Narrative:

I was en route to baf with plans to move a refueling stop at new castle; in (uwl). The WX briefing had indicated a threat of thunderstorms and as I approached uwl the sky became increasingly overcast. I saw some lightning at my 10 O'clock position but could not judge how far away it was. It was raining but I was VMC under the overcast. The controller began giving me vectors for the planned GPS approach. He instructed me to turn about 30 degrees left and descend to 4000 ft. As I was descending; still VMC; I felt a tremendous kick in the seat and the next thing I knew my head banged against the roof of the airplane. This happened twice; despite the fact that my seatbelt was fastened tight (it is an inertia seatbelt). I was stunned for a moment and the next thing I remember was the approach controller calling me asking for my altitude. I looked and at that time I was at 3300 ft. I explained to the controller that the turbulence was extreme and he offered me the nearest airport which was gez. It was raining heavily but I was able to make an uneventful landing. I completed my trip the next day as the WX steadily got worse with thunderstorms and hail. I believe this happened because I got too close to a cell. I was VMC but I had seen lightning and since I could not accurately judge how far away it was; I should not have accepted any vector in that direction. I also believe that effects of turbulence are also underappreciated in GA. We all learn 'first; fly the aircraft' but it can be difficult to do so when one has been struck in the head twice. I am thankful that the alert controller realized something was wrong and called my attention to it.

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Original NASA ASRS Text

Title: TB21 TRINIDAD PLT ENCOUNTERS SEVERE TURB; HAS SLIGHT INJURY; HAS ALTDEV AND DIVERTS TO ANOTHER ARPT.

Narrative: I WAS ENRTE TO BAF WITH PLANS TO MOVE A REFUELING STOP AT NEW CASTLE; IN (UWL). THE WX BRIEFING HAD INDICATED A THREAT OF TSTMS AND AS I APCHED UWL THE SKY BECAME INCREASINGLY OVCST. I SAW SOME LIGHTNING AT MY 10 O'CLOCK POS BUT COULD NOT JUDGE HOW FAR AWAY IT WAS. IT WAS RAINING BUT I WAS VMC UNDER THE OVCST. THE CTLR BEGAN GIVING ME VECTORS FOR THE PLANNED GPS APCH. HE INSTRUCTED ME TO TURN ABOUT 30 DEGS L AND DSND TO 4000 FT. AS I WAS DSNDING; STILL VMC; I FELT A TREMENDOUS KICK IN THE SEAT AND THE NEXT THING I KNEW MY HEAD BANGED AGAINST THE ROOF OF THE AIRPLANE. THIS HAPPENED TWICE; DESPITE THE FACT THAT MY SEATBELT WAS FASTENED TIGHT (IT IS AN INERTIA SEATBELT). I WAS STUNNED FOR A MOMENT AND THE NEXT THING I REMEMBER WAS THE APCH CTLR CALLING ME ASKING FOR MY ALT. I LOOKED AND AT THAT TIME I WAS AT 3300 FT. I EXPLAINED TO THE CTLR THAT THE TURB WAS EXTREME AND HE OFFERED ME THE NEAREST ARPT WHICH WAS GEZ. IT WAS RAINING HEAVILY BUT I WAS ABLE TO MAKE AN UNEVENTFUL LNDG. I COMPLETED MY TRIP THE NEXT DAY AS THE WX STEADILY GOT WORSE WITH TSTMS AND HAIL. I BELIEVE THIS HAPPENED BECAUSE I GOT TOO CLOSE TO A CELL. I WAS VMC BUT I HAD SEEN LIGHTNING AND SINCE I COULD NOT ACCURATELY JUDGE HOW FAR AWAY IT WAS; I SHOULD NOT HAVE ACCEPTED ANY VECTOR IN THAT DIRECTION. I ALSO BELIEVE THAT EFFECTS OF TURB ARE ALSO UNDERAPPRECIATED IN GA. WE ALL LEARN 'FIRST; FLY THE ACFT' BUT IT CAN BE DIFFICULT TO DO SO WHEN ONE HAS BEEN STRUCK IN THE HEAD TWICE. I AM THANKFUL THAT THE ALERT CTLR REALIZED SOMETHING WAS WRONG AND CALLED MY ATTN TO IT.

Data retrieved from NASA's ASRS site as of January 2009 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.