RPTR ERROR ADMITTED IN B727 HDG TRACK POS DEV. MISSED TURN AFTER MOL VOR AND WAS IN NON ADHERENCE TO ATC CLRNC.

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I WAS FLYING USING THE AUTOPLT IN HDG MODE. WE WERE NOT USING THE OMEGA. AFTER XING MOL WE WERE CLRED J24 TO FAK; THEN DIRECT RIC. I'M NOT SURE WHAT HAPPENED; BUT I MISSED THE TURN FOR J24. CTR CALLED US WHEN HE SAW US N OF J24. I REALLY CANNOT TELL YOU EXACTLY WHY I MISSED THE TURN. I KNEW THAT I HAD JUST CROSSED MOL; BUT I THINK I WAS DISTR. WE WERE DISPATCHED WITH 1 PACK AT FL250; BUT ONLY COULD MAINTAIN 4 LBS PER SQUARE INCH DIFFERENTIAL SO WE HAD TO MAINTAIN 17000 FT. EVEN AT THAT ALT; WE WERE HAVING A HARD TIME KEEPING THE CABIN BELOW 5000 FT. WE CROSSED THE VOR. THE CABIN STARTED CLBING AGAIN; AND I HAD ALSO PICKED THAT TIME TO SET UP MY CHARTS FOR EWR. I WAS SO BUSY I WAS DISTR FROM THE MOST IMPORTANT PART -- FLY THE AIRPLANE. I THOUGHT I WAS KEEPING UP WITH THE RTE BUT I THINK I DIALED IN THE RIC VOR COURSE INSTEAD OF THE FAK COURSE. THE PRESSURIZATION PROB CREATED A NONSTANDARD OP; WHICH I KNOW IS A CRITICAL TIME. SOMEHOW I MISSED KEEPING UP. SUPPLEMENTAL INFO FROM ACN 358909: PASSING MOL; NOTICED THAT CABIN WAS CLBING AND ACARS WAS PRINTING A MESSAGE. SUPPLEMENTAL INFO FROM ACN 358908: THE CAPT PROCEEDED DIRECT TO RICHMOND INSTEAD OF J24 FAK AS WE WERE CLRED. THE CREW WAS STILL WORKING ON THE PRESSURIZATION PROB AND THE CAPT TRIED TO FLY AND WORK THE PROB AT THE SAME TIME. RESULT WAS NO ONE WATCHING THE STORE.