Narrative:

On an IFR flight plan from rdu to cdw. On top at FL190 for most of flight. Flying the yardley 2 arrival (ard.ARD2) into cdw. Airplane is certified for flight into known icing. All system were operable. Prior to cloud penetration, following descent instructions from ATC, all deice system engaged. This included pitot heat #1 and #2, stall/warning heat, propeller deice and electric glass windshield on low. Light rime/mixed icing on descent. After ard VOR, issued radar vectors and 3000 ft altitude by new york approach, radar vectors for the localizer runway 22 approach into cdw. 15-20 NM west of the airport, began slowing the airplane in preparation for the approach. Continued checking leading edges of wings and spinners -- no significant accumulation noted. The procedure for wing and tail deicing is to wait until there is at least 1/4 inch of ice before inflating the boots. Earlier application of the boots could just lift a thin layer of ice upon which more ice might form rendering the boots ineffective. Level at 3000 ft at about 140 KIAS and now 14.5 NM west of cdw, the airplane began to buffet, elevator response became mushy and it appeared the airplane was ready to stall. While reaching to add more power, the airplane nosed over and began a left turn. I went with turn, trading altitude for airspeed while bringing the propellers and manifold pressure each to the top of the green arc and cycling the boots. The airplane felt as if it were operating at the edge of a stall. At this time I declared an emergency with new york approach control. New york approach asked me what I wanted to do, did I want to climb. I did not want to put the airplane into any confign which would result in slower airspeed because I assumed the airplane must have been carrying more ice than I was aware of, or there was another problem with the tail. I wanted to do everything I could to avoid another excursion. With the increased power and resultant airspeed and cycling of the boots, I got the airplane stabilized on a wbound heading (total of about a 180 degree turn) and was able to maintain 3000 ft. New york approach said any altitude between 3000-4000 ft would be fine. I climbed to 3500 ft. Since we were 8 mi from mmu airport, which has an ILS approach, I requested vectors for the ILS runway 23 approach at mmu. My reasoning was that there were less turns involved, lower approach minimums (200 ft versus 347 ft) and a longer runway (5999 ft versus 4553 ft). New york approach provided vectors for the ILS runway 23 approach at mmu and I elected to land straight-in although the winds were favoring runway 5. I felt comfortable with tailwind given the runway length and wanted to avoid turns which would be associated with circle-to-land procedures, or the additional flying time and higher minimums associated with the NDB approach to runway 5. New york approach informed me that a baron had just landed and reported ceiling ragged at 700 ft. We experienced no further difficulty flying the approach and came to a full stop using only slightly more than 1/2 of the available runway. During the approach the boots were clear of ice and inspection of the tail after landing showed boots clear there as well. There was some remaining ice on the nose, spinners, upper portion of the tail and other unprotected areas -- perhaps 1/4 inch I would estimate. I assume significant ice was shed while descending on the GS. Inspection of the airplane showed no other anomalies. Although I knew that ice accumulation was likely on descent, cdw was reporting 900 ft broken, 1300 ft overcast with visibility 2 1/2 mi. I felt that the aircraft was capable to handle those conditions and the ceilings were high enough to make a missed approach in possible ice unlikely. Perhaps I was too hasty to declare an emergency, but when the aircraft first broke from controled flight, I had but 1 single mission on my mind -- get the airplane safely on the ground using all the facilities available. At the time I declared the emergency, I wasn't sure whether or not I was going to be able to regain control of the airplane. As it turns out, the extra airspeed and continuous cycling of the boots did the job. From a more critical perspective, I have now become an even morecautious flight planner. When icing is possible, I will allow for higher ceilings and a cushion of 'above freezing altitude' below the bases at the destination airport. I now know first hand that icing conditions are unpredictable and how localized severe icing can be -- it can quickly overpwr a 'known icing' aircraft. We most likely experienced moderate to severe clear icing in addition to the mixed/rime which was not as noticeable from the pilot's viewpoint. In the future I will be quicker to avoid and will expect much worse than 'light to moderate' forecasts because I realize how quickly things can change for the worse. I will also maintain a higher than normal airspeed during flight in conditions conducive to icing of this nature. In hindsight, I believe the boots could have been cycled earlier. I am very grateful to new york approach for their assistance. They kept me apprised of my location and progress and helped me in a most professional manner throughout the occurrence. One other thing. I am an avid reader of ASRS reports and other information regarding aircraft incidents, etc. I always hope to learn from the experience of others. I believe those reports were helpful to me in my decision-making process. I knew that the use of flaps could alter flying qualities and I was resolved to avoid that situation. I knew airspeed was critical as others in similar sits have noted. The first rule every instructor has yelled to me in simulated emergencys, 'fly the airplane' rang loud and clear.

