Russian cargo airline Volga-Dnepr Group has signed a memorandum of understanding to buy and lease a total of 20 more Boeing (BA.N) 747-freighters in what would be a major boost for the U.S. planemaker’s struggling four-engined jumbo. Both Boeing and European rival Airbus (AIR.PA) have seen orders for their biggest planes dry up as customers opt for improved twin-engined jets that can fly almost as far. At Boeing, that has put a question mark over production of the 747, with analysts warning the company could face a $1 billion accounting charge if the program was shut down.