|37000 Feet||Browse and search NASA's
Aviation Safety Reporting System
|Local Time Of Day||0601 To 1200|
|Locale Reference||atc facility : dab|
|Altitude||msl bound lower : 3500|
msl bound upper : 3500
|Controlling Facilities||tower : dab|
tracon : dtw
|Operator||common carrier : air carrier|
|Make Model Name||Airliner 99|
|Operating Under FAR Part||Part 121|
|Flight Phase||descent : approach|
landing : missed approach
|Affiliation||government : faa|
|Function||controller : local|
|Experience||controller military : 9|
controller non radar : 3
controller radar : 25
|Affiliation||company : air carrier|
|Function||flight crew : captain|
oversight : pic
|Qualification||pilot : atp|
|Anomaly||inflight encounter : weather|
other anomaly other
|Independent Detector||other flight crewa|
|Air Traffic Incident||other|
ASOS is not representative of the true conditions over the airport. ASOS WX was reporting 36 scattered, 60 scattered, 10 plus mi visibility at XX56Z ob. At approximately XY20Z the BE99 attempted and ILS approach and at 2 mi final, reported missed approach. As the aircraft passed over the airport at 1600 ft, I could not see the aircraft. I reported the condition to my supervisor who in turn reported the inaccuracy to the NWS and the TRACON supervisor. NWS issued a special WX report a few mins later. The BE99 pilot made another approach and upon landing, advised me the bases of the lower layer were definitely broken and on final he broke out at 1200 ft. A LR35 pilot reported the same condition a few mins later. Other pilots in the pattern confirmed the broken layer plus the supervisor and other controls observed it. ASOS was not reporting the true WX condition. I understand ASOS only reports what is directly above the cellometer. However in this instance, it never did report the true condition. The broken layer was over the airport for at least 50 mins but was never reported by ASOS. The only correctable action as I see it is to have qualified personnel do the observations or somehow improve the ASOS equipment accuracy.
Original NASA ASRS Text
Title: WX RPTING EQUIP ASOS INACCURATE WX RPTED ACR MISSED APCH.
Narrative: ASOS IS NOT REPRESENTATIVE OF THE TRUE CONDITIONS OVER THE ARPT. ASOS WX WAS RPTING 36 SCATTERED, 60 SCATTERED, 10 PLUS MI VISIBILITY AT XX56Z OB. AT APPROX XY20Z THE BE99 ATTEMPTED AND ILS APCH AND AT 2 MI FINAL, RPTED MISSED APCH. AS THE ACFT PASSED OVER THE ARPT AT 1600 FT, I COULD NOT SEE THE ACFT. I RPTED THE CONDITION TO MY SUPVR WHO IN TURN RPTED THE INACCURACY TO THE NWS AND THE TRACON SUPVR. NWS ISSUED A SPECIAL WX RPT A FEW MINS LATER. THE BE99 PLT MADE ANOTHER APCH AND UPON LNDG, ADVISED ME THE BASES OF THE LOWER LAYER WERE DEFINITELY BROKEN AND ON FINAL HE BROKE OUT AT 1200 FT. A LR35 PLT RPTED THE SAME CONDITION A FEW MINS LATER. OTHER PLTS IN THE PATTERN CONFIRMED THE BROKEN LAYER PLUS THE SUPVR AND OTHER CTLS OBSERVED IT. ASOS WAS NOT RPTING THE TRUE WX CONDITION. I UNDERSTAND ASOS ONLY RPTS WHAT IS DIRECTLY ABOVE THE CELLOMETER. HOWEVER IN THIS INSTANCE, IT NEVER DID RPT THE TRUE CONDITION. THE BROKEN LAYER WAS OVER THE ARPT FOR AT LEAST 50 MINS BUT WAS NEVER RPTED BY ASOS. THE ONLY CORRECTABLE ACTION AS I SEE IT IS TO HAVE QUALIFIED PERSONNEL DO THE OBSERVATIONS OR SOMEHOW IMPROVE THE ASOS EQUIP ACCURACY.
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.