A B737-300 AT FL350 DECLARED AN EMER AND DIVERTED DUE TO THE FO WINDSHIELD UPPER RIGHT CORNER EMITTING SPARKS; SMOKE AND FLAMES.

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WHILE IN CRUISE AT FL350 AND APPROX ONE HR AFTER TURNING ON THE WINDOW HEAT; I HEARD A LOUD CRACKING OR POPPING NOISE BEHIND ME. I LOOKED BACK TO THE CB PANEL AND THEN TURNED AROUND AND NOTICED THAT THE ELECTRICAL TERMINAL CONNECTOR ON MY WINDOW (R1) BEGAN TO POP AND EMIT SMOKE. THIS WAS IMMEDIATELY FOLLOWED BY AN INCREASE IN THE SMOKE AND A SERIES OF SPARKS AND FLAMES VERY SIMILAR TO THAT PRODUCED BY A SPARKLER TYPE FIREWORK. THE POPPING AND FLAME SUBSIDED FOR A FEW SECONDS AND THEN 'RELIT' WITH ANOTHER SERIES OF SPARKS; FLAME AND FURTHER SMOKE. UPON SEEING THE FIRST SMOKE AND FLAME; I IMMEDIATELY DONNED MY OXYGEN MASK AND GOGGLES AND SAW THAT THE CAPT AND MECH JUMP SEATER HAD ALSO DONE THE SAME THING. WE EACH CHKED IN TO ESTABLISH COMS. THE CAPT THEN SAID HE HAD THE ACFT AND RADIOS AND INSTRUCTED ME TO ACCOMPLISH THE SMOKE AND FIRE CHKLIST; WHICH I PROCEEDED TO DO. THE CAPT DECLARED AN EMER; REQUESTED A LOWER ALT; AND COMMENCED A DSCNT AND TURN BACK TO THE COAST. I NOTICED THAT THE JUMP SEATER WAS CHECKING THE CB'S ON EACH SIDE OF THE COCKPIT. A COUPLE OF MINS LATER HE SAID THAT THE POWER WAS OFF TO THE WINDOW HEAT AS HE POINTED UP TO THE WINDOW HEAT CTLR. I ACCOMPLISHED THE SMOKE AND FIRE CHKLIST AND CALLED IT COMPLETE. I COMMUNICATED OUR INTENTIONS TO STOP ON THE RWY AT ZZZ; OPENED THE WINDOWS AND THEN COMMUNICATED WITH THE TWR AND FIRE RESCUE CREWS. THE FIRE CREWS FOLLOWED US BACK TO THE MAINT HANGAR WHERE THE CAPT TERMINATED THE EMER. NOTES OF INTEREST: 1. THE B737-300 EFIS ACFT HAD BEEN IN STORAGE FOR SEVERAL MONTHS. 2. THIS WAS A FUNCTIONAL CHK FLT AND THE ACFT HAD NOT BEEN IN REVENUE SVC SINCE LAST YEAR; HOWEVER; THE AIRPLANE HAD FLOWN AT LEAST ONE OTHER FCF FLT. 3. THERE WAS NO LOG BOOK ENTRY OR RECORD OF PREVIOUS WINDOW PROBS OR FAILURES. 4. THE COCKPIT DOOR HAD REMAINED OPENED THE ENTIRE FLT SINCE THERE WERE ONLY THREE PEOPLE ON BOARD. THIS PROBABLY HELPED TO DISSIPATE THE SMOKE AND FUMES QUICKER. 5. THE R1 WINDOW ITSELF REMAINED INTACT AND SHOWED NO SIGN OF DAMAGE. THE WINDSHIELD TERMINAL BLOCK AREA WAS CHARRED. 6. I ESTIMATE THAT THE WINDOW HEAT HAD BEEN APPLIED TO THE WINDOW FOR ABOUT ONE HR BASED ON OUR ENG START TIME. 7. IT IS MY BELIEF IF I HAD BEEN 'HEADS DOWN' TYPING ON THE FMC PANEL; THE FLAME OR SPARKS WOULD HAVE MADE CONTACT WITH MY HEAD AND HAIR. AS IT WAS; I HAD SPOTS OF BLACK ASH ON MY SHIRT AND PANTS. PLTS WHO APPLY ALCOHOL BASED HAIR SPRAYS OR GELS SHOULD BE MADE AWARE OF THE POTENTIAL FOR FIRE AND SPARKS IGNITING THEIR HAIR. SUPPLEMENTAL INFO FROM ACN 580949: I WAS THE PLT FLYING AN FCF FLT OUT OF ZZZ DESIGNATED FOR AN ELEVATOR AND AILERON ADJUSTMENT CHK. THE MECH; FLYING AS PART OF THE CREW; BRIEFED US ON WHAT NEEDED TO BE DONE AND HOW WE WERE GOING TO ACCOMPLISH THE CHK FLT. THE FLT WAS UNEVENTFUL CLBING TO FL350. AS WE BEGAN THE FCF CHK; I DISENGAGED THE AUTOPLT AND AUTOTHROTTLES AND AS I WAS FINE TUNING THE N1 INDICATORS; WE HEARD A LOUD BUZZING SOUND AND NOTICED THAT THE UPPER RIGHT HAND CORNER OF THE FO R1 WINDSHIELD BEGAN TO SPARK LIKE