Narrative:

Chain of events. WX: scattered to broken cumulus, tops typically under 9000' except for isolated cells, possibly thunderstorms, clearly visible at 11,000' cruise. Route of flight: cleared off airway then direct martinsburg VORTAC for avoidance of large cumulus clouds/possible thunderstorm in route of flight. Direction chosen was to the east of the buildup. This area was clear at the time of decision. This placed the aircraft near the approach corridors for dulles and national airports. Problem: I was enveloped from underneath by building cumulus. This fast rising cloud quickly caused a steep bank although the autoplt was engaged. The flight was for straight and level. Altitude compliance was lost at this time. Since there was other large cumulus to the west, I informed the controllers of my decision to turn east to get out of this cloud. He informed me that I was encroaching on the washington approach corridors. As the only time the plane was straight and level was the time that it was passing through that altitude, I was unable to comply with the controller's request until clear of that cloud (far 91.3). For many minutes after this problem, altitude compliance was sometimes impossible due to the strong convective activity. There were no other problems such as this regarding the flight. Communications: it amazed me as to how little I was able to communicate to the controller. Not only during, but for a long time after the problem occurred. I believe that I was able to keep the controller informed of my intentions, but due to extremely high workload, was not as clear as might be desirable. Perceptions: spatial disorientation was not a problem while fighting for control of the aircraft. It was a significant problem upon return to stable air. I found relief by engaging the autoplt. I expect that there could have been additional control problems when hand flying immediately after leaving that cloud. Other information: I recall fairly constant airspeed with sudden +/- 10 KT changes. Airspeed indication appeared to be independent of altitude. Vertical velocity ranged +/- 2000 FPM. I do not recall any sudden acceleration or deceleration that pressed me into the seat or seat belt. Prevention: I never saw this cloud coming. It's hard to speculate as to how one might prevent a future occurrence such as this.

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Original NASA ASRS Text

Title: ALT DEVIATION DUE TO TURBULENCE AND TSTM ACTIVITY. NEEDED TO CIRCUMNAVIGATE ISOLATED CELLS ON FLT PATH. ACFT FLEW NEAR APCH CORRIDORS FOR IAD AND DCA.

Narrative: CHAIN OF EVENTS. WX: SCATTERED TO BROKEN CUMULUS, TOPS TYPICALLY UNDER 9000' EXCEPT FOR ISOLATED CELLS, POSSIBLY TSTMS, CLEARLY VISIBLE AT 11,000' CRUISE. ROUTE OF FLT: CLRED OFF AIRWAY THEN DIRECT MARTINSBURG VORTAC FOR AVOIDANCE OF LARGE CUMULUS CLOUDS/POSSIBLE TSTM IN ROUTE OF FLT. DIRECTION CHOSEN WAS TO THE E OF THE BUILDUP. THIS AREA WAS CLEAR AT THE TIME OF DECISION. THIS PLACED THE ACFT NEAR THE APCH CORRIDORS FOR DULLES AND NATIONAL ARPTS. PROBLEM: I WAS ENVELOPED FROM UNDERNEATH BY BUILDING CUMULUS. THIS FAST RISING CLOUD QUICKLY CAUSED A STEEP BANK ALTHOUGH THE AUTOPLT WAS ENGAGED. THE FLT WAS FOR STRAIGHT AND LEVEL. ALT COMPLIANCE WAS LOST AT THIS TIME. SINCE THERE WAS OTHER LARGE CUMULUS TO THE WEST, I INFORMED THE CTLRS OF MY DECISION TO TURN EAST TO GET OUT OF THIS CLOUD. HE INFORMED ME THAT I WAS ENCROACHING ON THE WASHINGTON APCH CORRIDORS. AS THE ONLY TIME THE PLANE WAS STRAIGHT AND LEVEL WAS THE TIME THAT IT WAS PASSING THROUGH THAT ALT, I WAS UNABLE TO COMPLY WITH THE CTLR'S REQUEST UNTIL CLEAR OF THAT CLOUD (FAR 91.3). FOR MANY MINUTES AFTER THIS PROBLEM, ALT COMPLIANCE WAS SOMETIMES IMPOSSIBLE DUE TO THE STRONG CONVECTIVE ACTIVITY. THERE WERE NO OTHER PROBLEMS SUCH AS THIS REGARDING THE FLT. COMMUNICATIONS: IT AMAZED ME AS TO HOW LITTLE I WAS ABLE TO COMMUNICATE TO THE CTLR. NOT ONLY DURING, BUT FOR A LONG TIME AFTER THE PROBLEM OCCURRED. I BELIEVE THAT I WAS ABLE TO KEEP THE CTLR INFORMED OF MY INTENTIONS, BUT DUE TO EXTREMELY HIGH WORKLOAD, WAS NOT AS CLEAR AS MIGHT BE DESIRABLE. PERCEPTIONS: SPATIAL DISORIENTATION WAS NOT A PROBLEM WHILE FIGHTING FOR CONTROL OF THE ACFT. IT WAS A SIGNIFICANT PROBLEM UPON RETURN TO STABLE AIR. I FOUND RELIEF BY ENGAGING THE AUTOPLT. I EXPECT THAT THERE COULD HAVE BEEN ADDITIONAL CONTROL PROBLEMS WHEN HAND FLYING IMMEDIATELY AFTER LEAVING THAT CLOUD. OTHER INFORMATION: I RECALL FAIRLY CONSTANT AIRSPEED WITH SUDDEN +/- 10 KT CHANGES. AIRSPEED INDICATION APPEARED TO BE INDEPENDENT OF ALT. VERTICAL VELOCITY RANGED +/- 2000 FPM. I DO NOT RECALL ANY SUDDEN ACCELERATION OR DECELERATION THAT PRESSED ME INTO THE SEAT OR SEAT BELT. PREVENTION: I NEVER SAW THIS CLOUD COMING. IT'S HARD TO SPECULATE AS TO HOW ONE MIGHT PREVENT A FUTURE OCCURRENCE SUCH AS THIS.

Data retrieved from NASA's ASRS site as of August 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.