What was found
DURING ENGINE MAINTENANCE, SMOKE WAS NOTED COMING FROM THE APU INLET DOOR. MECHANICS TRIED TO DRY MOTOR THE APU TO EXTINGUISH THE FLAMES, BUT WERE UNSUCCESSFUL. DRY CHEMICAL WAS USED TO EXTINGUISH THE FLAMES. DURING INVESTIGATION AND TEARDOWN OF THE APU AT THE MFG REPAIR STATION, THE APU FUEL SOLENOID FAILED FUNCTIONAL CHECK AND WAS FOUND TO BE STUCK IN THE OPEN POSITION. TESTING OF THE SOLENOID IS ON-GOING WITH THE INVESTIGATION.