AN SMA PLT REQUEST DENIED FOR A FREQ CHANGE UPON COMPLETION OF HIS IFR APCH IN VMC.

Narrative

I WAS FLYING A PRACTICE INST APCH TO THE ILS RWY 19 AT PWT ON AN IFR FLT PLAN WITH A SAFETY PLT. I WAS VECTORED TO FOLLOW AN APACHE FOR THE SAME APCH. WHEN I RECEIVED MY APCH; I WAS INSTRUCTED TO STAY ON THE CTLR'S FREQ AND NOT CHANGE TO CTAF AT CHECO (FAF). SINCE WE COULD SEE TFC IN THE PATTERN AT PWT; THIS DID NOT SEEM LIKE A GOOD IDEA. I ASKED FOR A FREQ CHANGE AT CHECO; BUT IT WAS REFUSED. I ASKED AGAIN ABOUT 30 SECONDS LATER AND WAS AGAIN REFUSED. THE APACHE RPTED MISSED AND THE CTLR USED ANOTHER 30 SECONDS GIVING THE APACHE A LENGTHY CLRNC. BY THIS TIME WE HAD AN AIRPLANE ON BASE TO FINAL; AND I AGAIN REQUESTED A FREQ CHANGE AND GOT IT. I THINK THIS CTLR SHOULD NOT HAVE KEPT US ON HIS FREQ INSIDE OF CHECO. WE COULD EASILY HAVE MAINTAINED VISUAL SEPARATION WITH THE APACHE AND CHANGED TO ADVISORY FREQ AND SELF ANNOUNCED TO THE TFC IN THE PATTERN. I SHOULD HAVE SUGGESTED THIS. WHEN I RPTED MISSED APCH; THE CTLR CALLED TFC FOR US THAT WAS IN THE PATTERN; I RESPONDED THAT THERE WAS A LOT OF TFC DOWN HERE.