CAPT OF AN LTT TWIN OTTER LOST DIRECTIONAL CTL DURING TKOF ROLL RESULTING IN RUNNING OFF THE SIDE OF THE RWY.

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TO BEGIN IT IS IMPORTANT TO MENTION THE CONDITIONS THAT WERE PRESENT AT THE FIELD. IT WAS VFR; BUT WITH TAIL WINDS AT THE APCH END OF RWY 03/21 (THE ONLY RWY); AND A SHIFT ABOUT MIDWAY IN THE 2500 FT RWY. IT WAS THE CAPT'S LEG BACK TO HONOLULU; WE HAD OBTAINED OUR CANNED IFR CLRNC WITH A 2 MIN VOID LEFT. BEING THERE WAS A QUARTERING TAILWIND AT THE BOTH APCH ENDS OF THE RWYS; THE CAPT CHOSE TO DEPART AT THE END CLOSEST TO OUR POS. THIS WOULD GIVE US A RIGHT QUARTERING TAILWIND WITH A SLIGHT UPHILL GRADIENT. WE COMPLETED ALL CHKLISTS; CALLED CTAF AND ENTERED THE RWY. THE CAPT LINED THE ACFT UP ON CTRLINE AT THE END OF RWY 21; WITH THE TILLER BAR. HE THEN ADVANCED PWR WHILE HOLDING THE BRAKES TO ABOUT 25 LBS OF TORQUE. HE THEN RELEASED THE BRAKES; WITHIN 3 SECONDS THE ACFT SLOWLY VEERED ; HE CORRECTED TO THE R BUT THE TILLER INPUT SET US ON A 45 DEG COURSE TOWARDS THE R SIDE OF THE RWY; HE THEN CORRECTED BACK TO THE L WITH ABOUT THE SAME RESULT; (A 45 DEG CUT TOWARDS THE L EDGE). IT WAS THEN THAT HE BROUGHT THE PWR LEVERS TO FULL REVERSE BUT COULD NOT STOP PRIOR TO EXITING THE RWY INTO THE GRASS AND DECELERATING PARALLEL TO THE RWY. THERE WAS NO DAMAGE TO THE TWIN OTTER; A TOUGH AIRPLANE. THE ACFT DID NOT CONTACT ANY EDGE LIGHTS OR OBSTACLES. AFTER ALLOWING 4 OF THE 18 PAX TO DEPLANE AT THEIR REQUEST THE CAPT DEPARTED FROM RWY 3 (SAME RWY BUT DOWNHILL) WITHOUT EVENT; AND CONTINUED TO HNL. I THINK A CREW PROC THAT CALLED FOR THE PNF TO HOLD AILERON INTO THE WIND AT THE BEGINNING OF THE TKOF ROLL WHILE THE CAPT IS BUSY WITH THE TILLER AND PWR LEVERS WOULD HAVE HELPED MAINTAIN CTL IN THE SHEARING WINDS. THE ONLY OTHER CAUSES I CAN SEE MAY HAVE BEEN A RELUCTANCE TO DISCONTINUE THE TKOF SOONER AND DEPARTING DOWNHILL INITIALLY. I WOULD HAVE TO ATTRIBUTE THE MAJOR CAUSE TO WIND SHEAR. THE CAPT IS A RETIRED AIR FORCE PLT; A CHK AIRMAN WITH THE COMPANY; AND IS VERY CONSERVATIVE AND CONSCIENTIOUS WITH SEVERAL THOUSAND HRS IN THE OTTER. THE FLT WAS SCHEDULED AND ROUTINE.