AN ACR B727 HAD A NAV ERROR ENRTE TO 'ANADA.' 1 OF THE 2 OMEGA NAV SYS DEGRADED TO 'DEAD RECKONING' ENRTE.

Narrative

OUR B727 DEPARTED SJU TO GND AT XA20 LCL VIA SJU; RTE 2 ST CROIX; A555 PORQE; DIRECT ANADA; UG449 PERRY; DIRECT GND. AT SJU; THE OMEGA NAV SYS WERE LOADED AND CHKED IN ACCORDANCE WITH ACR PROCS. ON DEP; THE NAV SYS WERE CHKED AGAINST SJU VOR WITHOUT DISCREPANCIES. THE FLT WAS CLRED ON COURSE. PNF CHKED ENRTE COORDINATES AGAINST FLT PLAN AND SET-UP INTERCEPT ON #1 OMEGA NAV. THE ASSIGNED RTE WAS INTERCEPTED AND COUPLED TO THE AUTOPLT. APPROX 30 NM SE OF STT; SJU CTR CLRED FLT DIRECT TO ANADA INTXN. ANADA COORDINATES WERE CHKED ON BOTH OMEGA NAV SYS BY PNF; AND A DIRECT COURSE WAS ESTABLISHED TO ANADA. APPROX 30 NM SSW OF COY THE #1 NAV DOWNGRADED TO DEAD RECKONING (DR) AND STARTED TO DRIFT OFF TO THE S. PNF AND PF CHKED AMOUNT OF DRIFT AND; SINCE #2 NAV DID NOT DOWNGRADE; THE PF DISCONNECTED THE #1 NAV FROM THE AUTOPLT AND FLEW RAW DATA OFF #2 NAV. BOTH PLTS TUNED AND IDENTED DORADO NDB TO SET-UP INTERCEPT OF UG449 AT ANADA AND TO ACCOMPLISH A PRECISION UPDATE OF THE #1 NAV. PNF ESTABLISHED RADIO COM WITH PIARCO CTL 10 MINS FROM ANADA. SHORTLY THEREAFTER; SJU CTR CLRED FLT TO SWITCH TO PIARCO CTL AND INFORMED US THAT WE WERE 27 NM NE OF ANADA. A COURSE CORRECTION WAS MADE; BUT PIARCO CTL SUBSEQUENTLY CLRED FLT DIRECT TO GND NDB. THE #1 NAV DEAD RECKONING LIGHT DID NOT GO OUT UNTIL ON THE RAMP AT GND. BOTH OMEGA NAV SYS PERFORMED WITHIN LIMITS ON THE RETURN FLT TO SJU.