Narrative:

While en route to the danville airport I monitored danville AWOS. I had previously received a preflight FSS briefing and was informed that danville had no WX reporting and that the nearest reported terminal was champaign which was reporting and forecasting VFR conditions. The AWOS was reporting ceiling 1100 ft broken, 2500 overcast and 7 mi visibility. Then contacted unicom for TA's. However, approximately 8 mi west of the airport, I encountered a ceiling of about 1000 ft and visibilities 3 mi in rain and fog. I continued the approach in what appeared to be marginal VFR and after landing, was told by airport FBO personnel that the AWOS was continuing to report above VFR minimum conditions. I departed shortly thereafter and the rain had increased in intensity while departing the airport area. I understand that the sensor's location only reports conditions over the approach end of the runway. However, there can be a substantial difference in prevailing airport area conditions from what the AWOS is sensing. Since this airport is a not-twred airport with a part- time control zone, pilots relying on AWOS information could encounter IMC within the control zone while it is in effect and without a special VFR clearance that the pilot would have otherwise requested prior to entering the clear zone. I have also seen differences in what AWOS at another airport (ikk) greater kankakee has reported versus prevailing area conditions. The AWOS appears to generally report better conditions than the actual conditions that the pilot may encounter. I would recommend that, until future AWOS provide WX precipitation information that AWOS broadcast end with a statement stressing that AWOS does not provide airport area actual conditions but only conditions over the approach end of a runway. Many pilots, I believe, assume since being familiar with ATIS broadcasts information, that AWOS is, if not similar, the very same thing, and don't really distinguish any differences between the sources of the reported conditions -- human versus computer generated information.

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Original NASA ASRS Text

Title: FLT INSTRUCTOR LANDS AT ARPT WITH INACCURATE AWOS WX INFO. UNAUTH CTL ZONE ENTRY.

Narrative: WHILE ENRTE TO THE DANVILLE ARPT I MONITORED DANVILLE AWOS. I HAD PREVIOUSLY RECEIVED A PREFLT FSS BRIEFING AND WAS INFORMED THAT DANVILLE HAD NO WX RPTING AND THAT THE NEAREST RPTED TERMINAL WAS CHAMPAIGN WHICH WAS RPTING AND FORECASTING VFR CONDITIONS. THE AWOS WAS RPTING CEILING 1100 FT BROKEN, 2500 OVCST AND 7 MI VISIBILITY. THEN CONTACTED UNICOM FOR TA'S. HOWEVER, APPROX 8 MI W OF THE ARPT, I ENCOUNTERED A CEILING OF ABOUT 1000 FT AND VISIBILITIES 3 MI IN RAIN AND FOG. I CONTINUED THE APCH IN WHAT APPEARED TO BE MARGINAL VFR AND AFTER LNDG, WAS TOLD BY ARPT FBO PERSONNEL THAT THE AWOS WAS CONTINUING TO RPT ABOVE VFR MINIMUM CONDITIONS. I DEPARTED SHORTLY THEREAFTER AND THE RAIN HAD INCREASED IN INTENSITY WHILE DEPARTING THE ARPT AREA. I UNDERSTAND THAT THE SENSOR'S LOCATION ONLY RPTS CONDITIONS OVER THE APCH END OF THE RWY. HOWEVER, THERE CAN BE A SUBSTANTIAL DIFFERENCE IN PREVAILING ARPT AREA CONDITIONS FROM WHAT THE AWOS IS SENSING. SINCE THIS ARPT IS A NOT-TWRED ARPT WITH A PART- TIME CTL ZONE, PLTS RELYING ON AWOS INFO COULD ENCOUNTER IMC WITHIN THE CTL ZONE WHILE IT IS IN EFFECT AND WITHOUT A SPECIAL VFR CLRNC THAT THE PLT WOULD HAVE OTHERWISE REQUESTED PRIOR TO ENTERING THE CLR ZONE. I HAVE ALSO SEEN DIFFERENCES IN WHAT AWOS AT ANOTHER ARPT (IKK) GREATER KANKAKEE HAS RPTED VERSUS PREVAILING AREA CONDITIONS. THE AWOS APPEARS TO GENERALLY RPT BETTER CONDITIONS THAN THE ACTUAL CONDITIONS THAT THE PLT MAY ENCOUNTER. I WOULD RECOMMEND THAT, UNTIL FUTURE AWOS PROVIDE WX PRECIPITATION INFO THAT AWOS BROADCAST END WITH A STATEMENT STRESSING THAT AWOS DOES NOT PROVIDE ARPT AREA ACTUAL CONDITIONS BUT ONLY CONDITIONS OVER THE APCH END OF A RWY. MANY PLTS, I BELIEVE, ASSUME SINCE BEING FAMILIAR WITH ATIS BROADCASTS INFO, THAT AWOS IS, IF NOT SIMILAR, THE VERY SAME THING, AND DON'T REALLY DISTINGUISH ANY DIFFERENCES BTWN THE SOURCES OF THE RPTED CONDITIONS -- HUMAN VERSUS COMPUTER GENERATED INFO.

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.