A cessna 206 pilot descended below assigned altitude in turbulence near stl.

Attributes
ACN	443314
Time
Date	199907
Day	Sat
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : stl.airport
State Reference	MO
Altitude	msl bound lower : 4500 msl bound upper : 5000
Environment
Flight Conditions	Mixed
Weather Elements	Turbulence
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid.artcc
Operator	general aviation : personal
Make Model Name	Cessna Stationair/Turbo Stationair 6
Operating Under FAR Part	Part 91
Navigation In Use	other
Flight Phase	cruise : level
Route In Use	enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : private
Experience	flight time last 90 days : 25 flight time total : 1000 flight time type : 20
ASRS Report	443314
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : turbulence inflight encounter : weather non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to assigned airspace
Supplementary
Problem Areas	Weather Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

During this time I also went through an area of IMC that contained a severe downdraft, and could not maintain altitude even with full power, maximum propeller, etc. Altitude deviation was approximately 500 ft below assigned altitude.

Original NASA ASRS Text

Title: A CESSNA 206 PLT DSNDED BELOW ASSIGNED ALT IN TURB NEAR STL.

Narrative: DURING THIS TIME I ALSO WENT THROUGH AN AREA OF IMC THAT CONTAINED A SEVERE DOWNDRAFT, AND COULD NOT MAINTAIN ALT EVEN WITH FULL PWR, MAX PROP, ETC. ALTDEV WAS APPROX 500 FT BELOW ASSIGNED 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.