Narrative:

Checked into pit approach with ATIS while descending to 10000 ft. Pit approach assigned 300 degree heading after nesto intersection to intercept the localizer 32 at 10000 ft. As PNF I told the captain (PF) that I was off the radio to prepare cabin for landing. (ATC was very busy.) I made PA to cabin and looked down to hang up PA handset. Immediately I looked up as we passed 10000 ft MSL descending. I called altitude. PF arrested descent at 9600 ft MSL and returned to 10000 ft MSL. PF appeared to be reading a 'boat' magazine. Unknown to me (PNF) captain had turned off transponder including the altitude reporting and TCASII to hide altitude excursion. We continued inbound on localizer 32 pit. I (PNF) called traffic we were overtaking. I commented that this would not work at 15 DME southeast of pit. We were still 290-300 KIAS southeast of field at 10000 ft. I called approach, and asked him what was going on. He asked our location, which I gave him. Since turned off (transponder and TCASII) had occurred he (approach controller) had no return primary or secondary radar return. So we were unknown or rather forgotten about. Corrective flight path was assigned and landed safely. We were in the proximity of numerous aircraft. Please note first I idented our problem as a transponder failure, but all equipment was operational. After that fact became known to me, I neglected to change report due to frequency congestion.

Related reports:

Google
 

Original NASA ASRS Text

Title: CAPT TURNED OFF XPONDER TO HIDE A SIMPLE ALTDEV AND CAUSED TFC CONFLICT WITH PRECEDING TFC.

Narrative: CHKED INTO PIT APCH WITH ATIS WHILE DSNDING TO 10000 FT. PIT APCH ASSIGNED 300 DEG HDG AFTER NESTO INTXN TO INTERCEPT THE LOC 32 AT 10000 FT. AS PNF I TOLD THE CAPT (PF) THAT I WAS OFF THE RADIO TO PREPARE CABIN FOR LNDG. (ATC WAS VERY BUSY.) I MADE PA TO CABIN AND LOOKED DOWN TO HANG UP PA HANDSET. IMMEDIATELY I LOOKED UP AS WE PASSED 10000 FT MSL DSNDING. I CALLED ALT. PF ARRESTED DSCNT AT 9600 FT MSL AND RETURNED TO 10000 FT MSL. PF APPEARED TO BE READING A 'BOAT' MAGAZINE. UNKNOWN TO ME (PNF) CAPT HAD TURNED OFF XPONDER INCLUDING THE ALT RPTING AND TCASII TO HIDE ALT EXCURSION. WE CONTINUED INBOUND ON LOC 32 PIT. I (PNF) CALLED TFC WE WERE OVERTAKING. I COMMENTED THAT THIS WOULD NOT WORK AT 15 DME SE OF PIT. WE WERE STILL 290-300 KIAS SE OF FIELD AT 10000 FT. I CALLED APCH, AND ASKED HIM WHAT WAS GOING ON. HE ASKED OUR LOCATION, WHICH I GAVE HIM. SINCE TURNED OFF (XPONDER AND TCASII) HAD OCCURRED HE (APCH CTLR) HAD NO RETURN PRIMARY OR SECONDARY RADAR RETURN. SO WE WERE UNKNOWN OR RATHER FORGOTTEN ABOUT. CORRECTIVE FLT PATH WAS ASSIGNED AND LANDED SAFELY. WE WERE IN THE PROX OF NUMEROUS ACFT. PLEASE NOTE FIRST I IDENTED OUR PROB AS A XPONDER FAILURE, BUT ALL EQUIP WAS OPERATIONAL. AFTER THAT FACT BECAME KNOWN TO ME, I NEGLECTED TO CHANGE RPT DUE TO FREQ CONGESTION.

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.