A light aircraft experienced violent turbulence causing a deviation from assigned altitude.

Attributes
ACN	302514
Time
Date	199504
Day	Wed
Local Time Of Day	1201 To 1800
Place
Locale Reference	atc facility : lgc
State Reference	GA
Altitude	msl bound lower : 7500 msl bound upper : 9000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : ztl tower : lux
Operator	general aviation : personal
Make Model Name	Any Unknown or Unlisted Aircraft Manufacturer
Operating Under FAR Part	Part 91
Flight Phase	cruise other
Route In Use	enroute airway : ztl
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : instrument pilot : commercial
Experience	flight time last 90 days : 25 flight time total : 2265
ASRS Report	302514
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : returned to intended course or assigned course flight crew : exited adverse environment
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation other

Narrative:

Was flying from tampa to chattanooga on an instrument flight plan. Just north of lagrange, GA, the clouds were building up. My strike finder was showing lightning east of our course. I had ZTL approval to deviate west. I was also zigzagging around cumulus buildups. Entered a twring cloud too big to get around. The strike finder showed no lightning closer than 25 mi, but we were bounced around violently in what must have been vertical wind shear. Was at 8000 ft and quickly tossed up to 9000 ft. Attempting to correct went down to 7500 ft. Got the altitude under control and asked for lower. At 6000 ft the turbulence subsided. The lesson: stay away from big cumulus even if no strikes indicated.

Original NASA ASRS Text

Title: A LIGHT ACFT EXPERIENCED VIOLENT TURB CAUSING A DEV FROM ASSIGNED ALT.

Narrative: WAS FLYING FROM TAMPA TO CHATTANOOGA ON AN INST FLT PLAN. JUST N OF LAGRANGE, GA, THE CLOUDS WERE BUILDING UP. MY STRIKE FINDER WAS SHOWING LIGHTNING E OF OUR COURSE. I HAD ZTL APPROVAL TO DEVIATE W. I WAS ALSO ZIGZAGGING AROUND CUMULUS BUILDUPS. ENTERED A TWRING CLOUD TOO BIG TO GET AROUND. THE STRIKE FINDER SHOWED NO LIGHTNING CLOSER THAN 25 MI, BUT WE WERE BOUNCED AROUND VIOLENTLY IN WHAT MUST HAVE BEEN VERT WIND SHEAR. WAS AT 8000 FT AND QUICKLY TOSSED UP TO 9000 FT. ATTEMPTING TO CORRECT WENT DOWN TO 7500 FT. GOT THE ALT UNDER CTL AND ASKED FOR LOWER. AT 6000 FT THE TURB SUBSIDED. THE LESSON: STAY AWAY FROM BIG CUMULUS EVEN IF NO STRIKES INDICATED.

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.