Medium large transport flight crew attempting to avoid WX descends below assigned altitude.

Attributes
ACN	346800
Time
Date	199609
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : sdf
State Reference	KY
Altitude	msl bound lower : 4000 msl bound upper : 5000
Environment
Flight Conditions	Marginal
Light	Dusk
Aircraft 1
Controlling Facilities	tracon : sdf
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp pilot : commercial pilot : flight engineer pilot : instrument
Experience	flight time last 90 days : 270 flight time total : 11000 flight time type : 8000
ASRS Report	346800
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance
Independent Detector	other controllera other flight crewa
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

We were to level at 5000 ft MSL. There was a thunderstorm 5 mi south of the airport. I wanted to land on another runway. First officer was slow in asking approach control. I descended to 4000 ft MSL before we realized it. Approach gave us 4000 ft MSL right away. He didn't say anything about the altitude deviation.

Original NASA ASRS Text

Title: MLG FLC ATTEMPTING TO AVOID WX DSNDS BELOW ASSIGNED ALT.

Narrative: WE WERE TO LEVEL AT 5000 FT MSL. THERE WAS A TSTM 5 MI S OF THE ARPT. I WANTED TO LAND ON ANOTHER RWY. FO WAS SLOW IN ASKING APCH CTL. I DSNDED TO 4000 FT MSL BEFORE WE REALIZED IT. APCH GAVE US 4000 FT MSL RIGHT AWAY. HE DIDN'T SAY ANYTHING ABOUT THE ALTDEV.

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.