MD80 flight crew has an altitude deviation during cruise in rvsm airspace.

Attributes
ACN	713983
Time
Date	200610
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : ztl.artcc
State Reference	GA
Altitude	msl single value : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl.artcc
Operator	common carrier : air carrier
Make Model Name	MD-80 Series (DC-9-80) Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	713983
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	713984
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : returned to assigned altitude flight crew : overcame equipment problem
Consequence	Other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

Autoplt #2 previously written up as disconnecting in cruise. The signoff was that it tested correctly on the ground. Autoplt engaged at about FL180. About 15 mins into cruise it disengaged and it seemed to have some nose down trim. Aircraft descended 300 ft (captain saw 340 ft). I took the controls; started climb back up; a bit too aggressively; and overcorrected by 250 ft. Then returned to cruise. Switched autoplts and the rest of the flight was uneventful. Supplemental information from acn 713984: the MD80 autoplt is all the time trying to violate you by uncommanded actions. Seems to be getting more frequent in recent yrs. This aircraft had the same write-up the previous day and was cleared overnight by maintenance -- cannot duplicate. The first flight was my leg on autoplt #1 -- no problem. I should have been more attentive when we put it on autoplt #2 for second leg.

Original NASA ASRS Text

Title: MD80 FLT CREW HAS AN ALTDEV DURING CRUISE IN RVSM AIRSPACE.

Narrative: AUTOPLT #2 PREVIOUSLY WRITTEN UP AS DISCONNECTING IN CRUISE. THE SIGNOFF WAS THAT IT TESTED CORRECTLY ON THE GND. AUTOPLT ENGAGED AT ABOUT FL180. ABOUT 15 MINS INTO CRUISE IT DISENGAGED AND IT SEEMED TO HAVE SOME NOSE DOWN TRIM. ACFT DSNDED 300 FT (CAPT SAW 340 FT). I TOOK THE CTLS; STARTED CLB BACK UP; A BIT TOO AGGRESSIVELY; AND OVERCORRECTED BY 250 FT. THEN RETURNED TO CRUISE. SWITCHED AUTOPLTS AND THE REST OF THE FLT WAS UNEVENTFUL. SUPPLEMENTAL INFO FROM ACN 713984: THE MD80 AUTOPLT IS ALL THE TIME TRYING TO VIOLATE YOU BY UNCOMMANDED ACTIONS. SEEMS TO BE GETTING MORE FREQUENT IN RECENT YRS. THIS ACFT HAD THE SAME WRITE-UP THE PREVIOUS DAY AND WAS CLRED OVERNIGHT BY MAINT -- CANNOT DUPLICATE. THE FIRST FLT WAS MY LEG ON AUTOPLT #1 -- NO PROB. I SHOULD HAVE BEEN MORE ATTENTIVE WHEN WE PUT IT ON AUTOPLT #2 FOR SECOND LEG.

Data retrieved from NASA's ASRS site as of January 2009 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.