Date: 201809
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Light: Daylight
Aircraft: Skyhawk 172/Cutlass 172
Operator: FBO
Operating under: Part 91
Mission: Training
Flight phase: Taxi
ATC / advisory: Ground ZZZ
Aircraft component: Rudder Control System
Reporter organization: FBO
Reporter function: Instructor; Pilot Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Commercial; Flight Crew Flight Instructor
Anomaly: Aircraft Equipment Problem Less Severe; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Taxiway
Detector: Person Flight Crew
When detected: Taxi
Result: Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; Flight Crew Returned To Gate; General Flight Cancelled / Delayed
Contributing factors: Aircraft
Primary problem: Aircraft

Narrative: After instructing my student on conducting a thorough preflight inspection of the aircraft involved by following our company checklist; we entered the aircraft and proceeded to follow the Engine Starting Checklist. After starting the engine and conducting the 'Before Taxi' Checklist; I called ZZZ Ground and received taxi clearance to Runway XX via [two taxiways]. Upon beginning our taxi roll; we initiated a brake check and received a normal response; as expected. We made a series of right and left turns to exit the ramp; with the aircraft responding to all of them normally. As we were about to turn left onto taxiway [the second taxiway] from [the first taxiway]; my student applied force to the left rudder pedal; however; the aircraft did not turn. He then applied full left brake; but again; the aircraft did not turn. At this point; I assisted on the controls and applied full left rudder pedal and brake; only to have the aircraft not respond. I then assumed full control of the aircraft and reduced our engine power to idle as we slowly coasted into the grass off of [the second taxiway]. After a brief radio exchange with the Ground Controller; I attempted to return the aircraft to the pavement via a series of right turns; and received clearance to taxi back to the ramp via [the first taxiway]. Upon returning to the paved taxiway; I was able to obtain some response from the aircraft; and initiated a gentle left turn into the ramp; where I conducted a series of right and left turns to see if the aircraft would continue to respond (it did; but sluggishly). After shutting down; I called the Ground Controller via cell phone to briefly discuss what we believe occurred; and to verify that there was no noticeable damage to the aircraft resulting from the pavement departure. Upon asking if he required anything else from me; he replied in the negative; and the phone call terminated. I then contacted company maintenance personnel to have them inspect the aircraft; and a company manager also arrived.At no time did our aircraft pose a collision hazard to another aircraft. We also remained clear of the runway safety area at all times; so there was no runway incursion associated with this event.




Synopsis: C172S Instructor Pilot reported loss of rudder pedal steering during taxi resulting in a taxiway excursion.