CTLR CLRED A DC9 INTO POS AND HOLD THEN CLRED A SF34 TO LAND ON THE SAME RWY. THE CTLR INTENDED TO CLR THE DC9 FOR TKOF WHEN THE RWY WAS CLR; BUT BECAME DISTRACTED BY THE GND CTLR AND TFC LEAVING THE RWY. A GAR WAS ISSUED WHEN THE CTLR OBSERVED THE SF34 ON SHORT FINAL AND ISSUED ALTERNATE INSTRUCTIONS. THE SF34 FLEW OVER THE DC9 IN POS.

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I WAS WORKING LCL CTL IN MIAMI TWR. WE HAD JUST COMBINED THE LCL CTL POS; AFTER A VERY HECTIC ARR AND DEP PUSH COMBINED. ACR X; AN SF34; WAS ON FINAL FOR RWY 9R BUT WAS FOLLOWING TFC FAIRLY CLOSELY AND I WAS CONCERNED ABOUT A NEED FOR A GAR AS A RESULT. I HAD NO ONE INBOUND TO RWY 9L; SO I OFFERED ACR X LNDG ON RWY 9L; WHICH HE ACCEPTED. I CLRED ACR Y INTO POS AND HOLD ON RWY 9L; WAITING FOR TFC TO CLR DOWNFIELD. I BELIEVE I EXCHANGED TFC; BUT I'M NOT POSITIVE. EVEN THOUGH THE TWR TFC HAD SUBSIDED DRAMATICALLY; GND CTL WAS HAVING A TOUGH TIME DUE TO REPOSITIONING ACFT AND A FOREIGN ACR WHO PULLED INTO THE WRONG GATE; THEN PUSHED OR POWERED BACK ONTO THE TXWY WITHOUT CLRNC AND ENDED UP NOSE TO NOSE WITH INCOMING TFC. THE GND CTLR WAS BECOMING SOMEWHAT UPSET BY HIS SIT AND WAS EXPRESSING HIS FRUSTRATION FAIRLY LOUDLY; WHICH WAS DISTRACTING. I CLRED 2 ACR AIRLINES ARRS TO CROSS RWY 12; AND AS THE FIRST ONE ENTERED THE RWY HE INFORMED ME HIS GATE WAS OCCUPIED. I ASKED THE SECOND ONE ABOUT HIS; AND IT; TOO; WAS OCCUPIED. I THEN GAVE THEM BOTH ALTERNATE INSTRUCTIONS; SO AS NOT TO COMPOUND THE GND CTLR'S PROBS. I THEN DIRECTED MY ATTN BACK TO RWY 9L AND NOTICED THAT ACR X WAS ALREADY ON SHORT FINAL TO RWY 9L WITH ACR Y STILL IN POS ON THE RWY. I QUICKLY SCANNED RWY 12 TO SEE IF THE JET HAD CLRED YET (HE HADN'T) SO I COULD OFFER RWY 12 TO ACR X. ABOUT THIS TIME ACR X ASKED IF THERE WAS SOMEONE ON THE RWY. I ANSWERED AFFIRMATIVE AND INSTRUCTED HIM TO GAR. INSTEAD OF TURNING TO THE 060 DEG HDG I GAVE HIM; HE OVERFLEW ACR Y AND WAITED UNTIL THE OTHER END OF THE RWY TO TURN. THIS COULD HAVE BEEN VERY BAD IF I HADN'T TURNED TO SEE IT WHEN I DID AND ACR X ALSO DIDN'T SEE IT. THE #1 CAUSE; WAS MY ALLOWING MYSELF TO GET DISTRACTED BY GND CTL'S PROBS AND DIVERTING TOO MUCH ATTN TO TRYING TO HELP HIM. CONTRIBUTING WAS THE GND CTLR ALLOWING HIS FRUSTRATION TO BE DISPLAYED SO LOUDLY. ALSO CONTRIBUTING WAS ACR's ROUTINE HABIT OF SCHEDULING THEIR FLTS IN SUCH A MANNER THAT THEY DON'T HAVE AVAILABLE GATES FOR ARRS; TYING UP TXWYS WHILE THEY WAIT; THEREBY COMPOUNDING CTLR WORKLOAD. SUPPLEMENTAL INFO FROM ACN 357619: ACR Y WAS CLRED INTO POS RWY 9L AT MIA. ACR X AS CLRED TO LAND ON RWY 9L AT MIA. ACR X WAS NOT ADVISED OF ACFT IN POS. MIA TWR STARTED TALKING TO ANOTHER ACFT ABOUT A GATE PROB. ACR X ASKED MIA TWR IF AN ACFT WAS ON THE RWY. MIA TWR REPLY WAS 'ACR X GAR.' IT APPEARS THAT MIA TWR DID NOT FOLLOW ESTABLISHED PROCS FOR ACFT IN POS AT NIGHT WITH AN ACFT ON FINAL. TWR ALSO STARTED WORKING A GND CTL PROB AND FORGOT ABOUT US. GOOD VISUAL PICKUP BY ACR X PREVENTED ACCIDENT.