Air carrier medium large transport incurred altitude excursion at start of descent.

Attributes
ACN	89176
Time
Date	198806
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : dfw
State Reference	TX
Altitude	msl bound lower : 35000 msl bound upper : 35300
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zfw
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport
Navigation In Use	Other
Flight Phase	descent other
Route In Use	arrival other enroute airway : dfw
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
ASRS Report	89176
Person 2
Affiliation	company : air carrier
Function	flight crew : captain observation : company check pilot oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 16500 flight time type : 2200
ASRS Report	89177
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

Aircraft was in cruise at FL350. Performance management system was hooked up to the autoplt in cruise. We were cleared to FL240 at which time I commanded the autoplt to descend to FL240. (Armed altitude, 240, rolled pitch wheel to airplane nose down, pushed mach hold and reduced power.) airplane started a climb instead of descent. At 35200' I disconnected autoplt and stopped climb at 35300'. All autoplt indications were normal except aircraft climbed instead of descended. Workload was normal at the time. No unusual circumstances.

Original NASA ASRS Text

Title: ACR MLG INCURRED ALT EXCURSION AT START OF DESCENT.

Narrative: ACFT WAS IN CRUISE AT FL350. PERFORMANCE MGMNT SYS WAS HOOKED UP TO THE AUTOPLT IN CRUISE. WE WERE CLRED TO FL240 AT WHICH TIME I COMMANDED THE AUTOPLT TO DSND TO FL240. (ARMED ALT, 240, ROLLED PITCH WHEEL TO AIRPLANE NOSE DOWN, PUSHED MACH HOLD AND REDUCED PWR.) AIRPLANE STARTED A CLB INSTEAD OF DSCNT. AT 35200' I DISCONNECTED AUTOPLT AND STOPPED CLB AT 35300'. ALL AUTOPLT INDICATIONS WERE NORMAL EXCEPT ACFT CLBED INSTEAD OF DSNDED. WORKLOAD WAS NORMAL AT THE TIME. NO UNUSUAL CIRCUMSTANCES.

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.