UNAUTH LNDG. THE FLC WERE DISTR BY THE AUTOPLT DISENGAGING AND FORGOT TO SWITCH TO TWR FREQ FOR LNDG.

Narrative

WE LANDED AT DFW ARPT WITH THE WRONG FREQ SELECTED ON THE RADIO. I WAS THE FO AND THE PF; THE CAPT WAS THE PNF. THE OVERSIGHT OCCURRED ON FINAL APCH AS WE CONFIGURED THE ACFT. THE APCH CTLR CLRED US FOR THE VISUAL APCH TO RWY 36L AND INSTRUCTED US TO MAINTAIN 170 KTS TO THE OM. THE FREQ WAS VERY CONGESTED; AS IT VIRTUALLY ALWAYS IS WHEN YOU FLY INTO DFW AND THE APCH CTLR SEEMED VERY BUSY. AT THE OM; WITH THE ACFT ALREADY CONFIGURED WITH 15 DEGS OF FLAPS; I CALLED FOR THE GEAR DOWN; 20 DEGS OF FLAPS AND THE LNDG CHKLIST. AS THE FLAPS EXTENDED TO 20 DEGS; THE AUTOPLT (I WAS FLYING A COUPLED APCH) DISENGAGED ITSELF. I IMMEDIATELY TOOK CTL OF THE ACFT AND CONTINUED THE APCH. THE DISENGAGEMENT OF THE AUTOPLT AND THE CLOSE PROX OF THE ACFT TO THE GND FOCUSED MY ATTN COMPLETELY TO THE TASK AT HAND -- TO LAND THE ACFT SAFELY. AFTER LNDG THE ACFT SAFELY; AND CLRING THE RWY; THE CAPT CALLED FOR THE AFTER LNDG CHKLIST; WHICH I PERFORMED. AFTER THE CHKLIST WAS COMPLETED I NOTICED THAT THE RADIO SEEMED VERY QUIET SO I LOOKED AND FOUND THAT THE APCH FREQ WAS SELECTED ON THE RADIO. THIS; OF COURSE; MEANT THAT THE TWR FREQ WAS NEVER SELECTED AFTER THE DISENGAGEMENT OF THE AUTOPLT. AS I LOOKED UP TO INFORM THE CAPT; HE HAD ALSO REALIZED THE OVERSIGHT. I IMMEDIATELY SELECTED THE APPROPRIATE FREQ AND CHKED IN WITH THE TWR. THE CTLR ISSUED THE TAXI CLRNC AND WE TAXIED TO THE RAMP. LOOKING BACK ON THE INCIDENT; AND AFTER DISCUSSING IT WITH THE CAPT; IT IS CLR THAT NEITHER MYSELF NOR THE CAPT HEARD THE APCH CTLR'S HDOF. IT WAS OUR RESPONSIBILITY TO QUESTION THE CTLR AND TO ENSURE THAT THE CORRECT FREQ WAS SELECTED. IN THIS INSTANCE; THE FACT THAT WE AS A CREW WERE CONCENTRATING ON THE PROB AT HAND RESULTED IN NARROWING OUR ATTN TO LNDG THE ACFT SAFELY AND CONTRIBUTED TO THE OVERSIGHT.