B737 flight crew reported windshear conditions on short final caused an overspeed of the flaps.

Attributes
ACN	1359054
Time
Date	201605
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Final Approach
Flight Plan	IFR
Component
Aircraft Component	Trailing Edge Flap
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Total 8154 Flight Crew Type 1751
Person 2
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Procedural Published Material / Policy Inflight Event / Encounter Weather / Turbulence

Narrative:

On approach; windshear gain 10 to 15kts reported. Tail wind at altitude. Had a difficult time slowing down was at 190 gear down at FAF. Configured to flaps 30. Stable at about 900 feet. Sometime after completion of the landing checklist had a gust up to load relief limit. But stable again by 500 feet. Inside 500 got too low terrain calls on GPWS. We were on glide path and stable; elected to continue. During this evolution the captain realized the flaps were at 25; he rechecked the flap handle position. It was at 30. Flap load relief had activated after landing checklist had been completed; but flaps remained stuck at the 25 position with the speed at 160. We elected to land; due to the severe weather; and wind shear reports in the vicinity of the airport.I was confused by the too low terrain call; we were stable on the glide path when we got this call. It did cease; but am not sure when. We never did get a too low flaps; which was my expectation. Now; I think it is due to flap handle position logic but was unable to confirm it in the book.

Original NASA ASRS Text

Title: B737 flight crew reported windshear conditions on short final caused an overspeed of the flaps.

Narrative: On approach; windshear gain 10 to 15kts reported. Tail wind at altitude. Had a difficult time slowing down was at 190 gear down at FAF. Configured to flaps 30. Stable at about 900 feet. Sometime after completion of the landing checklist had a gust up to load relief limit. But stable again by 500 feet. Inside 500 got too low terrain calls on GPWS. We were on glide path and stable; elected to continue. During this evolution the captain realized the flaps were at 25; he rechecked the flap handle position. It was at 30. Flap load relief had activated after landing checklist had been completed; but flaps remained stuck at the 25 position with the speed at 160. We elected to land; due to the severe weather; and wind shear reports in the vicinity of the airport.I was confused by the too low terrain call; we were stable on the glide path when we got this call. It did cease; but am not sure when. We never did get a too low flaps; which was my expectation. Now; I think it is due to flap handle position logic but was unable to confirm it in the book.

Data retrieved from NASA's ASRS site 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.