FAILED TO DISENGAGE OMEGA FROM HSI RESULTING IN FAILURE TO MAINTAIN ASSIGNED HEADING.

Narrative

I WAS NOTIFIED TO COME TO WORK ON MY DAY OFF. CALLED AT XA00 PM WAKE UP AT YF15 AM TO BEGIN WORK DAY THAT WAS 8 + 15 AT THE TIME OF THE INCIDENT AND WE HAD ALL COMMENTED ON HOW GLAD WE WOULD BE TO GET TO THE HOTEL TO SLEEP. I WAS FLYING. I WAS THE CAPT. I WAS ABOUT 165 NM NE MSY (NEW ORLEANS) VORTAC AT FL290. MY CLRNC WAS OMEGA DIRECT TO MSY VORTAC. THE OMEGA WAS COUPLED TO THE AUTOPLT. WE WERE MONITORING OUR POS WITH VOR DME. HOUSTON CENTER GAVE US A HDG MORE TOWARD THE WEST. I DISCONNECTED OMEGA FROM AUTOPLT AND TURNED TO THE ASSIGNED HDG. I STARTED LISTENING TO THE MSY ARR ATIS. I WAS THEN CLRED TO ANOTHER HDG TO INTERCEPT A RADIAL OF MSY VOR AND FLY INBND. I SET THE INBND COURSE IN THE JOINT USE COURSE DEVIATION INDICATOR. EVERYTHING LOOKED NORMAL CROSS CHKED THE VOR NEEDLES AND WENT BACK TO THE MSY ATIS. FINISHED ATIS AND THE COURSE BAR WAS MOVING SO I STARTED TURN TO INTERCEPT. AFTER COURSE WAS CENTERED IT STARTED TO MOVE ERRATICALLY. TURNED BACK TO REINTERCEPT. THOUGHT WE HAD LARGE WIND SHIFT. THERE WAS A HIGH VELOCITY WIND BLOWING. WE MOVED AWAY FROM COURSE BAR SO I TURNED BACK TO ORIGINAL INTERCEPT HDG. ABOUT THEN CENTER NOTICED OUR EARLIER TURN TO THE SE AND QUESTIONED US. THEY ALSO GAVE US A NEW ASSIGNED HDG. I TOLD THEM I THOUGHT MSY VOR WAS NOT WORKING PROPERLY AND WHILE SORTING OUT THE MESS I DISCOVERED I HAD NOT DISENGAGED THE OMEGA FROM THE JOINT USE COURSE DEVIATION INDICATOR. I HAD BEEN CHASING THE OMEGA DESIRED TRACK. THE OMEGA ENGAGED ANNUNCIATOR LIGHT IS NOT IN VIEW OF THE CAPT AS IT IS HIDDEN BY THE GLARE SHIELD. A TIRED CREW. A LOGICAL LOOKING SITUATION SLOWLY CHANGING A LONG DAY. POORLY DESIGNED NAV INTERFACE. A HIDDEN ANNUNCIATOR LIGHT ALL ADDED UP TO A NAV EXCURSION.