Narrative:

I was flying a C414A in IMC. I had been at FL210, and was cleared to 16000 ft. At 16000 ft I began to get a steady accretion of rime ice on the airfoils. I asked center for FL190. During the ice encounter, I turned the windshield ice protection, a heated window, on. After the icing stopped as I climbed through 17500 ft, I turned the windshield ice off. I kept the propeller ice on at all times that I was IMC. I leveled off at FL190 for perhaps 10 mins. On the ground I inspected the windshield. Only the approximately 1/32 of an inch covering for the heating elements on the windshield were hurt. A piece of this very thin covering of the heating element was missing. This piece was high up on the windshield, perhaps 6 inches square, and had blown away. I suspect that some ice from the nose dislodged and struck a glancing blow to the windscreen in the central upper one third. The underlying heating element plastic strip remained intact and undamaged. The structural integrity of the stretched vinyl main windshield element was entirely undamaged. After the event, the windshield had held about 4 pounds of cabin pressure differential. Before and immediately after ice contacted the windshield, the window uneventfully held 4 pounds of over pressure. I electively depressurized the plane. During the descent, the window had taken perhaps 180-200 KTS IAS pressure. The main windshield structural element -- easily more than 1/2 inch of stretched vinyl - - and the overlying heating element were entirely intact. Only the thin plastic covering over the heating element had been damaged. I called my mechanic in las vegas, nv, for advice. After describing the extent of the damage to the flexible over-covering for the heating element only, and -- his concluding as I had based upon my observations -- that the airplane could safely be flown, this mechanic indicated that the plane could surely be safely flown to las vegas. The maintenance chief at the only FBO at the ase airport had indicated that his shop did not have the expertise to repair the windshield at any time. I went to the airplane, very carefully preflted the plane, and confirmed that there was no damage to the thick vinyl windshield that comprises the structural part of the windscreen. The only damage was to the approximately 1/32 inch plastic covering over the heating element. In effect, the flight following the trauma to the coverings to the heating elements of the windshield had demonstrated the structural integrity of the windshield, except for the purposes of deicing. The airplane held the 4 pounds of over pressure per square inch over a very large area with no demonstrable cracking in the structural parts of the windscreen. This represented more than a ton of force distributed over 56 through-bolt attachments on a frame stressed for pressurization. After elective depressurization, the airplane was subjected to about a 200 KT IAS -- far faster than anything contemplated in this flight. The undamaged strength of the vinyl windscreen element had been proven, if you will, by emergency flight testing at limits approaching the limits of the flight envelope of the airplane. My belief, then and now, was that the windshield had no visible or actual damage to the structural elements of the windshield, notwithstanding the damage to a part of the deicing mechanism, a very flexible 1/32 inch plastic covering to the undamaged underlying heating elements, and because of its flexibility and thinness, not contributing to the strength of the windshield. From the standpoint of strength, the windshield was sound and safe for flight in daylight visual conditions. The purpose of the 1/32 inch covering of the deicing element was to keep ice off the heating element alone. This very flexible damaged element has no structural significance whatever with respect to the strength of the windshield. I undertook the flight in an unpressurized state in cavu VMC to my mechanic -- also home. The flight was uneventful. Callback conversation with reporter revealed the following information: reporter stated that he learned that his opinion of the windshield was correct in that it was not in danger of failing in-flight, but that the FAA was threatening him with violation action since he flew the aircraft back to home base without a ferry permit, or an MEL that had a provision for operating the aircraft with the windshield heat system deferred. In conclusion, the failure of the thin shield over the ice protection element did not derogate the windshield structural integrity for flight in non icing conditions.

