LGT PWRS BACK WITHOUT PROPER CLRNC; THEN HAS TXWY EXCURSION ON RTE TO RWY.

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I WAS SERVING AS FO FOR A SCHEDULED ACR OP FROM ATL TO MSP. OUR COMPANY PROCS PERMITTED PWRBACK OPS FROM OUR GATE. CLRNC FROM RAMP CTL PRIOR TO PWRBACK WAS REQUIRED. (THE RAMP AT ATL IS CTLED BY OP-X; NOT ATC.) (IT SHOULD BE NOTED THAT BOTH THE CAPT AND MYSELF HAVE MANY YRS AND THOUSANDS OF HRS OF TIME IN THE B727. HOWEVER; WE ONLY OPERATE TO ATL 3-5 TIMES PER YR; ON AVERAGE.) PRIOR TO ENG START; I CALLED RAMP CTL TO INFORM RAMP THAT WE WOULD BE STARTING ENGS. RAMP 'ROGERED' THE ADVISORY. AT THAT POINT I BELIEVED RAMP SAID; 'CALL WHEN READY TO TAXI.' I INTERPRETED THAT CLRNC AS APPROVAL TO PWRBACK (THE CAPT WAS NOT MONITORING THE FREQ). WE STARTED ALL ENGS AND COMMENCED THE PWRBACK. AS WE BEGAN TO MOVE; AN MD-80 NEXT TO US RECEIVED CLRNC TO PWRBACK. AT THAT POINT RAMP CTL SAW A CONFLICT. RAMP ASKED US IF WE WERE PWRING BACK. I RESPONDED IN THE AFFIRMATIVE AND THE MD-80 WAS TOLD TO STOP HIS PWRBACK. ONCE OUR PWRBACK WAS COMPLETE RAMP CLRED US TO TAXI TO THE N HOLD POINT. WE WERE STILL MONITORING RAMP FREQ WHEN RAMP CTL CLRED THE MD-80 TO PWRBACK. RAMP TOLD THE MD-80 THE REASON HIS PWRBACK CLRNC WAS CANCELED WAS BECAUSE OUR JET DIDN'T 'GET A CALL IN' PRIOR TO PWRING BACK. THIS CAUGHT US BY SURPRISE. A DISCUSSION ENSUED. I CALLED GND CTL AND RECEIVED CLRNC TO RWY 8R (N PARALLEL) VIA TXWY E (OUTER TXWY). BOTH THE CAPT AND MYSELF HAD ARPT DIAGRAMS CLIPPED TO OUR APCH PLATE HOLDERS. IN THE DIAGRAM IT IS EASY TO CONFUSE THE INNER TXWY (F) FOR TXWY E. THE CAPT TAXIED L ONTO TXWY F (INNER) AND WAS SUBSEQUENTLY CLRED BY GND TO JOIN TXWY E AT THE NEXT INTXN. I SCANNED THE DIAGRAM AGAIN AND REALIZED OUR ERROR. GND CTL NEVER QUERIED US. THESE 2 EVENTS; THOUGH SEPARATE; ARE STILL RELATED. THE BEDROCK ISSUES: BACKUP AND COM. PRIOR TO PWRBACK THE CAPT FAILED TO BACK ME UP ON RAMP FREQ. THIS RESULTED IN A COM BREAKDOWN BTWN MYSELF AND THE CTLR (NORMALLY THE CAPT AND SO MONITOR ALL COMS). ONCE THE PWRBACK ANOMALY WAS RECOGNIZED; I BECAME DISTRACTED; THUS DEGRADING MY BACKUP EFFECTIVENESS FOR GND TAXI. THIS SIT CLRLY ILLUSTRATES HOW 1 MISTAKE CAN LEAD TO ANOTHER. THAT'S WHEN WE'RE MOST VULNERABLE.