ACFT DAMAGED ON TKOF ABORT EFFORT WHICH HAD TURNED INTO A RWY EXCURSION.

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THIS OCCURRENCE INVOLVES THE LTT FREIGHTER; A CHARTERED FLT TO RALEIGH COUNTY MEMORIAL FIELD; BECKLEY; WV. ALL PRE TKOF PROCS WERE COMPLETED AND THE FLT WAS CLRED TO DEPART RWY 19 STANDIFORD. AT THIS STAGE NO ABNORMALITIES OR DISCREPANCIES WERE NOTED BY THE FLC. TKOF PWR WAS APPLIED BY MYSELF AND MONITORED BY THE COPLT; PER COMPANY SOP. THE PROC FOR TKOF WAS STANDARD; ROTATE AT 84 KTS; FLAPS UP; OUTSIDE CONDITIONS WERE COOL AND VMC; DRY SURFACE WITH CALM WINDS. I REMEMBER NO ACFT DEPARTING PRIOR TO US. OPS WERE NORMAL UNTIL 75-80 KTS. AT THIS SPD THE L WING VERY ABRUPTLY ROSE AND THE ACFT STARTED TO VEER TO THE R. I IMMEDIATELY COUNTERED THIS BY APPLYING L RUDDER IN AN EFFORT TO MAINTAIN CTRLINE TRACKING. AT THIS POINT I DECIDED TO ABORT THE TKOF DUE TO AN UNKNOWN PROB. A LATERAL OSCILLATION ENSUED WHICH WAS SUBSEQUENTLY IMPOSSIBLE TO CTL AND THE ACFT DEPARTED THE RWY TO THE L. THE AREA TO THE L OF THE RWY WAS GRASSED AND HAD STANDARD FLT MARKINGS IN PLACE. BRAKING AND DIRECTIONAL CTL WERE DIFFICULT DUE TO WET GRASS (FROM DEW) AND THE ACFT'S HIGH SPD. TRYING TO EVADE OBSTACLES WAS ATTEMPTED; BUT REGRETTABLY A RWY DISTANCE MARKER AND TXWY LIGHT WERE HIT. BY THE TIME THE ACFT REACHED RWY 11/29 I HAD REGAINED SUFFICIENT CTL TO TAXI THE ACFT TO A SIDE TXWY STUB; CUT ENGS AND STOPPED THE ACFT. I ORDERED THE COPLT TO ASSIST IN THE VISUAL INSPECTION. I REMAINED ABOARD THE ACFT. THE CREW RPTED DAMAGE OF A 20-INCH TEAR TO THE L OUTBOARD FLAP; AND A TEAR OF 4-5 INCHES IN THE FABRIC ON THE L ELEVATOR. THE FLAP DAMAGE APPEARED TO BE CONSISTENT WITH AN IMPACT ON A RWY DISTANCE MARKER AND THE ELEVATOR DAMAGE WITH A RWY LIGHT. THE FLAP WAS ALSO SEEN TO BE HANGING APPROX 2 INCHES BELOW THE OTHER FLAPS. OTHERWISE; NO FURTHER DAMAGE TO THE ACFT OR INJURIES TO THE CREW WERE RPTED. LNDG GEAR LOCK PINS WERE POSITIONED AND THE ACFT WAS TAXIED BACK TO THE W RAMP. I AM UNABLE TO ASCERTAIN THE REASON FOR THIS INCIDENT. BOTH ENGS WERE ABLE TO START FOR THE RETURN TAXI TO THE UPS RAMMP; NO WIND GUSTS OR WAKE TURB WAS RPTED. ALL ACFT SYS SEEMED TO BE OPERATING NORMALLY PRIOR TO THE EXCURSION. SUPPLEMENTAL INFO FROM ACN 250746: UPON REANALYZING THE EVENTS DURING THE TKOF ROLL; WE (THE FLC) FEEL THAT IF THE L OUTBOARD FLAP HAD BEEN DROOPING DURING THE TKOF ROLL; THERE WOULD HAVE BEEN ADEQUATE ASYMMETRICAL FORCES TO MAKE THE ACFT DIFFICULT TO CTL. ALL CHKLIST PROCS WERE COMPLETED AS REQUIRED AND THE FLAPS HAD BEEN CYCLED; RETRACTED; AND INDICATING NORMAL PRIOR TO THE TKOF ROLL. HOWEVER; SINCE YOU CANNOT SEE THE FLAPS AND THEIR CONDITION FROM THE PLT SEATS; THERE IS NO WAY TO DETERMINE WHETHER THERE WAS A FLAP 'DROOP' ON THE TKOF ROLL.