A descending MD80 suddenly reverses its direction and starts an uncommanded climb from FL263 to FL270. Aircraft had had an autoplt trim light on during climb out in turbulence. Air, PA.

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Attributes
ACN	467870
Time
Date	200003
Day	Mon
Local Time Of Day	0601 To 1200
Place
State Reference	OH
Altitude	msl bound lower : 26300 msl bound upper : 27000
Environment
Flight Conditions	IMC
Weather Elements	Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zob.artcc
Operator	common carrier : air carrier
Make Model Name	MD-88
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : enroute altitude change
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : atp pilot : commercial pilot : flight engineer pilot : multi engine
Experience	flight time last 90 days : 190 flight time total : 8000 flight time type : 3000
ASRS Report	467870
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : commercial pilot : atp
Experience	flight time last 90 days : 180 flight time total : 5500 flight time type : 1000
ASRS Report	467423
Events
Anomaly	aircraft equipment problem : less severe inflight encounter : turbulence inflight encounter : weather other anomaly
Independent Detector	other flight crewa
Resolutory Action	flight crew : overrode automation flight crew : regained aircraft control flight crew : returned to assigned altitude
Consequence	Other
Supplementary
Problem Areas	Flight Crew Human Performance Weather Aircraft
Primary Problem	Aircraft

Narrative:

MD88 en route from phl to cvg, ZOB, IMC with continuous light and occasional moderate chop, doing a VNAV descent from FL350 to FL260. Last 1000 ft of descent, switched to vertical navigation approximately 1000 FPM. At FL263, aircraft still on autoplt #1 pitched up about 10 degrees and 1500 ft vertical climb. After unsuccessfully trying to correct with the autoplt controls, I disconnected the autoplt and manually flew the aircraft back to FL260. The climb topped out at about FL270. We did get an autoplt trim light during climb out indicating the trim was slow. Wrote up #1 autoplt and flew 2 more legs on autoplt #2 which worked fine. Suspect #1 autoplt problem compounded by moderate turbulence.

Original NASA ASRS Text

Title: A DSNDING MD80 SUDDENLY REVERSES ITS DIRECTION AND STARTS AN UNCOMMANDED CLB FROM FL263 TO FL270. ACFT HAD HAD AN AUTOPLT TRIM LIGHT ON DURING CLBOUT IN TURB. AIR, PA.

Narrative: MD88 ENRTE FROM PHL TO CVG, ZOB, IMC WITH CONTINUOUS LIGHT AND OCCASIONAL MODERATE CHOP, DOING A VNAV DSCNT FROM FL350 TO FL260. LAST 1000 FT OF DSCNT, SWITCHED TO VERT NAV APPROX 1000 FPM. AT FL263, ACFT STILL ON AUTOPLT #1 PITCHED UP ABOUT 10 DEGS AND 1500 FT VERT CLB. AFTER UNSUCCESSFULLY TRYING TO CORRECT WITH THE AUTOPLT CTLS, I DISCONNECTED THE AUTOPLT AND MANUALLY FLEW THE ACFT BACK TO FL260. THE CLB TOPPED OUT AT ABOUT FL270. WE DID GET AN AUTOPLT TRIM LIGHT DURING CLBOUT INDICATING THE TRIM WAS SLOW. WROTE UP #1 AUTOPLT AND FLEW 2 MORE LEGS ON AUTOPLT #2 WHICH WORKED FINE. SUSPECT #1 AUTOPLT PROB COMPOUNDED BY MODERATE TURB.

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.