DC10-30 ENCOUNTERS SEVERE VIBRATION DURING ENG FERRY IN ZAU AREA.

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THIS EVENT HAPPENED ON FLT XXX ORD-HNL DC10-30; I WAS THE OPERATING SO ON THIS FLT. THIS ACFT WAS ALSO CONFIGURED TO FERRY AN ENG LOCATED BTWN ENG #1 AND THE FUSELAGE. AT ABOUT CRUISE LEVEL OFF (FL310) APCHING CRUISE AIRSPD; THE ACFT BEGAN TO VIBRATE; THE CREW INITIALLY THOUGHT IT TO BE THE INSET OF MACH BUFFET -- BUT WHY AT SUCH A LOW MACH (.75)? AS THE CAPT DISENGAGED THE AUTOTHROTTLES AND BEGAN TO DECREASE THRUST; THE ACFT BEGAN TO INCREASE IN VIBRATION AS IF IT MIGHT BEGIN TO STALL. THE CAPT BEGAN TO THROTTLE BACK -- ASKED THE FO TO TELL ATC WE WERE DSNDING AND WE ARE IN TROUBLE AND WILL EXPLAIN LATER. GOT THE CLRNC; HOWEVER; THE ACFT WAS STILL VIOLENTLY VIBRATING AND BEGINNING TO YAW TO THE POINT THAT THE LEADING EDGE DEVICES EXTENDED AUTOMATICALLY AND THE STICK SHAKER BEGAN TO SHAKE. THE CAPT ATTEMPTED SEVERAL ALTS AND AIRSPDS DURING THE DSCNT WHILE THE ACFT KEPT SHUDDERING AND THE DEVICES KEPT DEPLOYING ALONG WITH INTERMITTENT STICK SHAKING DOWN TO ABOUT 25000 FT WHEN ALL THE ABOVE STOPPED. LEVEL OFF AND CLRNC WAS ESTABLISHED AT THAT ALT FOR CLRNC TO RETURN TO ORD FOR LNDG AFTER RECEIVING THE PRESENT WX THERE. AFTER THE ACFT SETTLED DOWN I WENT TO THE REAR JUST AFT OF DOOR 2L WHERE I COULD VIEW PART OF THE ENG WE WERE FERRYING TO SEE IF IT WAS LOOSE; OR IF THE FAIRING HAD COME OFF THAT ENG OR FOR THAT MATTER ANYTHING UNUSUAL. AS I WAS LEANING OVER SOME PAX THEY REMARKED THAT DURING ALL THE VIBRATIONS THEY WERE LOOKING AT BOTH ENGS AND THE WING. ALL 2 ROWS OF PAX CORROBORATED THE SAME SCENARIO OF THE FOLLOWING: WHILE THIS WAS ALL HAPPENING BOTH ENGS WERE 'SWAYING BACK AND FORTH AND THE WING WAS WAVING UP AND DOWN -- SORT OF LIKE A BIRD' HOWEVER THE FERRYING ENG DID NOT APPEAR TO BE LOOSE OR ACTING DIFFERENTLY THAN THE #1 ENG. I RETURNED TO THE CABIN AND RELATED THE SAME. FUEL WAS DUMPED AND SLOW FLT WAS CONDUCTED ABOVE THE OVCST IN A LNDG CONFIGN WITH TURNS AND DSCNTS WHICH TO OUR RELIEF; RESULTED IN NO PROBS. CLRNC FOR AN APCH INTO ORD WAS OBTAINED AND A NORMAL LNDG WAS ACCOMPLISHED. NONE OF THIS FLC CAN DETERMINE WHAT CAUSED SUCH A PHENOMENON AS NONE OF US HAD ENCOUNTERED SUCH AN ACCELERATED AIRFRAME VIBRATION BEFORE. DURING MY EXPERIENCE WHILE FLYING A7 ATTACK ACFT IN THE MIL WAS A MANEUVER CALLED A 'DEP;' IN WHICH THE ACFT PITCHED UP SLIGHTLY WENT INTO A SLIGHT ACCELERATED STALL MANEUVER WHILE LOSING ALT RAPIDLY; SORT OF IN A FLAT SPIN... ALTHOUGH