Corporate jet experiences altitude deviation due to pitot static system problem.

Attributes
ACN	116630
Time
Date	198907
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : lit
State Reference	AR
Altitude	msl bound lower : 33000 msl bound upper : 34000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme
Operator	general aviation : corporate
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Flight Phase	cruise other
Route In Use	enroute : direct
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : private
Experience	flight time last 90 days : 90 flight time total : 5000 flight time type : 800
ASRS Report	116630
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : became reoriented
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

At FL330, TAS 410 and mach .68, I noticed an airspeed increase and checked altitude and vsi. Everything was normal except airspeed increasing with normal thrust set. I reduced power but airspeed was still increasing. I had static problems with this aircraft before so I disconnected autoplt and pulled aircraft to 5 degree nose up which would give a climb rate of approximately 1000 FPM. We advised center of our problems holding altitude and altitude finally broke lose indicating 34,000' and 2000 FPM climb. We requested a descent to FL290 from center altimeter and vsi were erratic for next 10 min then finally stabilized. Flew rest of flight VMC and very careful of altitude and maintenance is now checking out static system and cleaning the system.

Original NASA ASRS Text

Title: CORPORATE JET EXPERIENCES ALT DEVIATION DUE TO PITOT STATIC SYSTEM PROBLEM.

Narrative: AT FL330, TAS 410 AND MACH .68, I NOTICED AN AIRSPEED INCREASE AND CHECKED ALT AND VSI. EVERYTHING WAS NORMAL EXCEPT AIRSPEED INCREASING WITH NORMAL THRUST SET. I REDUCED PWR BUT AIRSPEED WAS STILL INCREASING. I HAD STATIC PROBLEMS WITH THIS ACFT BEFORE SO I DISCONNECTED AUTOPLT AND PULLED ACFT TO 5 DEG NOSE UP WHICH WOULD GIVE A CLIMB RATE OF APPROX 1000 FPM. WE ADVISED CENTER OF OUR PROBLEMS HOLDING ALT AND ALT FINALLY BROKE LOSE INDICATING 34,000' AND 2000 FPM CLIMB. WE REQUESTED A DSCNT TO FL290 FROM CENTER ALTIMETER AND VSI WERE ERRATIC FOR NEXT 10 MIN THEN FINALLY STABILIZED. FLEW REST OF FLT VMC AND VERY CAREFUL OF ALT AND MAINT IS NOW CHECKING OUT STATIC SYSTEM AND CLEANING THE SYSTEM.

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