What was found
AT CRUISE ALT 20,000 FT, NOTICED CRACK AND SUBSEQUENT FLAME WITHIN LAYERS OF LT WINDSHIELD. FLAME SELF EXTINGUISHED WITH DE-SELECTION OF WINDSHIELD HEAT. DURING DESCENT ADDITIONAL CRACKING. DIVERTED TO CYMM. MX DISPATCHED, REPLACED WINDSHIELD. UPON MX REVIEW FOLLOWING WAS DETERMINED; THE PART WAS IN SERVICE ON THIS A/C ON REGISTER SINCE 2003 JANUARY AND PRIOR. NO ABNORMALITIES OBSERVED DURING REMOVAL REGARDING INSTALLATION, EXCEPT FOR PRC APPLIED OVER EXT SCREW HEADS. AIRFRAME VOLTAGE AND CURRENT OUTPUT TO LT WINDOW HEAT SYS FOUND NORMAL. NO EVIDENCE OF MISTORQUE OF SECURING SCREWS OBSERVED. MX PRELIMINARY CONCLUSION, MALFUNCTION LEADING TO A SHORT CIRCUIT OF INTERNAL HEAT FILAMENTS OF WINDSHIELD.