An air carrier F100 had a false warning from its GPWS.

Attributes
ACN	337037
Time
Date	199605
Day	Tue
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : ord
State Reference	IL
Altitude	msl bound lower : 10000 msl bound upper : 10600
Environment
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : ord
Operator	common carrier : air carrier
Make Model Name	Fokker 100
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	337037
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : commercial pilot : instrument
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude inflight encounter : weather non adherence : clearance non adherence : published procedure other anomaly other
Independent Detector	other flight crewa
Resolutory Action	aircraft : equipment problem dissipated flight crew : returned to intended course or assigned course
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	other

Narrative:

On approach to ord over lake michigan, heard GPWS voice warning, 'too low, terrain.' responded with immediate climb and request for confirmation of correct altimeter setting. ATC confirmed our altitude and correct altimeter setting, and at approximately 10600 ft, a descent was initiated back to our initial altitude of 10000 ft. We also had informed ATC of our GPWS warning. We had just flown over an area of precipitation which may have triggered the GPWS. I wrote up the GPWS for maintenance to check the system upon arrival at ord.

Original NASA ASRS Text

Title: AN ACR F100 HAD A FALSE WARNING FROM ITS GPWS.

Narrative: ON APCH TO ORD OVER LAKE MICHIGAN, HEARD GPWS VOICE WARNING, 'TOO LOW, TERRAIN.' RESPONDED WITH IMMEDIATE CLB AND REQUEST FOR CONFIRMATION OF CORRECT ALTIMETER SETTING. ATC CONFIRMED OUR ALT AND CORRECT ALTIMETER SETTING, AND AT APPROX 10600 FT, A DSCNT WAS INITIATED BACK TO OUR INITIAL ALT OF 10000 FT. WE ALSO HAD INFORMED ATC OF OUR GPWS WARNING. WE HAD JUST FLOWN OVER AN AREA OF PRECIP WHICH MAY HAVE TRIGGERED THE GPWS. I WROTE UP THE GPWS FOR MAINT TO CHK THE SYS UPON ARR AT ORD.

Data retrieved from NASA's ASRS site as of July 2007 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.