Narrative:

We reported for duty at XX15, in eau, wi, approximately 15 mins after sunrise, limited light. We brought the aircraft in the previous pm and it was parked on ramp overnight. Aircraft preflight was begun as soon as we reported. Although the first officer was doing a close up walkaround, I also did a casual walkaround looking at the extremities and evidence of leaks. I observed an object on the ramp approximately 25 ft aft of our plane but did not investigate it. When the first officer came aboard he reported that the object was the top cover of the gpu-ground power unit, and we speculated how it might have gotten where it was. Another aircraft, SF34, had been parked in front of us, but had already departed when we reported. It would have used the gpu too, but the unit was plugged into our aircraft at this point. No abnormalities were discovered inside or out on our plane. We flew 5 legs with 6 pressurization cycles. I personally spun down the left propeller 3 times during the legs, placing me near the left engine, wing leading edge, and left side of forward fuselage. After finishing the trip in minneapolis, a normal postflt walkaround was done by both pilots. No damage to outside of aircraft was noted. While waiting for the bus about 1/2 hour later the station manager came out and asked that I return to the aircraft account maintenance suspected a collision had taken place. I met the mechanic and he inquired if we had a collision -- answer, no. Had the aircraft been pressurizing ok -- answer, yes. He pointed out a 2-3 inch puncture in the side of the fuselage abeam the left engine, about 7 ft AGL. Also observed was a dent in the inboard wing leading edge and a missing vortex generator from the top of the wing. No apparent damage to the propeller, which has a large arc in front of wing damage and vortex generator area. Another scuff was observed on the fuselage, aft of puncture, long and narrow. Moments later I recalled the early am APU situation and asked a mechanic to locate one of those units and compare measurements of the top with the scars on the aircraft. After arriving home I had a call from the assistant chief pilot and indicated to him that I had no factual evidence as to how the damage might have occurred, but then speculated that the gpu top may have been propelled into the air when the other plane left, and came down on our plane. Our scars indicated the damaging object came from above, perhaps even from the rear, which is still a puzzle. Several days later the mechanic told me the gpu measurements and the scars matched.

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Original NASA ASRS Text

Title: A BA31 JETSTREAM WHILE PARKED OVERNIGHT INCURRED DAMAGE TO THE FUSELAGE, WING LEADING EDGE AND VORTEX GENERATOR. A SAAB 340 PARKED FORWARD OF ACFT 'X' IS SUSPECTED OF BLOWING THE GND PWR UNIT COVER ONTO ACFT 'X.'

Narrative: WE RPTED FOR DUTY AT XX15, IN EAU, WI, APPROX 15 MINS AFTER SUNRISE, LIMITED LIGHT. WE BROUGHT THE ACFT IN THE PREVIOUS PM AND IT WAS PARKED ON RAMP OVERNIGHT. ACFT PREFLT WAS BEGUN AS SOON AS WE RPTED. ALTHOUGH THE FO WAS DOING A CLOSE UP WALKAROUND, I ALSO DID A CASUAL WALKAROUND LOOKING AT THE EXTREMITIES AND EVIDENCE OF LEAKS. I OBSERVED AN OBJECT ON THE RAMP APPROX 25 FT AFT OF OUR PLANE BUT DID NOT INVESTIGATE IT. WHEN THE FO CAME ABOARD HE RPTED THAT THE OBJECT WAS THE TOP COVER OF THE GPU-GND PWR UNIT, AND WE SPECULATED HOW IT MIGHT HAVE GOTTEN WHERE IT WAS. ANOTHER ACFT, SF34, HAD BEEN PARKED IN FRONT OF US, BUT HAD ALREADY DEPARTED WHEN WE RPTED. IT WOULD HAVE USED THE GPU TOO, BUT THE UNIT WAS PLUGGED INTO OUR ACFT AT THIS POINT. NO ABNORMALITIES WERE DISCOVERED INSIDE OR OUT ON OUR PLANE. WE FLEW 5 LEGS WITH 6 PRESSURIZATION CYCLES. I PERSONALLY SPUN DOWN THE L PROP 3 TIMES DURING THE LEGS, PLACING ME NEAR THE L ENG, WING LEADING EDGE, AND L SIDE OF FORWARD FUSELAGE. AFTER FINISHING THE TRIP IN MINNEAPOLIS, A NORMAL POSTFLT WALKAROUND WAS DONE BY BOTH PLTS. NO DAMAGE TO OUTSIDE OF ACFT WAS NOTED. WHILE WAITING FOR THE BUS ABOUT 1/2 HR LATER THE STATION MGR CAME OUT AND ASKED THAT I RETURN TO THE ACFT ACCOUNT MAINT SUSPECTED A COLLISION HAD TAKEN PLACE. I MET THE MECH AND HE INQUIRED IF WE HAD A COLLISION -- ANSWER, NO. HAD THE ACFT BEEN PRESSURIZING OK -- ANSWER, YES. HE POINTED OUT A 2-3 INCH PUNCTURE IN THE SIDE OF THE FUSELAGE ABEAM THE L ENG, ABOUT 7 FT AGL. ALSO OBSERVED WAS A DENT IN THE INBOARD WING LEADING EDGE AND A MISSING VORTEX GENERATOR FROM THE TOP OF THE WING. NO APPARENT DAMAGE TO THE PROP, WHICH HAS A LARGE ARC IN FRONT OF WING DAMAGE AND VORTEX GENERATOR AREA. ANOTHER SCUFF WAS OBSERVED ON THE FUSELAGE, AFT OF PUNCTURE, LONG AND NARROW. MOMENTS LATER I RECALLED THE EARLY AM APU SIT AND ASKED A MECH TO LOCATE ONE OF THOSE UNITS AND COMPARE MEASUREMENTS OF THE TOP WITH THE SCARS ON THE ACFT. AFTER ARRIVING HOME I HAD A CALL FROM THE ASSISTANT CHIEF PLT AND INDICATED TO HIM THAT I HAD NO FACTUAL EVIDENCE AS TO HOW THE DAMAGE MIGHT HAVE OCCURRED, BUT THEN SPECULATED THAT THE GPU TOP MAY HAVE BEEN PROPELLED INTO THE AIR WHEN THE OTHER PLANE LEFT, AND CAME DOWN ON OUR PLANE. OUR SCARS INDICATED THE DAMAGING OBJECT CAME FROM ABOVE, PERHAPS EVEN FROM THE REAR, WHICH IS STILL A PUZZLE. SEVERAL DAYS LATER THE MECH TOLD ME THE GPU MEASUREMENTS AND THE SCARS MATCHED.

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.