 The engine has an overall thermal efficiency of 37 percent.On December 23, 2005, Antonov announced that the An-70-100 was awarded a noise certificate stating that the D-27-powered aircraft met Stage 3 noise regulations, which permitted international airlines to fly the aircraft unrestricted.In response to the US Stage 4 civil noise regulations adopted in 2006, the engine was modified in 2007 to reduce noise by increasing the separation between the front and back propellers.