A SPARKLER AND WAS SPITTING OUT BLACK PIECES ALL OVER THE R COCKPIT AREA. THE NEXT THING WE NOTICED WAS A SUBSTANTIAL AMOUNT OF SMOKE THAT BEGAN TO EMANATE FROM THAT UPPER RIGHT HAND CORNER OF THE WINDSHIELD AREA. AT THAT MOMENT; I ENGAGED THE AUTOPLT AND AUTOTHROTTLES AND WE ALL DONNED OUR OXYGEN MASKS AND GOGGLES AND ESTABLISHED CREW COM. AS THE FO ACKNOWLEDGED MY COM; I NOTICED FLAMES BEGINNING TO ERUPT FROM THE UPPER RIGHT HAND CORNER OF THE WINDSHIELD AREA. INITIALLY; A LARGE BLOW TORCH TYPE FLAME ERUPTED AND THEN ALMOST SEEMED TO RECEDE INTO THE UPPER CORNER OF THE WINDSHIELD/FOAM-CORE IN THAT AREA FOLLOWED IMMEDIATELY BY ANOTHER SHORTER FLAME THAT BEGAN TO CONTINUOUSLY BURN. AT THE SAME TIME; WE ALL NOTICED A POP OR NOISE FROM THE CB PANEL OR CORNER AREA BEHIND THE FO. I IMMEDIATELY DECLARED AN EMER REQUESTING AN IMMEDIATE TURN BACK TO ZZZ ARPT ALONG WITH AN IMMEDIATE LOWER ALT. AS SOON AS I MADE THE CALL TO ATC; I CALLED FOR THE SMOKE AND FIRE CHKLISTAND I TURNED TO THE MECH AND TOLD HIM 'DO WHATEVER YOU NEED TO DO TO GET THIS UNDER CTL.' THE MECH RESPONDED AND ACKNOWLEDGED MY REQUEST. I INITIATED AN EMER DSCNT DOWN TO 10000 FT. AS I WAS ESTABLISHED IN THE DSCNT; I NOTICED THAT THE FIRE HAD GONE OUT AND THE SMOKE WAS SUBSIDING. IT WAS ONLY RESIDUAL SMOKE THAT WAS EMANATING FROM THAT AREA. I COMMUNICATED TO THE MECH AND ASKED HOW WE WERE DOING -- HE ACKNOWLEDGED THAT HE WAS MONITORING THE SIT AND IT WAS UNDER CTL. HE HAD THE FIRE EXTINGUISHER OUT OF ITS HARNESS AND READY TO BE USED IF NECESSARY. I ALSO AT THAT TIME NOTICED THAT THE FO WAS STILL BUSY WITH THE EMER CHKLIST. I THEN TOLD THE FO TO TELL ZZZ APCH CTL TO INFORM THE TWR THAT WE WERE REQUESTING EMER EQUIP AND THAT WE WOULD STOP ON THE RWY IN ORDER TO OPEN OUR WINDOWS AND ELIMINATE ANY FUMES THAT MIGHT BE IN THE COCKPIT. I FLEW A VISUAL APCH AND LANDED. THE ACFT WAS STOPPED ON THE RWY AND BOTH SIDE WINDOWS WERE OPENED. WHILE HOLDING THE BRAKES ON THE RWY; WE COMMUNICATED WITH THE FIRE TRUCKS. A FIREFIGHTER HAD COME OUT OF THE TRUCK AND WAS INSPECTING THE FORWARD AREA OF THE ACFT. WE NOW FELT THAT IT WAS SAFE TO TAXI AND THAT THE SMOKE AND FIRE WAS NOT A FACTOR. WE ASKED TWR FOR PERMISSION TO TAXI AND WE TAXIED TO THE HANGAR. I TERMINATED THE EMER WITH GND CTL AND THE FIRE RESCUE PERSONNEL WHEN WE ARRIVED AND PARKED AT THE MAINT HANGAR RAMP AND BOTH ENGS WERE SHUT DOWN. CALLBACK CONVERSATION WITH RPTR ACN 581531 REVEALED THE FOLLOWING INFO: THE RPTR STATED THE SMOKE; SPARKS AND FLAMES CONTINUED ON FOR A COUPLE OF MINS AND THE RED RUBBER BOOT COVERING THE WINDOW HEAT POWER TERMINAL WAS CHARRED TO A CINDER. THE RPTR SAID MAINT BELIEVES CORROSION ON THE POWER TERMINAL CAUSED A SHORT CIRCUIT. THE RPTR STATED THE WINDOW HEAT POWER CB DID TRIP; BUT PUT ON A SPECTACULAR FIREWORKS DISPLAY BEFORE TRIPPING. THE RPTR SAID CONCERN WAS FELT BY THE CREW WHEN THE FLAME CURLED UPWARD TOWARDS THE OVERHEAD P-5 PANEL. CALLBACK CONVERSATION WITH RPTR ACN 580949 REVEALED THE FOLLOWING INFO: THE RPTR STATED THE SMOKE WAS HEAVY AND THE CREW DONNED THE EMER OXYGEN MASKS. THE RPTR SAID THE CAUSE OF THE WINDSHIELD FIRE IS UNKNOWN AS MAINT HAS NOT RELEASED ANY INFO. THE RPTR STATED THE CB FOR THE R1 WINDOW DID TRIP.