What was found
SMOKE IN THE CABIN ON CLIMB OUT RETURNED TO FIELD FA REPORTED THICK WHITE SMOKE. (FLIGHT 4937) COMPLIED WITH FIM 21-22-00 SMOKE AND/OR ABNORMAL SMELL IN PASSENGER CABIN AND SERVICE LETTER SL-21-028. WHEN THE DFW FIRE FIGHTERS INITIALLY ENTERED THE AIRCRAFT AFTER GATE RETURN THEY DID NOT FIND ANY SOURCE OF HEAT IN THE GALLEY OR CABIN (INCLUDING THE LIGHT BALLASTS) USING A THERMAL IMAGING CAMERA.