As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE IN CRUISE FLIGHT AT 40000 FT THE PILOT SIDE LEFT SIDE WINDOW DE ICE ELEMENT ON LOWER PANE BEGAN ARCING AND SPARKING. TRIED TO ISOLATE THE WINDOW FROM POWER AFTER FOLLOWING APPLICABLE CHECKLIST. THE ARC AND SPARKING GOT BIGGER AND STRECHED FURTHER ALONG THE ELEMENT UNTIL POWER WAS REMOVED. REMOVED & REPLACED PILOT SIDE HEATED WINDOW IAW CE-560XL M/M 56-12-00. OPS CHK GOOD.