B737-300 captain experiences a windshear warning during approach to runway 12R at stl on a calm VMC ...

Narrative:

Landing on runway 12R at stl yesterday in a B737-300; we got a windshear warning and initiated a go-around. We went around the pattern and on our second approach we got the same warning. I directed my first officer to land; and here's why: 1) weather was VFR day with light winds; 2) tower reported light winds on all of their instruments and no other reports of windshear; and 3) I also evaluated the highway configuration just short of the runway and felt that it was the main factor.after landing; we asked maintenance to come to the jet and our mechanic had the following to say: 1) we get bogus windshear warnings fairly often at stl; 2) company at some time in the past had evaluated the situation to include some test flights. No idea what their conclusions were; and 3) he was confident it was not a malfunctioning system on our aircraft.evaluate the windshear system for its tendencies to give false windshear warnings when highway traffic is present near the approach to a runway. Share any pertinent findings with the pilot group. Add a note to our stl briefing page.

Original NASA ASRS Text

Title: B737-300 Captain experiences a windshear warning during approach to Runway 12R at STL on a calm VMC day; and goes around. The next approach produces the same warning; but the approach is continued to landing. Highway traffic on final is thought to be the cause.

Narrative: Landing on Runway 12R at STL yesterday in a B737-300; we got a windshear warning and initiated a go-around. We went around the pattern and on our second approach we got the same warning. I directed my First Officer to land; and here's why: 1) Weather was VFR day with light winds; 2) Tower reported light winds on all of their instruments and no other reports of windshear; and 3) I also evaluated the highway configuration just short of the runway and felt that it was the main factor.After landing; we asked Maintenance to come to the jet and our Mechanic had the following to say: 1) We get bogus windshear warnings fairly often at STL; 2) Company at some time in the past had evaluated the situation to include some test flights. No idea what their conclusions were; and 3) He was confident it was not a malfunctioning system on our aircraft.Evaluate the windshear system for its tendencies to give false windshear warnings when highway traffic is present near the approach to a runway. Share any pertinent findings with the Pilot Group. Add a note to our STL briefing page.

Data retrieved from NASA's ASRS site as of July 2013 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.

Attributes
ACN	1099931
Time
Date	201307
Local Time Of Day	0001-0600
Place
Locale Reference	STL.Airport
State Reference	MO
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	Safety Instrumentation & Information
Person 1
Function	Captain
Experience	Flight Crew Last 90 Days 217
Events
Anomaly	Aircraft Equipment Problem Less Severe

B737-300 captain experiences a windshear warning during approach to runway 12R at stl on a calm VMC day; and goes around. The next approach produces the same warning; but the approach is continued to landing. Highway traffic on final is thought to be the cause.