VFR PA28 TURNING BASE TO FINAL AND FOLLOWING ANOTHER ACFT SPOTTED A TWIN ACFT IN CLOSE PROX AND DSNDED AND TURNED TO AVOID THE TWIN ACFT. RPTR ALLEGES THE TWR LCL CTLR LOST THE SITUATIONAL AWARENESS OF HIS TFC.

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I WAS RECEIVING A LCL CHKOUT FROM CFI IN A PA28-161. WE WERE TOLD TO ENTER A R DOWNWIND FOR RWY 30R AT GATEWAY ARPT BY THE TWR AND TO FOLLOW AN SMA AHEAD OF US. WE GOT A VISUAL ON THE SMA AND TURNED BASE JUST AS HE TURNED FINAL. WE WERE THEN INSTRUCTED TO FOLLOW THE SMA AGAIN BY TWR. AFTER I WAS ESTABLISHED ON BASE; I LOOKED L TO CLR THE FINAL. THE CFI AND I BOTH SAW 1 ACFT LOW AND L; OBVIOUSLY GOING TO EITHER RWY 30C OR 30L. A FEW SECONDS LATER; I PICKED UP A LIGHT TWIN HIGH AND L. THE CFI SAID HE WAS GOING TO THE CTR. WE HAD NOT BEEN WARNED OF THIS TFC. A FEW SECONDS LATER WE REALIZED THE SMT Y WAS ON FINAL TO THE R AND THAT THERE WOULD BE A CONFLICT. FORTUNATELY; THE SMT Y PICKED US UP AND BEGAN A GAR. WE CONTINUED A DSNDING R TURN. I DID NOT SEE THE EXACT MISS DISTANCE; BUT ESTIMATE WE PASSED 100 FT BELOW THE SMT Y TWIN. THE RESULT WAS EVERYONE BROKE OUT OF THE PATTERN AND TWR HAD TO SORT US OUT ONE BY ONE. IT WAS THEN THAT I REALIZED TWR HAD LOST SITUATIONAL AWARENESS WITH RESPECT TO THE SMT Y. WHY? SIMPLY PUT; I FEEL THE SMT Y WAS FLYING AN EXTREMELY WIDE PATTERN; 2-3 MI FINAL. IN DOING SO; HE PUT HIMSELF OUTSIDE THE VISUAL SCAN OF THE TWR AND OTHER ACFT IN THE PATTERN. I DON'T USUALLY LIKE TO CRITICIZE ATC; BUT I FELT THAT THE CTLR WAS NOT VERY DIRECTIVE IN HELPING US SORT OUT THE SIT. WE WERE BASICALLY ON OUR OWN FOR ABOUT 30 SECONDS. I DON'T HAVE ENOUGH KNOWLEDGE OF HOW IT LOOKED FROM THE OTHER COCKPITS OR THE TWR TO COMMENT FURTHER.