A boeing 737-200 descend below assigned altitude at gso.

Attributes
ACN	438220
Time
Date	199905
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : gso.airport
State Reference	NC
Altitude	msl bound lower : 3600 msl bound upper : 4000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : gso.tower
Operator	common carrier : air carrier
Make Model Name	B737-200
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : instrument pilot : multi engine
Experience	flight time last 90 days : 180 flight time total : 11000 flight time type : 4000
ASRS Report	438220
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : overshoot non adherence : clearance
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : returned to assigned airspace
Supplementary
Problem Areas	Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On downwind to runway 23 at gso, we were given 4000 ft. Approach controller called out traffic we were following. Both pilots were trying to locate the traffic and the PF allowed the aircraft to descend to 3600 ft. I instantly alerted the captain and he climbed back to 4000 ft. Controller never noticed the deviation and there was no conflict with other traffic. Flight proceeded normally and landed in gso. Deviation caused by both pilots looking for preceding traffic and not monitoring plane and altitude.

Original NASA ASRS Text

Title: A BOEING 737-200 DSND BELOW ASSIGNED ALT AT GSO.

Narrative: ON DOWNWIND TO RWY 23 AT GSO, WE WERE GIVEN 4000 FT. APCH CTLR CALLED OUT TFC WE WERE FOLLOWING. BOTH PLTS WERE TRYING TO LOCATE THE TFC AND THE PF ALLOWED THE ACFT TO DSND TO 3600 FT. I INSTANTLY ALERTED THE CAPT AND HE CLBED BACK TO 4000 FT. CTLR NEVER NOTICED THE DEV AND THERE WAS NO CONFLICT WITH OTHER TFC. FLT PROCEEDED NORMALLY AND LANDED IN GSO. DEV CAUSED BY BOTH PLTS LOOKING FOR PRECEDING TFC AND NOT MONITORING PLANE AND ALT.

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.