TKOF DELAYED WHEN ACR FO INADVERTENTLY SWITCHED RADIO FREQ TO DEP CTL WHILE IN HOLDING POS ON THE RWY IN A NIGHT OP.

Narrative

AFTER DEALING WITH A MAINT PROB PRIOR TO LEAVING THE GATE; WE WERE TAXIING FOR DEP. WE COMPLETED ALL CHKLIST ITEMS AND THE FO WAS COMPLETING LAST MIN FLOW ITEMS WHICH INCLUDED SETTING DEP CTL FREQ ON 1 HEAD OF THE COM #1 RADIO. THE TWR INSTRUCTED US TO 'TAXI INTO POS AND HOLD AWAITING WAKE TURB SEPARATION BEHIND A HVY JET.' THE FO ACKNOWLEDGED 'POS AND HOLD;' AND THEN EITHER BUMPED OR UNWITTINGLY SWITCHED THE RADIO TO THE DEP FREQ AS HE INSTRUCTED THE FLT ATTENDANTS TO BE SEATED. THE NEXT 30 SECONDS TO 1 MIN OF SILENCE DID NOT SEEM UNUSUAL AS WE EXPECTED A DELAY IN POS. WHEN WE HEARD AN ACFT ADDRESS HIS XMISSION TO DEP CTL WE IMMEDIATELY CORRECTED THE MISTAKE. THE TWR ADVISED HE HAD TRIED TO CONTACT US A NUMBER OF TIMES; AND HAD TO ISSUE A GAR TO ANOTHER ACFT. EVERYONE INVOLVED CAN BE THANKFUL THAT THE CONSEQUENCES OF THIS COMS INTERRUPTION WERE NOT MORE SERIOUS. WE HAD BEEN ON DUTY FOR ABOUT 10 AND ONE HALF HRS AT THE TIME OF THIS INCIDENT; AND WERE ON THE LAST LEG OF THE DAY (1 HR 45 MINS SCHEDULED LEG). WE HAD DEALT WITH VARIOUS COMPLICATIONS THROUGHOUT THE DAY; AND WERE SOMEWHAT TIRED ALTHOUGH WE HAD BEEN PROVIDED ADEQUATE REST THE NIGHT BEFORE.