It’s a big step towards zero-emission long-haul aviation, say its inventors. The aircraft, HY4, has completed 4 successful test flights fuelled by liquid hydrogen including one that lasted more than 3 hours. HY4 was developed by Stuttgart-based start-up H2FLY. Previously the plane was fuelled by gaseous hydrogen. However, using liquid hydrogen reduces the weight and size of its fuel tanks. The plane’s range has doubled as a result from 750km to 1,500km.