<< >> NASA ASRS Report 803234, August 2008

A high performance experimental small aircraft pilot reported unreliable airspeed and pitch information when he flew into clouds at 21000 ft. He was unable to maintain his altitude accurately and asked for a lower; warmer altitude.

Attributes
ACN	803234
Time
Date	200808
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : zzz.vortac
State Reference	US
Altitude	msl bound lower : 19000 msl bound upper : 21000
Environment
Flight Conditions	Mixed
Weather Elements	Ice Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zzz.artcc
Operator	general aviation : personal
Make Model Name	Experimental
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : commercial pilot : instrument pilot : private pilot : flight engineer pilot : atp
Experience	flight time last 90 days : 50 flight time total : 5000 flight time type : 35
ASRS Report	803234
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude inflight encounter : weather
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	Aircraft Weather
Primary Problem	Aircraft

Narrative:

IFR flight. FL210 clear; but with multiple thunderstorms and developing convective air either side of flight path. Flew into cloud layer at FL210. Pitot heat on. Unreliable airspeed and pitch attitude information. Turbulent air. Multiple altitude excursions. Asked for lower altitude for warmer air and to get VMC. Also asked ATC for block altitude as unable to maintain altitude reliably. Flight path marker slowly precessing +/-10 degrees in attitude. Suspect water in system or damage from previous flight where icing was encountered. Pitot system seemed to work more reliably at lower altitude with warmer temperature; but still not completely accurate.

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Original NASA ASRS Text

Title: A HIGH PERFORMANCE EXPERIMENTAL SMALL AIRCRAFT PILOT REPORTED UNRELIABLE AIRSPEED AND PITCH INFORMATION WHEN HE FLEW INTO CLOUDS AT 21000 FT. HE WAS UNABLE TO MAINTAIN HIS ALTITUDE ACCURATELY AND ASKED FOR A LOWER; WARMER ALT.

Narrative: IFR FLT. FL210 CLR; BUT WITH MULTIPLE TSTMS AND DEVELOPING CONVECTIVE AIR EITHER SIDE OF FLT PATH. FLEW INTO CLOUD LAYER AT FL210. PITOT HEAT ON. UNRELIABLE AIRSPD AND PITCH ATTITUDE INFO. TURBULENT AIR. MULTIPLE ALT EXCURSIONS. ASKED FOR LOWER ALT FOR WARMER AIR AND TO GET VMC. ALSO ASKED ATC FOR BLOCK ALT AS UNABLE TO MAINTAIN ALT RELIABLY. FLT PATH MARKER SLOWLY PRECESSING +/-10 DEGS IN ATTITUDE. SUSPECT WATER IN SYS OR DAMAGE FROM PREVIOUS FLT WHERE ICING WAS ENCOUNTERED. PITOT SYS SEEMED TO WORK MORE RELIABLY AT LOWER ALT WITH WARMER TEMP; BUT STILL NOT COMPLETELY ACCURATE.

Data retrieved from NASA's ASRS site as of May 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.