AN EMBRAER 145 #1 ENG BLEED AIR DUCT CLAMP FAILED DURING CLBOUT; FILLING THE COCKPIT AND CABIN WITH SMOKE AND FORCING THE CREW TO RETURN TO THE DEP ARPT.

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PASSING THROUGH ABOUT 9000 FT MSL ON CLBOUT; WE GOT BLEED AIR LEAK MESSAGE FOR BOTH ENGS #1 AND #2. WHILE WE WERE GOING THROUGH THE CHKLIST THAT DEALT WITH THIS PROB; WE HEARD A LOUD POP; WHICH WAS FOLLOWED BY SMOKE IN THE COCKPIT AND CABIN. WE DONNED OUR OXYGEN MASKS; DECLARED AN EMER AND TURNED BACK. WITH ALL BLEED VALVES CLOSED; THE SMOKE DID NOT SEEM TO GET WORSE AND BY THE TIME WE LANDED; ONLY A STRONG ODOR REMAINED. ON OUR DSCNT; WE GOT A MESSAGE SAYING THE #1 RADAR ALTIMETER HAD FAILED. TCASII; GPWS; AND THE LNDG GEAR WARNING SYS ALSO FAILED SINCE THESE ARE CONNECTED TO THE #1 RADAR ALTIMETER. WE LATER FOUND THAT THE LEAK HAD OCCURRED IN THE DUCTING FROM THE #1 ENG. A LARGE GAP IN THE DUCTING WAS CREATED WHEN A CLAMP THAT HOLDS TOGETHER 2 PIECES OF TUBING HAD BROKEN. THE AIR COMING OUT OF THE LEAK FROM THE #1 SIDE WAS SUFFICIENT ENOUGH IN VOLUME AND TEMP TO SET OFF THE LEAK SENSOR FOR THE #2 ENG BLEED SYS. THE LEAK SENSORS FOR THE #1 AND #2 SIDES WERE ABOUT 1.5 FT APART. THE RADAR ALTIMETER WAS LOCATED IN THIS AREA. ALL OF ITS EXTERNAL WIRING CONNECTIONS HAD BEEN MELTED. THE ONLY OTHER DAMAGE FOUND WAS DONE TO THE #1 BLEED LEAK SENSOR.