'Flight of the Silver Eagle' is a science-fiction novel by Arthur Leo Zagat. Against a sky glorious with flung streamers of scarlet and purple, New York's leaping towers and arching aerial streetways traced a prismatic arabesque epitomizing the wonder and the beauty of the Twenty-first Century. But Don Atkins, his lithe, compact body poised on big-thewed legs widespread and firmly planted, was as oblivious to that far-off glory as to the bustle of the Federal Skyport all about him.