TRACK DEV.

Narrative

IRS'S WERE ALIGNED AT THE GATE IN SNA. RTE WAS CHKED BY BOTH PLTS; NO DISCONTINUITIES NOTED. IRS'S INDICATED A PROPER ALIGNMENT WITH ZERO GND SPD. WE WERE CLRED VIA THE BACK BAY 2 DEP TKOF AND CLB WERE NORMAL. WE WERE ESTABLISHED ON A 175 DEG HDG. WE CLEANED UP THE ACFT AND CONTINUED CLBING AT 210 KTS. DEP GAVE US A HDG CHANGE OF APPROX 20 DEGS TO THE L FOR TFC. SOME TIME LATER WE WERE CLRED DIRECT TO BHOSE. BHOSE WAS SELECTED AS THE ACTIVE WAYPOINT; EXECUTED; AND L-NAV ENGAGED. THE FMS INDICATED A COURSE OF 082 DEGS TO BHOSE. SINCE THE CAPT'S FLT DIRECTOR WAS INOP; THE FO SELECTED NAV ON HIS HSI SWITCH IN ORDER TO CONFIRM HIS FLT DIRECTOR WAS CTRED AND INDICATING ON COURSE. AS WE APCHED BHOSE; THE FO SWITCHED BACK TO VOR MODE; TUNED IN SXC AND THE 061 DEG RADIAL. HE INDICATED THAT WE APPEARED S OF COURSE. THE FMS INDICATED A XING OF BHOSE AND THEN COMMANDED A COURSE CHANGE OF APPROX 062 DEGS TO THE NEXT WAYPOINT. AT THAT TIME; THE #2 VOR SHOWED US AT SXC 055 DEGS/44 DEGS BHOSE IS ABOUT SXC 061 DEGS/42 DEGS. SOON THEREAFTER CTR CALLED AND ASKED IF WE WERE ON THE DEP. WE RESPONDED THAT THE FMS SHOWED US ON COURSE BUT THE VOR SHOWED US S OF COURSE. HE SAID HE PAINTED US 4 MI S OF COURSE. HE THEN GAVE US A HDG CHANGE TO 050 DEGS FOR TFC. ONCE WE CLRED THE TFC. WE WERE CLRED DIRECT BLYTHE. BLYTHE WAS SELECTED AND L-NAV ENGAGED. THE COURSE TO BLYTHE WAS XCHKED ON THE #2 VOR. THE FMS COURSE AND THE VOR COURSE AGREED. SHORTLY THEREAFTER WE HAD TIME TO CHK THE POS REF PAGE. WE REMEMBER THE FOLLOWING: FMC POS N33 DEGS 34. -- W 117 DEGS. IRS L N33 DEGS 39. -- W 117 DEGS. IRS R N 33 DEGS 38. -- W 117 DEGS. IT SEEMS THE ACFT WAS NAVIGATING OFF AN ERRONEOUS FMC POS SINCE DEP. SINCE BOTH VORS WERE TUNED TO ISNA; I COULDN'T GET A GOOD UPDATE; OR THE NAV DATA BASE COULD HAVE AN ERROR ENTERED OR MAYBE 1 OF THE NAVAIDS IT WAS UPDATING OFF WASN'T WHERE THE COMPUTER THOUGHT IT SHOULD BE. I BELIEVE THIS HAPPENED TO A CREW GOING INTO ATL ONCE. FMS NAV WAS NORMAL THE REMAINDER OF THE FLT.