Narrative:

Being vectored to ILS runway 34R (WX) 4000 ft broken; visibility 2 NM. I was assigned heading 070 degrees. I just got stable at 8000 ft per tower. Aircraft was on autoplt heading and altitude preselect mode. I was checking frequency; ATIS; and decision ht for the ILS when the autoplt disconnected. Angle of attack indicator was slow at the bottom (1.3 versus at mid range; stick shaker at 91 KTS +8 clean). Stick shaker disconnected the autoplt while airspeed indicator showed 170 KTS. I initiated recovery at 7500 ft MSL. Tower advised I was low; then assigned me 6500 ft. The rest of the approach was hand flown. Whole event took place VMC with runway in sight. Cause: maintenance technicians found a broken pitot line going to the air data computer; ie; pressurization began driving airspeed. Contributing factors: ATC had assigned ILS runway 34L then at my request cleared me to ILS runway 34R; ie; diverting my attention to setting up for a new approach close in. Human factor: fatigue -- this was last leg of the night (5.5 hours flown in last 12 hours). Performance: it took 4 or 5 seconds and 500 ft to recognize the problem then respond with appropriate course of action. Fatigue may have been a factor in response time.

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Original NASA ASRS Text

Title: A PC12 FATIGUED PLT EXPERIENCED A STALL WARNING FOLLOWING A PITOT INPUT FAILURE TO THE ACFT'S ADC.

Narrative: BEING VECTORED TO ILS RWY 34R (WX) 4000 FT BROKEN; VISIBILITY 2 NM. I WAS ASSIGNED HDG 070 DEGS. I JUST GOT STABLE AT 8000 FT PER TWR. ACFT WAS ON AUTOPLT HDG AND ALT PRESELECT MODE. I WAS CHKING FREQ; ATIS; AND DECISION HT FOR THE ILS WHEN THE AUTOPLT DISCONNECTED. ANGLE OF ATTACK INDICATOR WAS SLOW AT THE BOTTOM (1.3 VERSUS AT MID RANGE; STICK SHAKER AT 91 KTS +8 CLEAN). STICK SHAKER DISCONNECTED THE AUTOPLT WHILE AIRSPD INDICATOR SHOWED 170 KTS. I INITIATED RECOVERY AT 7500 FT MSL. TWR ADVISED I WAS LOW; THEN ASSIGNED ME 6500 FT. THE REST OF THE APCH WAS HAND FLOWN. WHOLE EVENT TOOK PLACE VMC WITH RWY IN SIGHT. CAUSE: MAINT TECHNICIANS FOUND A BROKEN PITOT LINE GOING TO THE ADC; IE; PRESSURIZATION BEGAN DRIVING AIRSPD. CONTRIBUTING FACTORS: ATC HAD ASSIGNED ILS RWY 34L THEN AT MY REQUEST CLRED ME TO ILS RWY 34R; IE; DIVERTING MY ATTN TO SETTING UP FOR A NEW APCH CLOSE IN. HUMAN FACTOR: FATIGUE -- THIS WAS LAST LEG OF THE NIGHT (5.5 HRS FLOWN IN LAST 12 HRS). PERFORMANCE: IT TOOK 4 OR 5 SECONDS AND 500 FT TO RECOGNIZE THE PROB THEN RESPOND WITH APPROPRIATE COURSE OF ACTION. FATIGUE MAY HAVE BEEN A FACTOR IN RESPONSE TIME.

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.