Narrative:

While circumnaving very limited buildup en route iad-mia, we encountered very heavy rain shower of approximately 10 seconds in what appeared to be a stratus type cloud layer. Non-color radar was in use and target areas were very well defined. It was during this time that mod turbulence was encountered. The aircraft started to climb while on autoplt with altitude hold engaged. Knowing the aircraft would pitch over to try to hold altitude of FL180, I disengaged the altitude hold. The aircraft continued to rise to 18,320' setting off the altitude alert warning light. I did not attempt to push over aircraft to hold FL180 as my F/a's were up and about in the rear cabin. Within seconds the vertical lift stopped and I started returning the aircraft to FL180, at time time a loud pop was heard and my forward windshield L1 outer pane cracked. Cabin pressure was lowered. Cabin altitude raised, company maintenance, dispatcher and ATC notified. My cockpit was also occupied with an FAA/ATC operator riding on the observer jump seat. He was asked if he had observed anything other than heavy rain shower. Approximately 40 mins later my first F/a informed me that a passenger observed metal separating from the top surface of the wing starting at the leading edge behind the engine pylon area. After investigation by a pilot/observer in the cabin, my first officer and myself it was confirmed that indeed we had suffered structural aircraft damage to an identical area on both wings. Again company maintenance, dispatch, aircraft engineering, and ATC were informed that an emergency was being declared, cabin evacuate/evacuation preparations were underway. Emergency equipment standing by at mia on landing was requested. Aircraft was at FL180 speed 240 KTS indicated airspeed. Remainder of the flight was uneventful followed by a normal landing, aircraft evacuate/evacuation was cancelled and passenger were deplaned in a normal manner. Ground investigation revealed that not only was wing surface metal separating from the aircraft but metal lap seams were opening behind the nose radome and at the lower rear corner of the #1 service door, lower rear corner of the deactivated airstair door, the metal post behind the captain's sliding window L-2, the top rotating beacon was completely missing, the nose radome had a large hole in center. Our maintenance personnel feel at this time that a horizontal windshear was encountered in excess of 300 KTS causing the aircraft to go supersonic for a few seconds. No overspd warning was heard in the cockpit. Callback conversation with reporter revealed the following: the damage to the nose cone radar dome appears to have been caused by static discharge. Some melting around the fracture indicates it was heat induced. The windshield panel may also have been caused by static discharges. The metal peeling and ripping, and the rotating beacon wiped off could be attributed to a momentary supersonic wind shear. A satellite readout given to me later shows we were in a closed in clear airspace with storms all bout us, for what that is worth. Only word that I have had so far from my company is the ground maintenance theory of supersonic speed side shear wind. A company pilot riding in the cabin reported he detected one rather severe sideways motion but we in the cockpit felt nothing. Company voiced approval of the flight crew's actions and I have heard nothing from the FAA. I must presume the company has reported the event to FAA, but I have not been so advised.

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Original NASA ASRS Text

Title: MLG IN CRUISE AT FL180 EXPERIENCED VERTICAL LIFE BEYOND CAPABILITY OF AUTOPLT TO CONTROL. SKIN PEELING FROM WING WAS LATER REPORTED. CAPT OUTER WINDSHIELD PANE CRACKED. SKIN THEN OBSERVED PEELING FROM OTHER WING. EMERGENCY DECLARED, LANDED MIA. POSTFLT INSPECTION REVEALED FURTHER DAMAGE. POSTULATED BY GND MAINT THAT 300 KT HORIZONTAL WINDSHEAR OF BRIEF DURATION HAD BEEN ENCOUNTERED.

