Narrative:

From downwind a vector of 070 degrees was given to intercept the ILS for runway 4, cross crene (11.1 DME) at 2700 ft or above, cleared approach. On approaching the localizer, a GS capture was accomplished on my flight director, raw data confirmed on GS. Descent on GS started and localizer captured. Flight director presentation normal. At 2000 ft above ground I asked what VOR my first officer had on his navigation receiver. He replied that he had lga VOR tuned. DME at the time was 13 DME. Obviously a conflict. I climbed to 2700 ft after switching my navigation receiver to auxiliary which showed me full deflection below GS. A normal approach was made from that point. Conclusion: poor cockpit procedure. Grene was never idented at the start of the approach, resulting in the capture of a false GS or perhaps a faulty navigation receiver. Aircraft was 1000 ft low outside grene! Approach control never advised us of our altitude deviation. Better observance of published procedures by both pilot and controller a must. This could have been a disaster! Callback conversation with reporter revealed the following: reporter said that there was a problem with the GS receiver. On the next leg, to bos, the GS 'popped in and out with occasional flags.' reporter is most upset that nobody noticed the deviation for so long.

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Original NASA ASRS Text

Title: DUE TO NAV RECEIVER PROB, LGT BEGAN DSCNT EARLY.

Narrative: FROM DOWNWIND A VECTOR OF 070 DEGS WAS GIVEN TO INTERCEPT THE ILS FOR RWY 4, CROSS CRENE (11.1 DME) AT 2700 FT OR ABOVE, CLRED APCH. ON APCHING THE LOC, A GS CAPTURE WAS ACCOMPLISHED ON MY FLT DIRECTOR, RAW DATA CONFIRMED ON GS. DSCNT ON GS STARTED AND LOC CAPTURED. FLT DIRECTOR PRESENTATION NORMAL. AT 2000 FT ABOVE GND I ASKED WHAT VOR MY FO HAD ON HIS NAV RECEIVER. HE REPLIED THAT HE HAD LGA VOR TUNED. DME AT THE TIME WAS 13 DME. OBVIOUSLY A CONFLICT. I CLBED TO 2700 FT AFTER SWITCHING MY NAV RECEIVER TO AUX WHICH SHOWED ME FULL DEFLECTION BELOW GS. A NORMAL APCH WAS MADE FROM THAT POINT. CONCLUSION: POOR COCKPIT PROC. GRENE WAS NEVER IDENTED AT THE START OF THE APCH, RESULTING IN THE CAPTURE OF A FALSE GS OR PERHAPS A FAULTY NAV RECEIVER. ACFT WAS 1000 FT LOW OUTSIDE GRENE! APCH CTL NEVER ADVISED US OF OUR ALTDEV. BETTER OBSERVANCE OF PUBLISHED PROCS BY BOTH PLT AND CTLR A MUST. THIS COULD HAVE BEEN A DISASTER! CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: RPTR SAID THAT THERE WAS A PROB WITH THE GS RECEIVER. ON THE NEXT LEG, TO BOS, THE GS 'POPPED IN AND OUT WITH OCCASIONAL FLAGS.' RPTR IS MOST UPSET THAT NOBODY NOTICED THE DEV FOR SO LONG.

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.