CLRED VIA THE JASPA RNAV SID FROM RWY 18L; MD80 RECEIVES A CHANGE TO RWY 17R WHICH IS PROGRAMMED INTO THE FMS BUT NOT EXECUTED ON BOTH PLTS' DISPLAYS. TRACK DEV RESULTS.

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GROUND CLRED US TO TAXI TO RWY 18L; BRIDGE. FMS WAS SET UP FOR THE JASPA RNAV DEP; RWY 18L. APCHING TXWY Z; GND CHANGED OUR CLRNC TO; 'RWY 17R; TXWYS W; EG; CONTACT QUEUE ONCE YOUR RNAV IS SET UP.' CHANGED THE RNAV DEP AND RWY IN THE FMS USING COMPANY PROCS. CONTACTED QUEUE; READ RWY 17R FROM THE RTE PAGE; AND TREXX AS THE FIRST WAYPOINT ON THE LEGS PAGE. STARTED R ENG WITH ASSOCIATED ELECTRICAL POWER CHANGE. TKOF POSITION; EFIS DISPLAYED CORRECTLY WITH RWY 17R AND TREXX. AT 400 FT PREPARING TO ENGAGE NAV; EFIS DISPLAYED A MAGENTA LINE FROM RWY 18L TO TREXX; AND THE FLT DIRECTOR WAS COMMANDING A R TURN TO INTERCEPT THIS COURSE. A QUICK CHK OF THE PAPER SID WAS MADE TO CONFIRM THAT TREXX WAS THE CORRECT DEP FIX. WHEN RETURNING TO VIEW THE DEP ON THE EFIS; IT NOW SHOWED A MAGENTA LINE FROM RWY 18L TO LARNN; WITH A WHITE DOTTED LINE FROM RWY 17R TO TREXX. THE FO BEGAN A TURN TO THE L TO INTERCEPT THE CORRECT COURSE WHILE THE CAPT PRESSED THE ILLUMINATED 'EXECUTE' LIGHT. DEP THEN INSTRUCTED US TO MAKE A 15 DEG TURN L TURN. THE REST OF THE DEP WAS UNEVENTFUL WITH RADAR VECTORS TO JASPA.SUPPLEMENTAL INFO FROM ACN 639950: THIS AIRPLANE IS ONE OF THOSE THAT WITH THE #2 DFGC SELECTED AND PUSH OF NAV MY SIDE STAYS IN HDG SELECT UNLESS I GO FROM RAD TO NAV; SELECT NAV THEN GO BACK TO RAD. WHEN I SELECTED NAV ON DFGC; THE INFO DISPLAYED ON EFIS NAV DISPLAY SWITCHED BACK TO THE W SIDE DEP WHICH IS RWY 18L AND LARRN WITH A WHITE DOTTED LINE OFF OF RWY 17R TO TREXX. THE FO NOTICED THIS AND MADE A COMMENT ABOUT NAV; I SAW MYSELF IN HDG SELECT SO I TURNED MY HEAD TO SWITCH FROM RAD TO NAV; RE-ENGAGE NAV; AND GO BACK TO RAD. WHEN I FINISHED THAT'S WHEN I NOTICED THE EFIS DISPLAY BEING INCORRECT. THE FO WAS ALREADY WORKING TOWARDS THE PROPER GND TRACK THEN ATC INSTRUCTED US TO TURN L 15 DEGS. EVERYTHING WAS DISPLAYED CORRECTLY BEFORE GOING DOWN THE RWY. NO EXE LIGHT ILLUMINATED; PROPER RWY AND FIRST FIX. WHEN WE SELECTED NAV IT WENT BAD. I DON'T KNOW IF THE R ENG GENERATOR COMING ONLINE INTERRUPTED THE ACTUAL EXECUTE.CALLBACK CONVERSATION WITH RPTR ACN 693949 REVEALED THE FOLLOWING INFO: THE FO STATED THAT ON THE INITIAL PART OF THE TKOF; HIS NAV DISPLAY WAS SHOWING TREXX AND THE RWY 17R DEP TRACK BUT THE FLT DIRECTOR WAS COMMANDING A R TURN VICE THE ESSENTIALLY STRAIGHT AHEAD TRACK INDICATED BY THE ACTIVE RTE LINE. AFTER HE ATTEMPTED TO EVALUATE THIS CONTRADICTION WITH THE DEP PLATE HE CAME BACK TO THE NAV DISPLAY AND SAW THAT NOW THE RWY 18R TRACK WITH LARRN WAS THE ACTIVE RTE (SHOWN IN MAGENTA) AND THE RWY 17R TRACK NOW WAS SHOWN AS DASHED WHITE LINE INDICATIVE OF A SECONDARY; UN-EXECUTED RTE. IT IS LIKELY THAT THIS SWITCH WAS THE RESULT OF SOME MCDU INPUT FROM THE PNF ALTHOUGH THEY WERE UNABLE TO DETERMINE THAT WITH CERTITUDE. HE EXPANDED ON THE DIFFERENCES BETWEEN THIS ACFT AND THE MAJORITY OF THE ACR FLEET IN THAT A NAV/RAD (FMS NAVIGATION/RADIO NAVIGATION) SWITCH MUST BE PROPERLY SELECTED IN ORDER FOR RNAV FUNCTIONS TO DISPLAY ALTHOUGH THEY CAN; APPARENTLY; BE PROGRAMMED IN WHILE IN THE RAD MODE. RPTR SUGGESTED THAT SOME COMBINATION OF PROGRAMMING AND INAPPROPRIATE NAV/RAD SWITCH POSITION MIGHT WELL HAVE BEEN THE SOURCE OF THE PROBLEMS. HE ADVISED THAT THE ACR TRAINING CTR SUGGESTED THE USE OF THE 5 MILE RANGE FOR RNAV TKOFS TO ENSURE CLOSE TRACKING OF THE REQUIRED TRACK. HIS CONCERN WAS THAT DOING SO REMOVED THE INITIAL FIX (IN THIS CASE TREXX) FROM THE DISPLAY AND IT WAS THUS LESS OBVIOUS THAT THE COMMAND BAR INDICATIONS WERE ERRONEOUS.