Possible Clues:

• Old gas station symbol
• What flies may be driven home like us
• To keep the clothes on the line, as if flew with us
• Exceptional horse with a place in the firmament
• GP uses a novel treatment, producing fabulous horse
• Mount up evidence for origin of Greek myth
• Horse, say, needing to be kept in step's useless
• Steed in air
• Fabulous mount for the high-flying equestrian!
• Constellation between Cygnus and Pisces