Narrative:

The ASOS visibility and ceiling sensors at cos airport failed during marginal WX. Traffic density was moderate. The ASOS gives no prior notice of sensor failures so it was not until after the WX sequence was transmitted that the failure was noted. It may have been giving erroneous information prior to the time the failure was noted. At night there is no means of determining the accuracy of the ASOS ceiling sensor. ASOS equipment failures are becoming quite frequent.

Google
 

Original NASA ASRS Text

Title: A CTLR AT COS STATES THAT THE ASOS FAILED DURING MARGINAL WX. NO PRIOR INFO OR ALARMS WERE GIVEN. THE RPTR CLAIMS THAT ASOS FAILURES ARE BECOMING COMMON.

Narrative: THE ASOS VISIBILITY AND CEILING SENSORS AT COS ARPT FAILED DURING MARGINAL WX. TFC DENSITY WAS MODERATE. THE ASOS GIVES NO PRIOR NOTICE OF SENSOR FAILURES SO IT WAS NOT UNTIL AFTER THE WX SEQUENCE WAS XMITTED THAT THE FAILURE WAS NOTED. IT MAY HAVE BEEN GIVING ERRONEOUS INFO PRIOR TO THE TIME THE FAILURE WAS NOTED. AT NIGHT THERE IS NO MEANS OF DETERMINING THE ACCURACY OF THE ASOS CEILING SENSOR. ASOS EQUIP FAILURES ARE BECOMING QUITE FREQUENT.

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.