Narrative:

We were en route to the grene fix as directed by new york approach for the ILS runway 4 at lga; when new york approach advised us we were right of course and gave us a 020 degree heading to intercept the localizer. Our flight originated from rdu and shortly after takeoff our aircraft experienced dual FMS/GPS problems. Aircraft position was not reliable so en route to lga we navigation'ed using VOR navigation. At one point near pxt; we advised ZDC of our situation. Following the descent on the korry 3; we were directed to proceed direct grene. Per chart page 11-1; for new york; ILS 4; grene is listed as being located at D11.1 lga (frequency 113.1). Accordingly; a fix-to-fix was being executed from our position of approximately lga D50.0 to D11.1. The selected navigation radial was set as 044 and my pfd indicated we were west of the 044 degree radial at approximately 25 DME when we were advised by new york approach that we were right of course and got the subsequent vector to intercept the localizer. Localizer selection was being delayed until approximately 19 mi to ensure localizer signal reliability parameters (18.1 mi). In my opinion; I was on track to intercept the lga 044/11.1 fix to intercept grene as listed on page 11-1. Suspect that grene is listed incorrectly on new york page 11-1 as D11.1 lga when it should be D11.1 ilga. Callback conversation with reporter revealed the following information: reporter stated that the FMC/GPS was showing a message 'position not known' throughout the flight and that the flight crew was flying fix-to-fix using the VOR/DME method. After approaching korry intersection on the korry 3 arrival ATC directed the flight crew to fly direct grene intersection. The reporter stated that he tuned the lga VOR (113.1) and the 044 degree course inbound and flew to intercept the course. ATC indicated that the aircraft was right of course and gave a 020 degree heading to intercept the 044 localizer course. Reporter indicated that he showed the aircraft left of course. Reporter believed that grene should be depicted by the ilga (110.5) 044/11.1 not the lga (113.1) 044/11.1.

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Original NASA ASRS Text

Title: EMB135 FLT CREW HAS A TRACK HDG DEV WHILE ATTEMPTING TO NAV TO GRENE INTXN ON THE LGA ILS RWY 4 APCH.

Narrative: WE WERE ENRTE TO THE GRENE FIX AS DIRECTED BY NEW YORK APCH FOR THE ILS RWY 4 AT LGA; WHEN NEW YORK APCH ADVISED US WE WERE R OF COURSE AND GAVE US A 020 DEG HDG TO INTERCEPT THE LOC. OUR FLT ORIGINATED FROM RDU AND SHORTLY AFTER TKOF OUR ACFT EXPERIENCED DUAL FMS/GPS PROBS. ACFT POS WAS NOT RELIABLE SO ENRTE TO LGA WE NAV'ED USING VOR NAV. AT ONE POINT NEAR PXT; WE ADVISED ZDC OF OUR SITUATION. FOLLOWING THE DSCNT ON THE KORRY 3; WE WERE DIRECTED TO PROCEED DIRECT GRENE. PER CHART PAGE 11-1; FOR NEW YORK; ILS 4; GRENE IS LISTED AS BEING LOCATED AT D11.1 LGA (FREQ 113.1). ACCORDINGLY; A FIX-TO-FIX WAS BEING EXECUTED FROM OUR POS OF APPROX LGA D50.0 TO D11.1. THE SELECTED NAV RADIAL WAS SET AS 044 AND MY PFD INDICATED WE WERE W OF THE 044 DEG RADIAL AT APPROX 25 DME WHEN WE WERE ADVISED BY NEW YORK APCH THAT WE WERE R OF COURSE AND GOT THE SUBSEQUENT VECTOR TO INTERCEPT THE LOC. LOC SELECTION WAS BEING DELAYED UNTIL APPROX 19 MI TO ENSURE LOC SIGNAL RELIABILITY PARAMETERS (18.1 MI). IN MY OPINION; I WAS ON TRACK TO INTERCEPT THE LGA 044/11.1 FIX TO INTERCEPT GRENE AS LISTED ON PAGE 11-1. SUSPECT THAT GRENE IS LISTED INCORRECTLY ON NEW YORK PAGE 11-1 AS D11.1 LGA WHEN IT SHOULD BE D11.1 ILGA. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT THE FMC/GPS WAS SHOWING A MESSAGE 'POS NOT KNOWN' THROUGHOUT THE FLT AND THAT THE FLT CREW WAS FLYING FIX-TO-FIX USING THE VOR/DME METHOD. AFTER APCHING KORRY INTXN ON THE KORRY 3 ARR ATC DIRECTED THE FLT CREW TO FLY DIRECT GRENE INTXN. THE RPTR STATED THAT HE TUNED THE LGA VOR (113.1) AND THE 044 DEG COURSE INBOUND AND FLEW TO INTERCEPT THE COURSE. ATC INDICATED THAT THE ACFT WAS R OF COURSE AND GAVE A 020 DEG HDG TO INTERCEPT THE 044 LOC COURSE. RPTR INDICATED THAT HE SHOWED THE ACFT L OF COURSE. RPTR BELIEVED THAT GRENE SHOULD BE DEPICTED BY THE ILGA (110.5) 044/11.1 NOT THE LGA (113.1) 044/11.1.

Data retrieved from NASA's ASRS site as of January 2009 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.