Large transport with automated cockpit has equipment malfunction resulting in altitude deviation.

Attributes
ACN	147232
Time
Date	199006
Day	Fri
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : rmg
State Reference	GA
Altitude	msl bound lower : 21000 msl bound upper : 21400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl
Operator	common carrier : air carrier
Make Model Name	Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	cruise other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 25000 flight time type : 900
ASRS Report	147232
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
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 flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Aircraft was level at 21000'. INS LNAV VNAV and right autoplt engaged. We were given a turn to 030 degrees and to slow to 250 KTS. I set 250 KTS in crz page and MCP IAS window, and both showed FL210. The autothrottles were at idle and airspeed about 285 KTS. At this time autothrottles went to climb power and autoplt pitched up 12 degrees. Both were disengaged and aircraft was leveled at 21400' and returned to 21000' assigned. Atl center made no mention of this event. All system worked normal, autothrottle and autoplt, remainder of flight and no known reason for this aircraft irregular autothrottle autoplt action. I did submit a crew irregular operation report to my chief pilot atl office.

Original NASA ASRS Text

Title: LGT WITH AUTOMATED COCKPIT HAS EQUIPMENT MALFUNCTION RESULTING IN ALT DEVIATION.

Narrative: ACFT WAS LEVEL AT 21000'. INS LNAV VNAV AND R AUTOPLT ENGAGED. WE WERE GIVEN A TURN TO 030 DEGS AND TO SLOW TO 250 KTS. I SET 250 KTS IN CRZ PAGE AND MCP IAS WINDOW, AND BOTH SHOWED FL210. THE AUTOTHROTTLES WERE AT IDLE AND AIRSPD ABOUT 285 KTS. AT THIS TIME AUTOTHROTTLES WENT TO CLB PWR AND AUTOPLT PITCHED UP 12 DEGS. BOTH WERE DISENGAGED AND ACFT WAS LEVELED AT 21400' AND RETURNED TO 21000' ASSIGNED. ATL CTR MADE NO MENTION OF THIS EVENT. ALL SYS WORKED NORMAL, AUTOTHROTTLE AND AUTOPLT, REMAINDER OF FLT AND NO KNOWN REASON FOR THIS ACFT IRREGULAR AUTOTHROTTLE AUTOPLT ACTION. I DID SUBMIT A CREW IRREGULAR OPERATION RPT TO MY CHIEF PLT ATL OFFICE.

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.