MD80 had altitude excursion.

Attributes
ACN	475157
Time
Date	200006
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	intersection : delmo
State Reference	TX
Altitude	msl bound lower : 10700 msl bound upper : 11000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : d10.tracon
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : glenrose
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 180 flight time total : 8200 flight time type : 3000
ASRS Report	475157
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument pilot : multi engine
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude other anomaly other
Independent Detector	other controllera other flight crewa other flight crewb
Resolutory Action	controller : issued new clearance
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

While level at 11000 approaching delmo on the glen rose arrival into dfw we were required to slow to 210KTS and turn to a heading of 350 as per arrival instructions when the aircraft started an uncommanded descent. I noticed the situation passing FL108 and the aircraft descended to FL107 before I was able to stop the descent. Approach asked what our altitude was and then cleared us to FL100. No conflict was observed or reported. At times this autoplt has difficulty maintaining altitude while slowing and performing a lrg turn. I know they will not improve the autoplt so I will have to double my awareness in this situation. Callback conversation with reporter revealed the following information: the reporter stated the captain made a maintenance discrepancy in the aircraft maintenance log. He does not know what maintenance did to correct the problem. The captain reports that this is a wide spread problem in the MD80 series aircraft. The pitch control in the autoplt does not seem to be able to handle both a speed reduction and a bank at the same time.

Original NASA ASRS Text

Title: MD80 HAD ALT EXCURSION.

Narrative: WHILE LEVEL AT 11000 APCHING DELMO ON THE GLEN ROSE ARRIVAL INTO DFW WE WERE REQUIRED TO SLOW TO 210KTS AND TURN TO A HEADING OF 350 AS PER ARRIVAL INSTRUCTIONS WHEN THE ACFT STARTED AN UNCOMMANDED DESCENT. I NOTICED THE SIT PASSING FL108 AND THE ACFT DESCENDED TO FL107 BEFORE I WAS ABLE TO STOP THE DESCENT. APCH ASKED WHAT OUR ALT WAS AND THEN CLEARED US TO FL100. NO CONFLICT WAS OBSERVED OR RPTED. AT TIMES THIS AUTOPLT HAS DIFFICULTY MAINTAINING ALT WHILE SLOWING AND PERFORMING A LRG TURN. I KNOW THEY WILL NOT IMPROVE THE AUTOPLT SO I WILL HAVE TO DOUBLE MY AWARENESS IN THIS SIT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAPT MADE A MAINT DISCREPANCY IN THE ACFT MAINT LOG. HE DOES NOT KNOW WHAT MAINT DID TO CORRECT THE PROB. THE CAPT RPTS THAT THIS IS A WIDE SPREAD PROB IN THE MD80 SERIES ACFT. THE PITCH CTL IN THE AUTOPLT DOES NOT SEEM TO BE ABLE TO HANDLE BOTH A SPD REDUCTION AND A BANK AT THE SAME TIME.

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.