THE FLC DISABLED THEIR LNAV WHEN THEY ERRONEOUSLY THOUGHT THE PROGRAMMED TURN WAS SUPPOSED TO BE FARTHER AWAY. THE CREW THEREFORE WAS LATE IN TURNING ALONG THEIR COURSE.

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FLT X; A DC10-30 FROM IAD TO BOS FIELD VIA SWANN INTXN; BROSS INTXN; J42. FO FLYING; I WAS PNF. AFTER HDOF FROM IAD DEP CTL; CTR CLRED US DIRECT TO SWANN INTXN - FPR. INS WAS USED TO PROCEED DIRECT. AS BACKUP I USED VOR TO IDENT SWANN AND BROSS. SHORTLY THEREAFTER THE ACFT STARTED WHAT I THOUGHT WAS A PREMATURE TURN NBOUND ONTO J42. I ADVISED THE FO TO GO TO HDG SELECT UNTIL WE FIGURED OUT THE PROB. BY THE TIME WE DECIDED THE MACHINE WAS CORRECT IN TURNING; WE OVERFLEW J42. ZDC INQUIRED WHY WE DID NOT TURN ONTO J42. I ESTIMATE WE WERE 9 MI FROM THE CTRLINE OF J42. THERE WAS NO APPARENT LOSS OF SEPARATION; AND WE WERE CLRED DIRECT RBU VOR FPR. A CONTRIBUTING FACTOR MAY HAVE BEEN THE FACT THIS FLT HAD BEEN RERTED IN THE AIR. ORIGINALLY MEM-FLL-MEM; APPROX TLH VOR SBOUND; WE WERE ASKED TO PROCEED TO BOS. UNABLE TO MAKE BOS BECAUSE OF WX AND FUEL; I ELECTED TO STOP IN IAD AND THEN CONTINUE TO BOS. FROM THE RERTE POINT THE CREW WAS VERY BUSY WITH RERTE PAPERWORK; WX AVOIDANCE AND BRIEFING PROCS INTO IAD. I FEEL WE ALLOWED OURSELVES TO BE RUSHED TO MAKE SCHEDULE.