AN EMBRAER 145 ON DSCNT FROM FL200 TO 11000 FT EXPERIENCED A LIGHT BUT CONSTANT TAIL PLANE VIBRATION FELT IN THE FUSELAGE STRUCTURE BUT NOT IN THE YOKE.

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ACFT XYZ; EMBRAER REGIONAL JET. DSCNT FROM FL200 TO 11000 FT AT 315 KTS. CONSTANT TAILPLANE VIBRATION. THE VIBRATIONS WOULD 'SURGE' FROM STRONG VIBRATION TO WEAK. VIBRATIONS COULD BE AGGRAVATED BY PULLING BACK ON YOKE AND RELEASING BACK PRESSURE (MY CONCERN -- METAL FATIGUE OVER TIME). CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE ACFT IS AN EMBRAER 145 AND HAS A LIGHT AIRFRAME HARMONIC WAVE VIBRATION FELT IN THE FUSELAGE STRUCTURE. THE RPTR SAID THE VIBRATION IS NEVER FELT IN THE YOKE BUT PULLING BACK ON THE CTL COLUMN AND RELEASING BACK PRESSURE WILL INCREASE THE AMPLITUDE OR INTENSITY FROM LIGHT TO MODERATE. THE RPTR STATED THE LATEST THEORY OF THE CAUSE IS THE OUTER ELEVATOR HORNS AND VORTEX GENERATORS WERE ADDED TO THE LOWER SURFACE OF THE HORNS AS A TEST ON ONE AIRPLANE BUT APPEARS NOT TO HAVE HELPED. THE RPTR SAID THE VIBRATION IS NOT PRESENT WITH THE AUTOPLT ENGAGED. THE RPTR STATED IT IS SPD RELATED AND OCCURS AROUND 270 KIAS. THE RPTR SAYS THE MANUFACTURER INSTALLED SENSORS IN THE TAIL AND THE ACFT WAS TEST FLOWN TO DUPLICATE THE VIBRATION BUT NO RESULTS WERE PUBLISHED.