Narrative:

After being cleared for takeoff; I advanced the power levers and called 'set power.' the power was set around the same time we reached a speed that the tiller was no longer necessary (approximately 60 KIAS). At that moment the aircraft yawed approximately 20-30 degrees to the right; while I was trying to maintain directional control with the rudder. The rudder was ineffective at realigning the aircraft with the runway; however; no further yaw to the right occurred with full left rudder. My first officer and I immediately recognized an abnormal situation; I called for an abort at approximately 70 KIAS; and was able to realign the aircraft with the runway centerline using the tiller. We were able to exit the runway without drastic measures or excessive braking. The maximum speed never got above 80 KTS. When I realized the event; I called for an abort; retarded the power levers to ground idle (while maintaining full left rudder) and regained directional control through the tiller. The aircraft was moved off the active runway and an after landing checklist was accomplished. At that point; we contacted ground; told them we needed to return to the gate; notified operations on the field of the event and were assigned a gate. I am unsure as to what caused the aircraft to yaw to the right. It happened so quickly; and was idented at such a slow airspeed that the entire event only lasted a second or two. I really had no forwarding or foresight that this event would occur. I don't feel that much can be done by a flight crew to prevent this from happening again. I feel that it was just a mechanical irregularity that happened at that moment. I feel that our crew's early recognition of the problem and an immediate decision to abort the takeoff very well may have saved damage to the aircraft and possible injuries to those aboard. Callback conversation with reporter revealed the following information: the reporter stated that the aircraft remained grounded for several hours that day while maintenance crews checked for faults. They found nothing wrong and the aircraft was flown later that day. The reporter suspects that a transient fault of some sort developed during the time that steering control was xferred from the tiller to the rudder pedals. He has not heard of this problem redeveloping on this or other aircraft.

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Original NASA ASRS Text

Title: A SF340 DEVELOPED A SEVERE YAW DURING THE TKOF ROLL. THE CAPT REJECTED THE TKOF.

Narrative: AFTER BEING CLRED FOR TKOF; I ADVANCED THE PWR LEVERS AND CALLED 'SET PWR.' THE PWR WAS SET AROUND THE SAME TIME WE REACHED A SPD THAT THE TILLER WAS NO LONGER NECESSARY (APPROX 60 KIAS). AT THAT MOMENT THE ACFT YAWED APPROX 20-30 DEGS TO THE R; WHILE I WAS TRYING TO MAINTAIN DIRECTIONAL CTL WITH THE RUDDER. THE RUDDER WAS INEFFECTIVE AT REALIGNING THE ACFT WITH THE RWY; HOWEVER; NO FURTHER YAW TO THE R OCCURRED WITH FULL L RUDDER. MY FO AND I IMMEDIATELY RECOGNIZED AN ABNORMAL SITUATION; I CALLED FOR AN ABORT AT APPROX 70 KIAS; AND WAS ABLE TO REALIGN THE ACFT WITH THE RWY CTRLINE USING THE TILLER. WE WERE ABLE TO EXIT THE RWY WITHOUT DRASTIC MEASURES OR EXCESSIVE BRAKING. THE MAX SPD NEVER GOT ABOVE 80 KTS. WHEN I REALIZED THE EVENT; I CALLED FOR AN ABORT; RETARDED THE PWR LEVERS TO GND IDLE (WHILE MAINTAINING FULL L RUDDER) AND REGAINED DIRECTIONAL CTL THROUGH THE TILLER. THE ACFT WAS MOVED OFF THE ACTIVE RWY AND AN AFTER LNDG CHKLIST WAS ACCOMPLISHED. AT THAT POINT; WE CONTACTED GND; TOLD THEM WE NEEDED TO RETURN TO THE GATE; NOTIFIED OPS ON THE FIELD OF THE EVENT AND WERE ASSIGNED A GATE. I AM UNSURE AS TO WHAT CAUSED THE ACFT TO YAW TO THE R. IT HAPPENED SO QUICKLY; AND WAS IDENTED AT SUCH A SLOW AIRSPD THAT THE ENTIRE EVENT ONLY LASTED A SECOND OR TWO. I REALLY HAD NO FORWARDING OR FORESIGHT THAT THIS EVENT WOULD OCCUR. I DON'T FEEL THAT MUCH CAN BE DONE BY A FLT CREW TO PREVENT THIS FROM HAPPENING AGAIN. I FEEL THAT IT WAS JUST A MECHANICAL IRREGULARITY THAT HAPPENED AT THAT MOMENT. I FEEL THAT OUR CREW'S EARLY RECOGNITION OF THE PROB AND AN IMMEDIATE DECISION TO ABORT THE TKOF VERY WELL MAY HAVE SAVED DAMAGE TO THE ACFT AND POSSIBLE INJURIES TO THOSE ABOARD. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT THE ACFT REMAINED GNDED FOR SEVERAL HRS THAT DAY WHILE MAINT CREWS CHKED FOR FAULTS. THEY FOUND NOTHING WRONG AND THE ACFT WAS FLOWN LATER THAT DAY. THE RPTR SUSPECTS THAT A TRANSIENT FAULT OF SOME SORT DEVELOPED DURING THE TIME THAT STEERING CTL WAS XFERRED FROM THE TILLER TO THE RUDDER PEDALS. HE HAS NOT HEARD OF THIS PROB REDEVELOPING ON THIS OR OTHER ACFT.

Data retrieved from NASA's ASRS site as of May 2009 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.