What was found
DURING FLIGHT PIC/SIC NOTICED SLIGHT BURNING SMELL IN COCKPIT IN FWD FLIGHT AFTER DEPARTING DIP SITE. PIC IMMEDIATELY TURNED OFF THE HEAT VENT MASTER SWITCH, AFTER WHICH NO FURTHER SMELLS WERE NOTED. CONTINUED MISSION FOR APPROXIMATELY 15-20 MINUTES AND THEN RETURNED TO BASE. AFTER LANDING, DISCOVERED POPPED CIRCUIT BREAKER ON THE NO. 1 PDP. RESET CIRCUIT BREAKER AND IT REPEATEDLY POPPED. REMOVED CANON PLUG TO HEATER BLOWER AND RESET CIRCUIT BREAKER. TURNED ON HEATER BLOWER AND THE CIRCUIT BREAKER DID NOT POP. R&R HEATER BLOWER, OPS CHECKED GOOD.