They call it an "arctic cap" here: But they call it a "Ski Hat Ear Flap Russian Trapper Aviator Cap" here: They call it a "Trapper Hat Army Russian Flying Aviator" here: And it's called a "Outdoor Cap Trapper Hat" here: So, it' anyone's guess if there's an official name for it. But the words "trapper" and "Flyer or Aviator" seem to come up a lot, as does "cap". When I did a Google search for the term "trapper aviator cap", I got good results: So that's probably your best bet.
