WX reporting equipment ASOS inaccurate WX reported air carrier missed approach.

Attributes
ACN	306488
Time
Date	199506
Day	Mon
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : dab
State Reference	FL
Altitude	msl bound lower : 3500 msl bound upper : 3500
Environment
Flight Conditions	Marginal
Light	Daylight
Aircraft 1
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
Flight Plan	IFR
Person 1
Affiliation	government : faa
Function	controller : local
Experience	controller military : 9 controller non radar : 3 controller radar : 25
ASRS Report	306488
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	inflight encounter : weather other anomaly other
Independent Detector	other flight crewa
Resolutory Action	other
Consequence	Other
Supplementary
Air Traffic Incident	other

Narrative:

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.