Mdt has pitot static air data computer failure.

Attributes
ACN	270830
Time
Date	199405
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : gso
State Reference	NC
Altitude	msl bound lower : 8700 msl bound upper : 10000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	enroute airway : gso
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time total : 9000
ASRS Report	270830
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : atp
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	none taken : anomaly accepted other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Aircraft was cleared for en route descent from 11000 ft to 10000 ft by gso approach control. Autoplt was engaged. 10000 ft was selected and 1000 FPM descent rate selected. As aircraft approached 10000 ft altimeter suddenly wound down to 8700 ft and pilot's airspeed indicator went to 0 KIAS. Xchk of copilot's instruments showed 230 KIAS 12700 ft MSL. Crosschecked standby altimeter -- it showed approximately 9000 ft MSL. Queried gso approach as to altitude. They indicated we were at 8700 ft MSL. We advised gso of our problem and climbed back to assigned altitude of 10000 ft. We decided that we had a pitot static air data computer failure. Control of aircraft was turned over to copilot as he had operating airspeed and relied on the standby altimeter for altitude information. No further problems encountered en route to clt. At approximately 1500 ft AGL, system returned to normal readings. Pilot's altimeter had been replaced at maintenance base previous night and was signed off after satisfactory static system check. As of this time maintenance personnel have not determined cause of problem. Very unusual to lose airspeed on one side and altimeter on the other. Very distracting initially.

Original NASA ASRS Text

Title: MDT HAS PITOT STATIC AIR DATA COMPUTER FAILURE.

Narrative: ACFT WAS CLRED FOR ENRTE DSCNT FROM 11000 FT TO 10000 FT BY GSO APCH CTL. AUTOPLT WAS ENGAGED. 10000 FT WAS SELECTED AND 1000 FPM DSCNT RATE SELECTED. AS ACFT APCHED 10000 FT ALTIMETER SUDDENLY WOUND DOWN TO 8700 FT AND PLT'S AIRSPD INDICATOR WENT TO 0 KIAS. XCHK OF COPLT'S INSTS SHOWED 230 KIAS 12700 FT MSL. XCHKED STANDBY ALTIMETER -- IT SHOWED APPROX 9000 FT MSL. QUERIED GSO APCH AS TO ALT. THEY INDICATED WE WERE AT 8700 FT MSL. WE ADVISED GSO OF OUR PROB AND CLBED BACK TO ASSIGNED ALT OF 10000 FT. WE DECIDED THAT WE HAD A PITOT STATIC AIR DATA COMPUTER FAILURE. CTL OF ACFT WAS TURNED OVER TO COPLT AS HE HAD OPERATING AIRSPD AND RELIED ON THE STANDBY ALTIMETER FOR ALT INFO. NO FURTHER PROBS ENCOUNTERED ENRTE TO CLT. AT APPROX 1500 FT AGL, SYS RETURNED TO NORMAL READINGS. PLT'S ALTIMETER HAD BEEN REPLACED AT MAINT BASE PREVIOUS NIGHT AND WAS SIGNED OFF AFTER SATISFACTORY STATIC SYS CHK. AS OF THIS TIME MAINT PERSONNEL HAVE NOT DETERMINED CAUSE OF PROB. VERY UNUSUAL TO LOSE AIRSPD ON ONE SIDE AND ALTIMETER ON THE OTHER. VERY DISTRACTING INITIALLY.

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.