B727 crew had altitude excursion.

Attributes
ACN	468684
Time
Date	200004
Day	Wed
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : yyz.airport
State Reference	ON
Altitude	msl bound lower : 28000 msl bound upper : 28400
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : czyz.artcc
Operator	common carrier : air carrier
Make Model Name	B727-200
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 : first officer
Qualification	pilot : commercial pilot : flight engineer pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 30 flight time total : 12000 flight time type : 8000
ASRS Report	468684
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance
Independent Detector	other flight crewa other flight crewb other other : 3
Resolutory Action	flight crew : returned to assigned altitude other
Consequence	other
Supplementary
Problem Areas	Flight Crew Human Performance Aircraft
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

At FL280, while in cruise flight, the autoplt engaged, the aircraft entered an uncommanded 20 degree right bank. I disengaged the autoplt (including altitude hold). In doing so, I inadvertently gained 400 ft. I immediately corrected back to the assigned altitude of FL280.

Original NASA ASRS Text

Title: B727 CREW HAD ALT EXCURSION.

Narrative: AT FL280, WHILE IN CRUISE FLT, THE AUTOPLT ENGAGED, THE ACFT ENTERED AN UNCOMMANDED 20 DEG R BANK. I DISENGAGED THE AUTOPLT (INCLUDING ALT HOLD). IN DOING SO, I INADVERTENTLY GAINED 400 FT. I IMMEDIATELY CORRECTED BACK TO THE ASSIGNED ALT OF FL280.

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.