I cannot speak to anything at Osan after April of 1978. But I was there from April of the previous year until that time. I believe the 19th TASS had nothing but OV-10's back then, and the 36th TFS was flying F-4E's. The A-10's and the F-15's came over for "static display" during the late spring / early summer of 1977. Right after one of them (...and I can't remember which) went down at the Paris airshow.