AN ACR FK100 FLC HAS AN ABNORMAL VIBRATION BEGIN IN THE #2 ROLLS-ROYCE TAY-650 ENG. THE FLC INITIALLY THOUGHT THAT THE VIBRATION MAY BE DUE TO POSSIBLE ICING; BUT THEY LATER FOUND OUT THAT THIS PARTICULAR ENG HAS A HISTORY OF THIS PHENOMENON.

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DURING FIRST FEW MINS AT CRUISE THE MFDU CAME UP WITH THE HIGH ENG VIBRATION CHKLIST. IN SECONDS BEFORE REFERRING TO CHKLIST THE CHKLIST TITLE TURNED WHITE. MEANING THE PROB WENT AWAY HOWEVER THE VIBRATION WAS IN THE GREEN ABOVE WHAT WE NORMALLY SEE. SO WE DID THE THROTTLE SLAM PROC FOR POSSIBLE ICE REMOVAL AND WENT TO THE BACK TO THE CABIN TO LOOK IN THE ENG. ALSO WE DSNDED INTO THE CLR AND WARMER TEMPS; THE ENG RAN FINE; NO LONGER NEEDING ANY ATTN. AT OUR DEST WE TALKED TO MAINT AND THEY WENT AHEAD AND DID A SVC CHK. THE ENG RAN FINE THROUGHOUT THE RUN-UP AND TKOF AND CLB. HOWEVER; AS WE WERE GETTING UP IN ALT THE ENG WITHIN LIMITS WAS STARTING TO SHOW A TREND OF VIBRATION. DECIDING NOT TO GO ANY HIGHER OR TO FIND ANY PRECIPITATION WE PROCEEDED TO ORD AND WROTE THE ENG UP SO THEY COULD TAKE A CLOSER LOOK. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS RPTR WAS ALSO AN A&P MECH EARLY IN HIS AIRLINE CARRIER. HE SAID THAT HE HAD NOT WORKED ON THE TAY ENGS; BUT HE FEELS THAT HE UNDERSTANDS SOME OF THE PRINCIPLES BEHIND ITS OP. AT FIRST HE WAS CONCERNED THAT THEY HAD SOME ICING EFFECT; BUT AFTER VISUALLY INSPECTING THE INLET INFLT AND NOTING THAT THERE WAS NO ICE VISIBLE NOR HAD ICING CONDITIONS EXISTED DURING THE FLT HE DECIDED TO INVESTIGATE THE SIT FURTHER. HE SAID THAT HE REQUESTED A LOWER ALT AND THE WARMER; DENSER AIR SEEMED TO CAUSE THE #2 ENG TO RUN SMOOTHER. THE RPTR SAID THAT HE TENDS TO FAVOR FLYING AT ALTS BELOW 30000 FT WITH THIS ACFT ANYWAY BECAUSE HE THINKS THAT IT DOES NOT PERFORM WELL AT HIGHER ALTS. THE ENG RAN WELL FOR THE REMAINDER OF THE FLT. AFTER MAINT CHKED THE ENG DURING THE OVERNIGHT STAY HE AGAIN DEPARTED WITH THE ACFT. THE ENG RAN WITH THE VIBRATION INDICATION SOMEWHAT HIGHER THAN NORMAL; BUT WITHIN ACCEPTABLE PARAMETERS. HE AGAIN DISCUSSED THE SIT WITH MAINT CTL AND IT WAS AT THIS TIME HE DISCOVERED THAT THIS PARTICULAR ENG HAD BEEN REMOVED FROM ANOTHER FK100 BECAUSE OF VIBRATION. HIS FLT THE DAY BEFORE WAS THE FIRST SINCE THIS ENG HAD BEEN INSTALLED ON THIS ACFT. MAINT DECIDED TO AGAIN REMOVE THE ENG AND INSPECT IT. LATER HE WAS TOLD THAT THE FAN SECTION HAD TO BE TAKEN OFF OF THE ENG FOR REPAIR. HE ALSO MENTIONED THAT THE TECHNIQUE KNOWN AS THE THROTTLE SLAM PROC IS NOW BEING TAUGHT IN RECURRENT GND SCHOOL. THIS PROC; APPARENTLY; HELPS THE ENG CTL SYS RESET ITSELF.