American Airlines has entered into a conditional agreement to purchase 100 hydrogen-electric engines from British-American developer ZeroAvia.
The engines are intended to power regional jets with zero in-flight emissions, except for water vapor.
The agreement comes two years after American took a purchase option on those 100 ZeroAvia engines.
The companies did not reveal terms of the agreement, including the conditions under which the companies could opt out.
ZeroAvia is currently testing a hydrogen-electric prototype for a 10- to 20-seat plane and is designing an engine for larger aircraft such as the Bombardier CRJ700, which American operates with 65 seats on some regional routes.
By the end of next year, ZeroAvia is targeting certification of the 20-seat plane, which would have a range up to 300 nautical miles. It hopes to produce a powertrain capable of propelling 40- to 80-seat planes as far as 700 nautical miles by 2027.
In addition to the engine agreement, American has increased its investment in ZeroAvia following an initial investment in 2022. Specifics were not revealed.
ZeroAvia says it has taken more than 2,000 pre-orders, valued at more than $10 billion, of its hydrogen-electric engine. Among its other would-be customers are United and Alaska.
Hydrogen-electric engines rely on electricity created by a chemical reaction in a fuel cell to power an electric motor.