What was found
(CAN) LT FRONT WINDOW CRACKED AT FL 230 SPEED 240 KTS. (WINDOW HEAT ON) DESCEND TO FL 100, REDUCED SPEED TO 200 KTS, AND DIFF. PRESS TO 3,0 PSI. INVESTIGATION/ACTION, LT FRONT WINDSHIELD, S/N: 419 REPLACED. THE MFG HAS INVESTIGATED, BUT COULD NOT IDENTIFY THE CAUSE OF THE CRACK AS BEING MANUFACTURING OR HANDLING RELATED.