MD83 crew had an autoplt malfunction that resulted in a 700 ft altitude deviation, in ZME class a.

Attributes
ACN	631371
Time
Date	200409
Day	Sun
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : lit.vortac
Altitude	msl bound lower : 31000 msl bound upper : 31700
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zme.artcc tower : sgj.tower
Operator	common carrier : air carrier
Make Model Name	MD-83
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	631371
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	631267
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : returned to assigned altitude
Consequence	other other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

Deviation from clearance altitude. Over lit at FL310, ZME cleared us direct to tnp. After putting clearance into GPS, which required a right turn of 26 degrees, autoplt went into a bank which exceeded 30 degrees (approximately 35 degrees). I disconnected the autoplt. Aircraft immediately pitched up to a 700 ft altitude deviation. Aircraft brought back to altitude smoothly. ATC questioned our altitude. We reported leveling at FL310 and that we had experienced a problem with our autoplt. ATC wanted to know if everything was ok. We reported in the affirmative. ATC written up for excessive bank angle at altitude.

Original NASA ASRS Text

Title: MD83 CREW HAD AN AUTOPLT MALFUNCTION THAT RESULTED IN A 700 FT ALTDEV, IN ZME CLASS A.

Narrative: DEV FROM CLRNC ALT. OVER LIT AT FL310, ZME CLRED US DIRECT TO TNP. AFTER PUTTING CLRNC INTO GPS, WHICH REQUIRED A R TURN OF 26 DEGS, AUTOPLT WENT INTO A BANK WHICH EXCEEDED 30 DEGS (APPROX 35 DEGS). I DISCONNECTED THE AUTOPLT. ACFT IMMEDIATELY PITCHED UP TO A 700 FT ALTDEV. ACFT BROUGHT BACK TO ALT SMOOTHLY. ATC QUESTIONED OUR ALT. WE RPTED LEVELING AT FL310 AND THAT WE HAD EXPERIENCED A PROB WITH OUR AUTOPLT. ATC WANTED TO KNOW IF EVERYTHING WAS OK. WE RPTED IN THE AFFIRMATIVE. ATC WRITTEN UP FOR EXCESSIVE BANK ANGLE AT ALT.

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.