B737 autoplt malfunction caused altitude deviation of several hundred ft during cruise.

Attributes
ACN	432188
Time
Date	199903
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : pie.vortac
State Reference	FL
Altitude	msl single value : 27000
Environment
Flight Conditions	VMC
Light	Night
Aircraft 1
Controlling Facilities	artcc : zjx.artcc
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Navigation In Use	other vortac
Flight Phase	cruise : level
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer observation : company check pilot
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 18000 flight time type : 2000
ASRS Report	432188
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : overcame equipment problem flight crew : regained aircraft control
Consequence	other
Supplementary
Problem Areas	Maintenance Human Performance Aircraft Flight Crew Human Performance
Primary Problem	Aircraft

Narrative:

Autoplt/trim malfunction. Aircraft pitched up several hundred ft above intermediate cruise altitude inbound to tpa. Captain trainee in left seat disconnected autoplt and returned aircraft to original altitude of FL270. Altitude deviation was not detected by ZJX, as a descent by pilot's discretion had already been issued. The flight landed safely at tpa without further incident. Maintenance was debriefed fully.

Original NASA ASRS Text

Title: B737 AUTOPLT MALFUNCTION CAUSED ALTDEV OF SEVERAL HUNDRED FT DURING CRUISE.

Narrative: AUTOPLT/TRIM MALFUNCTION. ACFT PITCHED UP SEVERAL HUNDRED FT ABOVE INTERMEDIATE CRUISE ALT INBOUND TO TPA. CAPT TRAINEE IN L SEAT DISCONNECTED AUTOPLT AND RETURNED ACFT TO ORIGINAL ALT OF FL270. ALTDEV WAS NOT DETECTED BY ZJX, AS A DSCNT BY PLT'S DISCRETION HAD ALREADY BEEN ISSUED. THE FLT LANDED SAFELY AT TPA WITHOUT FURTHER INCIDENT. MAINT WAS DEBRIEFED FULLY.

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.