HEADING TRACK DEV BY THE FLT CREW IN A HAWKER CPR JET DEPARTING ON THE IDALE TWO RNAV PROC FROM LAS; NV.

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I DEPARTED LAS VEGAS MCCARRAN INTL FOR SAN DIEGO; CA; WITH THE FOLLOWING CLRNC: CLRED TO SAN VIA THE IDALE TWO TNP BARRET 4; MAINTAIN 7000 FT SQUAWK XXXX; DEP 134.65. OUR DEP RWY WAS RWY 19R AT LAS AND OUR FIRST RNAV FIX WAS NIPZO. AFTER PASSING NIPZO WITH THE FLT DIRECTOR SELECTED TO LONG RANGE NAV WE PROCEEDED TO IDALE. WHILE ENRTE TO IDALE ATC ADVISED THAT WE MISSED A TURN. I CHKED MY FLT DIRECTOR AND ALONG WITH THE COPLT'S INDICATED THAT WE WERE R OFF COURSE SO I CORRECTED TO THE L AN APPROX HEADING OF 110 DEGS THINKING THAT WE WERE R OFF COURSE AND MAKING A CORRECTION TO THE L WOULD ALLOW FOR AN INTERCEPT OF THE 3RD LEG FIX WHICH IS BOACH. ATC ASKED WHAT OUR HEADING WAS AND GAVE US A NEW HEADING OF 180 DEGS AND ASKED THAT WE CALL THEIR FACILITY AFTER LNDG. WHILE FLYING ENRTE TO SAN DIEGO I CHKED ALL THE DEP COORDINATES FOR THE IDALE TWO IN THE FMS AND THEY ALL AGREED WITH THE BEARINGS AND DISTANCES LISTED ON THE CHART. THEY WERE ALL CORRECT; BUT THE MAIN DISCREPANCY WAS IN THE CDI STEERING NEEDLE WITH SHORT RANGE SELECTED (25 OR 50) MI. THE NEEDLE DEV BECOMES MORE DISPLACED FROM CTRLINE WITH THE SHORTER RANGE SETTINGS. (BELIEVE THIS TO BE A SOFTWARE PROB.) TALKED WITH LAS OPS MGR AND HE UNDERSTOOD MY DILEMMA. HE INDICATED THAT THIS IDALE PROC WAS BEING CHANGED IN A FEW WKS. SUMMARY: RNAV PROCS SEEM ADEQUATE BUT THEY LEAVE THE PLT WITHOUT ANY BACKUP INFO NOT ONLY FOR EQUIP MALFUNCTION; BUT IT DOESN'T ALLOW FOR GND BASED BEARING AND DISTANCE INFO AS A MEANS OF NAVIGATIONAL ASSURANCE. IN REF TO THE ATTACHED RNAV SID THERE IS NO COURSE INFO BTWN NIPZO AND IDALE; AND SINCE THESE DEPS NOT BEING DRAWN TO SCALE IT ONLY ALLOWS THE PLTS TO GUESS AT THE NEXT COURSE IN THE EVENT OF AN EQUIP MALFUNCTION. I AM IN GOOD AGREEMENT WITH THE RNAV PROCS SYS AS A NEEDED PART OF OUR NATIONAL AIRSPACE SYS; BUT I DON'T FEEL THAT TOTAL ELIMINATION OF VHF NAVAIDS AS A BACKUP TO RNAV PROCS IS PRUDENT AT THIS POINT.