of carbon dioxide (CO₂eq) than Jet-A even under the most favorable pathway (renewable electrolysis, ERE). Additionally, hydrogen aircraft’s direct operating cost is significantly higher, with ERE increasing costs by 91% in medium twin-aisle aircraft and up to 132% in very large aircraft. A NO_x sensitivity analysis indicates that at least 15% NO_x reduction is required for medium twin-aisle aircraft to achieve lower emissions than Jet-A, while larger aircraft need reductions of 60–75%. The Eco-Efficiency Index confirms that even with NO_x mitigation, hydrogen aircraft remain less cost-efficient than Jet-A. Furthermore, hydrogen leakage penalties are higher in ERE for long-range aircraft, highlighting additional sustainability challenges.