<< >> NASA ASRS Report 694004, April 2006

MD80 flight crew has uncommanded climb while at FL310 in cruise. Flight crew disconnects autoplt and descend to a lower altitude.

Attributes
ACN	694004
Time
Date	200604
Local Time Of Day	0601 To 1200
Place
Locale Reference	navaid : bil.vortac
State Reference	MT
Altitude	msl bound lower : 31000 msl bound upper : 31400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : czeg.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
Navigation In Use	other other vortac
Flight Phase	cruise : level
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
ASRS Report	694004
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
ASRS Report	694005
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude
Independent Detector	aircraft equipment other aircraft equipment : auto plt other flight crewa other flight crewb
Resolutory Action	flight crew : overcame equipment problem flight crew : returned to intended or assigned course
Consequence	other
Supplementary
Problem Areas	Aircraft
Primary Problem	Aircraft

Narrative:

While in cruise the autoplt suddenly started a climb; the first officer disconnected the autoplt and pushed the nose over to return to our altitude. It took a few seconds to get the airplane back to our assigned altitude due to the unusually high stabilizer setting the autoplt had set. At the same time; I noticed that due to this problem our airspeed had decreased and that the throttles were having trouble accelerating the airplane; we had been switched over to ZLC at this time so I requested FL290; in doing so we were able to get our speed back. Once level we attempted to re-engage both autoplts; both continued to want to climb. We elected to continue the flight without autoplts and landed dfw with no further problems. Edmonton gave no indication that there were any problems with our altitude change which was approximately 350-400 ft high by the time we were able to get under control. Supplemental information from acn 694005: we decided that the airplane was perfectly ctlable with the autoplt off; so we continued the flight to dfw. During the initial uncommanded climb; however; we had a slight altitude deviation for a few seconds. ATC did not say anything about the altitude deviation.

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Original NASA ASRS Text

Title: MD80 FLT CREW HAS UNCOMMANDED CLB WHILE AT FL310 IN CRUISE. FLT CREW DISCONNECTS AUTOPLT AND DSND TO A LOWER ALT.

Narrative: WHILE IN CRUISE THE AUTOPLT SUDDENLY STARTED A CLB; THE FO DISCONNECTED THE AUTOPLT AND PUSHED THE NOSE OVER TO RETURN TO OUR ALT. IT TOOK A FEW SECONDS TO GET THE AIRPLANE BACK TO OUR ASSIGNED ALT DUE TO THE UNUSUALLY HIGH STABILIZER SETTING THE AUTOPLT HAD SET. AT THE SAME TIME; I NOTICED THAT DUE TO THIS PROB OUR AIRSPD HAD DECREASED AND THAT THE THROTTLES WERE HAVING TROUBLE ACCELERATING THE AIRPLANE; WE HAD BEEN SWITCHED OVER TO ZLC AT THIS TIME SO I REQUESTED FL290; IN DOING SO WE WERE ABLE TO GET OUR SPD BACK. ONCE LEVEL WE ATTEMPTED TO RE-ENGAGE BOTH AUTOPLTS; BOTH CONTINUED TO WANT TO CLB. WE ELECTED TO CONTINUE THE FLT WITHOUT AUTOPLTS AND LANDED DFW WITH NO FURTHER PROBS. EDMONTON GAVE NO INDICATION THAT THERE WERE ANY PROBS WITH OUR ALT CHANGE WHICH WAS APPROX 350-400 FT HIGH BY THE TIME WE WERE ABLE TO GET UNDER CTL. SUPPLEMENTAL INFO FROM ACN 694005: WE DECIDED THAT THE AIRPLANE WAS PERFECTLY CTLABLE WITH THE AUTOPLT OFF; SO WE CONTINUED THE FLT TO DFW. DURING THE INITIAL UNCOMMANDED CLB; HOWEVER; WE HAD A SLIGHT ALTDEV FOR A FEW SECONDS. ATC DID NOT SAY ANYTHING ABOUT THE ALTDEV.

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.