With more than a decade of development work under its belt, hydrogen propulsion pioneer H2Fly is now advancing efforts on a sixth-generation powertrain that it says has the potential to go into commercial service with 40-seat airliners on flights of up to around 2,500 km. The Germany-based company has already had talks with several airlines about their requirements and in the next few months expects to announce partnerships and plans for the next stage of testing of a sustainable powertrain incorporating fuel cells and liquid hydrogen.In 2020, H2Fly received a permit to fly its HY4 technology demonstrator aircraft powered by a 130 kW hydrogen-electric propulsion system. The company, formed in 2014 by five engineers from the German Aerospace Center in Stuttgart and the University of Ulm, conducted 76 flights, with some sorties lasting an hour or two. In July 2021, H2Fly and Munich-based Deutsche Aircraft agreed to collaborate on plans to convert a 1990s-vintage Dornier 328 regional airliner to hydrogen power. The partners are working to be ready to start flight testing the former twin turboprop in 2025 as part of a timeline that H2Fly founder and CEO Josef Kallo told FutureFlight could lead to an aircraft being certified under EASA’s Part CS-25 rules in about seven to eight years.H2Fly’s business plan is open to developing an aircraft in-house and/or to working with other manufacturers to provide propulsion for another new airframe or convert an existing type. The company believes that it could eventually scale up the power rating for its system to around 1.5 MW. The purpose of the HY4 was to show that it is possible to build a fully redundant powertrain, with two hydrogen storage systems, and redundancy for the fuel cells, cooling, and power distribution. It also featured an electric motor that was completely redundant in three phases.