Narrative:

Made turn at very low speed onto the runway for takeoff. Allowed aircraft to roll straight before adding power. Just started to add power (engines spooled evenly) when nose wheels cocked full right without input from tiller or pedals. Nose pulled right. Aircraft straightened by pulling off power and left brake. Event happened at very low speed. Aircraft stayed on runway. Nose tires were felt to be scrubbing when airplane nose tires turned full right. I am aware of 3 previous incidents with nose steering on the B-737. On 2 occasions on wet runways with low aircraft gross weight and relatively rapid turns, I have had nose steering over center. In both cases it was necessary to retard power to straighten out the nose wheels. In this case the turn speed was very slow and the engines spooled evenly and the nose locked the opposite direction of the turn. I am also aware of a 737-300 that at 60 KTS on rollout with a dry runway, highly experienced crew and no crosswind departed the runway for still unexplained reasons. In the last case the nose steering system was removed and sent to boeing for evaluation. No defects were noted but hydraulic contamination was suspected. Callback conversation with reporter revealed the following information: the reason the reporter sent the report in was he thought the symptom was hydraulic problem and related to previous incidents. He later learned that the problem was in the fuel control. The flight was the first of the day and the aircraft had just come from the hangar where adjustments had been made on the fuel control. There were no previous write-ups related to the reported problem. The runway was wet, he was making a left turn using asymmetrical brakes (left) and applying power symmetrically, but the fuel control responded with asymmetrical power causing the nosewheel to caster. Maintenance is alleged to have control difficulty while taxiing the aircraft back to the hangar. In the narrative of the report the reporter states the engines spooled evenly, but, on reflection he realizes that the event happened so fast the gauges would not have had time to manifest the power asymmetry.

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Original NASA ASRS Text

Title: UNCOMMANDED THE NOSEWHEEL STEERING TURNED FULL R AS THE PLT WAS ATTEMPTING TO LINE UP ON THE RWY FOR TKOF.

Narrative: MADE TURN AT VERY LOW SPD ONTO THE RWY FOR TKOF. ALLOWED ACFT TO ROLL STRAIGHT BEFORE ADDING PWR. JUST STARTED TO ADD PWR (ENGS SPOOLED EVENLY) WHEN NOSE WHEELS COCKED FULL R WITHOUT INPUT FROM TILLER OR PEDALS. NOSE PULLED R. ACFT STRAIGHTENED BY PULLING OFF PWR AND L BRAKE. EVENT HAPPENED AT VERY LOW SPD. ACFT STAYED ON RWY. NOSE TIRES WERE FELT TO BE SCRUBBING WHEN AIRPLANE NOSE TIRES TURNED FULL R. I AM AWARE OF 3 PREVIOUS INCIDENTS WITH NOSE STEERING ON THE B-737. ON 2 OCCASIONS ON WET RWYS WITH LOW ACFT GROSS WT AND RELATIVELY RAPID TURNS, I HAVE HAD NOSE STEERING OVER CTR. IN BOTH CASES IT WAS NECESSARY TO RETARD PWR TO STRAIGHTEN OUT THE NOSE WHEELS. IN THIS CASE THE TURN SPD WAS VERY SLOW AND THE ENGS SPOOLED EVENLY AND THE NOSE LOCKED THE OPPOSITE DIRECTION OF THE TURN. I AM ALSO AWARE OF A 737-300 THAT AT 60 KTS ON ROLLOUT WITH A DRY RWY, HIGHLY EXPERIENCED CREW AND NO XWIND DEPARTED THE RWY FOR STILL UNEXPLAINED REASONS. IN THE LAST CASE THE NOSE STEERING SYS WAS REMOVED AND SENT TO BOEING FOR EVALUATION. NO DEFECTS WERE NOTED BUT HYD CONTAMINATION WAS SUSPECTED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REASON THE RPTR SENT THE RPT IN WAS HE THOUGHT THE SYMPTOM WAS HYD PROB AND RELATED TO PREVIOUS INCIDENTS. HE LATER LEARNED THAT THE PROB WAS IN THE FUEL CTL. THE FLT WAS THE FIRST OF THE DAY AND THE ACFT HAD JUST COME FROM THE HANGAR WHERE ADJUSTMENTS HAD BEEN MADE ON THE FUEL CTL. THERE WERE NO PREVIOUS WRITE-UPS RELATED TO THE RPTED PROB. THE RWY WAS WET, HE WAS MAKING A L TURN USING ASYMMETRICAL BRAKES (L) AND APPLYING PWR SYMMETRICALLY, BUT THE FUEL CTL RESPONDED WITH ASYMMETRICAL PWR CAUSING THE NOSEWHEEL TO CASTER. MAINT IS ALLEGED TO HAVE CTL DIFFICULTY WHILE TAXIING THE ACFT BACK TO THE HANGAR. IN THE NARRATIVE OF THE RPT THE RPTR STATES THE ENGS SPOOLED EVENLY, BUT, ON REFLECTION HE REALIZES THAT THE EVENT HAPPENED SO FAST THE GAUGES WOULD NOT HAVE HAD TIME TO MANIFEST THE PWR ASYMMETRY.

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.