Narrative:

Approaching the mso airport, we were advised that reported mso visibility was 1/2 mi varying upward to 1 1/4 mi broken, was able to see mso airport, approach lights, city and all surrounding areas from 80 NM west. Night was clear, and no ceiling was being reported. An MD80 was also approaching mso as was a B727. All 3 of us were approaching mso from 3 directions and would be landing about 5 mins apart. The mso tower was closed. A light aircraft had just departed on a SVFR. He stated that there was no fog or obscuration. All approaching aircraft concurred that visibility was unrestr and that there must be something wrong with the electronic observation equipment. The MD80 landed first after being cleared for an ILS approach. He reported no obscuration or fog, etc. I landed next, followed by the B727. At no point was any point on the runway, airport or surrounding area obscured. Visibility was absolutely unrestr. All surrounding terrain was clearly visible. It was our opinion, and geg approach's opinion that there was a malfunction in the reporting equipment. Safety was in no way compromised. Callback conversation with reporter revealed the following information: called reporter to learn if problem still exists but was told that he was not been back to mso. Called the facility and learned there have been problems with the ASOS visibility reporting primarily during snow or fog conditions. Facility stated the equipment is slow to change values especially when the visibility changes rapidly up or down. He also stated that once the controllers called the administrator's hotline to report an incident in which the rptd visibility made the airport IMC when the actual tower visibility was 8 mi and as a result caused an aircraft to make an ILS circle to land with a tailwind rather than a visual approach into the wind. The facility representative stated that WX personnel are on the airport and alleges they have been reluctant to change the WX report when there have been discrepancies between the reported and actual conditions. He indicated they may be more responsive since the hotline call.

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Original NASA ASRS Text

Title: WX RPTING EQUIP FOR MSO RPTS VISIBILITY BTWN 1 AND 1 PT 25 MI. RPTR AND 2 OTHER ACRS INBOUND AS WELL AS A DEPARTING GA RPT NO OBSCURATION AND UNRESTR VISIBILITY.

Narrative: APCHING THE MSO ARPT, WE WERE ADVISED THAT RPTED MSO VISIBILITY WAS 1/2 MI VARYING UPWARD TO 1 1/4 MI BROKEN, WAS ABLE TO SEE MSO ARPT, APCH LIGHTS, CITY AND ALL SURROUNDING AREAS FROM 80 NM W. NIGHT WAS CLR, AND NO CEILING WAS BEING RPTED. AN MD80 WAS ALSO APCHING MSO AS WAS A B727. ALL 3 OF US WERE APCHING MSO FROM 3 DIRECTIONS AND WOULD BE LNDG ABOUT 5 MINS APART. THE MSO TWR WAS CLOSED. A LIGHT ACFT HAD JUST DEPARTED ON A SVFR. HE STATED THAT THERE WAS NO FOG OR OBSCURATION. ALL APCHING ACFT CONCURRED THAT VISIBILITY WAS UNRESTR AND THAT THERE MUST BE SOMETHING WRONG WITH THE ELECTRONIC OBSERVATION EQUIP. THE MD80 LANDED FIRST AFTER BEING CLRED FOR AN ILS APCH. HE RPTED NO OBSCURATION OR FOG, ETC. I LANDED NEXT, FOLLOWED BY THE B727. AT NO POINT WAS ANY POINT ON THE RWY, ARPT OR SURROUNDING AREA OBSCURED. VISIBILITY WAS ABSOLUTELY UNRESTR. ALL SURROUNDING TERRAIN WAS CLRLY VISIBLE. IT WAS OUR OPINION, AND GEG APCH'S OPINION THAT THERE WAS A MALFUNCTION IN THE RPTING EQUIP. SAFETY WAS IN NO WAY COMPROMISED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CALLED RPTR TO LEARN IF PROB STILL EXISTS BUT WAS TOLD THAT HE WAS NOT BEEN BACK TO MSO. CALLED THE FACILITY AND LEARNED THERE HAVE BEEN PROBS WITH THE ASOS VISIBILITY RPTING PRIMARILY DURING SNOW OR FOG CONDITIONS. FACILITY STATED THE EQUIP IS SLOW TO CHANGE VALUES ESPECIALLY WHEN THE VISIBILITY CHANGES RAPIDLY UP OR DOWN. HE ALSO STATED THAT ONCE THE CTLRS CALLED THE ADMINISTRATOR'S HOTLINE TO RPT AN INCIDENT IN WHICH THE RPTD VISIBILITY MADE THE ARPT IMC WHEN THE ACTUAL TWR VISIBILITY WAS 8 MI AND AS A RESULT CAUSED AN ACFT TO MAKE AN ILS CIRCLE TO LAND WITH A TAILWIND RATHER THAN A VISUAL APCH INTO THE WIND. THE FACILITY REPRESENTATIVE STATED THAT WX PERSONNEL ARE ON THE ARPT AND ALLEGES THEY HAVE BEEN RELUCTANT TO CHANGE THE WX RPT WHEN THERE HAVE BEEN DISCREPANCIES BTWN THE RPTED AND ACTUAL CONDITIONS. HE INDICATED THEY MAY BE MORE RESPONSIVE SINCE THE HOTLINE CALL.

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.