Narrative:

According to aircraft manufacturer, freezing rain or drizzle can be idented by either side window accruing ice on the ATR-42. We were level at 16000 ft, outside air temperature minus 10 degrees C when we entered an area with large droplets. The side windows immediately were covered with ice. Following the emergency procedure outlined, I disconnected the autoplt and my first officer requested a lower altitude. We were issued a descent to 14000 ft. This altitude proved no better and we were cleared to 12000 ft. Exited the icing area at 13800 ft and the side windows cleared at 13500 ft. The entire deicing boot was covered with ice, not just a few inches around the wing's stagnation point, as is usual. It took several cycles for the deicing boot to clear the ice. After most of the buildup had cleared, a line of ice remained at the top of the inboard boot continuing through the outboard boot along the same mean aerodynamic chord. The outboard boot goes back on top of the wing. The cycles of the boot did not clear this line, and it finally cleared about 15-20 mins later. All available anti-icing and deicing equipment was in use at the time. There were no abnormal flight characteristics as a result of the amount of ice. The indicated airspeed was about 210 KIAS. The outboard boot on the ATR fleet had been modified to protect the upper surface of the wing from ice buildup and to eliminate the concern for aileron hinge movement diversions. This did not happen here, and any prolonged exposure on our part might have led to a more serious problem. The bottom line: pay attention to the ice building up, and get out. Do not become complacent and put your life in the hands of the equipment.

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Original NASA ASRS Text

Title: WX FACTORS ICING. ACR ATR-42 ENCOUNTERS ICING AND FLC DSNDS WHILE USING DEICE SYS TO REMOVE ICE ON THE ACFT.

Narrative: ACCORDING TO ACFT MANUFACTURER, FREEZING RAIN OR DRIZZLE CAN BE IDENTED BY EITHER SIDE WINDOW ACCRUING ICE ON THE ATR-42. WE WERE LEVEL AT 16000 FT, OUTSIDE AIR TEMP MINUS 10 DEGS C WHEN WE ENTERED AN AREA WITH LARGE DROPLETS. THE SIDE WINDOWS IMMEDIATELY WERE COVERED WITH ICE. FOLLOWING THE EMER PROC OUTLINED, I DISCONNECTED THE AUTOPLT AND MY FO REQUESTED A LOWER ALT. WE WERE ISSUED A DSCNT TO 14000 FT. THIS ALT PROVED NO BETTER AND WE WERE CLRED TO 12000 FT. EXITED THE ICING AREA AT 13800 FT AND THE SIDE WINDOWS CLRED AT 13500 FT. THE ENTIRE DEICING BOOT WAS COVERED WITH ICE, NOT JUST A FEW INCHES AROUND THE WING'S STAGNATION POINT, AS IS USUAL. IT TOOK SEVERAL CYCLES FOR THE DEICING BOOT TO CLR THE ICE. AFTER MOST OF THE BUILDUP HAD CLRED, A LINE OF ICE REMAINED AT THE TOP OF THE INBOARD BOOT CONTINUING THROUGH THE OUTBOARD BOOT ALONG THE SAME MEAN AERODYNAMIC CHORD. THE OUTBOARD BOOT GOES BACK ON TOP OF THE WING. THE CYCLES OF THE BOOT DID NOT CLR THIS LINE, AND IT FINALLY CLRED ABOUT 15-20 MINS LATER. ALL AVAILABLE ANTI-ICING AND DEICING EQUIP WAS IN USE AT THE TIME. THERE WERE NO ABNORMAL FLT CHARACTERISTICS AS A RESULT OF THE AMOUNT OF ICE. THE INDICATED AIRSPD WAS ABOUT 210 KIAS. THE OUTBOARD BOOT ON THE ATR FLEET HAD BEEN MODIFIED TO PROTECT THE UPPER SURFACE OF THE WING FROM ICE BUILDUP AND TO ELIMINATE THE CONCERN FOR AILERON HINGE MOVEMENT DIVERSIONS. THIS DID NOT HAPPEN HERE, AND ANY PROLONGED EXPOSURE ON OUR PART MIGHT HAVE LED TO A MORE SERIOUS PROB. THE BOTTOM LINE: PAY ATTN TO THE ICE BUILDING UP, AND GET OUT. DO NOT BECOME COMPLACENT AND PUT YOUR LIFE IN THE HANDS OF THE EQUIP.

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.