AN SF340 CAPT ADMITTED NOT HAVING PERMISSION TO LAND AT DFW.

Narrative

I WAS THE PNF AND OPERATING THE RADIOS. REGIONAL APCH CLRED US FOR THE VISUAL APCH TO RWY 18 AT DFW FROM APPROX 5 MI. APCH REFERENCED OUR ONLY TFC TO FOLLOW ON 1/2 MI FINAL AND INSTRUCTED US TO CONTACT TWR ON 124.15. AS I DIALED IN 124.15 INTO THE RADIO STANDBY POS; THE FO CALLED FOR THE GEAR DOWN AND I FORGOT TO FLIP THE RADIO TO THE ACTIVE POS. WE COMPLETED OUR CHKLISTS AND CONDUCTED THE APCH AND LNDG AS NORMAL. UPON CLRING THE RWY; AFTER LNDG; APCH CTL QUERIED US ON APCH FREQ. AT THIS TIME BOTH THE FO AND MYSELF REALIZED WE WERE STILL ON APCH CTL FREQ AND HAD NEVER CONTACTED TWR. WE; THEREFORE; NEVER RECEIVED A LNDG CLRNC. WE CONTACTED GND CTL AND WERE CLRED TO TAXI NORMALLY WITH NO COMMENTS OR CONCERNS BY THE CTLR. ALTHOUGH I HAVE BEEN MULTITASKED COUNTLESS TIMES BEFORE; I BELIEVE THE FLOW OF SWITCHING TO; AND CONTACTING; TWR MAY HAVE BEEN INTERRUPTED BY THE PROCS THAT ARE INITIATED WHEN THE PF CALLS FOR GEAR DOWN. ALTHOUGH NOT ASSOCIATED WITH MY FLOW BEING BROKEN; I DID BREAK MY HABIT OF RECONFIRMING THAT MY TAXI LIGHT WAS ON TO INDICATE WE WERE CLRED TO LAND. ADDITIONALLY; ATC DID NOT CONDUCT A SUCCESSFUL RADIO SEARCH FOR US UNTIL ENOUGH TIME HAD ELAPSED THAT WE WERE ALREADY ON THE GND.