MD80 CREW LOST COM WITH ATL TRACON.

Narrative

FLT X WAS THE LAST LEG OF A 4 DAY ROTATION. FLT TIME THAT DAY WAS 7 HRS 48 MINS. WE WERE FLYING THE MACEY ARR INTO ATL. ATL WAS USING VISUAL APCHS TO RWY 26R. ATC HAD CLRED US TO CROSS WOMAC AT 13000 FT AND 250 KTS. DURING OUR DSCNT; WE CONTACTED APCH CTL ON 126.9. AFTER PASSING WOMAC; APCH CLRED US TO 10000 FT. DURING THE DSCNT TO 10000 FT; WE COMPLETED THE APCH CHKLIST DOWN TO THE FINAL ITEMS. APPROX 20 MI FROM THE ARPT; WE COMPLETED THE FINAL ITEMS ON THE APCH CHKLIST. SINCE THE WX WAS CLR; I NOTICED WE PASSED A POINT ON THE GND WHERE WE USUALLY TURN FOR VISUAL APCHS. I LOOKED DOWN AT THE COM PANEL AND FOUND THE FREQ WAS 126.92. WE IMMEDIATELY RETURNED TO 126.9. APCH CTL HAD BEEN LOOKING FOR US AND GAVE US VECTORS TO REJOIN THE TFC PATTERN. NEITHER THE FO NOR I CAN REMEMBER HAVING OUR HANDS CLOSE TO THE COM PANEL AFTER ITS ORIGINAL SETTING OF 126.9. I AM UNSURE HOW LONG WE WERE OFF THE APCH FREQ. THERE WERE ENOUGH RADIO XMISSIONS ON 126.92 -- PERHAPS BLEED THROUGH OR JUST PROPAGATION FROM OTHER AREAS; THAT WE WEREN'T AWARE OF THE FREQ CHANGE. WHILE WE COMPLETED CHKLIST ITEMS; WE PROBABLY 'TUNED OUT' THE RADIO -- ONLY LISTENING FOR OUR CALL SIGN. I ALSO FEEL FATIGUE MAY HAVE CAUSED US TO NOT HAVE BEEN AS SITUATIONALLY AWARE AS WE NEEDED TO BE.