ACR B727 FLC PUSH BACK FROM PARKING WITHOUT TWR GND CTLR CLRNC AND BLOCK ANOTHER TAXIING ACFT.

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AS WE (ACFT X) PUSHED BACK FROM OUR RAMP AT RNO; WE HEARD ANOTHER ACFT (ACFT Y) ADVISE GND CTL THAT AN ACFT WAS BLOCKING HIS MOVEMENT ON THE TXWY. AFTER REALIZING OUR ACFT MIGHT BE THE ONE WHO WAS IN HIS WAY; WE CHKED OUR CHARTS TO FIND OUT THAT AN ATC CLRNC WAS REQUIRED PRIOR TO PUSHBACK FROM OUR GATE. WE APOLOGIZED TO THE CTLR FOR OUR OVERSIGHT TO CALL HIM AND RECEIVED A TAXI CLRNC TO RWY 16R. THE REMAINDER OF THE FLT WAS UNEVENTFUL. WHAT I BELIEVE CONTRIBUTED TO THIS ERROR OF NOT CONTACTING ATC FOR CLRNC; WAS THE FACT THAT WE WERE IN A HURRY AND NOT FOLLOWING SOP. THIS CAUSED US TO MISS REVIEWING SOME PERTINENT INFO ON THE CHARTS. ALSO; BEFORE WE PUSHED BACK; WE HAD JUST BRIEFED THE HIGHLY COMPLEX DEP PROC OUT OF THIS ARPT. ALL OF THESE FACTORS PUT TOGETHER CREATED AN ENVIRONMENT OF NOT FOLLOWING OUR SET HABIT PATTERNS IN ENSURING WE WERE PROPERLY BACKING EACH OTHER UP. TO PREVENT A RECURRENCE OF THIS ERROR; I BELIEVE CREWS SHOULD ALLOW THEMSELVES THE EXTRA TIME TO BRIEF HIGHLY COMPLEX PROCS AND TO ALWAYS FOLLOW SOP'S. THIS WILL ENSURE THAT CREWS ESTABLISH SET HABIT PATTERNS TO PREVENT ERRORS OF OMISSION AND ARE NOT RUSHED SO THEY CAN BACK EACH OTHER UP. SUPPLEMENTAL INFO FROM ACN 425593: AT THE COMPLETION OF THE PUSHBACK FROM THE GATE AT RNO; WE WERE IN POS TO TAXI N ON TXWY A FOR DEP ON RWY 16R. ALL WAS NORMAL EXCEPT THAT WE FORGOT TO GET GND CTL CLRNC TO PUSH BACK ONTO AN ACTIVE TXWY.