Narrative:

Briefer supplied WX as requested and apparently made at least 3 separate searches for PIREPS. Pilot recalls receiving reports of ice at altitudes from 9000 to 15000 in places including shb (shelbyville), day, cmh by various aircraft. 1 report indicated some layering around 5000 to 8000. Reports quoted were somewhat north of area of flight. No applicable PIREPS were provided for the specific flight area. Conditions indicated the strong potential for rime ice in clouds between the freezing level and 15000 MSL. This was supported by the previous flight with a very light trace of rime on climb out and rapid sublimation between layers. In general, sa reports indicated ceilings below forecast, but within approach requirements, and amended forecasts indicated slowly improving conditions. As a result of the briefing, the alternate was revised from cvg to lex. The plan was to divert to lex if icing could not be effectively avoided by flying between layers. Flight departed in VFR conditions with surface temperature in the low to mid 40's. Flight proceeded normally until just south of the trent intersection. The aircraft began picking up a very slight trace of rime ice on the struts. Having listened to other aircraft discussing flight conditions at various altitudes, a decision was made to divert for a landing. Loz was considered a southerly possibility, however, reported conditions at that time raised the chance that ceilings may have forced a missed approach and thereby extended the time the aircraft would be exposed to additional icing. At the time, the accretion rate was slow (estimated 1/16 inch in 15 mins) and given the uncertainty of a climb into irregular layers, the best choice seemed to be to head directly to lex which was 42 NM away and offered an ILS approach. Lex was reporting acceptable ceilings and light rain/drizzle. ATC was advised of the flight conditions and provided a clearance direct to hyk with an expected ILS approach. Regular updates were provided to ATC regarding ice accretion which continued at a slow pace. It became evident that actual winds aloft were considerablystronger than forecast. A slight decrease in IAS was noted (107 KTS to 100 KTS) which seemed to point to propeller involvement in the ice pickup. Propeller RPM was cycled in an effort to shed some of any buildup. Pitot heat appeared to be keeping the tube free of ice and the alternate air was cycled to confirm accuracy of instrument readings. ATC was requested to provide the most direct route to the final approach course and descent to min safe altitude in an effort to stop further accretion and minimize flight duration. 'Priority handling' was not requested. ATC indicated that GS was showing 50 KTS despite aircraft IAS of 97 KTS. 10 mi out from lex the accretion rate picked up to the point that just prior to joining the localizer the aircraft had acquired between 1/2 to 3/4 inch of rime ice on the struts. The visible portion of the wings appeared to have less than 1/2 inch. Upon advising ATC that the aircraft did not want to maintain altitude without a reduction in airspeed, ATC provided clearance to lower altitude and revised clearance from an ILS to an ASR approach (without pilot request). Ice was shed periodically after the last altitude reduction. The approach and landing was conducted without incident. Aircraft control was maintained at all times. It became evident after landing that, although ATC did not communicate it, they must have declared some degree of emergency for the airport. Fire and life squad equipment was waiting which frightened the passenger to a significant degree. An ATC advisory would have been helpful in alerting the passenger prior to the encounter. It was learned later that the aircraft on the immediately preceding approach (twin) had the equipment scrambled for him as well. The service provided by ATC was professionally delivered and appreciated. The pilot has read many accident reports arising from a failure to communicate in a clear manner and act in a timely fashion. This incident is an example of how problems of this sort may be mitigated. Although it may appear that from the pilot's perspective that ATC may have read too much into the situation based upon their ground speed indication, the potential outcome, if their interpretation was correct, was clearly unacceptable. If it was an error, it was a recoverable one.

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Original NASA ASRS Text

Title: SMA ENCOUNTERS ICING DIVERTS TO ALTERNATE, EMER EQUIP STANDING BY.

