United Airlines says it's acquired a stake in hydrogen-electric engine developer ZeroAvia and could add dozens of zero-emissions, 100% hydrogen engines to its fleet by 2028.

The airline said in a press release on Monday that it's the largest airline to invest in the hydrogen engines. The move is part of the carrier's goal to cut all greenhouse gas emissions by 2050.

Officials said the ZeroAvia engines will be added to the United Express fleet.

A conditional purchase of an initial 50 engines will be followed by another 50, which the carrier says will be enough to power 50 twin-engine planes.

A smaller engine will be tested on a 19-seat plane with the aim of entering commercial service in 2024.

ZeroAvia said it's raised millions from investors like Alaska Air Group and Alongside United and a total of $115 million from stakeholders that include Shell Ventures, Amazon's Climate Pledge Fund and Breakthrough Energy Ventures.

A number of other airlines have also made moves recently to accelerate a move to zero-emissions aircraft and all-electric planes. United announced in July that it will buy 100 fully electric aircraft from Heart Aerospace.

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