RWY EXCURSION FROM A DIRT RWY IN A DHC6-300.

Narrative

THE PF TOOK OFF FOR ZZZ. ALL PHASES OF FLT WERE NORMAL. ALL CHKLISTS WERE USED. ENRTE WE HEARD 2 OTHER ACFT TKOF OFF ZZZ. WE THEN ASKED THE WINDS AND CONDITIONS AT ZZZ; THEY RESPONDED AS SAYING 'ALL RIGHT.' A COMPANY ACFT LANDED A FEW MINS AHEAD OF US WITH NO PROBS. WE OVERFLEW THE FIELD AND CONFIRM TO LAND ON RWY XX. WE DID THE BEFORE LNDG CHK. ON FINAL WE OBSERVED THAT THE WIND HAD MOVED TO A R QUARTERING TAILWIND. THE PF APPLIED THE RIGHT AMOUNT OF AILERON AND RUDDER TO MAINTAIN CTRLINE. THE REST OF THE APCH WAS NORMAL. SHORTLY AFTER TOUCHDOWN THE ACFT STARTED TO GO TO THE L. THE PF APPLIED FIRST R RUDDER THEN R BRAKE. HOWEVER THE ACFT CONTINUED TO DRIVE OFF THE DIRT RWY. WE HOP OVER A SMALL DITCH WHICH CAUSE THE PLANE TO TURN TO THE L. THE PLANE NOW PARALLEL RWY XX. AFTER A FEW 100 FT THE PLANE SLOWED TO A STOP. WE SHUT DOWN THE PLANE AND DEPLANED THE PAX. AFTERWARDS; WE BOTH WALKED THE ACFT'S TRACK AND NOTICED THAT THE NOSEWHEEL WAS WIDER AND MORE PRONOUNCED THAN BOTH OF THE MAIN WHEELS. ALSO; THERE WAS GROOVES AND TIRE MARKS. WE BOTH BELIEVED THAT THE NOSEWHEEL OF THE ACFT WAS NOT CTRED ON TOUCHDOWN. EVEN THOUGH WE CONFIRMED THAT THE TILLER WAS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE CREW COULD FIND NO PROB WITH THE NOSEWHEEL DURING POSTFLT INSPECTION. MAINT DETERMINED NO PROBS WITH THE ACFT. THE RPTED QUARTERING TAILWIND WAS ESTIMATED TO BE MORE THAN 8 KTS.