SMA X LANDED ON OCCUPIED RWY WITH SMA Y IN POS CLRED FOR TKOF. LTSS. NMAC. SYS ERROR. PLTDEV.

Narrative

THIS SITUATION HAPPENED WHILE WORKING LCL CTL IN A VFR TWR. -- A LOSS OF SEPARATION WITH 2 ACFT AT A RWY INTXN. SMA X ILS RWY 8; WAS INSTRUCTED TO COME OVERHEAD FOR L TFC RWY 13. WHILE SMA X CAME UP OVER RWY 8; AN SMT WAS PUT INTO POS AND HOLD RWY 8; AS SMA X STARTED HIS L TURN OVER THE TWR ROOF FOR RWY 13. I CLRED THE SMT FOR TKOF AND PUT AN SMA Y INTO POS AND HOLD RWY 8. IT'S ABOUT 500 FT TO THE RWY 8/13 INTXN. AS THE SMT LIFTED OFF AND APCHED THE DISTANCE NEEDED FOR RWY SEPARATION; I CHKED RWY 13 FINAL APCH FOR SMA X; DID NOT SEE HIM; SO I CLRED SMA Y FOR TKOF. WENT BACK TO LOOK FOR SMA X ON BASE LEG; THEN FINAL; THEN I LOOKED BACK AT SMA Y ON RWY 8 AND SAW SMA X OVERFLYING SMA Y; THEN LANDED. I SHOULD HAVE FOUND SMA X IN MY SCAN BEFORE I CLRED SMA Y FOR TKOF. FROM MY POS IN THE CAB; SMA X COULD HAVE BEEN BEHIND A SUPPORT POLE TO THE ROOF; POSSIBLY SHORT FINAL. SMA X MADE A VERY SHORT APCH WHICH WAS UNEXPECTED AND I WAS LOOKING FOR HIM FURTHER OUT ON HIS CIRCLING APCH; INSTEAD OF OVER THE RWY.