Inside the company building hydrogen-electric engines for airplanes

About two hours away from the U.K.'s capital in the Cotswolds, ZeroAvia has a research and development facility where it's assembling and developing fuel cell systems, integrating hydrogen electric engines into aircraft and testing them in the air. 

It's all part of an effort to decarbonize aviation with hydrogen, which has earned ZeroAvia a spot in TIME Magazine's top "green tech" companies list.  

"ZeroAvia is solving the climate emission problem caused by aviation. We're developing engines that run on hydrogen to generate electricity and power aircraft without emissions," said James McMicking, chief strategy officer at ZeroAvia, in an interview with "CNBC Tech: The Edge."

Displayed in the hangar during CNBC's visit was a Dornier 228. The aircraft has been retrofitted with a left-side propeller powered by a hydrogen-electric engine and used in ten flight tests. Also in the hangar was a 19-seat Cessna Caravan, which will carry ZeroAvia's first certified hydrogen engine.  

In addition to the facility in the British countryside, ZeroAvia has a fuel cell research lab in Kent, in southeast England. It is also developing applied technology and engineering in California, and it has a manufacturing facility in Washington state where it's retrofitting a 76-seat Alaska Airlines Dash 8 plane with a hydrogen-electric propulsion system.  

With operations in the U.S. and the U.K., the hydrogen engine manufacturer is looking to certify its products with regulators in both countries.  

"At the moment, ZeroAvia is going through a certification process with two regulators: the CAA in the U.K. and the FAA in the U.S. We're certifying the electric propulsion system with the FAA and the whole engine with the CAA," McMicking said.  

ZeroAvia,