What was found
DURING IFR FLIGHT AT 5,000 FEET, PILOT EXPERIENCED SMOKE IN THE CABIN. PILOT OPENED THE VENT AND EMERG WINDOWS AND LOWERED THE LANDING GEAR AND FLAPS FOR A DIVERT. THE SMOKE BECAME HEAVY AND AN UNEVENTFUL LANDING ACCOMPLISHED ON RUNWAY 14 AND PILOT SECURED THE ENG AND MASTER SWITCH WHILE ON RUNWAY. INVEST FND AIR PUMP FOR INFLATABLE DOOR SEAL SOURCE OF THE FIRE. PUMP HAD OVERHEATED AND MELTED, THEN IGNITED THE PLASTIC HOUSING. FURTHER INVEST FND PUMP MOUNTED ON THE FWD SIDE OF UPPER LEFT-HAND BULKHEAD P/N 2113041-13 AT FS 18.0. THIS LOCATION CONTAINED THE PUMP BEWEEN THE OUTER SKIN AND UPHOLSTERED INTERIOR SIDE PANEL IN APPROX A 4 INCH SPACE. THE PUMP WAS FUSED FOR 10 AMPS IN A 28-VOLT ELEC SYS.