B737-300 ON DSCNT AND APCH IN ICING CONDITIONS. SUBSTANTIAL ICE BUILDUP FOR 5 MIN PERIOD; CAUSED ENG VIBRATIONS FROM ICE. RPTR CAPT ADVANCED PWR IN ACCORDANCE WITH SOP AND VIBRATIONS REDUCED. LNDG UNEVENTFUL; BUT POSTFLT INSPECTION OF ENG REVEALED SOME ICE DAMAGE TO ACOUSTICAL PANEL FROM SHEDDING ICE.

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ACFT WAS ON R BASE BEING VECTORED FOR AN APCH TO THE N RWY 35L. DSNDING FROM 13000 FT TO 11000 FT THE ACFT ENTERED THE CLOUDS. ENG ANTI-ICE WAS ON PRIOR TO ENTERING CLOUDS AND WING ANTI-ICE WAS TURNED ON AFTER ENTERING CLOUDS. RPTS FROM ATC ADVISED OF PIREPS RPTING MODERATE MIXED ICING BELOW 10000 FT. AFTER LOC CAPTURE AND JUST PRIOR TO GS CAPTURE; A PERIOD OF APPROX 4-5 MINS; SUBSTANTIAL ICING WAS NOTED ON THE WINDSCREEN AND WIPER BLADES. CONCURRENT WITH THE ICING WAS ENG VIBRATION; AS VERIFIED BY BOTH THE ENG VIBRATION METERS READING FULL SCALE DEFLECTION. IN ACCORDANCE WITH PROCS; 1 THROTTLE AT A TIME WAS ADVANCED TO 80 PERCENT N1 PWR SETTING. THIS REDUCED THE VIBRATION SIGNIFICANTLY AND THE PROC WAS REPEATED ON THE GS TO REDUCE THE VIBRATION READINGS TO NORMAL INDICATIONS. NORMAL LNDG ACCOMPLISHED. MAINT WAS CONTACTED DURING TAXI-IN. ENG INSPECTION REVEALED SUBSTANTIAL ICE BUILDUP ON THE SPINNER; THE P-T PROBES; AND BACK SIDE OF FAN BLADES. ACOUSTICAL PANEL DAMAGE WAS NOTED IN THE L ENG AS A RESULT OF ICE BEING SHED FROM FAN BLADES. CONTRIBUTING FACTORS: ONLY RPTS AVAILABLE ARE PIREPS. INTENSITY AND ALT OF ICING MAY VARY CONSIDERABLY FROM PIREPS DUE TO CONSTANTLY CHANGING CONDITIONS OR PLT PERCEPTIONS (IE; DIFFERENT ACFT TYPES; DIFFERENT ICE TYPES). ALTHOUGH EXPOSURE SEEMED MINIMAL; ATC SLOWING ACFT DOWN TO 210 KTS; THEN 170 KTS; INCREASED EXPOSURE TIME AND REDUCED ENG RPM AND ICE SHEDDING ABILITY. INFLEXIBILITY OF CHANGING ALT WHILE ON APCH DUE TO PARALLEL RWY CONSTRAINTS TFC; NOISE CORRIDORS; REDUCES OPTIONS OF CHANGING ALTS. ABILITY OF MODERN ACFT TO OPERATE IN ICING CONDITIONS IS OVERRATED. FLT MANUAL DEFINITIONS ARE VAGUE (IE; 'EXTENDED OPS NOT RECOMMENDED' IN MODERATE ICING); YET PROCS ARE DOCUMENTED FOR RUNNING UP ENGS INFLT (AS WELL AS ON THE GND) EVERY 15 MINS WHEN OPERATING IN ICING CONDITIONS.