Small cargo pilot encountered turbulence which caused an altitude deviation with ZID.

Attributes
ACN	586749
Time
Date	200307
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : iiu.vortac
State Reference	KY
Altitude	msl bound lower : 17000 msl bound upper : 17300
Environment
Weather Elements	Turbulence Ice Thunderstorm
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid.artcc
Operator	common carrier : air taxi
Make Model Name	Small Transport
Operating Under FAR Part	Part 135
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : atp pilot : commercial
Experience	flight time last 90 days : 150 flight time total : 8200 flight time type : 600
ASRS Report	586749
Person 2
Affiliation	government : faa
Function	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather inflight encounter : turbulence non adherence : clearance non adherence : company policies non adherence : far other anomaly
Resolutory Action	flight crew : regained aircraft control none taken : anomaly accepted
Supplementary
Problem Areas	Flight Crew Human Performance Weather
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Upon just passing through a hole, 8-10 mi wide, in an area of thunderstorms, I reported to the controller that I only encountered light to moderate chop and light rime icing. 1 1/2-2 mins later, my aircraft entered an updraft. The autoplt could not maintain altitude, so at 200 ft above my assigned altitude, I turned off the autoplt. The aircraft was already trimmed down. I strayed below my assigned altitude by approximately 300 ft before I was able to stop the descent. Immediately, I started climbing back to my assigned altitude. I believe I encountered a downdraft very shortly after disconnecting the aircraft's autoplt. I was unable to immediately inform the controller of my deviation, until climbing back up to my assigned altitude.

Original NASA ASRS Text

Title: SMALL CARGO PLT ENCOUNTERED TURB WHICH CAUSED AN ALTDEV WITH ZID.

Narrative: UPON JUST PASSING THROUGH A HOLE, 8-10 MI WIDE, IN AN AREA OF TSTMS, I RPTED TO THE CTLR THAT I ONLY ENCOUNTERED LIGHT TO MODERATE CHOP AND LIGHT RIME ICING. 1 1/2-2 MINS LATER, MY ACFT ENTERED AN UPDRAFT. THE AUTOPLT COULD NOT MAINTAIN ALT, SO AT 200 FT ABOVE MY ASSIGNED ALT, I TURNED OFF THE AUTOPLT. THE ACFT WAS ALREADY TRIMMED DOWN. I STRAYED BELOW MY ASSIGNED ALT BY APPROX 300 FT BEFORE I WAS ABLE TO STOP THE DSCNT. IMMEDIATELY, I STARTED CLBING BACK TO MY ASSIGNED ALT. I BELIEVE I ENCOUNTERED A DOWNDRAFT VERY SHORTLY AFTER DISCONNECTING THE ACFT'S AUTOPLT. I WAS UNABLE TO IMMEDIATELY INFORM THE CTLR OF MY DEV, UNTIL CLBING BACK UP TO MY 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.