Narrative:

On an IFR flight plan from gnv to new, I diverted from new (without making an approach) to msy because new was reporting below minimums, msy was above minimums at 500 ft and 3 mi visibility. New orleans approach gave me a descent to 3000 ft and vectors to the msy ILS runway 01. Nearing abart, they cleared me for the ILS runway 01 approach, descending to 2000 ft until established on the localizer and turning to 350 degrees to intercept. Approach added that I was to maintain my 'present speed' until the OM. My 'present speed' in the descent was 165 KTS, easy for a descending lance, but hard to maintain in level flight at cruise power. There was nearly continuous moderate turbulence. At this point, the ILS indicator seemed to be giving normal readings for that phase of the approach. My #1 navigation was set for the ILS. My #2 navigation was set-up for the missed approach radial (082 degrees) off rqr. The marker beacon receiver was activated, and I had set the DME on i-jfi (the localizer) slaved to the #1 navigation, to identify abart and to backup the identify of the OM. Continuing the descent at 165 KTS, I noticed that I was not getting a reading on the DME. I double checked the control settings without success, and then switched to its internal frequency control, still without success. While this was going on, I got established on the localizer without any problem. I gave up on the DME and then noticed that: 1) the GS needle was centered, but the signal flag was red (inoperative), 2) the altitude was approaching 1000 ft, 3) the airspeed was still about 165 KTS, 4) the OM beacon was just coming in (altitude minimum 1500 ft), and 5) the ceiling was fairly ragged and I had ground contact much of the time. I went to climb power and brought the nose up. The (clean) aircraft struggled and climbed only very slowly. In the meantime, new orleans warned me to 'watch my altitude.' I acknowledged and continued to try to climb. I managed to reach 1200 ft and then, now being inside the marker, I conducted a normal and uneventful localizer approach and landing (charted minimums 416 ft and 1 mi visibility). Comments: I am quite convinced, from the poor aircraft performance in the attempted climb, that we were caught in the grip of a fairly strong downdraft. This was the primary cause of the undershoot and would have resulted in a descent below 1500 ft in any case. Although neither the aircraft on the approach immediately in front of me or behind reported a shear, they were both transport category ships, and the shear may have been short lived. I was so busy working out the recovery that I never called it in either. ATC's insistence that I maintain a higher than level cruise speed in the descent exacerbated the potential for an inadvertent undershoot of the GS. I should have taken exception to this request, but I was trying to give them what they wanted. My attention to the DME problem reduced the time available for monitoring the GS and altitude, so I am not sure how long the unusual descent had gone on. My guess is that it was less than a min. The GS receiver had failed about a month before and had been repaired. It had been operating normally during this trip. I did the ILS runway 28 at gnv a few days before. There is no question that the receiver failed again, either during the approach itself, or earlier -- with turbulence-induced needle motion giving me the false impression of initial function (though I hate to think that I would have missed the red flag). The DME was working fine before and since. I have to assume that it was having a problem reading a localizer, or that the localizer DME was not operating. Of course, the plane has gone to the avionics shop.

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Original NASA ASRS Text

Title: PA32RT-300T PLT ON IFR APCH HAS DME FAIL AND WHILE TROUBLESHOOTING AND MAINTAINING REQUESTED SPD HE DSNDS BELOW PUBLISHED ALT.

