B737-300 on descent and approach in icing conditions. Substantial ice buildup for 5 min period, caus...

Attributes
ACN	363621
Time
Date	199703
Day	Thu
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : den
State Reference	CO
Altitude	agl bound lower : 0 agl bound upper : 11000
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : den
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent : approach descent other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 6000 flight time type : 50
ASRS Report	363621
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : instrument pilot : commercial
Events
Anomaly	aircraft equipment problem : less severe inflight encounter : weather other anomaly other
Independent Detector	other flight crewa
Resolutory Action	flight crew : exited adverse environment
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	other

Narrative:

Aircraft was on right base being vectored for an approach to the north runway 35L. Descending from 13000 ft to 11000 ft the aircraft entered the clouds. Engine anti-ice was on prior to entering clouds and wing anti-ice was turned on after entering clouds. Reports from ATC advised of PIREPS reporting moderate mixed icing below 10000 ft. After localizer capture and just prior to GS capture, a period of approximately 4-5 mins, substantial icing was noted on the windscreen and wiper blades. Concurrent with the icing was engine vibration, as verified by both the engine vibration meters reading full scale deflection. In accordance with procedures, 1 throttle at a time was advanced to 80 percent N1 power setting. This reduced the vibration significantly and the procedure was repeated on the GS to reduce the vibration readings to normal indications. Normal landing accomplished. Maintenance was contacted during taxi-in. Engine 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 left engine as a result of ice being shed from fan blades. Contributing factors: only reports available are PIREPS. Intensity and altitude of icing may vary considerably from PIREPS due to constantly changing conditions or pilot perceptions (ie, different aircraft types, different ice types). Although exposure seemed minimal, ATC slowing aircraft down to 210 KTS, then 170 KTS, increased exposure time and reduced engine RPM and ice shedding ability. Inflexibility of changing altitude while on approach due to parallel runway constraints traffic, noise corridors, reduces options of changing altitudes. Ability of modern aircraft to operate in icing conditions is overrated. Flight manual definitions are vague (ie, 'extended operations not recommended' in moderate icing), yet procedures are documented for running up engines in-flight (as well as on the ground) every 15 mins when operating in icing conditions.

Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.