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Original NASA ASRS Text

Title: A C421B PVT PLT LOSES CTL IN ICING CONDITIONS DURING DSCNT. DIVERTS TO ALTERNATE. N90 CTLR A GREAT HELP.

Narrative: ON AN IFR FLT PLAN FROM RDU TO CDW. ON TOP AT FL190 FOR MOST OF FLT. FLYING THE YARDLEY 2 ARR (ARD.ARD2) INTO CDW. AIRPLANE IS CERTIFIED FOR FLT INTO KNOWN ICING. ALL SYS WERE OPERABLE. PRIOR TO CLOUD PENETRATION, FOLLOWING DSCNT INSTRUCTIONS FROM ATC, ALL DEICE SYS ENGAGED. THIS INCLUDED PITOT HEAT #1 AND #2, STALL/WARNING HEAT, PROP DEICE AND ELECTRIC GLASS WINDSHIELD ON LOW. LIGHT RIME/MIXED ICING ON DSCNT. AFTER ARD VOR, ISSUED RADAR VECTORS AND 3000 FT ALT BY NEW YORK APCH, RADAR VECTORS FOR THE LOC RWY 22 APCH INTO CDW. 15-20 NM W OF THE ARPT, BEGAN SLOWING THE AIRPLANE IN PREPARATION FOR THE APCH. CONTINUED CHKING LEADING EDGES OF WINGS AND SPINNERS -- NO SIGNIFICANT ACCUMULATION NOTED. THE PROC FOR WING AND TAIL DEICING IS TO WAIT UNTIL THERE IS AT LEAST 1/4 INCH OF ICE BEFORE INFLATING THE BOOTS. EARLIER APPLICATION OF THE BOOTS COULD JUST LIFT A THIN LAYER OF ICE UPON WHICH MORE ICE MIGHT FORM RENDERING THE BOOTS INEFFECTIVE. LEVEL AT 3000 FT AT ABOUT 140 KIAS AND NOW 14.5 NM W OF CDW, THE AIRPLANE BEGAN TO BUFFET, ELEVATOR RESPONSE BECAME MUSHY AND IT APPEARED THE AIRPLANE WAS READY TO STALL. WHILE REACHING TO ADD MORE PWR, THE AIRPLANE NOSED OVER AND BEGAN A L TURN. I WENT WITH TURN, TRADING ALT FOR AIRSPD WHILE BRINGING THE PROPS AND MANIFOLD PRESSURE EACH TO THE TOP OF THE GREEN ARC AND CYCLING THE BOOTS. THE AIRPLANE FELT AS IF IT WERE OPERATING AT THE EDGE OF A STALL. AT THIS TIME I DECLARED AN EMER WITH NEW YORK APCH CTL. NEW YORK APCH ASKED ME WHAT I WANTED TO DO, DID I WANT TO CLB. I DID NOT WANT TO PUT THE AIRPLANE INTO ANY CONFIGN WHICH WOULD RESULT IN SLOWER AIRSPD BECAUSE I ASSUMED THE AIRPLANE MUST HAVE BEEN CARRYING MORE ICE THAN I WAS AWARE OF, OR THERE WAS ANOTHER PROB WITH THE TAIL. I WANTED TO DO EVERYTHING I COULD TO AVOID ANOTHER EXCURSION. WITH THE INCREASED PWR AND RESULTANT AIRSPD AND CYCLING OF THE BOOTS, I GOT THE AIRPLANE STABILIZED ON A WBOUND HDG (TOTAL OF ABOUT A 180 DEG TURN) AND WAS ABLE TO MAINTAIN 3000 FT. NEW YORK APCH SAID ANY ALT BTWN 3000-4000 FT WOULD BE FINE. I CLBED TO 3500 FT. SINCE WE WERE 8 MI FROM MMU ARPT, WHICH HAS AN ILS APCH, I REQUESTED VECTORS FOR THE ILS RWY 23 APCH AT MMU. MY REASONING WAS THAT THERE WERE LESS TURNS INVOLVED, LOWER APCH MINIMUMS (200 FT VERSUS 347 FT) AND A LONGER RWY (5999 FT VERSUS 4553 FT). NEW YORK APCH PROVIDED VECTORS FOR THE ILS RWY 23 APCH AT MMU AND I ELECTED TO LAND STRAIGHT-IN ALTHOUGH THE WINDS WERE FAVORING RWY 5. I FELT COMFORTABLE WITH TAILWIND GIVEN THE RWY LENGTH AND WANTED TO AVOID TURNS WHICH WOULD BE ASSOCIATED WITH CIRCLE-TO-LAND PROCS, OR THE ADDITIONAL FLYING TIME AND HIGHER MINIMUMS ASSOCIATED WITH THE