FAILURE OF THE AA-1A PILOT TO SEE-AND-AVOID THE PIPER PA-28 WHICH HAD ENTERED TRAFFIC FIRST. A FACTOR RELATED TO THE ACCIDENT WAS: FAILURE OF THE PA-28 PILOT TO SEE THE AMERICAN AA-1A, WHEN THE AA-1A WAS ON A BASE LEG AND THE PA-28 WAS FURTHER OUT ON FINAL APPROACH.