Super-fast speed � think Tokyo to L.A. in 2 1/2 hours � isn't the only cool feature of the Zero Emission Hyper Sonic Transport proposed by EADS. At the Paris Air Show this week, the aircraft manufacturer and Airbus parent revealed its proposed passenger aircraft, which would be run on, among other sources, liquid hydrogen and biofuel. The aircraft, which EADS said could be standard by 2050, would cruise at Mach 4 speeds nearly 20 miles high � inside the Earth's atmosphere. Demonstration technologies could be ready by the end of this decade. Companies at the Paris show were buzzing about clean-fuel options. Airbus and Parker Aerospace said they would look into fuel-cell technology that converts hydrogen and oxygen into electricity and creates water as exhaust. The pair said that flight tests could happen by mid-decade. The Air Transport Assn. of America, the industry trade group, said a slew of member airlines signed letters of intent to partner with Solena Group. The company produces its GreenSky California fuel from biomass at a Santa Clara County facility.