NDB APCH TO RWY 5. NEW YORK APCH INFORMED ME THAT A BARON HAD JUST LANDED AND RPTED CEILING RAGGED AT 700 FT. WE EXPERIENCED NO FURTHER DIFFICULTY FLYING THE APCH AND CAME TO A FULL STOP USING ONLY SLIGHTLY MORE THAN 1/2 OF THE AVAILABLE RWY. DURING THE APCH THE BOOTS WERE CLR OF ICE AND INSPECTION OF THE TAIL AFTER LNDG SHOWED BOOTS CLR THERE AS WELL. THERE WAS SOME REMAINING ICE ON THE NOSE, SPINNERS, UPPER PORTION OF THE TAIL AND OTHER UNPROTECTED AREAS -- PERHAPS 1/4 INCH I WOULD ESTIMATE. I ASSUME SIGNIFICANT ICE WAS SHED WHILE DSNDING ON THE GS. INSPECTION OF THE AIRPLANE SHOWED NO OTHER ANOMALIES. ALTHOUGH I KNEW THAT ICE ACCUMULATION WAS LIKELY ON DSCNT, CDW WAS RPTING 900 FT BROKEN, 1300 FT OVCST WITH VISIBILITY 2 1/2 MI. I FELT THAT THE ACFT WAS CAPABLE TO HANDLE THOSE CONDITIONS AND THE CEILINGS WERE HIGH ENOUGH TO MAKE A MISSED APCH IN POSSIBLE ICE UNLIKELY. PERHAPS I WAS TOO HASTY TO DECLARE AN EMER, BUT WHEN THE ACFT FIRST BROKE FROM CTLED FLT, I HAD BUT 1 SINGLE MISSION ON MY MIND -- GET THE AIRPLANE SAFELY ON THE GND USING ALL THE FACILITIES AVAILABLE. AT THE TIME I DECLARED THE EMER, I WASN'T SURE WHETHER OR NOT I WAS GOING TO BE ABLE TO REGAIN CTL OF THE AIRPLANE. AS IT TURNS OUT, THE EXTRA AIRSPD AND CONTINUOUS CYCLING OF THE BOOTS DID THE JOB. FROM A MORE CRITICAL PERSPECTIVE, I HAVE NOW BECOME AN EVEN MORECAUTIOUS FLT PLANNER. WHEN ICING IS POSSIBLE, I WILL ALLOW FOR HIGHER CEILINGS AND A CUSHION OF 'ABOVE FREEZING ALT' BELOW THE BASES AT THE DEST ARPT. I NOW KNOW FIRST HAND THAT ICING CONDITIONS ARE UNPREDICTABLE AND HOW LOCALIZED SEVERE ICING CAN BE -- IT CAN QUICKLY OVERPWR A 'KNOWN ICING' ACFT. WE MOST LIKELY EXPERIENCED MODERATE TO SEVERE CLR ICING IN ADDITION TO THE MIXED/RIME WHICH WAS NOT AS NOTICEABLE FROM THE PLT'S VIEWPOINT. IN THE FUTURE I WILL BE QUICKER TO AVOID AND WILL EXPECT MUCH WORSE THAN 'LIGHT TO MODERATE' FORECASTS BECAUSE I REALIZE HOW QUICKLY THINGS CAN CHANGE FOR THE WORSE. I WILL ALSO MAINTAIN A HIGHER THAN NORMAL AIRSPD DURING FLT IN CONDITIONS CONDUCIVE TO ICING OF THIS NATURE. IN HINDSIGHT, I BELIEVE THE BOOTS COULD HAVE BEEN CYCLED EARLIER. I AM VERY GRATEFUL TO NEW YORK APCH FOR THEIR ASSISTANCE. THEY KEPT ME APPRISED OF MY LOCATION AND PROGRESS AND HELPED ME IN A MOST PROFESSIONAL MANNER THROUGHOUT THE OCCURRENCE. ONE OTHER THING. I AM AN AVID READER OF ASRS RPTS AND OTHER INFO REGARDING ACFT INCIDENTS, ETC. I ALWAYS HOPE TO LEARN FROM THE EXPERIENCE OF OTHERS. I BELIEVE THOSE RPTS WERE HELPFUL TO ME IN MY DECISION-MAKING PROCESS. I KNEW THAT THE USE OF FLAPS COULD ALTER FLYING QUALITIES AND I WAS RESOLVED TO AVOID THAT SIT. I KNEW AIRSPD WAS CRITICAL AS OTHERS IN SIMILAR SITS HAVE NOTED. THE FIRST RULE EVERY INSTRUCTOR HAS YELLED TO ME IN SIMULATED EMERS, 'FLY THE AIRPLANE' RANG LOUD AND CLR.

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.