Narrative: ON AN IFR FLT PLAN FROM GNV TO NEW, I DIVERTED FROM NEW (WITHOUT MAKING AN APCH) TO MSY BECAUSE NEW WAS RPTING BELOW MINIMUMS, MSY WAS ABOVE MINIMUMS AT 500 FT AND 3 MI VISIBILITY. NEW ORLEANS APCH GAVE ME A DSCNT TO 3000 FT AND VECTORS TO THE MSY ILS RWY 01. NEARING ABART, THEY CLRED ME FOR THE ILS RWY 01 APCH, DSNDING TO 2000 FT UNTIL ESTABLISHED ON THE LOC AND TURNING TO 350 DEGS TO INTERCEPT. APCH ADDED THAT I WAS TO MAINTAIN MY 'PRESENT SPD' UNTIL THE OM. MY 'PRESENT SPD' IN THE DSCNT WAS 165 KTS, EASY FOR A DSNDING LANCE, BUT HARD TO MAINTAIN IN LEVEL FLT AT CRUISE PWR. THERE WAS NEARLY CONTINUOUS MODERATE TURB. AT THIS POINT, THE ILS INDICATOR SEEMED TO BE GIVING NORMAL READINGS FOR THAT PHASE OF THE APCH. MY #1 NAV WAS SET FOR THE ILS. MY #2 NAV WAS SET-UP FOR THE MISSED APCH RADIAL (082 DEGS) OFF RQR. THE MARKER BEACON RECEIVER WAS ACTIVATED, AND I HAD SET THE DME ON I-JFI (THE LOC) SLAVED TO THE #1 NAV, TO IDENT ABART AND TO BACKUP THE IDENT OF THE OM. CONTINUING THE DSCNT AT 165 KTS, I NOTICED THAT I WAS NOT GETTING A READING ON THE DME. I DOUBLE CHKED THE CTL SETTINGS WITHOUT SUCCESS, AND THEN SWITCHED TO ITS INTERNAL FREQ CTL, STILL WITHOUT SUCCESS. WHILE THIS WAS GOING ON, I GOT ESTABLISHED ON THE LOC WITHOUT ANY PROB. I GAVE UP ON THE DME AND THEN NOTICED THAT: 1) THE GS NEEDLE WAS CTRED, BUT THE SIGNAL FLAG WAS RED (INOP), 2) THE ALT WAS APCHING 1000 FT, 3) THE AIRSPD WAS STILL ABOUT 165 KTS, 4) THE OM BEACON WAS JUST COMING IN (ALT MINIMUM 1500 FT), AND 5) THE CEILING WAS FAIRLY RAGGED AND I HAD GND CONTACT MUCH OF THE TIME. I WENT TO CLB PWR AND BROUGHT THE NOSE UP. THE (CLEAN) ACFT STRUGGLED AND CLBED ONLY VERY SLOWLY. IN THE MEANTIME, NEW ORLEANS WARNED ME TO 'WATCH MY ALT.' I ACKNOWLEDGED AND CONTINUED TO TRY TO CLB. I MANAGED TO REACH 1200 FT AND THEN, NOW BEING INSIDE THE MARKER, I CONDUCTED A NORMAL AND UNEVENTFUL LOC APCH AND LNDG (CHARTED MINIMUMS 416 FT AND 1 MI VISIBILITY). COMMENTS: I AM QUITE CONVINCED, FROM THE POOR ACFT PERFORMANCE IN THE ATTEMPTED CLB, THAT WE WERE CAUGHT IN THE GRIP OF A FAIRLY STRONG DOWNDRAFT. THIS WAS THE PRIMARY CAUSE OF THE UNDERSHOOT AND WOULD HAVE RESULTED IN A DSCNT BELOW 1500 FT IN ANY CASE. ALTHOUGH NEITHER THE ACFT ON THE APCH IMMEDIATELY IN FRONT OF ME OR BEHIND RPTED A SHEAR, THEY WERE BOTH TRANSPORT CATEGORY SHIPS, AND THE SHEAR MAY HAVE BEEN SHORT LIVED. I WAS SO BUSY WORKING OUT THE RECOVERY THAT I NEVER CALLED IT IN EITHER. ATC'S INSISTENCE THAT I MAINTAIN A HIGHER THAN LEVEL CRUISE SPD IN THE DSCNT EXACERBATED THE POTENTIAL FOR AN INADVERTENT UNDERSHOOT OF THE GS. I SHOULD HAVE TAKEN EXCEPTION TO THIS REQUEST, BUT I WAS TRYING TO GIVE THEM WHAT THEY WANTED. MY ATTN TO THE DME PROB REDUCED THE TIME AVAILABLE FOR MONITORING THE GS AND ALT, SO I AM NOT SURE HOW LONG THE UNUSUAL DSCNT HAD GONE ON. MY GUESS IS THAT IT WAS LESS THAN A MIN. THE GS RECEIVER HAD FAILED ABOUT A MONTH BEFORE AND HAD BEEN REPAIRED. IT HAD BEEN OPERATING NORMALLY DURING THIS TRIP. I DID THE ILS RWY 28 AT GNV A FEW DAYS BEFORE. THERE IS NO QUESTION THAT THE RECEIVER FAILED AGAIN, EITHER DURING THE APCH ITSELF, OR EARLIER -- WITH TURB-INDUCED NEEDLE MOTION GIVING ME THE FALSE IMPRESSION OF INITIAL FUNCTION (THOUGH I HATE TO THINK THAT I WOULD HAVE MISSED THE RED FLAG). THE DME WAS WORKING FINE BEFORE AND SINCE. I HAVE TO ASSUME THAT IT WAS HAVING A PROB READING A LOC, OR THAT THE LOC DME WAS NOT OPERATING. OF COURSE, THE PLANE HAS GONE TO THE AVIONICS SHOP.

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.