Corp aircraft has static air blockage. Altitude deviation. Switch to alternate air source.

Attributes
ACN	181504
Time
Date	199106
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : dfw
State Reference	TX
Altitude	msl bound lower : 35000 msl bound upper : 36500
Aircraft 1
Operator	general aviation : corporate
Make Model Name	Light Transport, Low Wing, 2 Turbojet Eng
Flight Phase	climbout : intermediate altitude cruise other
Route In Use	enroute airway : zfw
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 60 flight time total : 4500 flight time type : 550
ASRS Report	181504
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : overcame equipment problem
Consequence	faa : reviewed incident with flight crew
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

We were cleared to climb to FL350 from FL270. The autoplt was set to maintain a 900 FPM climb. Upon reaching FL350, I selected altitude hold. After several mins (2) I noticed the airspeed and mach # slowing down. I checked all engine and gauges and my altitude and vsi. All showed normal, but the aircraft was still slowing down. We checked the copilot side altimeter and vsi and it showed us at 36500' and a 500 FPM climb. Leveling the aircraft per the copilot side gave us a 500 FPM descent on the captain's side. We asked center to give us our mode C readout which was the same as what the captain's said. I suspected a blocked static source, and selected alternate static on the captain's side. The captain's altimeter would quickly up to agree with the copilot's side at 36700'. Center then came on to tell us that we were reading 36500'. We replied that we were having static system problems and would descend back down to FL350. We continued the flight on alternate static west/O further incident. On reaching destination, we left the aircraft with maintenance to rectify problem.

Original NASA ASRS Text

Title: CORP ACFT HAS STATIC AIR BLOCKAGE. ALT DEVIATION. SWITCH TO ALTERNATE AIR SOURCE.

Narrative: WE WERE CLRED TO CLB TO FL350 FROM FL270. THE AUTOPLT WAS SET TO MAINTAIN A 900 FPM CLB. UPON REACHING FL350, I SELECTED ALT HOLD. AFTER SEVERAL MINS (2) I NOTICED THE AIRSPD AND MACH # SLOWING DOWN. I CHKED ALL ENG AND GAUGES AND MY ALT AND VSI. ALL SHOWED NORMAL, BUT THE ACFT WAS STILL SLOWING DOWN. WE CHKED THE COPLT SIDE ALTIMETER AND VSI AND IT SHOWED US AT 36500' AND A 500 FPM CLB. LEVELING THE ACFT PER THE COPLT SIDE GAVE US A 500 FPM DSNT ON THE CAPT'S SIDE. WE ASKED CENTER TO GIVE US OUR MODE C READOUT WHICH WAS THE SAME AS WHAT THE CAPT'S SAID. I SUSPECTED A BLOCKED STATIC SOURCE, AND SELECTED ALTERNATE STATIC ON THE CAPT'S SIDE. THE CAPT'S ALTIMETER WOULD QUICKLY UP TO AGREE WITH THE COPLT'S SIDE AT 36700'. CENTER THEN CAME ON TO TELL US THAT WE WERE READING 36500'. WE REPLIED THAT WE WERE HAVING STATIC SYS PROBS AND WOULD DSND BACK DOWN TO FL350. WE CONTINUED THE FLT ON ALTERNATE STATIC W/O FURTHER INCIDENT. ON REACHING DEST, WE LEFT THE ACFT WITH MAINT TO RECTIFY PROB.

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.