FLC OF AN MD11 LOST CTL OF THE ACFT DURING SEVERE TURB CAUSED BY A PASSING LINE OF TSTMS. THE ACFT AUTOPLT SYS DISCONNECTED; AND RECONNECTED; SEVERAL TIMES; DURING WHICH THE ACFT LOST 800 FT FROM ASSIGNED ALT. COMS WERE LOST FOR SEVERAL MINS WITH ARTCC AND REGAINED AFTER THE FLC WAS GIVEN ANOTHER FREQ BY ANOTHER NEARBY CARRIER. THERE WERE NO INJURIES.

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WE WERE DEVIATING TO PARALLEL A VERY NARROW BUT CONCENTRATED AND ACTIVE LINE THAT RAN FROM PAWNEE CITY; NE; TO LIBERAL; KS; (ONE OF THE LONGEST I'VE EVER SEEN). AS THE LINE STARTED TO BREAK UP NEAR LBL; ATC GAVE US DIRECT CIVET WHEN CLR OF WX. WE REQUESTED AND CLBED TO FL350. AT ABOUT XX50Z WE LOST ATC DUE TO A PROB WITH THEIR FREQ (I THINK 134.67). THE AIR WAS SMOOTH AND WE WERE ABOVE THE WX. AS WE CROSSED THE AREA OF THE LINE WE FELT A COUPLE OF JOLTS FOLLOWED BY MODERATE TO SEVERE TURB. THE AUTOPLT DISCONNECTED/RECONNECTED 7-8 TIMES ALONG WITH STICK SHAKER (CONSTANT) AND OVERSPD WARNINGS. THE AIRPLANE CLBED 300 FT AND SHORTLY DSNDED RAPIDLY TO FL342. FOR 10-15 SECONDS IT WAS COMPLETELY OUT OF CTL. DURING THIS TIME WE WERE ATTEMPTING TO CONTACT ATC OR ANYONE ELSE. NONE OF THIS STUFF SHOWED ON RADAR; AND IT WAS PITCH BLACK. AFTER 5-10 MINS OF THIS; THINGS SETTLED DOWN AND FINALLY AN ACR Y FLT GAVE US A NEW FREQ. WE CONTACTED CTR AND THEY SAID THEY SAW THE LOST ALT BUT THERE WAS NO CONFLICT. NO ONE GOT HURT OR SICK. THE SEAT BELT LIGHT HAD BEEN ON FOR 30-40 MINS AND THE FLT ATTENDANTS HAD BEEN TOLD TO DISCONTINUE SVC AND SIT DOWN. BEFORE THE EVENT; WHILE SMOOTH; THEY ASKED IF THEY COULD PICK UP THE DINNER TRAYS (STILL OUT) AND WERE TOLD OK BUT SIT DOWN AT THE FIRST SIGN OF BUMPS -- THEY DID. NOTES: 1) THIS AIRPLANE (MD11) CONTINUES TO BE THE MOST UNSTABLE AIRPLANE I HAVE EVER FLOWN IN MODERATE OR GREATER TURB. AT THE FIRST JOLT; MOST AUTOPLTS TRIP OFF AND THE AIRSPD GOES INTO THE RED. THERE IS NO TURB MODE. THE TURB PROCS DIFFER BTWN LINE CHK AIRMEN AND MANUAL; IE; AUTOPLT ON/OFF AUTOTHROTTLE ON/OFF. 2) WE CONTINUED TO HAVE TO MAKE SEVERAL BRIEFINGS TO DIFFERENT FLT ATTENDANTS WHO CALL THE COCKPIT.