Black Flyers aren't that different from Black Walkers aside from the obvious loss of legs and ability to fly circles around anyone. These enemies are seen in the opening cutscene for Report 1, but aren't fought until "Report 2: Nature's Revenge!" They are later replaced by Silver Flyers.
"A Walker robot upgraded with flying capability in the form of a Reactive Force System (RFS). Six AAAAA batteries can power 1 robot for 320 days."