Narrative:

This summarizes how a series of misunderstandings, assumptions and indecisiveness can lead to serious ice trouble. Thorough preflight planning and WX checking preceded a final cross country for an aspiring instrument candidate. Terminal WX was IMC, but well above minimums, cloud tops modest (low) and an annoying airmet for IFR and 'light to moderate ice in clouds or precipitation.' no PIREPS the evening before to confirm ice. Early in the morning of the flight day, rechk of WX and copying void time and clearance yielded similar data: 'occasional light to moderate rime/mixed ice above freezing level' was accompanied by no confirming PIREPS. The forecast from the airmet was concluded by myself (cfii) as a condition of unknown ice and an invitation to check it out. Our aircraft is not ice equipped and is prohibited in 'known ice.' the game plan was to fly to an altitude to 'get on top' and if unable, return to base as soon as possible. Departure conditions at dawn were high cirrus with VFR (VMC) beyond cruise altitude. A hood had to be used to get the private pilot any instrument credit. Brief wisps of clouds gave way to a regular layer at 8000 ft MSL, where we got a brief patch of trace ice. A PIREP to FSS to report new conditions followed a request and approval for climb to 10000 ft MSL in VMC. An hour later, abrupt break in cloud pattern revealed clear skies down to a very low undercast. Descent into msp class B airspace no sweat and ATIS only calling for 600 ft ceilings, ILS being assured. Level at 4000 ft, we started getting brief dusting of trace ice with penetrations of cloud tops. Outside air temperature right at 31 degrees F. Vectors down to 3000 ft into the soup at first was welcome as wet moisture beaded off the windshield while I mistakenly assumed 3.50 lapse rate would put us up to 34 degrees F. Trace ice persisted on wings and struts although moisture was clearly dribbling back on windshield, struts and wing bottom. Trace turned to light mixed. Outside air temperature still 31-32 degrees F. I asked for lower. Light mixed became thicker with prolonged vectors to ILS 9 final. IAS tended lower requiring near full power. ILS and circle to land got us on ground with 1/2 inch thick smooth deposit 3 inches wide on every leading edge. Lessons: PIREPS do not equal 'known ice' and airmets should be respected without confirmation. Climbing above 4000 ft would have eliminated problem, since temperature inversions don't always guarantee heat down lower. Finally, more urgency at first ice pastings might have motivated a diversion to earlier landing (like crystal airport near gep) and spared the anxiety of cruising in gentle, but ever accumulating icing conditions. Also, liquid moisture may be rain on the windshield but a cold- soaked metal-wing can precipitate that out as solid ice if at 31-32 degrees F in the drizzle.

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Original NASA ASRS Text

Title: C172 PLT AND CHK PLT ENCOUNTERED ICING PROBS AT CRUISE AND APCH INTO MSP.

Narrative: THIS SUMMARIZES HOW A SERIES OF MISUNDERSTANDINGS, ASSUMPTIONS AND INDECISIVENESS CAN LEAD TO SERIOUS ICE TROUBLE. THOROUGH PREFLT PLANNING AND WX CHKING PRECEDED A FINAL XCOUNTRY FOR AN ASPIRING INST CANDIDATE. TERMINAL WX WAS IMC, BUT WELL ABOVE MINIMUMS, CLOUD TOPS MODEST (LOW) AND AN ANNOYING AIRMET FOR IFR AND 'LIGHT TO MODERATE ICE IN CLOUDS OR PRECIP.' NO PIREPS THE EVENING BEFORE TO CONFIRM ICE. EARLY IN THE MORNING OF THE FLT DAY, RECHK OF WX AND COPYING VOID TIME AND CLRNC YIELDED SIMILAR DATA: 'OCCASIONAL LIGHT TO MODERATE RIME/MIXED ICE ABOVE FREEZING LEVEL' WAS ACCOMPANIED BY NO CONFIRMING PIREPS. THE FORECAST FROM THE AIRMET WAS CONCLUDED BY MYSELF (CFII) AS A CONDITION OF UNKNOWN ICE AND AN INVITATION TO CHK IT OUT. OUR ACFT IS NOT ICE EQUIPPED AND IS PROHIBITED IN 'KNOWN ICE.' THE GAME PLAN WAS TO FLY TO AN ALT TO 'GET ON TOP' AND IF UNABLE, RETURN TO BASE ASAP. DEP CONDITIONS AT DAWN WERE HIGH CIRRUS WITH VFR (VMC) BEYOND CRUISE ALT. A HOOD HAD TO BE USED TO GET THE PVT PLT ANY INST CREDIT. BRIEF WISPS OF CLOUDS GAVE WAY TO A REGULAR LAYER AT 8000 FT MSL, WHERE WE GOT A BRIEF PATCH OF TRACE ICE. A PIREP TO FSS TO RPT NEW CONDITIONS FOLLOWED A REQUEST AND APPROVAL FOR CLB TO 10000 FT MSL IN VMC. AN HR LATER, ABRUPT BREAK IN CLOUD PATTERN REVEALED CLR SKIES DOWN TO A VERY LOW UNDERCAST. DSCNT INTO MSP CLASS B AIRSPACE NO SWEAT AND ATIS ONLY CALLING FOR 600 FT CEILINGS, ILS BEING ASSURED. LEVEL AT 4000 FT, WE STARTED GETTING BRIEF DUSTING OF TRACE ICE WITH PENETRATIONS OF CLOUD TOPS. OUTSIDE AIR TEMP RIGHT AT 31 DEGS F. VECTORS DOWN TO 3000 FT INTO THE SOUP AT FIRST WAS WELCOME AS WET MOISTURE BEADED OFF THE WINDSHIELD WHILE I MISTAKENLY ASSUMED 3.50 LAPSE RATE WOULD PUT US UP TO 34 DEGS F. TRACE ICE PERSISTED ON WINGS AND STRUTS ALTHOUGH MOISTURE WAS CLRLY DRIBBLING BACK ON WINDSHIELD, STRUTS AND WING BOTTOM. TRACE TURNED TO LIGHT MIXED. OUTSIDE AIR TEMP STILL 31-32 DEGS F. I ASKED FOR LOWER. LIGHT MIXED BECAME THICKER WITH PROLONGED VECTORS TO ILS 9 FINAL. IAS TENDED LOWER REQUIRING NEAR FULL PWR. ILS AND CIRCLE TO LAND GOT US ON GND WITH 1/2 INCH THICK SMOOTH DEPOSIT 3 INCHES WIDE ON EVERY LEADING EDGE. LESSONS: PIREPS DO NOT EQUAL 'KNOWN ICE' AND AIRMETS SHOULD BE RESPECTED WITHOUT CONFIRMATION. CLBING ABOVE 4000 FT WOULD HAVE ELIMINATED PROB, SINCE TEMP INVERSIONS DON'T ALWAYS GUARANTEE HEAT DOWN LOWER. FINALLY, MORE URGENCY AT FIRST ICE PASTINGS MIGHT HAVE MOTIVATED A DIVERSION TO EARLIER LNDG (LIKE CRYSTAL ARPT NEAR GEP) AND SPARED THE ANXIETY OF CRUISING IN GENTLE, BUT EVER ACCUMULATING ICING CONDITIONS. ALSO, LIQUID MOISTURE MAY BE RAIN ON THE WINDSHIELD BUT A COLD- SOAKED METAL-WING CAN PRECIPITATE THAT OUT AS SOLID ICE IF AT 31-32 DEGS F IN THE DRIZZLE.

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.