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Original NASA ASRS Text

Title: PLT OF A C414A CHANCELLOR, DECLARED, AND MADE, AN EMER DSCNT DUE TO A SUDDEN BANG, AND THEN A NOTICEABLE CRACK, IN THE WINDSHIELD. AFTER LNDG AT HIS NEARBY DEST, HE INSPECTED THE WINDSHIELD AND CONFERRED WITH HIS MECH BY TELEPHONE. THE MECH VERBALLY OKAYED THE ACFT FOR A VFR LOW UNPRESSURIZED FLT TO HOME BASE. NO FERRY PERMIT WAS OBTAINED FOR THE DEFECTIVE WINDSHIELD HEAT SYS.

Narrative: I WAS FLYING A C414A IN IMC. I HAD BEEN AT FL210, AND WAS CLRED TO 16000 FT. AT 16000 FT I BEGAN TO GET A STEADY ACCRETION OF RIME ICE ON THE AIRFOILS. I ASKED CTR FOR FL190. DURING THE ICE ENCOUNTER, I TURNED THE WINDSHIELD ICE PROTECTION, A HEATED WINDOW, ON. AFTER THE ICING STOPPED AS I CLBED THROUGH 17500 FT, I TURNED THE WINDSHIELD ICE OFF. I KEPT THE PROP ICE ON AT ALL TIMES THAT I WAS IMC. I LEVELED OFF AT FL190 FOR PERHAPS 10 MINS. ON THE GND I INSPECTED THE WINDSHIELD. ONLY THE APPROX 1/32 OF AN INCH COVERING FOR THE HEATING ELEMENTS ON THE WINDSHIELD WERE HURT. A PIECE OF THIS VERY THIN COVERING OF THE HEATING ELEMENT WAS MISSING. THIS PIECE WAS HIGH UP ON THE WINDSHIELD, PERHAPS 6 INCHES SQUARE, AND HAD BLOWN AWAY. I SUSPECT THAT SOME ICE FROM THE NOSE DISLODGED AND STRUCK A GLANCING BLOW TO THE WINDSCREEN IN THE CENTRAL UPPER ONE THIRD. THE UNDERLYING HEATING ELEMENT PLASTIC STRIP REMAINED INTACT AND UNDAMAGED. THE STRUCTURAL INTEGRITY OF THE STRETCHED VINYL MAIN WINDSHIELD ELEMENT WAS ENTIRELY UNDAMAGED. AFTER THE EVENT, THE WINDSHIELD HAD HELD ABOUT 4 LBS OF CABIN PRESSURE DIFFERENTIAL. BEFORE AND IMMEDIATELY AFTER ICE CONTACTED THE WINDSHIELD, THE WINDOW UNEVENTFULLY HELD 4 LBS OF OVER PRESSURE. I ELECTIVELY DEPRESSURIZED THE PLANE. DURING THE DSCNT, THE WINDOW HAD TAKEN PERHAPS 180-200 KTS IAS PRESSURE. THE MAIN WINDSHIELD STRUCTURAL ELEMENT -- EASILY MORE THAN 1/2 INCH OF STRETCHED VINYL - - AND THE OVERLYING HEATING ELEMENT WERE ENTIRELY INTACT. ONLY THE THIN PLASTIC COVERING OVER THE HEATING ELEMENT HAD BEEN DAMAGED. I CALLED MY MECH IN LAS VEGAS, NV, FOR ADVICE. AFTER DESCRIBING THE EXTENT OF THE DAMAGE TO THE FLEXIBLE OVER-COVERING FOR THE HEATING ELEMENT ONLY, AND -- HIS CONCLUDING AS I HAD BASED UPON MY OBSERVATIONS -- THAT THE AIRPLANE COULD SAFELY BE FLOWN, THIS MECH INDICATED THAT THE PLANE COULD SURELY BE SAFELY FLOWN TO LAS VEGAS. THE MAINT CHIEF AT THE ONLY FBO AT THE ASE ARPT HAD INDICATED THAT HIS SHOP DID NOT HAVE THE EXPERTISE TO REPAIR THE WINDSHIELD