Narrative:

Had to have aircraft deiced prior to first takeoff of the day. Takeoff normal. After clean-up on climb out; tower asks 'what's your altitude?' I had just gone from outside to inside visual cues. All outside indications normal; however; captain altimeter is still reading field elevation (no climb indicated). I told tower that altimeter was inaccurate (copilot's side looked ok). Also told tower that I wanted to return for landing because of this problem -- landing normal. On short final; the altimeter started working and the airspeed on the captain's side fluctuated a couple of times; as if it was gusty outside (no wind to speak of). Shut down on ramp and inspected pitot tubes (both hot) with 5 static ports. Found visible moisture in one and removed it. Made test flight around the pattern. All normal. Picked up passenger and went on way. All remained normal. FSDO maintenance inspector called later that day and I relayed the above to him. I question the wisdom of deicing without maybe placing tape over static vents. I will do this in future. The reporter stated the airplane was overnight in a freezing rain and was being deiced with a mixture of water and deicing fluid at 170 degrees. The reporter observed the deicing crew spraying the fuselage but did not consider the spray affecting the static ports. On return to the field; one aft static port was discovered with sticky deicer fluid and visible moisture and this was cleared. A test flight proved the altimeter now worked properly. The reporter now carries a roll of tape to cover the static ports when deicing is required.

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Original NASA ASRS Text

Title: AN AC90 ON TKOF CLB BTWN 700-1000 FT RETURNED TO THE DEP ARPT DUE TO CAPT'S ALTIMETER READING FIELD ELEVATION.

Narrative: HAD TO HAVE ACFT DEICED PRIOR TO FIRST TKOF OF THE DAY. TKOF NORMAL. AFTER CLEAN-UP ON CLBOUT; TWR ASKS 'WHAT'S YOUR ALT?' I HAD JUST GONE FROM OUTSIDE TO INSIDE VISUAL CUES. ALL OUTSIDE INDICATIONS NORMAL; HOWEVER; CAPT ALTIMETER IS STILL READING FIELD ELEVATION (NO CLB INDICATED). I TOLD TWR THAT ALTIMETER WAS INACCURATE (COPLT'S SIDE LOOKED OK). ALSO TOLD TWR THAT I WANTED TO RETURN FOR LNDG BECAUSE OF THIS PROB -- LNDG NORMAL. ON SHORT FINAL; THE ALTIMETER STARTED WORKING AND THE AIRSPD ON THE CAPT'S SIDE FLUCTUATED A COUPLE OF TIMES; AS IF IT WAS GUSTY OUTSIDE (NO WIND TO SPEAK OF). SHUT DOWN ON RAMP AND INSPECTED PITOT TUBES (BOTH HOT) WITH 5 STATIC PORTS. FOUND VISIBLE MOISTURE IN ONE AND REMOVED IT. MADE TEST FLT AROUND THE PATTERN. ALL NORMAL. PICKED UP PAX AND WENT ON WAY. ALL REMAINED NORMAL. FSDO MAINT INSPECTOR CALLED LATER THAT DAY AND I RELAYED THE ABOVE TO HIM. I QUESTION THE WISDOM OF DEICING WITHOUT MAYBE PLACING TAPE OVER STATIC VENTS. I WILL DO THIS IN FUTURE. THE RPTR STATED THE AIRPLANE WAS OVERNIGHT IN A FREEZING RAIN AND WAS BEING DEICED WITH A MIXTURE OF WATER AND DEICING FLUID AT 170 DEGS. THE RPTR OBSERVED THE DEICING CREW SPRAYING THE FUSELAGE BUT DID NOT CONSIDER THE SPRAY AFFECTING THE STATIC PORTS. ON RETURN TO THE FIELD; ONE AFT STATIC PORT WAS DISCOVERED WITH STICKY DEICER FLUID AND VISIBLE MOISTURE AND THIS WAS CLRED. A TEST FLT PROVED THE ALTIMETER NOW WORKED PROPERLY. THE RPTR NOW CARRIES A ROLL OF TAPE TO COVER THE STATIC PORTS WHEN DEICING IS REQUIRED.

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.