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

• Evaluates six hydrogen production pathways for long-range aviation feasibility. • Retrofitted long-range hydrogen aircraft emit 8.6–58.6% more CO 2 eq than Jet-A. • Retrofitted long-range hydrogen-powered aircraft incur 91–132% higher DOC than Jet-A. • NO x must be reduced by 15–75% for hydrogen to be environmentally competitive. • Penalty factor for hydrogen leakage in renewable electrolysis is about 1.8 kg CO 2 eq/kg H 2 . 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 (CO 2 eq) 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.