Narrative:

While cruising at 41000' en route to jyp center informed us of WX that they were painting approximately 30 NM dead ahead. At the time there were numerous thunderstorms in the vicinity and our on board WX radar showed heavy precipitation (ie, thunderstorms) to our left and right, but what appeared to be clear sailing straight ahead. According to center the line to our left use 180 mi long and to our right 90 NM long, so we elected to continue straight ahead. It was a dark night, but there was no visibility indication of any exceptionally rough WX ahead. Approximately 5 mins after making our decision we went IMC and approximately 2 mins later hit moderate turbulence. Shortly thereafter and west/O warning we encountered severe to extreme turbulence. Bank angles approached 90 degrees left and right, nose attitude changed by as much as 20-30 degrees up and down, and we lost and gained several thousands of ft in what seemed like seconds. Although there was a considerable amount of lightning, (we later found out we were struck several times) there was very little rain. Sometime after the severe turbulence started (it's hard to say when, possibly 30 seconds, possibly several mins) the captain (who was in the right seat) called that we were losing the cabin (slow decompression). We quickly donned masks and went through the appropriate checklist while I continued to attempt to maintain proper attitude and keep the aircraft upright. We were unsure of the cause of the lack (the power settings should have been high enough to maintain cabin pressure), so we began a gradual emergency descend (spoilers and gear were not used because of the severe turbulence). Because of the severe/extreme turbulence we were not able to make (reestablish) radio contact with ATC until we passed through FL330, although we were able to squawk 7700. Center eventually cleared us to 10000' and gave us vectors away from most of the storm. We eventually made an uneventful approach and landing at yip. Fortunately, just prior to entering the severe WX,I had slowed to 0.74 mach, tightened my belt, turned up the instrument lights and turned on the continuous air ignition (just in case the WX got rough). We're still not sure why we encountered such severe turbulence, but I have 2 theories. First, radar picks up precipitation, not turbulence or electrical activity, hence our radar didn't present an entirely accurate picture to us (this might be a good commercial for a stormscope). Second, we might have flown into an area before an anvil and since it was night we wouldn't have known this visually. In any case, we probably should have gone around to one side or another, or requested an early descent out of 41000'. Fortunately, the engines didn't flame out, we didn't panic; we flew the aircraft before doing anything else and we were flying an small transport. Incidentally, after we were level at 10000', they started broadcasting several convective segments for our area.

Related reports:

Google
 

Original NASA ASRS Text

Title: FLT CREW OF SMT AT HIGH ALT ENCOUNTERS SEVERE TURB IN AREA OF TSTMS. RESULTS IN LOSS OF CONTROL OF ACFT.

Narrative: WHILE CRUISING AT 41000' ENRTE TO JYP CENTER INFORMED US OF WX THAT THEY WERE PAINTING APPROX 30 NM DEAD AHEAD. AT THE TIME THERE WERE NUMEROUS TSTMS IN THE VICINITY AND OUR ON BOARD WX RADAR SHOWED HEAVY PRECIPITATION (IE, TSTMS) TO OUR LEFT AND RIGHT, BUT WHAT APPEARED TO BE CLR SAILING STRAIGHT AHEAD. ACCORDING TO CENTER THE LINE TO OUR LEFT USE 180 MI LONG AND TO OUR RIGHT 90 NM LONG, SO WE ELECTED TO CONTINUE STRAIGHT AHEAD. IT WAS A DARK NIGHT, BUT THERE WAS NO VIS INDICATION OF ANY EXCEPTIONALLY ROUGH WX AHEAD. APPROX 5 MINS AFTER MAKING OUR DECISION WE WENT IMC AND APPROX 2 MINS LATER HIT MODERATE TURB. SHORTLY THEREAFTER AND W/O WARNING WE ENCOUNTERED SEVERE TO EXTREME TURB. BANK ANGLES APCHED 90 DEGS LEFT AND RIGHT, NOSE ATTITUDE CHANGED BY AS MUCH AS 20-30 DEGS UP AND DOWN, AND WE LOST AND GAINED SEVERAL THOUSANDS OF FT IN WHAT SEEMED LIKE SECS. ALTHOUGH THERE WAS A CONSIDERABLE AMOUNT OF LIGHTNING, (WE LATER FOUND OUT WE WERE STRUCK SEVERAL TIMES) THERE WAS VERY LITTLE RAIN. SOMETIME AFTER THE SEVERE TURB STARTED (IT'S HARD TO SAY WHEN, POSSIBLY 30 SECS, POSSIBLY SEVERAL MINS) THE CAPT (WHO WAS IN THE RIGHT SEAT) CALLED THAT WE WERE LOSING THE CABIN (SLOW DECOMPRESSION). WE QUICKLY DONNED MASKS AND WENT THROUGH THE APPROPRIATE CHKLIST WHILE I CONTINUED TO ATTEMPT TO MAINTAIN PROPER ATTITUDE AND KEEP THE ACFT UPRIGHT. WE WERE UNSURE OF THE CAUSE OF THE LACK (THE PWR SETTINGS SHOULD HAVE BEEN HIGH ENOUGH TO MAINTAIN CABIN PRESSURE), SO WE BEGAN A GRADUAL EMER DSND (SPOILERS AND GEAR WERE NOT USED BECAUSE OF THE SEVERE TURB). BECAUSE OF THE SEVERE/EXTREME TURB WE WERE NOT ABLE TO MAKE (REESTABLISH) RADIO CONTACT WITH ATC UNTIL WE PASSED THROUGH FL330, ALTHOUGH WE WERE ABLE TO SQUAWK 7700. CENTER EVENTUALLY CLRED US TO 10000' AND GAVE US VECTORS AWAY FROM MOST OF THE STORM. WE EVENTUALLY MADE AN UNEVENTFUL APCH AND LNDG AT YIP. FORTUNATELY, JUST PRIOR TO ENTERING THE SEVERE WX,I HAD SLOWED TO 0.74 MACH, TIGHTENED MY BELT, TURNED UP THE INSTRUMENT LIGHTS AND TURNED ON THE CONTINUOUS AIR IGNITION (JUST IN CASE THE WX GOT ROUGH). WE'RE STILL NOT SURE WHY WE ENCOUNTERED SUCH SEVERE TURB, BUT I HAVE 2 THEORIES. FIRST, RADAR PICKS UP PRECIPITATION, NOT TURB OR ELECTRICAL ACTIVITY, HENCE OUR RADAR DIDN'T PRESENT AN ENTIRELY ACCURATE PICTURE TO US (THIS MIGHT BE A GOOD COMMERCIAL FOR A STORMSCOPE). SECOND, WE MIGHT HAVE FLOWN INTO AN AREA BEFORE AN ANVIL AND SINCE IT WAS NIGHT WE WOULDN'T HAVE KNOWN THIS VISUALLY. IN ANY CASE, WE PROBABLY SHOULD HAVE GONE AROUND TO ONE SIDE OR ANOTHER, OR REQUESTED AN EARLY DSCNT OUT OF 41000'. FORTUNATELY, THE ENGS DIDN'T FLAME OUT, WE DIDN'T PANIC; WE FLEW THE ACFT BEFORE DOING ANYTHING ELSE AND WE WERE FLYING AN SMT. INCIDENTALLY, AFTER WE WERE LEVEL AT 10000', THEY STARTED BROADCASTING SEVERAL CONVECTIVE SEGMENTS FOR OUR AREA.

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.