Narrative:

At top of descent started to receive PIREPS of moderate icing on approach to den. During descent, received 5 or 6 PIREPS of severe icing at 11000 ft. First officer and I discussed the definition of severe icing -- even pulled out manual and read definition. On long final to runway 35R we picked up the same icing as previous aircraft. We did experience some engine vibrations on final and flight control difficulties on final. Since the first officer was flying and he did the postflt walkaround, his comments are later. I know that when he clicked off the autoplt, the wings immediately started to rock. The control inputs did not seem to correspond to aircraft movements. I asked if he was doing that -- referring to ailerons. He said 'no.' based on a postflt debrief, I now believe that the aileron effectiveness was impaired by the icing. It seems the control wheel inputs may have gone negative or counter. The first officer states in his debrief: started getting icing on descent to 11000 ft on downwind. Engine and wing anti-ice on. Ran engines up to 70% N1 every 5 mins. Maintained above idle rest of time. Autoplt coupled approach. Field in sight at 700 ft. Disconnected at 500 ft (flaps 30 degrees). Noted fair amount of icing on final. About 2 inches of ice built up on window wiper nut. Side window (R2) covered and did not clear till after landing. Aircraft controls felt odd, but aircraft was controllable. There was a flutter that rocked the plane mildly from side to side. Counter aileron movement to correct, then it would go to the other side. Corrections were approximately 2-3 per second. Corrected for left to right crosswind with left aileron down and right rudder. Only the right main touched first, but winds were not steady. Conducted walkaround (postflt) and noted ice about everywhere you could put it. Nose had about 1/4 to 3/4 inches of clear ice. Gear had a good coating also. Bullet nose in engine inlet had shrouds (ice) sticking out 2 inches or so. Stators and rotors had some ice close to center. Tail was covered as were flap underside. Ailerons had 1/2 to 1 inch chunks stuck on them. Top and bottom, about 10-15 per aileron side. Corrective action/comment. The only visible ice from the cockpit is what formed on the wiper blades and attaching bolts. Pilots need a better and more accurate detection system. We need more studies done on the effect of icing on the flight controls of large jet aircraft.

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Original NASA ASRS Text

Title: ACR CREW ENTERS AREA OF KNOWN SEVERE ICING WHEREUPON THEY ENCOUNTERED SEVERE ICING FOLLOWED BY CONTROLLABILITY PROBS WITH THE ACFT. LNDG WAS SUCCESSFUL.

Narrative: AT TOP OF DSCNT STARTED TO RECEIVE PIREPS OF MODERATE ICING ON APCH TO DEN. DURING DSCNT, RECEIVED 5 OR 6 PIREPS OF SEVERE ICING AT 11000 FT. FO AND I DISCUSSED THE DEFINITION OF SEVERE ICING -- EVEN PULLED OUT MANUAL AND READ DEFINITION. ON LONG FINAL TO RWY 35R WE PICKED UP THE SAME ICING AS PREVIOUS ACFT. WE DID EXPERIENCE SOME ENG VIBRATIONS ON FINAL AND FLT CTL DIFFICULTIES ON FINAL. SINCE THE FO WAS FLYING AND HE DID THE POSTFLT WALKAROUND, HIS COMMENTS ARE LATER. I KNOW THAT WHEN HE CLICKED OFF THE AUTOPLT, THE WINGS IMMEDIATELY STARTED TO ROCK. THE CTL INPUTS DID NOT SEEM TO CORRESPOND TO ACFT MOVEMENTS. I ASKED IF HE WAS DOING THAT -- REFERRING TO AILERONS. HE SAID 'NO.' BASED ON A POSTFLT DEBRIEF, I NOW BELIEVE THAT THE AILERON EFFECTIVENESS WAS IMPAIRED BY THE ICING. IT SEEMS THE CTL WHEEL INPUTS MAY HAVE GONE NEGATIVE OR COUNTER. THE FO STATES IN HIS DEBRIEF: STARTED GETTING ICING ON DSCNT TO 11000 FT ON DOWNWIND. ENG AND WING ANTI-ICE ON. RAN ENGS UP TO 70% N1 EVERY 5 MINS. MAINTAINED ABOVE IDLE REST OF TIME. AUTOPLT COUPLED APCH. FIELD IN SIGHT AT 700 FT. DISCONNECTED AT 500 FT (FLAPS 30 DEGS). NOTED FAIR AMOUNT OF ICING ON FINAL. ABOUT 2 INCHES OF ICE BUILT UP ON WINDOW WIPER NUT. SIDE WINDOW (R2) COVERED AND DID NOT CLR TILL AFTER LNDG. ACFT CTLS FELT ODD, BUT ACFT WAS CONTROLLABLE. THERE WAS A FLUTTER THAT ROCKED THE PLANE MILDLY FROM SIDE TO SIDE. COUNTER AILERON MOVEMENT TO CORRECT, THEN IT WOULD GO TO THE OTHER SIDE. CORRECTIONS WERE APPROX 2-3 PER SECOND. CORRECTED FOR L TO R XWIND WITH L AILERON DOWN AND R RUDDER. ONLY THE R MAIN TOUCHED FIRST, BUT WINDS WERE NOT STEADY. CONDUCTED WALKAROUND (POSTFLT) AND NOTED ICE ABOUT EVERYWHERE YOU COULD PUT IT. NOSE HAD ABOUT 1/4 TO 3/4 INCHES OF CLR ICE. GEAR HAD A GOOD COATING ALSO. BULLET NOSE IN ENG INLET HAD SHROUDS (ICE) STICKING OUT 2 INCHES OR SO. STATORS AND ROTORS HAD SOME ICE CLOSE TO CTR. TAIL WAS COVERED AS WERE FLAP UNDERSIDE. AILERONS HAD 1/2 TO 1 INCH CHUNKS STUCK ON THEM. TOP AND BOTTOM, ABOUT 10-15 PER AILERON SIDE. CORRECTIVE ACTION/COMMENT. THE ONLY VISIBLE ICE FROM THE COCKPIT IS WHAT FORMED ON THE WIPER BLADES AND ATTACHING BOLTS. PLTS NEED A BETTER AND MORE ACCURATE DETECTION SYS. WE NEED MORE STUDIES DONE ON THE EFFECT OF ICING ON THE FLT CTLS OF LARGE JET ACFT.

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.