Narrative:

I leveled aircraft off at 6000 ft and set cruise power. Noted lower than normal airspeed. Checked gear and flaps and found them to be retracted. Airspeed dropped further (slowly). I added power and checked for ice; suspecting pitot ice. Noted outside air temperature was -2 degrees C and only a trace of ice on the wings. On this particular aircraft; the anti-ice switches are on the left sidewall near the captain's knees; and are hard to see in dim lighting. I looked and thought I saw pitot heat on. During this time; evidently the altimeter and vsi froze somehow. ATC cued me in to this as they said first I was at approximately 7800 ft MSL; then a few moments later; at 10700 ft MSL. Altimeter read approximately 5950 ft; vsi indicated zero FPM; and airspeed indicator read zero. I was able to level the aircraft off briefly and then turned on all switches on the left sidewall in the row with the deice equipment. A few moments later; all indications came back to normal. Altitude wound up to 10300 ft MSL; airspeed read 160 KTS; and vsi approximately zero. I think I might have failed to turn on pitot heat in the dim light as the switches are hard to read. The emergency was declared when ATC indicated I was at 10700 ft. After everything came back to life; the flight was uneventful.

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Original NASA ASRS Text

Title: PA31 PLT DECLARES EMER WHEN HE EXPERIENCED ERRONEOUS PITOT STATIC INDICATIONS BECAUSE PITOT HEAT SWITCHES WERE OFF.

Narrative: I LEVELED ACFT OFF AT 6000 FT AND SET CRUISE PWR. NOTED LOWER THAN NORMAL AIRSPD. CHKED GEAR AND FLAPS AND FOUND THEM TO BE RETRACTED. AIRSPD DROPPED FURTHER (SLOWLY). I ADDED PWR AND CHKED FOR ICE; SUSPECTING PITOT ICE. NOTED OUTSIDE AIR TEMP WAS -2 DEGS C AND ONLY A TRACE OF ICE ON THE WINGS. ON THIS PARTICULAR ACFT; THE ANTI-ICE SWITCHES ARE ON THE L SIDEWALL NEAR THE CAPT'S KNEES; AND ARE HARD TO SEE IN DIM LIGHTING. I LOOKED AND THOUGHT I SAW PITOT HEAT ON. DURING THIS TIME; EVIDENTLY THE ALTIMETER AND VSI FROZE SOMEHOW. ATC CUED ME IN TO THIS AS THEY SAID FIRST I WAS AT APPROX 7800 FT MSL; THEN A FEW MOMENTS LATER; AT 10700 FT MSL. ALTIMETER READ APPROX 5950 FT; VSI INDICATED ZERO FPM; AND AIRSPD INDICATOR READ ZERO. I WAS ABLE TO LEVEL THE ACFT OFF BRIEFLY AND THEN TURNED ON ALL SWITCHES ON THE L SIDEWALL IN THE ROW WITH THE DEICE EQUIP. A FEW MOMENTS LATER; ALL INDICATIONS CAME BACK TO NORMAL. ALT WOUND UP TO 10300 FT MSL; AIRSPD READ 160 KTS; AND VSI APPROX ZERO. I THINK I MIGHT HAVE FAILED TO TURN ON PITOT HEAT IN THE DIM LIGHT AS THE SWITCHES ARE HARD TO READ. THE EMER WAS DECLARED WHEN ATC INDICATED I WAS AT 10700 FT. AFTER EVERYTHING CAME BACK TO LIFE; THE FLT WAS UNEVENTFUL.

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.