Narrative:

Dispatcher briefed me on flight to ord with MEL 34-17B windshear reactive mode. Previous dispatcher released the flight. I then amended the release before departure due to ATC reroute which required more fuel. Taf for ord for arrival time was winds 090 at 06 KTS visibility greater than 6 miles and ceiling 25000 ft with a prob 30 of 4 miles visible tsra and 5000 ft broken ceiling. Previous dispatcher checked with metro as well as I and confirmed no expected windshear at ord a long as the flight not landing in a thunderstorm; which we would not do. One small rain shower developed over ord about 1.5 hours prior to landing. Sent an ACARS message to flight briefing them on that and would advise if any problems with that rain shower or windshear. That small rain shower moved southeast of ord towards mdw and died down. Flight got about 50 minutes from landing ord and said ATIS showed windshear advisories in affect. I called ord tower and he said it was reported mechanically from itws and no windshear at ord and he would take it out which they did. Just before the flight landed another ATIS came out with windshear advisories for ord so flight went into a hold. Winds were 290 at 06KTS when they were reported. I called the ASOS about 5 minutes later and winds were reported 310 at 10KTS. There were no weather within 100 miles of ord and no aircraft reporting any windshear but the mechanical reporting system was still reporting windshear advisories. Captain agreed no weather but windshear advisories on ATIS caused the concern. We decided to play it on the safe side and hold until the system corrected itself; which it didn't do in time. Cockpit crew was going to go illegal if we diverted so diverted where another crew and aircraft were available. In summary I believe no windshear was at ord for flights arrival time by the winds 310 at 10 KTS and aircraft reporting no windshear. Played it safe going to an alternate due to windshear advisories being reported on the ATIS which I believe to be incorrect.

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Original NASA ASRS Text

Title: Dispatcher reports on diversion caused by MEL on aircraft reactive windshear system requiring avoidance of any possible windshear.

Narrative: Dispatcher briefed me on flight to ORD with MEL 34-17B windshear reactive mode. Previous Dispatcher released the flight. I then amended the release before departure due to ATC reroute which required more fuel. TAF for ORD for arrival time was winds 090 at 06 KTS visibility greater than 6 miles and ceiling 25000 FT with a prob 30 of 4 miles visible TSRA and 5000 FT broken ceiling. Previous Dispatcher checked with Metro as well as I and confirmed no expected windshear at ORD a long as the flight not landing in a thunderstorm; which we would not do. One small rain shower developed over ORD about 1.5 hours prior to landing. Sent an ACARS message to flight briefing them on that and would advise if any problems with that rain shower or windshear. That small rain shower moved SE of ORD towards MDW and died down. Flight got about 50 minutes from landing ORD and said ATIS showed windshear advisories in affect. I called ORD Tower and he said it was reported mechanically from ITWS and no windshear at ORD and he would take it out which they did. Just before the flight landed another ATIS came out with windshear advisories for ORD so flight went into a hold. Winds were 290 at 06KTS when they were reported. I called the ASOS about 5 minutes later and winds were reported 310 at 10KTS. There were no weather within 100 miles of ORD and no aircraft reporting any windshear but the mechanical reporting system was still reporting windshear advisories. Captain agreed no weather but windshear advisories on ATIS caused the concern. We decided to play it on the safe side and hold until the system corrected itself; which it didn't do in time. Cockpit crew was going to go illegal if we diverted so diverted where another crew and aircraft were available. In summary I believe no windshear was at ORD for flights arrival time by the winds 310 at 10 KTS and aircraft reporting no windshear. Played it safe going to an alternate due to windshear advisories being reported on the ATIS which I believe to be incorrect.

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.