THERE WAS NO SPIN ASSOCIATED WITH THIS INSTANCE; THE AIRFRAME VIBRATION WAS SIMILAR. ANOTHER RELATION WOULD BE FLYING INTO A JET BLAST TOSSING THE ACFT AROUND AND ADD; WITH AIRFRAME VIBRATIONS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR WAS AN EXPERIENCED PLT OF THE DC10 AS WELL AS BEING THE SO ON THIS FLT. HE STATED THAT WHEN THE ENG TO BE FERRIED WAS ADDED TO THE ACFT; THE CENTRAL AIR DATA COMPUTER WAS REPLACED. IT WAS REPLACED BECAUSE THE ENG FERRY REQUIRES IT TO BE REPLACED WITH A CENTRAL AIR DATA COMPUTER OF ITS OWN. THE ACFT WAS LEVELED AT FL305 AND CHKED TO MAKE CERTAIN ALL WAS WELL. SHORTLY AFTER THE ACFT LEVELED AT FL310; THE VIBRATION STARTED. MACH WAS .75 AND SOON THE LEADING EDGE SLATS STARTED TO EXTEND; AND STICK SHAKER CAME INTO MOTION. THE ACFT WAS SLOWLY DSNDED TO LOWER ALTS UNTIL AT FL250 THE ACFT STOPPED THE VIBRATION. THEN AN EMER WAS DECLARED AND THE ACFT WAS RETURNED TO THE POINT OF DEP; ORD. FLC AND FLT MGRS MET WITH OTHERS FROM MAINT AND REVIEWED ALL HAPPENINGS. NO DETERMINATION AS TO WHY IT HAPPENED HAS BEEN MADE. ENTIRE ACFT WAS SHAKING AND ALL PAX KNEW SOMETHING WAS WRONG. FLC SUSPECTED SOMETHING WRONG WITH THE 4TH ENG MOUNTING; MAINT SUSPECTS THEIR AIRSPD INDICATORS WERE WRONG BECAUSE THE CENTRAL AIR DATA COMPUTER THAT CAME WITH THE 4TH ENG WAS IN ERROR. ONLY THING FOUND WRONG WAS THE BOLTS THAT HELD THE 4TH ENG WERE TOO LONG AND AS A RESULT; THEY PUNCTURED THE FUEL TANK IN THE WING. SUPPLEMENTAL INFO FROM ACN 363008: LEVELED AT FL305 AND GOT AN ALT READOUT FROM ZAU. CONTINUED CLB TO FL310. AT LEVEL OFF WE STARTED TO FEEL AND HEAR A VIBRATION. WE ALL THOUGHT THAT THE 4TH ENG POD WAS LOOSE; THE VIBRATION GOT VERY INTENSE; VERY QUICKLY. THE CAPT REDUCED PWR; BUT THE VIBRATION CONTINUED. WE REDUCED PWR TO TRY AND FIND A SPD TO STOP THE VIBRATIONS. WE HAD TO REDUCE PWR ALL THE WAY BACK TO AUTO SLATS EXTEND SPD. WE TOOK A DSCNT TO FL240 AND GOT THE VIBRATIONS TO STOP AT 260 KTS AND FL240. DUMPED FUEL (120000 LBS); DID A CTL CHK AND MADE AN UNEVENTFUL LNDG AT ORD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: FO THOUGHT THEY WERE IN A DEEP STALL ALL THE TIME THE ACFT WAS VIBRATING. NOT ONLY DID THE ACFT SHAKE; BUT THE LOSS OF ALT WAS QUICK. HE NEVER THOUGHT ANYTHING FELT LIKE A MACH BUFFET. HE ALSO ADDED THAT THE ACFT WAS ON AUTOPLT AT THE TIME OF THE ENCOUNTER. IN A CONFERENCE CALL THE NEXT DAY; THE MAINT PEOPLE BELIEVED THEY HAD A FAULTY AIRSPD INDICATOR. NO DEFINITE CAUSE HAS BEEN GIVEN TO EXPLAIN WHY ALL THIS HAPPENED.