Narrative:

The AWOS was reporting; 'winds calm.' the windsock at (across the road) the start end of runway 34 showed about 10 plus KTS. The skydiving operation was estimating 15 KTS for their jumpers. The pilot of baron confirmed the AWOS 'calm' report. During flight; the garmin 1000 showed winds generally 300 degrees +/- at 9-13 usually. The safety item involved in this type of situations is 'object fixation.' sometimes this factor is called 'single input decision making' or lack of 'triangles of agreement.' imagine a pilot on first solo cross country to 2q3 and the AWOS reporting 'winds calm.' the AFD states runway 34 is the calm wind runway. With just these two factors as an input; can you imagine a pilot landing runway 34 with a tailwind of some unacceptable value? I can. To add to this problem; the only county supplied on airport windsock is at the midfield tetrahedron and is difficult to see from the start end of runway 34 or runway 16 -- the pilot who knows of the windsock on the flying horse ranch or the drop zone windsock has more information. Of course; trees and ponds nearby offer more information. Suggestive corrective action: place a windsock (frangible if required) at the start end of runways 34 and 16. These smaller windsocks are cheap and provide a last few seconds of decision making input to a landing pilot. Please note also that the aim say not to trust tetrahedrons.callback conversation with reporter revealed the following information: reporter stated that the windsock at south end of the runway rarely agrees with the AWOS reported wind. Reporter stated that the sensors for AWOS wind reports are located between large hangars; and the AWOS reported winds are often inaccurate; affected by those structures.

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Original NASA ASRS Text

Title: C172 PLT REPORTS THAT AWOS REPORTED WINDS AT YOLO COUNTY ARPT; 2Q3; ARE OFTEN ERRONEOUS DUE TO THE LOCATION OF THE WIND SENSORS.

Narrative: THE AWOS WAS REPORTING; 'WINDS CALM.' THE WINDSOCK AT (ACROSS THE ROAD) THE START END OF RWY 34 SHOWED ABOUT 10 PLUS KTS. THE SKYDIVING OPERATION WAS ESTIMATING 15 KTS FOR THEIR JUMPERS. THE PLT OF BARON CONFIRMED THE AWOS 'CALM' REPORT. DURING FLT; THE GARMIN 1000 SHOWED WINDS GENERALLY 300 DEGS +/- AT 9-13 USUALLY. THE SAFETY ITEM INVOLVED IN THIS TYPE OF SITUATIONS IS 'OBJECT FIXATION.' SOMETIMES THIS FACTOR IS CALLED 'SINGLE INPUT DECISION MAKING' OR LACK OF 'TRIANGLES OF AGREEMENT.' IMAGINE A PLT ON FIRST SOLO XCOUNTRY TO 2Q3 AND THE AWOS REPORTING 'WINDS CALM.' THE AFD STATES RWY 34 IS THE CALM WIND RWY. WITH JUST THESE TWO FACTORS AS AN INPUT; CAN YOU IMAGINE A PLT LNDG RWY 34 WITH A TAILWIND OF SOME UNACCEPTABLE VALUE? I CAN. TO ADD TO THIS PROBLEM; THE ONLY COUNTY SUPPLIED ON ARPT WINDSOCK IS AT THE MIDFIELD TETRAHEDRON AND IS DIFFICULT TO SEE FROM THE START END OF RWY 34 OR RWY 16 -- THE PLT WHO KNOWS OF THE WINDSOCK ON THE FLYING HORSE RANCH OR THE DROP ZONE WINDSOCK HAS MORE INFO. OF COURSE; TREES AND PONDS NEARBY OFFER MORE INFO. SUGGESTIVE CORRECTIVE ACTION: PLACE A WINDSOCK (FRANGIBLE IF REQUIRED) AT THE START END OF RWYS 34 AND 16. THESE SMALLER WINDSOCKS ARE CHEAP AND PROVIDE A LAST FEW SECONDS OF DECISION MAKING INPUT TO A LNDG PLT. PLEASE NOTE ALSO THAT THE AIM SAY NOT TO TRUST TETRAHEDRONS.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: REPORTER STATED THAT THE WINDSOCK AT SOUTH END OF THE RWY RARELY AGREES WITH THE AWOS REPORTED WIND. RPTR STATED THAT THE SENSORS FOR AWOS WIND REPORTS ARE LOCATED BETWEEN LARGE HANGARS; AND THE AWOS REPORTED WINDS ARE OFTEN INACCURATE; AFFECTED BY THOSE STRUCTURES.

Data retrieved from NASA's ASRS site as of January 2009 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.