B727 CREW ON FINAL TO MDW INITIATED A GAR DUE TO ACFT IN POS.

Narrative

I WAS WORKING WITH 1 OTHER CTLR WHO LEFT THE CAB. ALL POS WERE COMBINED AND I WAS SIGNED ON AS CIC BECAUSE I WAS THE ONLY ONE IN THE TWR AT THAT TIME. I WAS BUSY SEPARATING TFC ON THE GND; ATTENDING TO PAPERWORK THAT IS COMPLETED ON THIS SHIFT. I HAVE NOT BEEN TRAINED ON HOW TO DO THIS TASK. COORDINATING WITH CHICAGO APCH CTL WHEN ACR X INITIATED A GAR BECAUSE THERE WAS AN ACFT ON THE RWY. I KNEW A SIT WAS ARISING AND NEEDED ATTN AND ACTION NEEDED TO BE TAKEN. I WAS AWARE OF THE ACFT HOLDING IN POS AND AWARE OF THE ACFT ON FINAL APCH FOR RWY 4 AND KNEW EVASIVE ACTION NEEDED TO BE TAKEN TO PREVENT LOSS OF SEPARATION. I WAS DISTR WITH DUTIES OF LOW PRIORITY AND FELT AT THE TIME WHEN THE PLT INITIATED THE GAR THERE WAS STILL ENOUGH TIME FOR ME TO ISSUE THE CLRNC; AND I WAS ABOUT TO DO SO; BUT THE PLT BEAT ME TO IT. IT IS A STANDARD PRACTICE AT MDW TO DEPART AN ACFT IN A 3 MI GAP. WE ARE TRAINED TO DO THIS. WE ALLOW MINIMUM SPACING FOR GARS DUE TO THE SHORT RWYS. IT IS NOT UNUSUAL TO SEND AN ACFT AROUND AT THE LAST POSSIBLE SECOND BEFORE SEPARATION LOSS OCCURS. FROM WHAT I SAW; THE ACFT WAS WELL ABOVE THE TWR AND HAD AMPLE LATERAL SEPARATION TO EXECUTE A GAR. AN ACFT-INITIATED GAR OR CTLR-INITIATED GAR IS A COMMON OCCURRENCE AT MDW.