NON ADHERENCE TO ATC CLRNC DUE TO A RADIO EQUIP PROB.

Narrative

I WAS ACTING AS THE PF AND THE FO WAS HANDLING COMS WITH ATC. UNKNOWN TO ME; MY COM RECEIVER WAS INTERMITTENT DUE TO A FAULT IN MY AVIONICS CTL PANEL. AS A RESULT; I DID NOT HEAR AN OFF COURSE VECTOR THAT WAS ASSIGNED TO MY FLT BY ZTL. THE FO DID HEAR AND ACKNOWLEDGE THE CLRNC; BUT HE DID NOT NOTICE THAT I FAILED TO RESPOND BY INITIATING THE ASSIGNED HDG CHANGE. SINCE THE FO ASSUMED THAT I HEARD THE CLRNC; HE CONTINUED TO PERFORM OTHER PRELNDG FUNCTIONS (CALLING IN-RANGE; ETC). I DID NOT NOTICE THE FO HAD BEEN SPEAKING ON THE RADIO DUE TO COCKPIT NOISE AND THE FACT THAT WE USE HEADSET/MIKES INSTEAD OF HAND HELD MIKES. ATC SUBSEQUENTLY NOTED OUR FAILURE TO TURN AND ISSUED A NEW HDG AND ALT TO AVOID TFC. AT THAT POINT; IT BECAME OBVIOUS THAT I COULD NOT HEAR ATC; THE FO TOOK CTL OF THE ACFT AND COMPLIED WITH THE INSTRUCTIONS. A CONTRIBUTING FACTOR WAS THE HIGH WORKLOAD PRIOR TO LNDG THAT KEPT THE FO FROM CHALLENGING MY FAILURE TO COMPLY WITH THE ORIGINAL OFF-COURSE VECTOR. WHILE WE HAVE BECOME VERY CAREFUL ABOUT VERIFYING ALT CHANGES; WE DO NOT HANDLE LATERAL FLT PLAN MODIFICATIONS IN THE SAME MANNER. FORCING BOTH CREW MEMBERS TO VERIFY LATERAL AS WELL AS VERT CLRNCS WOULD IMMEDIATELY DETECT COM PROBS LIKE THE ONE I ENCOUNTERED.