CARJ FLT CREW RECEIVE MULTIPLE FALSE EGPWS WARNINGS ON DSCNT INTO AVP.

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THE SIT STARTED WITH THE FO AS THE PF. I WAS OFF GETTING THE ATIS AND NOTICED THAT THIS WAS A SPECIAL ARPT DUE TO TERRAIN. I TOLD HIM I WOULD BE MAKING THE APCH. WHILE HE WAS BRINGING ME UP TO SPD WAS WHEN ALL THIS STARTED. FAILURE OF THE GPWS AND RADAR ALT CAUSED AN ALTDEV. ENRTE TO AVP AT 10000 FT WE ENTERED IMC. WE GOT AN ICE 'CWP;' MINS LATER DSNDING THROUGH 12000 FT WE GOT CONTINUOUSLY THE 'GEAR HORN; TERRAIN; TERRAIN' SINK RATE AND 'PULL UP' WARNINGS. IN ADDITION; THE RADAR ALTIMETER SHOWED IMMINENT GND CONTACT. THINKING WE MAY NOT BE WHERE WE SHOULD I STARTED A CLB AT WHICH TIME EVERYTHING EXCEPT THE GEAR HORN STOPPED. WE SILENCED THE HORN AND LEVELED AT 13500 FT AND STARTED DOWN PER ATC INSTRUCTIONS. THE TERRAIN; SINK RATE AND PULL UP STARTED AGAIN. THE RADAR ALT SHOWED GND CONTACT ALSO. THIS CONTINUED UNTIL WE WERE OUT OF 10000 FT AND IN VFR CONDITIONS. AFTER LNDG IN AVP; MAINT DETERMINED THAT ICE PROBABLY CAUSED THE PROB. UPON RETURNING TO PHL WE GOT THE TERRAIN WARNING TWICE AT 8500 FT WITH THE STATIC AIR TEMP 6C AND TOTAL AIR TEMP 5C BUT NO OTHER WARNINGS. I CALLED MAINT UPON LNDG IN PHL. WHILE LOOKING INTO ANOTHER ISSUE MAINT FOUND THE #1 PACK SUPPLY LINE CRACKED IN TWO AND THE #2 PACK BLEED SUPPLY DUCK CRACKED WHICH THEY THINK COULD HAVE CAUSED HOT AIR IN AND AROUND THE RADAR ALTIMETER ANTENNA. A NUMBER OF FACTORS WERE INVOLVED WITH SIT. 1) WE WERE DSNDING AT 1500/MIN IN IMC TO A SPECIAL ARPT WITH RISING TERRAIN. 2) ALL WARNINGS WERE SAYING THE SAME THING INCLUDING THE RADAR ALTIMETER. IF THERE WERE JUST ONE WARNING IN A CLB OR CRUISE IT WOULD HAVE BEEN EASY TO DISREGARD. HOWEVER; WITH A NEW FO AND ALL THE WARNINGS I FELT IT WAS SAFER TO GET TO AN ALT AND EVALUATE THE SIT.