AT ANY TIME. I WENT TO THE AIRPLANE, VERY CAREFULLY PREFLTED THE PLANE, AND CONFIRMED THAT THERE WAS NO DAMAGE TO THE THICK VINYL WINDSHIELD THAT COMPRISES THE STRUCTURAL PART OF THE WINDSCREEN. THE ONLY DAMAGE WAS TO THE APPROX 1/32 INCH PLASTIC COVERING OVER THE HEATING ELEMENT. IN EFFECT, THE FLT FOLLOWING THE TRAUMA TO THE COVERINGS TO THE HEATING ELEMENTS OF THE WINDSHIELD HAD DEMONSTRATED THE STRUCTURAL INTEGRITY OF THE WINDSHIELD, EXCEPT FOR THE PURPOSES OF DEICING. THE AIRPLANE HELD THE 4 LBS OF OVER PRESSURE PER SQUARE INCH OVER A VERY LARGE AREA WITH NO DEMONSTRABLE CRACKING IN THE STRUCTURAL PARTS OF THE WINDSCREEN. THIS REPRESENTED MORE THAN A TON OF FORCE DISTRIBUTED OVER 56 THROUGH-BOLT ATTACHMENTS ON A FRAME STRESSED FOR PRESSURIZATION. AFTER ELECTIVE DEPRESSURIZATION, THE AIRPLANE WAS SUBJECTED TO ABOUT A 200 KT IAS -- FAR FASTER THAN ANYTHING CONTEMPLATED IN THIS FLT. THE UNDAMAGED STRENGTH OF THE VINYL WINDSCREEN ELEMENT HAD BEEN PROVEN, IF YOU WILL, BY EMER FLT TESTING AT LIMITS APCHING THE LIMITS OF THE FLT ENVELOPE OF THE AIRPLANE. MY BELIEF, THEN AND NOW, WAS THAT THE WINDSHIELD HAD NO VISIBLE OR ACTUAL DAMAGE TO THE STRUCTURAL ELEMENTS OF THE WINDSHIELD, NOTWITHSTANDING THE DAMAGE TO A PART OF THE DEICING MECHANISM, A VERY FLEXIBLE 1/32 INCH PLASTIC COVERING TO THE UNDAMAGED UNDERLYING HEATING ELEMENTS, AND BECAUSE OF ITS FLEXIBILITY AND THINNESS, NOT CONTRIBUTING TO THE STRENGTH OF THE WINDSHIELD. FROM THE STANDPOINT OF STRENGTH, THE WINDSHIELD WAS SOUND AND SAFE FOR FLT IN DAYLIGHT VISUAL CONDITIONS. THE PURPOSE OF THE 1/32 INCH COVERING OF THE DEICING ELEMENT WAS TO KEEP ICE OFF THE HEATING ELEMENT ALONE. THIS VERY FLEXIBLE DAMAGED ELEMENT HAS NO STRUCTURAL SIGNIFICANCE WHATEVER WITH RESPECT TO THE STRENGTH OF THE WINDSHIELD. I UNDERTOOK THE FLT IN AN UNPRESSURIZED STATE IN CAVU VMC TO MY MECH -- ALSO HOME. THE FLT WAS UNEVENTFUL. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATED THAT HE LEARNED THAT HIS OPINION OF THE WINDSHIELD WAS CORRECT IN THAT IT WAS NOT IN DANGER OF FAILING INFLT, BUT THAT THE FAA WAS THREATENING HIM WITH VIOLATION ACTION SINCE HE FLEW THE ACFT BACK TO HOME BASE WITHOUT A FERRY PERMIT, OR AN MEL THAT HAD A PROVISION FOR OPERATING THE ACFT WITH THE WINDSHIELD HEAT SYS DEFERRED. IN CONCLUSION, THE FAILURE OF THE THIN SHIELD OVER THE ICE PROTECTION ELEMENT DID NOT DEROGATE THE WINDSHIELD STRUCTURAL INTEGRITY FOR FLT IN NON ICING CONDITIONS.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.