This thorough book written in japanese has english summaries of the text of each bird chapter. I cite the id tips the book give for flying adult birds of Accipiter.

One mark are the fingers at the wingtips

Northern Goshawk		6
European Sparrowhawk		6
Japanese Sparrowhawk		5
Chinese Sparrowhhawk		4

But that is probably only useful for photographers.

Northern Goshawk: wings and tail appear long, with head thrust forward. Tail is rounded or may show very slight wedge-shape.

European Sparrowhawk: tail appears long in proportion to wings. [On photos: wing is shorter than 2 x tail]. Dark bars on underwing flight feathers show a wider interval than those of NG and ES; while in contrast latertal bars on underwing coverst appear denser.

Japanese Sparrowhawk: wings appear long in proportion to total length. [On photos: wing is longer than 2 x tail]. 4-8 narrow lateral bands visible on flight feathers. numerous narrow wavy markings appear on underwing coverts. Black band on central tailfeathers.

Chinese Sparrowhhawk: wings appear long and narrow, with sharply pointed tips. In adult, wingtips are black, underwing-coverts pale-rufous, and rest of flight feathers without markings, or with only very fine bars on some or all feathers. No black band on tail feathers.

the Eurasian, Japanese and Chinese Sparrowhawks can be distinguished by their flight pattern. Being mush bigger birds, Eurasian Sparrowhawks have deeper wingbeats when migrating, while the other two are very shallow flappers.