Medium large transport aircraft automatic equipment made uncommanded climb.

Attributes
ACN	134267
Time
Date	199001
Day	Thu
Local Time Of Day	1801 To 2400
Place
Locale Reference	atc facility : bsr
State Reference	CA
Altitude	msl bound lower : 28000 msl bound upper : 28500
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other
Flight Phase	cruise other descent other
Route In Use	arrival other enroute airway : zoa
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : atp pilot : commercial
Experience	flight time last 90 days : 175 flight time total : 9700 flight time type : 400
ASRS Report	134267
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : instrument pilot : commercial
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 : overcame equipment problem flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

En route from lax to sfo on J501 at FL330. We were directed to descend to FL280 and maintain 250 KTS for sequencing. The flight guidance system wa set and armed, and began the descent. The system leveled at FL280 and slowed to 250 KTS. Shortly thereafter, the autothrottles went to climb power, the aircraft accelerated to 280 KTS and started a quick climb. The flight guidance system was still set for FL280 at 250 KTS. I disconnected the autoplt with the altitude peaking at FL285. The aircraft was returned to FL280 at 250 KTS. There was no traffic conflict. This is the fourth time in 5 months that I have had uncommanded actions with this particular flight guidance system that caused a deviation. Each incident was completely different from the others, varying from uncommanded climbs to failures to capture and hold altitudes.

Original NASA ASRS Text

Title: MLG ACFT AUTO EQUIPMENT MADE UNCOMMANDED CLIMB.

Narrative: ENRTE FROM LAX TO SFO ON J501 AT FL330. WE WERE DIRECTED TO DSND TO FL280 AND MAINTAIN 250 KTS FOR SEQUENCING. THE FLT GUIDANCE SYS WA SET AND ARMED, AND BEGAN THE DSCNT. THE SYS LEVELED AT FL280 AND SLOWED TO 250 KTS. SHORTLY THEREAFTER, THE AUTOTHROTTLES WENT TO CLB PWR, THE ACFT ACCELERATED TO 280 KTS AND STARTED A QUICK CLB. THE FLT GUIDANCE SYS WAS STILL SET FOR FL280 AT 250 KTS. I DISCONNECTED THE AUTOPLT WITH THE ALT PEAKING AT FL285. THE ACFT WAS RETURNED TO FL280 AT 250 KTS. THERE WAS NO TFC CONFLICT. THIS IS THE FOURTH TIME IN 5 MONTHS THAT I HAVE HAD UNCOMMANDED ACTIONS WITH THIS PARTICULAR FLT GUIDANCE SYS THAT CAUSED A DEVIATION. EACH INCIDENT WAS COMPLETELY DIFFERENT FROM THE OTHERS, VARYING FROM UNCOMMANDED CLBS TO FAILURES TO CAPTURE AND HOLD ALTS.

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.