Altitude deviation altitude excursion during approach on autoplt.

Attributes
ACN	268726
Time
Date	199404
Day	Sat
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : msp
State Reference	MN
Altitude	msl bound lower : 4000 msl bound upper : 4350
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : msp
Operator	common carrier : air carrier
Make Model Name	A320
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	cruise other descent : approach
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : cfi pilot : flight engineer
Experience	flight time last 90 days : 150 flight time total : 11500 flight time type : 150
ASRS Report	268726
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 other anomaly other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : overcame equipment problem flight crew : regained aircraft control
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

While on a heading to intercept the ILS 29R at msp we called the airport in sight and we were cleared for the visual approach. At this time we were level at an assigned altitude of 4000 ft. Prior to localizer intercept, the GS came into view and I armed the approach function of the autoplt. (The latest version of software allows GS capture prior to localizer intercept.) the GS captured and we began a descent for a couple hundred ft. For an unknown reason (possibly a false GS) we began to climb, while still in GS capture mode. This transition to a climb was not noticed immediately due to confign changes, turbulent conditions and a power increase that was not obvious, since the thrust levers do not move. I became aware of the climb at about 4100 ft and attempted to level off by pulling the vertical speed knob and rotating it to a descent. The aircraft continued to climb on the autoplt, which I then disconnected. By this time we had ballooned through 4350 ft. I was surprised to find that the vertical speed selector window showing a climb. I don't know why this was the case -- possibly because of pulling and turning the knob at the same time, and the system accepted the aircraft current vertical speed rather than the requested vertical speed. There is no altitude hold button. No conflict occurred. There is a lot to dislike about the design and implementation of this automated cockpit.

Original NASA ASRS Text

Title: ALTDEV ALT EXCURSION DURING APCH ON AUTOPLT.

Narrative: WHILE ON A HDG TO INTERCEPT THE ILS 29R AT MSP WE CALLED THE ARPT IN SIGHT AND WE WERE CLRED FOR THE VISUAL APCH. AT THIS TIME WE WERE LEVEL AT AN ASSIGNED ALT OF 4000 FT. PRIOR TO LOC INTERCEPT, THE GS CAME INTO VIEW AND I ARMED THE APCH FUNCTION OF THE AUTOPLT. (THE LATEST VERSION OF SOFTWARE ALLOWS GS CAPTURE PRIOR TO LOC INTERCEPT.) THE GS CAPTURED AND WE BEGAN A DSCNT FOR A COUPLE HUNDRED FT. FOR AN UNKNOWN REASON (POSSIBLY A FALSE GS) WE BEGAN TO CLB, WHILE STILL IN GS CAPTURE MODE. THIS TRANSITION TO A CLB WAS NOT NOTICED IMMEDIATELY DUE TO CONFIGN CHANGES, TURBULENT CONDITIONS AND A PWR INCREASE THAT WAS NOT OBVIOUS, SINCE THE THRUST LEVERS DO NOT MOVE. I BECAME AWARE OF THE CLB AT ABOUT 4100 FT AND ATTEMPTED TO LEVEL OFF BY PULLING THE VERT SPD KNOB AND ROTATING IT TO A DSCNT. THE ACFT CONTINUED TO CLB ON THE AUTOPLT, WHICH I THEN DISCONNECTED. BY THIS TIME WE HAD BALLOONED THROUGH 4350 FT. I WAS SURPRISED TO FIND THAT THE VERT SPD SELECTOR WINDOW SHOWING A CLB. I DON'T KNOW WHY THIS WAS THE CASE -- POSSIBLY BECAUSE OF PULLING AND TURNING THE KNOB AT THE SAME TIME, AND THE SYS ACCEPTED THE ACFT CURRENT VERT SPD RATHER THAN THE REQUESTED VERT SPD. THERE IS NO ALT HOLD BUTTON. NO CONFLICT OCCURRED. THERE IS A LOT TO DISLIKE ABOUT THE DESIGN AND IMPLEMENTATION OF THIS AUTOMATED COCKPIT.

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.