A DHC6-300 PIC RPT ON THE LOSS OF ACFT CTL AND RWY EXCURSION ON TKOF FROM MONUMENT VALLEY ARPT; 71V; UT.

Narrative

I WAS LAST FOR TKOF FROM 4 TWIN OTTERS THAT CAME TO MONUMENT VALLEY THAT DAY. I WATCHED THIRD ONE TAKE OFF WHILE WAITING FOR MY TURN TO TAXI BACK TO RWY 34 FOR TKOF. WE WERE READY. ALL CHKLISTS WERE DONE WITH PERFORMANCE DATA. THE WIND WAS ERRATIC AS USUAL. AS I WAS TAXIING; I CHKED THE WINDSOCK. IT WAS SWINGING FROM SOUTHERLY TO WESTERLY DIRECTION. AFTER I LINED UP FOR RWY 34 FOR TKOF; I TOOK ONE LAST LOOK AT THE WINDSOCK. IT APPEARED THAT WIND WAS DYING AND I WAS GLAD FOR A LULL. AS WE PERFORMED HOLD ITEMS AND MADE SURE THAT CABIN WAS READY FOR TKOF; I APPLIED PWR GRADUALLY TO APPROX 30 LBS OF TORQUE; WAITING FOR ENGS TO STABILIZE FOR 5 SECONDS BEFORE BRAKE RELEASE. I WANTED TO ESTABLISH AN EARLY RUDDER AUTH FOR THE NARROW DIRT RWY. I WAS CONFIDENT SINCE I SAW 3 OTHER OTTERS TAKE OFF JUST MINS BEFORE US. I RELEASED BRAKES AND CONTINUED TO APPLY PWR AND SUDDENLY; JUST A COUPLE OF HUNDRED YARDS INTO THE TKOF; ACFT VIOLENTLY VEERED 20-30 DEGS TO THE L. I WAS AT MAX PWR WITH FULL R RUDDER; UNABLE TO STOP THE TURN. I WAS HOPING THAT AIRSPD WOULD GIVE ME AN ADDITIONAL RUDER AUTH; AND I CONTINUED WITH TKOF. I PULLED BACK ON R PWR LEVER SLIGHTLY USING ASYMMETRICAL THRUST AND SOON I WAS REGAINING CTL. HOWEVER; I WAS ALREADY OFF THE RWY APPROX 30 FT. THE SURROUNDING ENVIRONMENT WAS RELATIVELY LEVEL -- SOFT SAND AND LOW BRUSH. I CONTINUED WITH TKOF AS A SOFT FIELD TECHNIQUE; KEEPING NOSEWHEEL OFF THE GND AND GAINING AIRSPD WITH PWR AT MAX; TRYING TO BRING ACFT IN GND EFFECT. THE ACFT WAS AIRBORNE ABOUT 3/4 OF THE RWY. I KNEW I HAD TO FLY BECAUSE AN ABORTED TKOF ON THE SOFT TERRAIN WOULD HAVE CONCLUDED IN A CRASH. THE GND WAS DOWNSLOPING AND IT WAS RELATIVELY LEVEL. I WAS COMMITTED TO FLT; BELIEVING THAT IT WAS THE ONLY WAY OUT. WE FLEW TO GRAND CANYON AND SAFELY LANDED. WE DID COMPLETE WALKAROUND AND ESTABLISHED THAT THERE WAS NO DAMAGE TO THE ACFT. I RPTED THE INCIDENT IMMEDIATELY TO THE CHIEF PLT. MONUMENT VALLEY ARPT IS A 4000 FT LONG DIRT STRIP WITH THE LAST 1/4 OF THE RWY 16 PAVED. THE RWY IS 1-WAY IN; AND 1-WAY OUT. THE RWY 16 IS DIRECTED INTO THE CLIFF OF ONE OF THE MONUMENTS. WHAT CAUSED MY ACFT TO VEER SUDDENLY; I AM NOT SURE. IF I WOULD BLAME SOMETHING; IT WOULD BE WIND. I AM VERY AWARE OF THE DANGER AT ARPTS LIKE THIS ONE. I AM VERY ALERT AND PREPARED WHEN I PUSH PWR FORWARD. I KNOW MY OPTIONS WELL; AND I BELIEVE I CHOSE THE RIGHT ACTION TO AVOID AN ACCIDENT.