Aviation is responsible for approximately 2.5% of global CO₂ emissions — equivalent to Germany’s entire annual output — and remains among the hardest industrial sectors to decarbonize. Batteries are too heavy for a meaningful range. Biofuels face supply constraints. Sustainable aviation fuel can be blended into existing engines, but cannot alone achieve net zero. Hydrogen fuel cell technology has emerged as the most credible long-term pathway, and in March 2025, Airbus confirmed the feasibility of a 100-seat fuel cell aircraft with four 2.4-megawatt electric motors capable of flying routes up to 1,000 nautical miles. AIMultiple This documentary examines the full scientific, engineering, and geopolitical architecture of hydrogen aviation. We analyze the thermodynamic paradox at hydrogen’s core: while hydrogen carries 2.8 times more energy per kilogram than kerosene, it is 3.7 times less energy-dense by volume and must be stored at −253°C — just 20 degrees above absolute zero. In June 2025, Airbus and MTU Aero Engines signed a Memorandum of Understanding at the Paris Air Show to jointly develop hydrogen fuel cell propulsion systems, following a three-phase roadmap from technology maturation through to full-scale propulsion development. We investigate why Boeing has adopted studied silence while Airbus commits hundreds of millions of euros, why Universal Hydrogen closed in June 2024 despite $100 million raised and a flying testbed, and why the airport infrastructure challenge — cryogenic storage at scale, green hydrogen supply, and capital investment across thousands of hub airports — may prove harder than building the aircraft itself. The verdict: hydrogen will not replace the A320 or 737. It will complement them — on short-haul routes, at airports that commit early, from the 2040s onward.