AN ACR MLG HAD A FAILURE OF ITS RADIO ALTIMETER AND ITS GPWS CAUSING A TERRAIN WARNING. THE PLT PULLED UP; IN THE WX; TO FOLLOW THE WARNING.

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FO FLYING ACFT; APCHING ORD ACR X ONT-ORD; MAY/FRI/92. ORD ILS 14R IN USE; BEING VECTORED FROM S TOWARD 14R LOC; GIVEN SERIES DSCNTS TO 7000 FT; THEN 6000 FT AND THEN 5000 FT. CONDITIONS WERE SCATTERED THUNDER/RAIN SHOWERS; WITH OCCASIONAL VIEW OF GND THROUGH CLOUDS. GIVEN VECTOR TO NNW APPROX 5 MI TO S OF LOC AND 5 MI OUTSIDE FINAL APCH FIX; WITH DSCNTS AS DESCRIBED ABOVE. VECTOR TOOK US BY CELL; WE DEVIATED SLIGHTLY W TO PASS BTWN 2 CELLS. DSNDING THROUGH 6600 FT (6000 FT AGL) WHILE IN CLOUD; GPWS ACTIVATED 'TERRAIN; TERRAIN; PULL UP.' RADAR ALTIMETER INDICATED 1250 FT DSNDING RAPIDLY THOUGH BAROMETRIC ALTIMETER INDICATED 6600 FT. CAPT INITIATED RAPID CLB. AT APPROX 7000 FT BAROMETRIC; RADAR ALTIMETER INDICATED 2500 FT PLUS (NOT IN VIEW) AND DSCNT WAS CONTINUED AFTER NOTIFYING APCH. GPWS WARNING CONTINUED AND COULD ONLY BE SHUT OFF BY DEACTIVATING/OVERRIDING GPWS SYS. QUERIED CTLR ABOUT POSSIBILITY OF ANY OTHER ACFT PASSING BENEATH US WHICH MIGHT HAVE INITIATED GPWS ALERT. NEAREST ACFT HE KNEW OF WAS MORE THAN 1 MI AWAY AND MORE THAN 1000 FT BELOW US. 1) THERE ARE PERIODIC WRITE-UPS IN ACR X MLG FLEET ABOUT GPWS ALERTS CAUSED BY KNOWN TFC PASSING UNDERNEATH. 2) LIKEWISE; THERE ARE PERIODIC WRITE-UPS ABOUT THE FACT THAT THE GPWS ALERT CONTINUES EVEN BEYOND THE TIME THE KNOWN ACTIVATOR (SUCH AS AN ACFT PASSING BENEATH) WILL NOT SHUT OFF. 3) THE DEAFENING NOISE OF THE ALERT; PARTICULARLY AT A PHASE OF FLT WITH VERY HVY WORKLOAD; WHICH DOES NOT STOP; IS DANGEROUSLY DISTRACTING. 4) THE FACT THAT THE GPWS IS PRONE TO GIVING FALSE ALARMS; AND CONTINUES WHEN NO ALARM CONDITION EXISTS IS ALSO DANGEROUS. THE FACT THAT THIS SEEMS TO OCCUR PERIODICALLY STRONGLY IMPLIES A SYS WITH SOME FAULTY LOGIC/PROGRAMMING. THIS IS NOT TO IMPLY I FEEL GPWS IS A POOR SYS; BUT THAT THE FAULTS SHOULD BE RECTIFIED.