SMA X ATTEMPTED LNDG ON OCCUPIED RWY. ISSUED GAR; HAD NMAC WITH ACFT Y IN POS ON RWY. NMAC. PLTDEV.

Narrative

I WAS WORKING LCL CTL AT YAKIMA. I HAD RECEIVED A CALL FROM A SENECA X INBOUND FROM THE SW. THE SENECA WAS DIRECTED TO ENTER A L DOWNWIND FOR RWY 27 AND RPT THE DOWNWIND. SUBSEQUENTLY; I HAD A BONANZA ENTER THE TFC PATTERN FROM THE N AND LAND ON RWY 27; AND WAS ARRANGING FOR IFR CLRNCS FOR 3 ACFT TAXIING OUT. I HAD WORKED 1 IFR DEP OUT AND HAD A SECOND 'IN POS' ON RWY 27 AWAITING IFR RELEASE. I WENT TO LOOK TO THE SW FOR BINOCULARS TO FIND THE SENECA SINCE IT SEEMED TO ME THAT I SHOULD HAVE HAD A DOWNWIND RPT. AT THAT POINT; THE SENECA RADIOED THAT HE WOULD OVERFLY THE ACFT Y THAT WAS IN POS ON THE RWY. I IMMEDIATELY LOOKED TO THE END OF THE RWY AND SAW THAT THE SENECA WAS OVER THE LIGHT LANE. I ISSUED A GAR TO THE SENECA; WHICH HE EXECUTED AND ENTERED L TFC FOR RWY 4. IT'S IMPORTANT TO NOTE THAT; AFTER THE INITIAL CONTACT BY THE SENECA; HE RPTED THAT HE WOULD ACTUALLY BE LOOKING FOR A STOP AND GO BECAUSE HE HAD A LOOSE DOOR LATCH. I'M NOT SURE IF THE DISTR CAUSED THE PLT OF THE SENECA TO FORGET TO CALL THE DOWNWIND RPT. PERHAPS IF I HAD NOT BEEN BUSY WITH GND CTL AND CLRNC DELIVERY DUTIES I WOULD HAVE NOTICED THE ACFT SOONER. TWR CTLRS AT LOWER VOLUME FACILITIES RELY HEAVILY ON PLT RPTS FOR TFC SEQUENCING. FAILURE TO MAKE THESE RPTS CAN RESULT IN SERIOUS DEGRADATION OF SAFETY.