Business Green: The US Air Force’s green credentials really took off last week after it completed a successful test flight of a military aircraft using a 50:50 blend of biofuel and conventional jet fuel. The 90-minute flight in an A-10C Thunderbolt II out of Eglin Air Force Base in Florida marked the first time that any aircraft has been powered using a biofuel blend in all engines. Up to now test flights undertaken by commercial operators have tended to run only one or two engines using …