Narrative:

Prior to taking command of a md-82 from lga to rdu, maintenance was on board replacing a vlfirst officermega navigation unit. The previous crew wrote a complaint in the aircraft log stating that the unit was unreliable for navigation due to track errors in excess of 30 NM. The unit was replaced and tested by maintenance personnel. After witnessing its test, I proceeded to initialize and test its accuracy. It tested to be within acceptable limits and appeared to operate normally. Soon after departing the lga terminal area, we were instructed to navigation from our present position to white intersection. We proceeded direct to that intersection accurately. Afterward I recall being vectored off course for traffic. We were then cleared back on course. At this time the navigation system was becoming unreliable evidenced by a 'dr' annunciator. We were off the airway system and found it difficult to return to our course with accuracy. We were drifting east of course near a restr area near the pxt VOR. We were vectored back on course by ATC. We reported the failure of the RNAV equipment and asked and received vectors back to the airway system. Both vors' were tuned properly but were not stable, not allowing for very accurate navigation. Brooke (brv) VOR was part of the course and was particularly unstable. After passing pxt VOR we misread our filed flight plan. We were on J191 when we should have been on a separate radial not depicted on the charts. ATC asked our clearance. We stated J191 to hopewell VOR. It should have been a separate radial to intercept another from hopewell. We were then reclred directly to hopewell VOR. Although we were never more than a few mi off our airway, it is a very tight area as far as airways. We were not in conflict with any other traffic. Contributing to the errors was an inaccurate RNAV system in compacted airway system, and unstable VOR indications. Misreading the filed clearance was a lack of attention to the details of what was filed and not what was obvious on the chart. Additionally there was an eastbound crosswind in excess of 120 KTS requiring 30-40 degrees correction angles which complicated the situation.

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Original NASA ASRS Text

Title: NAV ERROR.

Narrative: PRIOR TO TAKING COMMAND OF A MD-82 FROM LGA TO RDU, MAINT WAS ON BOARD REPLACING A VLF/OMEGA NAV UNIT. THE PREVIOUS CREW WROTE A COMPLAINT IN THE ACFT LOG STATING THAT THE UNIT WAS UNRELIABLE FOR NAV DUE TO TRACK ERRORS IN EXCESS OF 30 NM. THE UNIT WAS REPLACED AND TESTED BY MAINT PERSONNEL. AFTER WITNESSING ITS TEST, I PROCEEDED TO INITIALIZE AND TEST ITS ACCURACY. IT TESTED TO BE WITHIN ACCEPTABLE LIMITS AND APPEARED TO OPERATE NORMALLY. SOON AFTER DEPARTING THE LGA TERMINAL AREA, WE WERE INSTRUCTED TO NAV FROM OUR PRESENT POS TO WHITE INTXN. WE PROCEEDED DIRECT TO THAT INTXN ACCURATELY. AFTERWARD I RECALL BEING VECTORED OFF COURSE FOR TFC. WE WERE THEN CLRED BACK ON COURSE. AT THIS TIME THE NAV SYS WAS BECOMING UNRELIABLE EVIDENCED BY A 'DR' ANNUNCIATOR. WE WERE OFF THE AIRWAY SYS AND FOUND IT DIFFICULT TO RETURN TO OUR COURSE WITH ACCURACY. WE WERE DRIFTING E OF COURSE NEAR A RESTR AREA NEAR THE PXT VOR. WE WERE VECTORED BACK ON COURSE BY ATC. WE RPTED THE FAILURE OF THE RNAV EQUIP AND ASKED AND RECEIVED VECTORS BACK TO THE AIRWAY SYS. BOTH VORS' WERE TUNED PROPERLY BUT WERE NOT STABLE, NOT ALLOWING FOR VERY ACCURATE NAV. BROOKE (BRV) VOR WAS PART OF THE COURSE AND WAS PARTICULARLY UNSTABLE. AFTER PASSING PXT VOR WE MISREAD OUR FILED FLT PLAN. WE WERE ON J191 WHEN WE SHOULD HAVE BEEN ON A SEPARATE RADIAL NOT DEPICTED ON THE CHARTS. ATC ASKED OUR CLRNC. WE STATED J191 TO HOPEWELL VOR. IT SHOULD HAVE BEEN A SEPARATE RADIAL TO INTERCEPT ANOTHER FROM HOPEWELL. WE WERE THEN RECLRED DIRECTLY TO HOPEWELL VOR. ALTHOUGH WE WERE NEVER MORE THAN A FEW MI OFF OUR AIRWAY, IT IS A VERY TIGHT AREA AS FAR AS AIRWAYS. WE WERE NOT IN CONFLICT WITH ANY OTHER TFC. CONTRIBUTING TO THE ERRORS WAS AN INACCURATE RNAV SYS IN COMPACTED AIRWAY SYS, AND UNSTABLE VOR INDICATIONS. MISREADING THE FILED CLRNC WAS A LACK OF ATTN TO THE DETAILS OF WHAT WAS FILED AND NOT WHAT WAS OBVIOUS ON THE CHART. ADDITIONALLY THERE WAS AN EBOUND XWIND IN EXCESS OF 120 KTS REQUIRING 30-40 DEGS CORRECTION ANGLES WHICH COMPLICATED THE SIT.

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.