What was found
FLT#1152, MCO-BOS. "DURING DESCENT FROM FL 370 TO APPROX FL 270, MODERATE ELECTRIC OR BURNING PLASTIC SMELL, ANTI ICE WAS ON BUT LATER USED AGAIN WITH NO SMELL SO I DO NOT SUSPECT A CONNECTION TO ANTI-ICE. ; UPON ARRIVAL ON A/C FOUND C/B X18 TO BE TRIPPED. REMOVED AND REPLACED C/B X18 REF. AMM 21-21-00. PERFORMED OPS CHK IAW AMM 21-21-00 OPS CHK FAILED C/B X18 CONTINUED TO TRIP. REMOVED AND REPLACED #1 CABIN RECIRE FAN IAW AMM 21-21-51 OPS CHK OK ND ELECTRIC/BURNING PLASTIC SMELL NOTED. A/C OK FOR SVC AT THIS TIME,"