Narrative:

About 20 DME from mmj at 4000' in visibility flight conditions we were given ILS approach instructions. I believe it was '...turn to (intercept heading) maintain 4000' till established on localizer cleared ILS 28L.' at the time we were still below the G/south with corresponding indications. I began to follow G/south indicator as it descended. Shortly after, the captain said he thought we were at a lower altitude than we should be at that stage of the approach. In response to this I checked the captain's G/south indicator which was not in view (I think he was still tuned to mmj VOR) and referred to my approach plate. Believing I was still within 1/2 DOT of the G/south I looked back to my instruments where I discovered the G/south indicator to be near the top of the scale. Almost at the same time ATC said they were getting a low altitude warning. Immediately I arrested our descent and corrected to re-intercept the G/south. The remainder of the approach and landing was uneventful with no further discussion with ATC. After talking on the ground the captain said he thought we had been cleared for a visibility approach thereby explaining his delay in pointing out my deviations from the approach procedure. I can only explain this event as the result of distraction and failure to utilize all available information. As mentioned earlier the WX was good and I was dividing my attention between my visibility observation of the airport and my instrument indications. In addition I think I could have paid closer attention to approach procedures, data from the captain's flight/navigation instruments and my control of the aircraft.

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Original NASA ASRS Text

Title: MLG FLT CREW SETS OFF MSAW ON ATTEMPT TO INTERCEPT GLIDE SLOPE.

Narrative: ABOUT 20 DME FROM MMJ AT 4000' IN VIS FLT CONDITIONS WE WERE GIVEN ILS APCH INSTRUCTIONS. I BELIEVE IT WAS '...TURN TO (INTERCEPT HDG) MAINTAIN 4000' TILL ESTABLISHED ON LOC CLRED ILS 28L.' AT THE TIME WE WERE STILL BELOW THE G/S WITH CORRESPONDING INDICATIONS. I BEGAN TO FOLLOW G/S INDICATOR AS IT DSNDED. SHORTLY AFTER, THE CAPT SAID HE THOUGHT WE WERE AT A LOWER ALT THAN WE SHOULD BE AT THAT STAGE OF THE APCH. IN RESPONSE TO THIS I CHKED THE CAPT'S G/S INDICATOR WHICH WAS NOT IN VIEW (I THINK HE WAS STILL TUNED TO MMJ VOR) AND REFERRED TO MY APCH PLATE. BELIEVING I WAS STILL WITHIN 1/2 DOT OF THE G/S I LOOKED BACK TO MY INSTRUMENTS WHERE I DISCOVERED THE G/S INDICATOR TO BE NEAR THE TOP OF THE SCALE. ALMOST AT THE SAME TIME ATC SAID THEY WERE GETTING A LOW ALT WARNING. IMMEDIATELY I ARRESTED OUR DSCNT AND CORRECTED TO RE-INTERCEPT THE G/S. THE REMAINDER OF THE APCH AND LNDG WAS UNEVENTFUL WITH NO FURTHER DISCUSSION WITH ATC. AFTER TALKING ON THE GND THE CAPT SAID HE THOUGHT WE HAD BEEN CLRED FOR A VIS APCH THEREBY EXPLAINING HIS DELAY IN POINTING OUT MY DEVIATIONS FROM THE APCH PROC. I CAN ONLY EXPLAIN THIS EVENT AS THE RESULT OF DISTR AND FAILURE TO UTILIZE ALL AVAILABLE INFO. AS MENTIONED EARLIER THE WX WAS GOOD AND I WAS DIVIDING MY ATTN BTWN MY VIS OBSERVATION OF THE ARPT AND MY INSTRUMENT INDICATIONS. IN ADDITION I THINK I COULD HAVE PAID CLOSER ATTN TO APCH PROCS, DATA FROM THE CAPT'S FLT/NAV INSTRUMENTS AND MY CTL OF THE ACFT.

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.