Narrative:

I was the flying pilot and initiated a descent from 12000 ft to our assigned altitude of 10000 ft in IMC. As the thrust levers were retarded, we got a 'gear horn.' a few seconds later, descending through approximately 11000 ft we got multiple GPWS warnings including: 'terrain terrain..whoop whoop pull up' and 'sink rate' all the while with our gear horn going off and the radio altimeter indicating imminent ground impact. In response, the captain immediately took the controls and initiated a climb. We reached an altitude of approximately 13500 ft and the warnings stopped. ATC called us and said that they needed best rate down to 10000 ft for traffic. As the captain started our descent back down, the warnings came back on, including the radio altimeter indicating close proximity to the ground. We verified that we were not in danger of impacting terrain and proceeded to our new assigned altitude of 9000 ft where we came into VFR conditions. After landing, maintenance determined that the probable cause of our false warnings was ice. We were released to takeoff back to ZZZ. Climbing back out, we again got the GPWS warnings around 8500 ft MSL. We noted a sat of -6, tat of five and no ice annunciation. Upon landing in ZZZ, maintenance again inspected the airplane and found that the #1 pack supply line was sheared in two and that the #2 supply line was also cracked. The broken supply line was causing hot bleed air to leak into the aft equipment bay where the radio altimeter antenna is located. Factors leading to the altitude deviation: 1. Descent in IMC at 1500 FPM with rising terrain. 2. Multiple GPWS warnings and radio altimeter reading all indicating imminent ground impact. Had the indications occurred during cruise or in VMC, we would not have made the climb in response. However, with multiple warnings in IMC, with rising terrain, a climb was made which led to our altitude deviation. Callback conversation with reporter revealed the following information: the reporter stated the cause of the false warning was hot bleed air directed onto the radio altimeter antenna from a sheared #1 pack bleed supply line duct. The #2 pack bleed supply line was also found cracked. The ducting and antenna are all located in the aft equipment bay.

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Original NASA ASRS Text

Title: A CRJ-200 ON DSCNT FROM 12000 FT REACHING 11000 FT GOT MULTIPLE GND PROX WARNINGS. INITIATED CLB TO 13000 FT, WARNINGS STOPPED. ON APCH TO LNDG WARNINGS CONTINUED. CAUSED BY BLEED AIR LEAK ON RADIO ALTIMETER ANTENNA.

Narrative: I WAS THE FLYING PLT AND INITIATED A DSCNT FROM 12000 FT TO OUR ASSIGNED ALT OF 10000 FT IN IMC. AS THE THRUST LEVERS WERE RETARDED, WE GOT A 'GEAR HORN.' A FEW SECONDS LATER, DSNDING THROUGH APPROX 11000 FT WE GOT MULTIPLE GPWS WARNINGS INCLUDING: 'TERRAIN TERRAIN..WHOOP WHOOP PULL UP' AND 'SINK RATE' ALL THE WHILE WITH OUR GEAR HORN GOING OFF AND THE RADIO ALTIMETER INDICATING IMMINENT GND IMPACT. IN RESPONSE, THE CAPT IMMEDIATELY TOOK THE CTLS AND INITIATED A CLB. WE REACHED AN ALT OF APPROX 13500 FT AND THE WARNINGS STOPPED. ATC CALLED US AND SAID THAT THEY NEEDED BEST RATE DOWN TO 10000 FT FOR TFC. AS THE CAPT STARTED OUR DSCNT BACK DOWN, THE WARNINGS CAME BACK ON, INCLUDING THE RADIO ALTIMETER INDICATING CLOSE PROXIMITY TO THE GND. WE VERIFIED THAT WE WERE NOT IN DANGER OF IMPACTING TERRAIN AND PROCEEDED TO OUR NEW ASSIGNED ALT OF 9000 FT WHERE WE CAME INTO VFR CONDITIONS. AFTER LNDG, MAINT DETERMINED THAT THE PROBABLE CAUSE OF OUR FALSE WARNINGS WAS ICE. WE WERE RELEASED TO TKOF BACK TO ZZZ. CLBING BACK OUT, WE AGAIN GOT THE GPWS WARNINGS AROUND 8500 FT MSL. WE NOTED A SAT OF -6, TAT OF FIVE AND NO ICE ANNUNCIATION. UPON LNDG IN ZZZ, MAINT AGAIN INSPECTED THE AIRPLANE AND FOUND THAT THE #1 PACK SUPPLY LINE WAS SHEARED IN TWO AND THAT THE #2 SUPPLY LINE WAS ALSO CRACKED. THE BROKEN SUPPLY LINE WAS CAUSING HOT BLEED AIR TO LEAK INTO THE AFT EQUIP BAY WHERE THE RADIO ALTIMETER ANTENNA IS LOCATED. FACTORS LEADING TO THE ALT DEV: 1. DSCNT IN IMC AT 1500 FPM WITH RISING TERRAIN. 2. MULTIPLE GPWS WARNINGS AND RADIO ALTIMETER READING ALL INDICATING IMMINENT GND IMPACT. HAD THE INDICATIONS OCCURRED DURING CRUISE OR IN VMC, WE WOULD NOT HAVE MADE THE CLB IN RESPONSE. HOWEVER, WITH MULTIPLE WARNINGS IN IMC, WITH RISING TERRAIN, A CLB WAS MADE WHICH LED TO OUR ALT DEV. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE CAUSE OF THE FALSE WARNING WAS HOT BLEED AIR DIRECTED ONTO THE RADIO ALTIMETER ANTENNA FROM A SHEARED #1 PACK BLEED SUPPLY LINE DUCT. THE #2 PACK BLEED SUPPLY LINE WAS ALSO FOUND CRACKED. THE DUCTING AND ANTENNA ARE ALL LOCATED IN THE AFT EQUIP BAY.

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.