Narrative:

Our B727 departed sju to ground at XA20 local via sju, route 2 st croix, A555 porqe, direct anada, UG449 perry, direct ground. At sju, the omega navigation system were loaded and checked in accordance with air carrier procedures. On departure, the navigation system were checked against sju VOR without discrepancies. The flight was cleared on course. PNF checked en route coordinates against flight plan and set-up intercept on #1 omega navigation. The assigned route was intercepted and coupled to the autoplt. Approximately 30 NM southeast of stt, sju center cleared flight direct to anada intersection. Anada coordinates were checked on both omega navigation system by PNF, and a direct course was established to anada. Approximately 30 NM ssw of coy the #1 navigation downgraded to dead reckoning (dr) and started to drift off to the south. PNF and PF checked amount of drift and, since #2 navigation did not downgrade, the PF disconnected the #1 navigation from the autoplt and flew raw data off #2 navigation. Both pilots tuned and idented dorado NDB to set-up intercept of UG449 at anada and to accomplish a precision update of the #1 navigation. PNF established radio communication with piarco control 10 mins from anada. Shortly thereafter, sju center cleared flight to switch to piarco control and informed us that we were 27 NM northeast of anada. A course correction was made, but piarco control subsequently cleared flight direct to ground NDB. The #1 navigation dead reckoning light did not go out until on the ramp at ground. Both omega navigation system performed within limits on the return flight to sju.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.