Flight crew of an air carrier widebody transport aircraft overshot altitude due to a malfunctioned AFDS (automatic flight director system).

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Attributes
ACN	242565
Time
Date	199305
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : mqp
State Reference	TX
Altitude	msl bound lower : 31000 msl bound upper : 31600
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : dfw
Operator	common carrier : air carrier
Make Model Name	Widebody, 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 : instrument pilot : atp pilot : commercial
Experience	flight time last 90 days : 150 flight time total : 10000 flight time type : 1500
ASRS Report	242565
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : unspecified other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

While flying a widebody transport with autoplt engaged and climbing to FL310, I noticed that at approximately 700 ft prior to reaching FL310, the altitude alerter light illuminated normally, which indicated the impending level off. The ADI display annunciated altitude 'capture' and the AFDS panel annunciated 'altitude hold' which would also be a normal indication. However, the autoplt continued climbing the aircraft through FL310 and at 31300 ft I disengaged the autoplt. The climb was arrested at 31600 ft and I commenced an immediate descent back to FL310. There was no conflicting traffic in the area at that time. The flight continued to its destination with no further incident.

Original NASA ASRS Text

Title: FLC OF AN ACR WDB ACFT OVERSHOT ALT DUE TO A MALFUNCTIONED AFDS (AUTO FLT DIRECTOR SYS).

Narrative: WHILE FLYING A WDB WITH AUTOPLT ENGAGED AND CLBING TO FL310, I NOTICED THAT AT APPROX 700 FT PRIOR TO REACHING FL310, THE ALT ALERTER LIGHT ILLUMINATED NORMALLY, WHICH INDICATED THE IMPENDING LEVEL OFF. THE ADI DISPLAY ANNUNCIATED ALT 'CAPTURE' AND THE AFDS PANEL ANNUNCIATED 'ALT HOLD' WHICH WOULD ALSO BE A NORMAL INDICATION. HOWEVER, THE AUTOPLT CONTINUED CLBING THE ACFT THROUGH FL310 AND AT 31300 FT I DISENGAGED THE AUTOPLT. THE CLB WAS ARRESTED AT 31600 FT AND I COMMENCED AN IMMEDIATE DSCNT BACK TO FL310. THERE WAS NO CONFLICTING TFC IN THE AREA AT THAT TIME. THE FLT CONTINUED TO ITS DEST WITH NO FURTHER INCIDENT.

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.