What was found
(CAN) IT WAS REPORTED TO BELL:SHORTLY AFTER TAKEOFF, SMOKE STARTED TO FILL THE COCKPIT. THE PILOT TURNED OFF THE BATTERY, OPENED THE SIDE WINDOW, AND MADE AN EMERGENCY LANDING BACK AT THE POINT OF DEPARTURE. ONCE ALL ELECTRICAL POWER HAD BEEN TURNED OFF, INCLUDING THE GENERATOR, THE SMOKE CEASED. SUBSEQUENT INSPECTION REVEALED A FAULTY DIRECTIONAL GYRO. (TC# 20190716009)