Pilot encountered a thermal and departed assigned altitude without clearance.

Attributes
ACN	428394
Time
Date	199901
Day	Sun
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : i49.airport
State Reference	KY
Altitude	msl bound lower : 6000 msl bound upper : 7800
Environment
Flight Conditions	VMC
Weather Elements	other
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zid.artcc
Operator	general aviation : personal
Make Model Name	Baron 58/58TC
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	IFR
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
ASRS Report	428394
Person 2
Affiliation	government : faa
Function	controller : radar
Qualification	controller : radar
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter other non adherence : far non adherence : clearance
Independent Detector	other controllera
Resolutory Action	controller : issued advisory flight crew : returned to assigned airspace
Supplementary
Problem Areas	Flight Crew Human Performance Weather
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

On a routine IFR flight from isz I asked to leave the frequency to check on WX. While off frequency, I flew into a cumulus cloud. The thermal caused the plane to ascend to 7800 ft MSL while off frequency with FSS. Upon returning to frequency, I was informed by the controller that I was at the wrong altitude and did not have permission. I was already in a descent back to 6000 ft MSL. I should have returned to the frequency and advised ATC that I was unable to maintain 6000 ft assigned altitude. Instead I stayed on with FSS and concentrated on flying the airplane.

Original NASA ASRS Text

Title: PLT ENCOUNTERED A THERMAL AND DEPARTED ASSIGNED ALT WITHOUT CLRNC.

Narrative: ON A ROUTINE IFR FLT FROM ISZ I ASKED TO LEAVE THE FREQ TO CHK ON WX. WHILE OFF FREQ, I FLEW INTO A CUMULUS CLOUD. THE THERMAL CAUSED THE PLANE TO ASCEND TO 7800 FT MSL WHILE OFF FREQ WITH FSS. UPON RETURNING TO FREQ, I WAS INFORMED BY THE CTLR THAT I WAS AT THE WRONG ALT AND DID NOT HAVE PERMISSION. I WAS ALREADY IN A DSCNT BACK TO 6000 FT MSL. I SHOULD HAVE RETURNED TO THE FREQ AND ADVISED ATC THAT I WAS UNABLE TO MAINTAIN 6000 FT ASSIGNED ALT. INSTEAD I STAYED ON WITH FSS AND CONCENTRATED ON FLYING THE AIRPLANE.

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.