Air carrier with automated cockpit on autoplt with pms engaged for descent finds aircraft climbing.

Attributes
ACN	201063
Time
Date	199201
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : hyp
State Reference	CA
Altitude	msl bound lower : 20000 msl bound upper : 20700
Environment
Light	Night
Aircraft 1
Controlling Facilities	artcc : zoa
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : commercial pilot : instrument
Experience	flight time last 90 days : 140 flight time total : 4800
ASRS Report	201063
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 90 flight time total : 20500 flight time type : 3600
ASRS Report	200740
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 other
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation other

Narrative:

On the arrival STAR to sjc, the captain had the medium large transport on autoplt with pms. FMA indicated perf descent (or CR2) we were level at FL200 and both looked at our approach chart for sjc to just 1-2 seconds and noticed the aircraft climbing at 2000 FPM. Power was being advanced by the autothrottles. The FMA said perf descent. While the aircraft was climbing, the captain disconnected the autoplt at 20700 ft and we resumed our profile. We entered this autoplt malfunction in the aircraft maintenance log. We have heard of other similar medium large transport autoplt malfunctions. My recommendation to other medium large transport crews is to not use pms on descent with the autoplt connected unless they monitor the aircraft 100 percent of the time, especially with crossing waypoints. The pms and autoplt seem to do fine in the climb and level flight and 99.9 percent of the time in descent but every once in a while it will cause the aircraft to do something which it is not supposed to do. Note: we had been given a discretionary descent clearance to FL200 with a further clearance later issued to 12000 ft. The altitude armed in the altitude select was 12000 'altitude' was armed in the FMA.

Original NASA ASRS Text

Title: ACR WITH AUTOMATED COCKPIT ON AUTOPLT WITH PMS ENGAGED FOR DSCNT FINDS ACFT CLBING.

Narrative: ON THE ARR STAR TO SJC, THE CAPT HAD THE MLG ON AUTOPLT WITH PMS. FMA INDICATED PERF DSCNT (OR CR2) WE WERE LEVEL AT FL200 AND BOTH LOOKED AT OUR APCH CHART FOR SJC TO JUST 1-2 SECONDS AND NOTICED THE ACFT CLBING AT 2000 FPM. PWR WAS BEING ADVANCED BY THE AUTOTHROTTLES. THE FMA SAID PERF DSCNT. WHILE THE ACFT WAS CLBING, THE CAPT DISCONNECTED THE AUTOPLT AT 20700 FT AND WE RESUMED OUR PROFILE. WE ENTERED THIS AUTOPLT MALFUNCTION IN THE ACFT MAINT LOG. WE HAVE HEARD OF OTHER SIMILAR MLG AUTOPLT MALFUNCTIONS. MY RECOMMENDATION TO OTHER MLG CREWS IS TO NOT USE PMS ON DSCNT WITH THE AUTOPLT CONNECTED UNLESS THEY MONITOR THE ACFT 100 PERCENT OF THE TIME, ESPECIALLY WITH XING WAYPOINTS. THE PMS AND AUTOPLT SEEM TO DO FINE IN THE CLB AND LEVEL FLT AND 99.9 PERCENT OF THE TIME IN DSCNT BUT EVERY ONCE IN A WHILE IT WILL CAUSE THE ACFT TO DO SOMETHING WHICH IT IS NOT SUPPOSED TO DO. NOTE: WE HAD BEEN GIVEN A DISCRETIONARY DSCNT CLRNC TO FL200 WITH A FURTHER CLRNC LATER ISSUED TO 12000 FT. THE ALT ARMED IN THE ALT SELECT WAS 12000 'ALT' WAS ARMED IN THE FMA.

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.