A B737-800 crew, on approach at 7000 ft, where executing a right turn when the stabilizer 'out of trim' light illuminated. The autoplt induced a nose down attitude exceeding clearance.

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Attributes
ACN	557320
Time
Date	200208
Day	Sun
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord.airport
State Reference	IL
Altitude	msl bound lower : 3800 msl bound upper : 7000
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : c90.tracon
Operator	common carrier : air carrier
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
ASRS Report	557320
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	557321
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : stab out of trim light other flight crewa other flight crewb
Resolutory Action	aircraft : automation overrode flight crew flight crew : regained aircraft control
Consequence	other other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft

Narrative:

At approximately XA17Z while being vectored by chicago approach control, the autoplt stabilizer out of trim light illuminated. When the captain announced the light I saw that we were nose low and in a r-hand turn. We had been given a course change to 180 degrees just prior to this so the r-hand turn was not unexpected. Glancing at the altitude we were around 6800 ft and descending. Our assigned altitude was 7000 ft. I immediately disconnected the autoplt, arrested the descent at around 6400 ft and started a climb back to our assigned altitude. During the climb we were cleared to descend to 4000 ft. When I turned off autoplt, the aircraft was not too much out of trim. I only had to trim nose up for the climb. Callback conversation with reporter revealed the following information: the reporter stated after the autoplt was disconnected the airplane flew normally. The reporter said the item was entered in the maintenance logbook but no report has been received by the flight crew from maintenance on the corrective action.

Original NASA ASRS Text

Title: A B737-800 CREW, ON APCH AT 7000 FT, WHERE EXECUTING A R TURN WHEN THE STABILIZER 'OUT OF TRIM' LIGHT ILLUMINATED. THE AUTOPLT INDUCED A NOSE DOWN ATTITUDE EXCEEDING CLRNC.

Narrative: AT APPROX XA17Z WHILE BEING VECTORED BY CHICAGO APCH CTL, THE AUTOPLT STABILIZER OUT OF TRIM LIGHT ILLUMINATED. WHEN THE CAPT ANNOUNCED THE LIGHT I SAW THAT WE WERE NOSE LOW AND IN A R-HAND TURN. WE HAD BEEN GIVEN A COURSE CHANGE TO 180 DEGS JUST PRIOR TO THIS SO THE R-HAND TURN WAS NOT UNEXPECTED. GLANCING AT THE ALT WE WERE AROUND 6800 FT AND DSNDING. OUR ASSIGNED ALT WAS 7000 FT. I IMMEDIATELY DISCONNECTED THE AUTOPLT, ARRESTED THE DSCNT AT AROUND 6400 FT AND STARTED A CLB BACK TO OUR ASSIGNED ALT. DURING THE CLB WE WERE CLRED TO DSND TO 4000 FT. WHEN I TURNED OFF AUTOPLT, THE ACFT WAS NOT TOO MUCH OUT OF TRIM. I ONLY HAD TO TRIM NOSE UP FOR THE CLB. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED AFTER THE AUTOPLT WAS DISCONNECTED THE AIRPLANE FLEW NORMALLY. THE RPTR SAID THE ITEM WAS ENTERED IN THE MAINT LOGBOOK BUT NO RPT HAS BEEN RECEIVED BY THE FLC FROM MAINT ON THE CORRECTIVE ACTION.

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.