B737 Next Generation Undifferentiated
Flight Crew Air Transport Pilot (ATP)
Situational Awareness; Troubleshooting; Distraction
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Maintenance
Flight Crew Overcame Equipment Problem; Flight Crew Regained Aircraft Control; General Maintenance Action
Procedure; Company Policy; Aircraft
After completion of the Before Taxi Checklist; I began a slow turn toward the taxiway centerline and noticed the nose wheel steering tiller was frozen in place.  I used a little more thrust and differential braking to try to straighten the nose wheel but it was stuck in a hard left turn position. I set the parking brake and asked the F/O to call Ground Control to let them know we would be staying in position to run a checklist for a steering malfunction. I considered calling Maintenance through the Dispatcher; but decided instead to call local Maintenance via aircraft radio/Company frequency as there was no such checklist and it was clear the aircraft could not taxi.  Local Maintenance responded to our radio call by telling us to 'stay right there; engines running;' and that they 'would be out to meet the aircraft' on the taxiway. In just a few minutes; a Mechanic showed up with something in his hand and walked toward the nose wheel.  He reappeared after a minute and motioned with hand signals for me to try to move the tiller.  Freedom of movement was not 100 percent so he again walked under the nose and reappeared in a minute with the same request. This time the nose wheel steering was perfect. The Mechanic scurried away (it was 18 degrees F and windy) and I proceeded on and completed the flight uneventfully; until it happened again two legs later. This time I elected to shut down the aircraft and have it towed back to the gate. The local Mechanic inspected the aircraft and said that the nose wheel steering bypass valve had excessive dirt and grime on it and the problem could be solved by a thorough cleaning of the valve at the gate. That was accomplished. This time; I wrote up the malfunction in the aircraft logbook. I am writing this report because I believe I should have documented the original complaint because a Maintenance action was actually performed on the aircraft; even though the Mechanic waved us off after completing his activity on the taxiway. At the very least; there would have been a second record of this event occurring on this aircraft.
B737 Captain reported the tiller would not turn the nose wheel. The tiller became operable after maintenance; but a flight 2 legs later the same anomaly occurred.