Narrative:

Flight from gtr-tup. After being cleared to land, we flew a straight-in visual approach and made a normal landing in the touchdown zone. As soon as we touched down and the first officer, who was flying, pulled back the power levers, we began to pull hard right. I corrected to the left using the tiller when I realized he had full left rudder. The aircraft began to surge left and then back to the right again. I was able to keep the airplane over the centerline, but we were yawing unctlably left and right. I felt power surges and heard abnormal engine noises. The aircraft became more uncontrollable as we slowed and we seemed to actually speed up for a second during a final power surge. When I realized that the engines were causing this, I shut down both to maintain directional control. As soon as the engines shut down and the propellers feathered, we were able to bring the aircraft to a controled stop on the centerline, about 1/2 way down the runway. I did not declare an emergency because I did not believe we were in any more danger after the aircraft came to a stop. We did not get on the brakes in what I would consider to be an abnormal manner and the engine indications appeared very normal after shutdown. I made the decision not to evacuate/evacuation (or deplane) also, because of the above factors and because I thought it would create more problems than it would solve. Tower immediately asked if we needed assistance when they saw our rollout and crash fire rescue equipment responded swiftly even though we did not request it. I initially notified tower that I did not want to restart and would ask to be towed off the runway. After talking to maintenance, however, I made the decision to restart the right engine. They were able to convince me that any abnormalities as I described would not endanger the passenger and that I could shut down and discontinue the start if necessary. We performed the restart and taxied back to the gate without further incident. Callback conversation with reporter revealed the following information: the reporter stated the yawing problem was caused by the right engine changing power output above and below idle or beta. The reporter said the automatic coursing computer on the right engine was malfunctioning.

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Original NASA ASRS Text

Title: A SAAB 340B ON LNDG ROLLOUT THE ACFT BEGAN YAWING UNCTLABLY DUE TO THE R ENG SURGING CAUSED BY A FAILED AUTO COURSING COMPUTER.

Narrative: FLT FROM GTR-TUP. AFTER BEING CLRED TO LAND, WE FLEW A STRAIGHT-IN VISUAL APCH AND MADE A NORMAL LNDG IN THE TOUCHDOWN ZONE. AS SOON AS WE TOUCHED DOWN AND THE FO, WHO WAS FLYING, PULLED BACK THE PWR LEVERS, WE BEGAN TO PULL HARD R. I CORRECTED TO THE L USING THE TILLER WHEN I REALIZED HE HAD FULL L RUDDER. THE ACFT BEGAN TO SURGE L AND THEN BACK TO THE R AGAIN. I WAS ABLE TO KEEP THE AIRPLANE OVER THE CTRLINE, BUT WE WERE YAWING UNCTLABLY L AND R. I FELT PWR SURGES AND HEARD ABNORMAL ENG NOISES. THE ACFT BECAME MORE UNCTLABLE AS WE SLOWED AND WE SEEMED TO ACTUALLY SPD UP FOR A SECOND DURING A FINAL PWR SURGE. WHEN I REALIZED THAT THE ENGS WERE CAUSING THIS, I SHUT DOWN BOTH TO MAINTAIN DIRECTIONAL CTL. AS SOON AS THE ENGS SHUT DOWN AND THE PROPS FEATHERED, WE WERE ABLE TO BRING THE ACFT TO A CTLED STOP ON THE CTRLINE, ABOUT 1/2 WAY DOWN THE RWY. I DID NOT DECLARE AN EMER BECAUSE I DID NOT BELIEVE WE WERE IN ANY MORE DANGER AFTER THE ACFT CAME TO A STOP. WE DID NOT GET ON THE BRAKES IN WHAT I WOULD CONSIDER TO BE AN ABNORMAL MANNER AND THE ENG INDICATIONS APPEARED VERY NORMAL AFTER SHUTDOWN. I MADE THE DECISION NOT TO EVAC (OR DEPLANE) ALSO, BECAUSE OF THE ABOVE FACTORS AND BECAUSE I THOUGHT IT WOULD CREATE MORE PROBS THAN IT WOULD SOLVE. TWR IMMEDIATELY ASKED IF WE NEEDED ASSISTANCE WHEN THEY SAW OUR ROLLOUT AND CFR RESPONDED SWIFTLY EVEN THOUGH WE DID NOT REQUEST IT. I INITIALLY NOTIFIED TWR THAT I DID NOT WANT TO RESTART AND WOULD ASK TO BE TOWED OFF THE RWY. AFTER TALKING TO MAINT, HOWEVER, I MADE THE DECISION TO RESTART THE R ENG. THEY WERE ABLE TO CONVINCE ME THAT ANY ABNORMALITIES AS I DESCRIBED WOULD NOT ENDANGER THE PAX AND THAT I COULD SHUT DOWN AND DISCONTINUE THE START IF NECESSARY. WE PERFORMED THE RESTART AND TAXIED BACK TO THE GATE WITHOUT FURTHER INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THE YAWING PROB WAS CAUSED BY THE R ENG CHANGING PWR OUTPUT ABOVE AND BELOW IDLE OR BETA. THE RPTR SAID THE AUTO COURSING COMPUTER ON THE R ENG WAS MALFUNCTIONING.

Data retrieved from NASA's ASRS site as of July 2007 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.