Narrative: BRIEFER SUPPLIED WX AS REQUESTED AND APPARENTLY MADE AT LEAST 3 SEPARATE SEARCHES FOR PIREPS. PLT RECALLS RECEIVING RPTS OF ICE AT ALTS FROM 9000 TO 15000 IN PLACES INCLUDING SHB (SHELBYVILLE), DAY, CMH BY VARIOUS ACFT. 1 RPT INDICATED SOME LAYERING AROUND 5000 TO 8000. RPTS QUOTED WERE SOMEWHAT N OF AREA OF FLT. NO APPLICABLE PIREPS WERE PROVIDED FOR THE SPECIFIC FLT AREA. CONDITIONS INDICATED THE STRONG POTENTIAL FOR RIME ICE IN CLOUDS BTWN THE FREEZING LEVEL AND 15000 MSL. THIS WAS SUPPORTED BY THE PREVIOUS FLT WITH A VERY LIGHT TRACE OF RIME ON CLB OUT AND RAPID SUBLIMATION BTWN LAYERS. IN GENERAL, SA RPTS INDICATED CEILINGS BELOW FORECAST, BUT WITHIN APCH REQUIREMENTS, AND AMENDED FORECASTS INDICATED SLOWLY IMPROVING CONDITIONS. AS A RESULT OF THE BRIEFING, THE ALTERNATE WAS REVISED FROM CVG TO LEX. THE PLAN WAS TO DIVERT TO LEX IF ICING COULD NOT BE EFFECTIVELY AVOIDED BY FLYING BTWN LAYERS. FLT DEPARTED IN VFR CONDITIONS WITH SURFACE TEMPERATURE IN THE LOW TO MID 40'S. FLT PROCEEDED NORMALLY UNTIL JUST S OF THE TRENT INTXN. THE ACFT BEGAN PICKING UP A VERY SLIGHT TRACE OF RIME ICE ON THE STRUTS. HAVING LISTENED TO OTHER ACFT DISCUSSING FLT CONDITIONS AT VARIOUS ALTS, A DECISION WAS MADE TO DIVERT FOR A LNDG. LOZ WAS CONSIDERED A SOUTHERLY POSSIBILITY, HOWEVER, RPTED CONDITIONS AT THAT TIME RAISED THE CHANCE THAT CEILINGS MAY HAVE FORCED A MISSED APCH AND THEREBY EXTENDED THE TIME THE ACFT WOULD BE EXPOSED TO ADDITIONAL ICING. AT THE TIME, THE ACCRETION RATE WAS SLOW (ESTIMATED 1/16 INCH IN 15 MINS) AND GIVEN THE UNCERTAINTY OF A CLB INTO IRREGULAR LAYERS, THE BEST CHOICE SEEMED TO BE TO HEAD DIRECTLY TO LEX WHICH WAS 42 NM AWAY AND OFFERED AN ILS APCH. LEX WAS RPTING ACCEPTABLE CEILINGS AND LIGHT RAIN/DRIZZLE. ATC WAS ADVISED OF THE FLT CONDITIONS AND PROVIDED A CLRNC DIRECT TO HYK WITH AN EXPECTED ILS APCH. REGULAR UPDATES WERE PROVIDED TO ATC REGARDING ICE ACCRETION WHICH CONTINUED AT A SLOW PACE. IT BECAME EVIDENT THAT ACTUAL WINDS ALOFT WERE CONSIDERABLYSTRONGER THAN FORECAST. A SLIGHT DECREASE IN IAS WAS NOTED (107 KTS TO 100 KTS) WHICH SEEMED TO POINT TO PROP INVOLVEMENT IN THE ICE PICKUP. PROP RPM WAS CYCLED IN AN EFFORT TO SHED SOME OF ANY BUILDUP. PITOT HEAT APPEARED TO BE KEEPING THE TUBE FREE OF ICE AND THE ALTERNATE AIR WAS CYCLED TO CONFIRM ACCURACY OF INST READINGS. ATC WAS REQUESTED TO PROVIDE THE MOST DIRECT RTE TO THE FINAL APCH COURSE AND DSCNT TO MIN SAFE ALT IN AN EFFORT TO STOP FURTHER ACCRETION AND MINIMIZE FLT DURATION. 'PRIORITY HANDLING' WAS NOT REQUESTED. ATC INDICATED THAT GS WAS SHOWING 50 KTS DESPITE ACFT IAS OF 97 KTS. 10 MI OUT FROM LEX THE ACCRETION RATE PICKED UP TO THE POINT THAT JUST PRIOR TO JOINING THE LOC THE ACFT HAD ACQUIRED BTWN 1/2 TO 3/4 INCH OF RIME ICE ON THE STRUTS. THE VISIBLE PORTION OF THE WINGS APPEARED TO HAVE LESS THAN 1/2 INCH. UPON ADVISING ATC THAT THE ACFT DID NOT WANT TO MAINTAIN ALT WITHOUT A REDUCTION IN AIRSPD, ATC PROVIDED CLRNC TO LOWER ALT AND REVISED CLRNC FROM AN ILS TO AN ASR APCH (WITHOUT PLT REQUEST). ICE WAS SHED PERIODICALLY AFTER THE LAST ALT REDUCTION. THE APCH AND LNDG WAS CONDUCTED WITHOUT INCIDENT. ACFT CTL WAS MAINTAINED AT ALL TIMES. IT BECAME EVIDENT AFTER LNDG THAT, ALTHOUGH ATC DID NOT COMMUNICATE IT, THEY MUST HAVE DECLARED SOME DEG OF EMER FOR THE ARPT. FIRE AND LIFE SQUAD EQUIP WAS WAITING WHICH FRIGHTENED THE PAX TO A SIGNIFICANT DEG. AN ATC ADVISORY WOULD HAVE BEEN HELPFUL IN ALERTING THE PAX PRIOR TO THE ENCOUNTER. IT WAS LEARNED LATER THAT THE ACFT ON THE IMMEDIATELY PRECEDING APCH (TWIN) HAD THE EQUIP SCRAMBLED FOR HIM AS WELL. THE SVC PROVIDED BY ATC WAS PROFESSIONALLY DELIVERED AND APPRECIATED. THE PLT HAS READ MANY ACCIDENT RPTS ARISING FROM A FAILURE TO COMMUNICATE IN A CLR MANNER AND ACT IN A TIMELY FASHION. THIS INCIDENT IS AN EXAMPLE OF HOW PROBLEMS OF THIS SORT MAY BE MITIGATED. ALTHOUGH IT MAY APPEAR THAT FROM THE PLT'S PERSPECTIVE THAT ATC MAY HAVE READ TOO MUCH INTO THE SITUATION BASED UPON THEIR GND SPD INDICATION, THE POTENTIAL OUTCOME, IF THEIR INTERPRETATION WAS CORRECT, WAS CLRLY UNACCEPTABLE. IF IT WAS AN ERROR, IT WAS A RECOVERABLE ONE.

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.