Narrative: WHILE CIRCUMNAVING VERY LIMITED BUILDUP ENRTE IAD-MIA, WE ENCOUNTERED VERY HEAVY RAIN SHOWER OF APPROX 10 SECONDS IN WHAT APPEARED TO BE A STRATUS TYPE CLOUD LAYER. NON-COLOR RADAR WAS IN USE AND TARGET AREAS WERE VERY WELL DEFINED. IT WAS DURING THIS TIME THAT MOD TURBULENCE WAS ENCOUNTERED. THE ACFT STARTED TO CLIMB WHILE ON AUTOPLT WITH ALT HOLD ENGAGED. KNOWING THE ACFT WOULD PITCH OVER TO TRY TO HOLD ALT OF FL180, I DISENGAGED THE ALT HOLD. THE ACFT CONTINUED TO RISE TO 18,320' SETTING OFF THE ALT ALERT WARNING LIGHT. I DID NOT ATTEMPT TO PUSH OVER ACFT TO HOLD FL180 AS MY F/A'S WERE UP AND ABOUT IN THE REAR CABIN. WITHIN SECONDS THE VERTICAL LIFT STOPPED AND I STARTED RETURNING THE ACFT TO FL180, AT TIME TIME A LOUD POP WAS HEARD AND MY FORWARD WINDSHIELD L1 OUTER PANE CRACKED. CABIN PRESSURE WAS LOWERED. CABIN ALT RAISED, COMPANY MAINT, DISPATCHER AND ATC NOTIFIED. MY COCKPIT WAS ALSO OCCUPIED WITH AN FAA/ATC OPERATOR RIDING ON THE OBSERVER JUMP SEAT. HE WAS ASKED IF HE HAD OBSERVED ANYTHING OTHER THAN HEAVY RAIN SHOWER. APPROX 40 MINS LATER MY FIRST F/A INFORMED ME THAT A PAX OBSERVED METAL SEPARATING FROM THE TOP SURFACE OF THE WING STARTING AT THE LEADING EDGE BEHIND THE ENGINE PYLON AREA. AFTER INVESTIGATION BY A PLT/OBSERVER IN THE CABIN, MY F/O AND MYSELF IT WAS CONFIRMED THAT INDEED WE HAD SUFFERED STRUCTURAL ACFT DAMAGE TO AN IDENTICAL AREA ON BOTH WINGS. AGAIN COMPANY MAINT, DISPATCH, ACFT ENGINEERING, AND ATC WERE INFORMED THAT AN EMER WAS BEING DECLARED, CABIN EVAC PREPARATIONS WERE UNDERWAY. EMER EQUIPMENT STANDING BY AT MIA ON LNDG WAS REQUESTED. ACFT WAS AT FL180 SPEED 240 KTS INDICATED AIRSPEED. REMAINDER OF THE FLT WAS UNEVENTFUL FOLLOWED BY A NORMAL LNDG, ACFT EVAC WAS CANCELLED AND PAX WERE DEPLANED IN A NORMAL MANNER. GND INVESTIGATION REVEALED THAT NOT ONLY WAS WING SURFACE METAL SEPARATING FROM THE ACFT BUT METAL LAP SEAMS WERE OPENING BEHIND THE NOSE RADOME AND AT THE LOWER REAR CORNER OF THE #1 SERVICE DOOR, LOWER REAR CORNER OF THE DEACTIVATED AIRSTAIR DOOR, THE METAL POST BEHIND THE CAPT'S SLIDING WINDOW L-2, THE TOP ROTATING BEACON WAS COMPLETELY MISSING, THE NOSE RADOME HAD A LARGE HOLE IN CENTER. OUR MAINT PERSONNEL FEEL AT THIS TIME THAT A HORIZONTAL WINDSHEAR WAS ENCOUNTERED IN EXCESS OF 300 KTS CAUSING THE ACFT TO GO SUPERSONIC FOR A FEW SECONDS. NO OVERSPD WARNING WAS HEARD IN THE COCKPIT. CALLBACK CONVERSATION WITH REPORTER REVEALED THE FOLLOWING: THE DAMAGE TO THE NOSE CONE RADAR DOME APPEARS TO HAVE BEEN CAUSED BY STATIC DISCHARGE. SOME MELTING AROUND THE FRACTURE INDICATES IT WAS HEAT INDUCED. THE WINDSHIELD PANEL MAY ALSO HAVE BEEN CAUSED BY STATIC DISCHARGES. THE METAL PEELING AND RIPPING, AND THE ROTATING BEACON WIPED OFF COULD BE ATTRIBUTED TO A MOMENTARY SUPERSONIC WIND SHEAR. A SATELLITE READOUT GIVEN TO ME LATER SHOWS WE WERE IN A CLOSED IN CLEAR AIRSPACE WITH STORMS ALL BOUT US, FOR WHAT THAT IS WORTH. ONLY WORD THAT I HAVE HAD SO FAR FROM MY COMPANY IS THE GND MAINT THEORY OF SUPERSONIC SPEED SIDE SHEAR WIND. A COMPANY PLT RIDING IN THE CABIN REPORTED HE DETECTED ONE RATHER SEVERE SIDEWAYS MOTION BUT WE IN THE COCKPIT FELT NOTHING. COMPANY VOICED APPROVAL OF THE FLT CREW'S ACTIONS AND I HAVE HEARD NOTHING FROM THE FAA. I MUST PRESUME THE COMPANY HAS REPORTED THE EVENT TO FAA, BUT I HAVE NOT BEEN SO ADVISED.

Data retrieved from NASA's ASRS site as of August 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.