Narrative:

During our arrival into miami; we were vectored around thunderstorms in southern florida. Finally clear of the weather; miami approach cleared us direct to gritt intersection and the ILS approach to runway 9. As we approached gritt we watched a line of weather as it approached the miami airport from the north. It was still several miles to the north; as we got closer to gritt. Passing gritt we started descending out of 3000 ft at 200 KTS and began to configure for landing. The radar now showed that a return coming out of the line had just reached the localizer at the FAF. The first officer called for flaps 10; but as he did; the airspeed suddenly went from 200 KTS to almost 220 KTS; too fast for flaps 10. This happened as we neared the weather at the marker. We both came to the decision to abandon the approach and go-around. We flew a normal go-around; turning to the south and climbing to 4000 ft. During the turn we encountered the edge of the weather cell and flew through moderate turbulence; which did not activate the windshear warning in the aircraft but did cause the airspeed to gain 40-50 KTS very quickly. We observed 270 KTS while the flaps were still at 1. We entered holding south of miami and notified dispatch of our hold. During discussion of holding or diversion we informed dispatch of the flaps overspeed and the need for maintenance on arrival. It was then decided to divert to avoid weather and have the aircraft inspected. Upon arrival the flight data was downloaded and our overspeed of 20 KTS was confirmed. The aircraft was taken out of service.

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Original NASA ASRS Text

Title: B737 flight crew experienced windshear during ILS approach to Runway 9 at MIA. Thunderstorm adjacent to the final course causes increasing airspeed and a flap overspeed during the missed approach. Crew diverted to an airport with clear weather.

Narrative: During our arrival into Miami; we were vectored around thunderstorms in southern Florida. Finally clear of the weather; Miami approach cleared us direct to GRITT Intersection and the ILS approach to Runway 9. As we approached GRITT we watched a line of weather as it approached the Miami airport from the north. It was still several miles to the north; as we got closer to GRITT. Passing GRITT we started descending out of 3000 FT at 200 KTS and began to configure for landing. The radar now showed that a return coming out of the line had just reached the localizer at the FAF. The First Officer called for Flaps 10; but as he did; the airspeed suddenly went from 200 KTS to almost 220 KTS; too fast for Flaps 10. This happened as we neared the weather at the marker. We both came to the decision to abandon the approach and go-around. We flew a normal go-around; turning to the south and climbing to 4000 FT. During the turn we encountered the edge of the weather cell and flew through moderate turbulence; which did not activate the windshear warning in the aircraft but did cause the airspeed to gain 40-50 KTS very quickly. We observed 270 KTS while the flaps were still at 1. We entered holding south of Miami and notified Dispatch of our hold. During discussion of holding or diversion we informed Dispatch of the flaps overspeed and the need for maintenance on arrival. It was then decided to divert to avoid weather and have the aircraft inspected. Upon arrival the flight data was downloaded and our overspeed of 20 KTS was confirmed. The aircraft was taken out of service.

Data retrieved from NASA's ASRS site as of April 2012 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.