FLC OF A SUPER MD80 EXPERIENCE UNRPTED HIGH ALT WINDSHEAR TURB RESULTING IN NO KNOWN PAX OR FLT ATTENDANT INJURIES.

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LOCATION: 60 NM S OF BNA APPROX 180 DEG RADIAL DIRECT LAGRA. AT CRUISE ALT OF FL290; COMPANY FLT PLAN SHOWED THAT ANY ROUGH AIR WAS TO TERMINATE IN THE VICINITY OF POCKET CITY. RADAR RETURNS SHOWED NOTHING ON WSI DURING PREFLT AND NOTHING WAS SEEN ON THE SHIP RADAR PRIOR TO OR DURING THE ENCOUNTER. THE SUDDEN ONSET OF IMMEDIATE MODERATE TO SEVERE CHOP AND WING ROCK IS THE REASON FOR THIS RPT. DESPITE FREQUENT INQUIRIES WITH ATC DURING EACH HDOF PRIOR TO THE POS; THERE WERE NO RPTS OF ANYTHING LIKE WHAT WE EXPERIENCED; ONLY LIGHT CHOP. A FULL MOON INDICATED THAT WE WERE IN THE CLR ON TOP OF ALL CLOUD AT FL290. WINDS WERE GENERALLY 250 DEGS AND 50 KTS AS PER THE FLT PLAN. DURING THE ENCOUNTER; WINDS INSTANTLY BECAME 270 DEGS 100 KTS PER OUR GPS READOUT. LOWER ALT WAS REQUESTED AND A DSCNT TO FL270 WAS MADE. A PA WAS MADE FORM THE COCKPIT TO HAVE THE FLT ATTENDANTS BE SEATED IMMEDIATELY WHEN THE ENCOUNTER OCCURRED. SEVERAL PA'S WERE MADE LATER TO CALM PAX. UPON LNDG I COULD NOT BE CERTAIN OF THE NUMBER OF G FORCES THAT WE HAD EXPERIENCED AND ENTERED IN THE E-6 LOG THAT THE G METER BE READ TO DETERMINE IF AN ADDITIONAL ACFT INSPECTION WAS NECESSARY. NO PAX OR FLT ATTENDANT INJURIES WERE RPTED.