Narrative:

Clearance was received from FL290 to FL230. While descending we also were deviating from some widely scattered thunderstorms. Approaching one twring cumulous, and nearing FL240, the cloud exhibited certain characteristics that would indicate turbulence and strong updrafts. (Top was estimated at FL270 or higher with what looked like a lenticular cap just above its top.) a turn from this cloud was made and subsequent penetration into an area of IMC conditions began. The ride conditions were moderate turbulence. The plane's autoplt then pitched the nose up to prevent overspd. The airspeed was 30-40 KTS from overspd. The activation of the overspd protection was a surprise especially the aggressiveness. I continued a power reduction yet the nose still pitched up. In a short time after reaching FL240, we were approaching FL255, before a smooth transition to, 'autoplt off' and reinitiation of the descent to FL230 could begin. I had never experienced the autoplt's overspd protection create a climb condition -- from a condition it anticipated, would create an overspd. I feel sure the turbulence was a contributing factor, yet almost 40 KTS below vmo seems overly protective. Could an aural warning (subtle in volume) to warn the pilot that the autoplt is about to enter or near an overspd protection condition be developed. Currently the only aural overspd warning is after vmo is reached. Also there is no way to anticipate the autoplt's impending overspd protection mode. In conclusion it may have been a very strong updraft that complicated things. Fearing a shear effect was another reason that corrective action was smooth and evenly paced so as not to suddenly change attitude, airspeed or power. Hope this helps.

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Original NASA ASRS Text

Title: FLC OF A BRITISH HAWKER, HS25, LOST PITCH CTL OF ACFT DURING DSCNT IN TSTM ACTIVITY DUE TO TURB AND WINDSHEAR. THE ACFT PITCHED UP IN CLB TO PREVENT OVERSPD. AFTER THE FLC DISCONNECTED THE AUTOPLT, THEY WERE ABLE TO REESTABLISH DSCNT TO ASSIGNED ALT.

Narrative: CLRNC WAS RECEIVED FROM FL290 TO FL230. WHILE DSNDING WE ALSO WERE DEVIATING FROM SOME WIDELY SCATTERED TSTMS. APCHING ONE TWRING CUMULOUS, AND NEARING FL240, THE CLOUD EXHIBITED CERTAIN CHARACTERISTICS THAT WOULD INDICATE TURB AND STRONG UPDRAFTS. (TOP WAS ESTIMATED AT FL270 OR HIGHER WITH WHAT LOOKED LIKE A LENTICULAR CAP JUST ABOVE ITS TOP.) A TURN FROM THIS CLOUD WAS MADE AND SUBSEQUENT PENETRATION INTO AN AREA OF IMC CONDITIONS BEGAN. THE RIDE CONDITIONS WERE MODERATE TURB. THE PLANE'S AUTOPLT THEN PITCHED THE NOSE UP TO PREVENT OVERSPD. THE AIRSPD WAS 30-40 KTS FROM OVERSPD. THE ACTIVATION OF THE OVERSPD PROTECTION WAS A SURPRISE ESPECIALLY THE AGGRESSIVENESS. I CONTINUED A PWR REDUCTION YET THE NOSE STILL PITCHED UP. IN A SHORT TIME AFTER REACHING FL240, WE WERE APCHING FL255, BEFORE A SMOOTH TRANSITION TO, 'AUTOPLT OFF' AND REINITIATION OF THE DSCNT TO FL230 COULD BEGIN. I HAD NEVER EXPERIENCED THE AUTOPLT'S OVERSPD PROTECTION CREATE A CLB CONDITION -- FROM A CONDITION IT ANTICIPATED, WOULD CREATE AN OVERSPD. I FEEL SURE THE TURB WAS A CONTRIBUTING FACTOR, YET ALMOST 40 KTS BELOW VMO SEEMS OVERLY PROTECTIVE. COULD AN AURAL WARNING (SUBTLE IN VOLUME) TO WARN THE PLT THAT THE AUTOPLT IS ABOUT TO ENTER OR NEAR AN OVERSPD PROTECTION CONDITION BE DEVELOPED. CURRENTLY THE ONLY AURAL OVERSPD WARNING IS AFTER VMO IS REACHED. ALSO THERE IS NO WAY TO ANTICIPATE THE AUTOPLT'S IMPENDING OVERSPD PROTECTION MODE. IN CONCLUSION IT MAY HAVE BEEN A VERY STRONG UPDRAFT THAT COMPLICATED THINGS. FEARING A SHEAR EFFECT WAS ANOTHER REASON THAT CORRECTIVE ACTION WAS SMOOTH AND EVENLY PACED SO AS NOT TO SUDDENLY CHANGE ATTITUDE, AIRSPD OR PWR. HOPE THIS HELPS.

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.