An small aircraft private pilot may have broken an assigned altitude after the pitot tube iced over.

Attributes
ACN	233605
Time
Date	199302
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : slc
State Reference	UT
Altitude	msl bound lower : 7500 msl bound upper : 8000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : slc
Operator	general aviation : personal
Make Model Name	Small Aircraft, Low Wing, 1 Eng, Fixed Gear
Flight Phase	cruise other descent : approach descent other
Route In Use	approach : straight in enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 24 flight time total : 459 flight time type : 22
ASRS Report	233605
Person 2
Affiliation	government : faa
Function	other personnel other
Qualification	other
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : exited adverse environment flight crew : overcame equipment problem other
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

Uneventful flight from phoenix, az, to salt lake city, ut, until being vectored at approximately 8000 ft MSL. Temporary loss of entire pitot static system even prior to visible airframe ice. While attempting to switch to alternate air (located under left hand side of instrument panel), was slow to respond to ATC instructions and may have busted altitude based on loss of altimeter. After switch to alternate static source, was unable to accurately judge airspeed and had to use power settings to approximate appropriate airspeed. The icing was limited to a narrow band of altitude, approximately 7000- 8500 ft MSL. Pilot had contacted FSS twice prior to flight to check on icing, the possibility of which was forecast, and specifically asked for PIREPS of icing of which there were none. Pilot also contacted prescott radio en route and was given negative PIREPS regarding icing. Near bryce canyon, pilot contacted cedar city FSS and was given updated WX for slc including airmet Z and SIGMET south. Once again, pilot requested if there were any reports of actual icing or flight delays based on adverse WX (landing ILS delays). Again, response was negative. Pilot amended flight plan to have cedar city as alternate based on WX at cedar city. Possible causes of altitude/ATC instruction compliance delays: icing, causing pilot's attention to be diverted to (appropriately) aviating versus communicating. Alternate static source is located down under the panel and is difficult to judge whether fully on or not because it can't be viewed from pilot position. Also, not easy to turn on because of location. Flight into SIGMET/airmet forecast and dependence on PIREPS regarding icing. Air carrier jets may not ice up when an small aircraft will.

Original NASA ASRS Text

Title: AN SMA PVT PLT MAY HAVE BROKEN AN ASSIGNED ALT AFTER THE PITOT TUBE ICED OVER.

Narrative: UNEVENTFUL FLT FROM PHOENIX, AZ, TO SALT LAKE CITY, UT, UNTIL BEING VECTORED AT APPROX 8000 FT MSL. TEMPORARY LOSS OF ENTIRE PITOT STATIC SYS EVEN PRIOR TO VISIBLE AIRFRAME ICE. WHILE ATTEMPTING TO SWITCH TO ALTERNATE AIR (LOCATED UNDER L HAND SIDE OF INST PANEL), WAS SLOW TO RESPOND TO ATC INSTRUCTIONS AND MAY HAVE BUSTED ALT BASED ON LOSS OF ALTIMETER. AFTER SWITCH TO ALTERNATE STATIC SOURCE, WAS UNABLE TO ACCURATELY JUDGE AIRSPD AND HAD TO USE PWR SETTINGS TO APPROXIMATE APPROPRIATE AIRSPD. THE ICING WAS LIMITED TO A NARROW BAND OF ALT, APPROX 7000- 8500 FT MSL. PLT HAD CONTACTED FSS TWICE PRIOR TO FLT TO CHK ON ICING, THE POSSIBILITY OF WHICH WAS FORECAST, AND SPECIFICALLY ASKED FOR PIREPS OF ICING OF WHICH THERE WERE NONE. PLT ALSO CONTACTED PRESCOTT RADIO ENRTE AND WAS GIVEN NEGATIVE PIREPS REGARDING ICING. NEAR BRYCE CANYON, PLT CONTACTED CEDAR CITY FSS AND WAS GIVEN UPDATED WX FOR SLC INCLUDING AIRMET Z AND SIGMET S. ONCE AGAIN, PLT REQUESTED IF THERE WERE ANY RPTS OF ACTUAL ICING OR FLT DELAYS BASED ON ADVERSE WX (LNDG ILS DELAYS). AGAIN, RESPONSE WAS NEGATIVE. PLT AMENDED FLT PLAN TO HAVE CEDAR CITY AS ALTERNATE BASED ON WX AT CEDAR CITY. POSSIBLE CAUSES OF ALT/ATC INSTRUCTION COMPLIANCE DELAYS: ICING, CAUSING PLT'S ATTN TO BE DIVERTED TO (APPROPRIATELY) AVIATING VERSUS COMMUNICATING. ALTERNATE STATIC SOURCE IS LOCATED DOWN UNDER THE PANEL AND IS DIFFICULT TO JUDGE WHETHER FULLY ON OR NOT BECAUSE IT CAN'T BE VIEWED FROM PLT POS. ALSO, NOT EASY TO TURN ON BECAUSE OF LOCATION. FLT INTO SIGMET/AIRMET FORECAST AND DEPENDENCE ON PIREPS REGARDING ICING. ACR JETS MAY NOT ICE UP WHEN AN SMA WILL.

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.