A B737-400 first officer reported an altitude deviation in zan airspace.

Attributes
ACN	515850
Time
Date	200106
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	navaid : ssr.vortac
State Reference	AK
Altitude	msl bound lower : 16600 msl bound upper : 17000
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Make Model Name	B737-400
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 5000 flight time type : 1000
ASRS Report	515850
Events
Anomaly	altitude deviation : excursion from assigned altitude non adherence : far non adherence : published procedure non adherence : company policies non adherence : clearance
Resolutory Action	flight crew : overrode automation flight crew : returned to assigned altitude
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Leveled at assigned altitude of 17000 ft and turned autoplt on. Aircraft started a gradual descent to 16600 ft when altitude alerter warned us of deviation. Disengaged autoplt and climbed back to 17000 ft.

Original NASA ASRS Text

Title: A B737-400 FO RPTED AN ALTDEV IN ZAN AIRSPACE.

Narrative: LEVELED AT ASSIGNED ALT OF 17000 FT AND TURNED AUTOPLT ON. ACFT STARTED A GRADUAL DSCNT TO 16600 FT WHEN ALT ALERTER WARNED US OF DEV. DISENGAGED AUTOPLT AND CLBED BACK TO 17000 FT.

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.