'MAP' SHIFT ON FMS CREATES A HDG TRACK DEV DURING THE CRI VOR RWY 13 L R APCH PROC.

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WE WERE BEING VECTORED FOR THE 'CANARSIE APCH' (VOR RWY 13L/R) AT JFK. APCH CTL HAD GIVEN US A HDG OF 010 DEGS TO INTERCEPT THE APCH RADIAL BTWN THE ASALT INTXN AND THE FAF (CRI VOR). THE PNF INFORMED APCH CTL (AFTER WE ROLLED OUT ON HDG 010 DEGS) THAT OUR HDG OF 010 DEGS WAS TOO E AND THAT IT LOOKED LIKE THAT HDG WOULD TAKE US ALMOST DIRECT TO THE CRI VOR. APCH CTLR THEN CLRED US DIRECT TO THE CRI VOR AT 1500 FT; AND CLRED US FOR THE APCH. ON OUR COCKPIT 'NAV' DISPLAY; THE CRI VOR WAS AT 12 O'CLOCK (STRAIGHT AHEAD); ABOUT 5 MI. THE PNF INDICATED TO ME SHORTLY THEREAFTER THAT THE USUAL VISUAL REF POINTS JUST BELOW US WERE NOT WHAT THEY SHOULD BE. I CHKED MY RMI NEEDLES (WE BOTH HAD THE CRI VOR TUNED AND IDENTED) AND SAW THEM SWINGING OFF TO THE R; ABOUT 2.5 DME. I RECHKED MY 'NAV' (FMS) DISPLAY; AND IT WAS NO LONGER AT 12 O'CLOCK; BUT NOW WAS OFF TO THE R (SEE NOTE). IT HAD BEEN AT 12 O'CLOCK; 5 MI; ONLY 4-5 SECONDS PRIOR TO THAT. WE INITIATED A R TURN AND I IMMEDIATELY SWITCHED TO 'RAW DATA' TO COMPLETE THE APCH. AT ABOUT THE SAME TIME; THE APCH CTLR GAVE US AN E CORRECTION VECTOR. WE SAW THE ARPT AND THE APCH LEAD-IN LIGHTS AT THIS TIME AND REQUESTED A VISUAL APCH TO RWY 13L; AND WERE CLRED TO DO SO. FMS 'NAV' DISPLAY 'MAP SHIFTS' AT THIS POINT IN AN APCH CAN ONLY BE COUNTERED BY HAVING 1 CREWMEMBER ON 'RAW DATA' PRIOR TO THE COMMENCEMENT OF AN APCH; WHICH OF COURSE; TAKES PRIORITY. BUT WHEN VECTORS ARE CHANGED CLOSE TO THE FAF; MORE THAN THE NORMAL XCHK MUST BE ACCOMPLISHED BY THE PLT WHO HAS TO QUICKLY GO FROM FMS INFO TO RAW DATA INFO; DECIPHER; SWITCH DISPLAYS; FLAG THE APCH; CONFIGURE; DSND TO MDA; ETC. PERHAPS 'MAP SHIFTS' (SUBTLE AS THEY ARE) COULD BE INCLUDED IN RECURRENT TRAINING DURING APCH (ESPECIALLY NON-PRECISION) PRACTICE. THE 'CAUSE OF CONFUSION' MAY HAVE VERY WELL HAVE BEEN A CONTRIBUTOR TO THIS SIT. NOTE: THE MAP SHIFT OCCURRED WHEN; AFTER HAVING BEEN CLRED DIRECT TO THE CRI VOR; THE PNF ENTERED 'DIRECT TO' CRI ON HIS FMS CDU JUST AS WE WERE APCHING THE VOR OVERHEAD.