A320 crew had aircraft uncommanded pitch down in ZOB class a airspace.

Attributes
ACN	489660
Time
Date	200010
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : mia.vortac
Altitude	msl bound lower : 32600 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob.artcc
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : multi engine pilot : instrument pilot : atp
Experience	flight time last 90 days : 200 flight time total : 18800 flight time type : 500
ASRS Report	489660
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial pilot : multi engine
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other
Independent Detector	aircraft equipment : altitude alert other flight crewa other flight crewb
Resolutory Action	other
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

At FL330 on autoplt #1 near mkg VOR, aircraft started uncommanded fast descent. Altitude alerter on FCU set at FL330. No reason for aircraft to start descent. Autoplt was disconnected. Aircraft did not go below FL326. Aircraft was level at FL330 within 20 seconds. No comment from ATC. Callback conversation with reporter revealed the following information: the crew entered a discrepancy in the aircraft logbook. Air carrier maintenance did a complete self check of the system. All tested items passed the self check, and the aircraft was returned to service. Upon learning this, the captain called the air carrier chief pilot to voice concern that nothing had been done to fix the problem. The aircraft was returned to the air carrier maintenance base for engineering evaluation. Components were removed from the aircraft and tested on the air carrier main computer shop test rig. All tested normal except the 'second computer' spoiler and elevator computer, which showed a fault. This computer was replaced and the aircraft has flown without further problem. The reporter is concerned that maintenance released the aircraft for service on the basis of the self test, which showed the 'second' to be fault free.

Original NASA ASRS Text

Title: A320 CREW HAD ACFT UNCOMMANDED PITCH DOWN IN ZOB CLASS A AIRSPACE.

Narrative: AT FL330 ON AUTOPLT #1 NEAR MKG VOR, ACFT STARTED UNCOMMANDED FAST DSCNT. ALT ALERTER ON FCU SET AT FL330. NO REASON FOR ACFT TO START DSCNT. AUTOPLT WAS DISCONNECTED. ACFT DID NOT GO BELOW FL326. ACFT WAS LEVEL AT FL330 WITHIN 20 SECONDS. NO COMMENT FROM ATC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CREW ENTERED A DISCREPANCY IN THE ACFT LOGBOOK. ACR MAINT DID A COMPLETE SELF CHK OF THE SYS. ALL TESTED ITEMS PASSED THE SELF CHK, AND THE ACFT WAS RETURNED TO SVC. UPON LEARNING THIS, THE CAPT CALLED THE ACR CHIEF PLT TO VOICE CONCERN THAT NOTHING HAD BEEN DONE TO FIX THE PROB. THE ACFT WAS RETURNED TO THE ACR MAINT BASE FOR ENGINEERING EVALUATION. COMPONENTS WERE REMOVED FROM THE ACFT AND TESTED ON THE ACR MAIN COMPUTER SHOP TEST RIG. ALL TESTED NORMAL EXCEPT THE 'SEC COMPUTER' SPOILER AND ELEVATOR COMPUTER, WHICH SHOWED A FAULT. THIS COMPUTER WAS REPLACED AND THE ACFT HAS FLOWN WITHOUT FURTHER PROB. THE RPTR IS CONCERNED THAT MAINT RELEASED THE ACFT FOR SVC ON THE BASIS OF THE SELF TEST, WHICH SHOWED THE 'SEC' TO BE FAULT FREE.

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.