A DC9 in cruise at FL330 has alternate trim system malfunction resulting in an altitude deviation to...

Attributes
ACN	570724
Time
Date	200212
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : bna.airport
State Reference	TN
Altitude	msl bound lower : 33000 msl bound upper : 33500
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zkc.artcc
Operator	common carrier : air carrier
Make Model Name	DC-9 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	cruise : level
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 200 flight time total : 6500 flight time type : 1500
ASRS Report	570724
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	aircraft equipment problem : critical other anomaly other
Independent Detector	aircraft equipment other aircraft equipment : altimeter other flight crewa other flight crewb
Resolutory Action	flight crew : overcame equipment problem flight crew : regained aircraft control
Consequence	other
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

With autoplt on at FL330, the plane began to climb quickly with no input from a pilot. The trim horn was activating showing a runaway in the alternate trim system. The aircraft was placed off autoplt and the non-normal checklist completed. The aircraft climbed 500 ft to FL335 before enough forward trim could be added to stop the forced climb. ATC did call to query the altitude change. The aircraft continued to atl with no other abnormality.

Original NASA ASRS Text

Title: A DC9 IN CRUISE AT FL330 HAS ALTERNATE TRIM SYS MALFUNCTION RESULTING IN AN ALTDEV TO FL335.

Narrative: WITH AUTOPLT ON AT FL330, THE PLANE BEGAN TO CLB QUICKLY WITH NO INPUT FROM A PLT. THE TRIM HORN WAS ACTIVATING SHOWING A RUNAWAY IN THE ALTERNATE TRIM SYS. THE ACFT WAS PLACED OFF AUTOPLT AND THE NON-NORMAL CHKLIST COMPLETED. THE ACFT CLBED 500 FT TO FL335 BEFORE ENOUGH FORWARD TRIM COULD BE ADDED TO STOP THE FORCED CLB. ATC DID CALL TO QUERY THE ALT CHANGE. THE ACFT CONTINUED TO ATL WITH NO OTHER ABNORMALITY.

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.

A DC9 in cruise at FL330 has alternate trim system malfunction resulting in an altitude deviation to FL335.