Air carrier medium large transport autoplt fails to capture altitude in climb.

Attributes
ACN	130539
Time
Date	198912
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : pbi
State Reference	FL
Altitude	msl bound lower : 10000 msl bound upper : 10300
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zma
Operator	common carrier : air carrier
Make Model Name	Medium Large Transport, Low Wing, 2 Turbojet Eng
Navigation In Use	Other Other
Flight Phase	climbout : intermediate altitude
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : cfi pilot : atp
Experience	flight time last 90 days : 150 flight time total : 5002 flight time type : 2470
ASRS Report	130539
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	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 : returned to intended course or assigned course flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During climb out the aircraft was on autoplt and coupled to the performance computer. The first officer was flying. 10000' was set and armed in the altitude window. The aircraft leveled off at 10000', and the FMA showed that it was in the performance cruise mode. It was accelerating and the first officer was entering a cruise speed of 280 KTS in the performance computer. I was doing the 10000' check. The altitude warning horn went off at 10200'. The first officer disengaged the autoplt and autothrottles and flew it back to 10000'. We had reached 10300' before going back to 10000'. We inspected the performance computer and discovered it had dumped some of its data and would not accept commands. Should we trust these computers? One never knows when they will fail!

Original NASA ASRS Text

Title: ACR MLG AUTOPLT FAILS TO CAPTURE ALT IN CLIMB.

Narrative: DURING CLBOUT THE ACFT WAS ON AUTOPLT AND COUPLED TO THE PERFORMANCE COMPUTER. THE F/O WAS FLYING. 10000' WAS SET AND ARMED IN THE ALT WINDOW. THE ACFT LEVELED OFF AT 10000', AND THE FMA SHOWED THAT IT WAS IN THE PERFORMANCE CRUISE MODE. IT WAS ACCELERATING AND THE F/O WAS ENTERING A CRUISE SPD OF 280 KTS IN THE PERFORMANCE COMPUTER. I WAS DOING THE 10000' CHK. THE ALT WARNING HORN WENT OFF AT 10200'. THE F/O DISENGAGED THE AUTOPLT AND AUTOTHROTTLES AND FLEW IT BACK TO 10000'. WE HAD REACHED 10300' BEFORE GOING BACK TO 10000'. WE INSPECTED THE PERFORMANCE COMPUTER AND DISCOVERED IT HAD DUMPED SOME OF ITS DATA AND WOULD NOT ACCEPT COMMANDS. SHOULD WE TRUST THESE COMPUTERS? ONE NEVER KNOWS WHEN THEY WILL FAIL!

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.