ACR LANDS JUST AS AN SMA LIFTS OFF RESULTING IN LTSS BTWN THE 2 ACFTS.

Narrative

I WAS WORKING LCL CTL. 2 ACFT WERE TOLD TO TAXI INTO POS ON RWY 29. AN SMA AT MIDFIELD; THEN SMA X AT THE END. ACR Y WAS ON 3 MI FINAL; TFC ROLLING OUT ON THE RWY. I CLRED THE SMA FOR TKOF; R TURN HDG 330; THEN CLRED SMA X FOR AN IMMEDIATE TKOF RWY HDG. SMA X WAS JUST ON THE EDGE OF THE RWY WHEN CLRED AND ACR Y ON 1 1/2 MI FINAL. AS HE (SMA X) LIFTED OFF; I ISSUED A R TURN HDG 320 'AS SOON AS PRACTICAL.' ACR Y WAS LNDG AS SMA X TOOK OFF; AND WOULD HAVE PASSED DIRECTLY UNDERNEATH ON THE RWY IF SMA X HAD NOT STARTED THE TURN IMMEDIATELY. ACR Y CAPT CALLED THE TWR AFTER LNDG AND SAID HE HAD NOT SEEN SMA X ROLLING; ONLY THE SMA. BUT HIS COPLT HAD. HE WAS CONCERNED ABOUT WHAT HE WOULD HAVE DONE ON A GAR OR IF SMA X HAD ABORTED. I HAVE BEEN WORKING MOSTLY IN THE TRACON RECENTLY IN TRAINING FOR CHKOUT; AND WORKING TWR AFTERWARDS FOR SEASONING; AND HAVE NOT BEEN VERY BUSY ON LCL WHEN I HAVE WORKED. I WAS NOT PAYING ENOUGH ATTN TO SMA X POS; OR ACR Y'S SPD ON FINAL. I SHOULD HAVE GOTTEN SMA X OFF THE RWY; OR SENT ACR Y AROUND; EARLIER ON. ONCE ACR Y WAS ON SHORT FINAL AND SMA X WAS ROLLING; I FELT IT WOULD BE SAFER FOR ACR Y TO LAND RATHER THAN TO ATTEMPT A GAR GIVEN THE ACFT'S POS. ALTHOUGH MY DECISIONS WERE AT FAULT; I THINK THAT THE PLT AND COPLT SHOULD HAVE COMMUNICATED BETTER AS TO THE TFC EACH SAW; AND IF THE COPLT WAS IN DOUBT AS TO THE SAFETY REF SMA X; HE HAS THE RESPONSIBILITY AND AUTHORITY TO TAKE THE PLANE AND EXECUTE A GAR. I PLAN TO ASK FOR MORE EVEN ASSIGNMENTS OF TWR; TRACON TIME; AND TO BE VERY CAREFUL TO RUN MY TFC SAFELY AND ORDERLY BEFORE EXPEDITIOUSLY.