A C-172 instructor reported the aircraft began veering right while taxiing while the student was und...

Attributes
ACN	1255580
Time
Date	201504
Local Time Of Day	0601-1200
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Skyhawk 172/Cutlass 172
Operating Under FAR Part	Part 91
Flight Phase	Taxi
Flight Plan	VFR
Component
Aircraft Component	Normal Brake System
Person 1
Function	Instructor
Qualification	Flight Crew Commercial Flight Crew Flight Instructor Flight Crew Multiengine Flight Crew Instrument
Experience	Flight Crew Last 90 Days 150 Flight Crew Total 330 Flight Crew Type 170
Events
Anomaly	Aircraft Equipment Problem Less Severe Ground Event / Encounter Loss Of Aircraft Control Ground Excursion Taxiway

Narrative:

On the taxi out to take off both student and I performed initial brake check at slow speed and brake operation was normal. Continued taxi for takeoff and made two right turns with normal steering and brake operation. After crossing a runway the taxiway made a turn to the left; the student was at the controls and I noticed us veer from taxiway centerline to the right; slowly. Then after looking and verifying that she was making the correct control input on the rudder pedal and seeing the taxi continue to the left I applied my rudder and brake control to get back to the taxiway centerline and follow the left turn. With full rudder pedal deflection and full brake application on the left brake the airplane was still not controllable and exited the taxiway onto the grass at a slow speed. Upon rolling off the asphalt I shut down the engine and contacted ground and had the aircraft towed to maintenance. No damage was noted on the aircraft or on any airport equipment.

Original NASA ASRS Text

Title: A C-172 Instructor reported the aircraft began veering right while taxiing while the student was under control of the airplane. The instructor took the controls and tried to turn to the taxiway but was unable and shutdown the engine as the aircraft exited the taxiway.

Narrative: On the taxi out to take off both student and I performed initial brake check at slow speed and brake operation was normal. Continued taxi for takeoff and made two right turns with normal steering and brake operation. After crossing a runway the taxiway made a turn to the left; the student was at the controls and I noticed us veer from taxiway centerline to the right; slowly. Then after looking and verifying that she was making the correct control input on the rudder pedal and seeing the taxi continue to the left I applied my rudder and brake control to get back to the taxiway centerline and follow the left turn. With full rudder pedal deflection and full brake application on the left brake the airplane was still not controllable and exited the taxiway onto the grass at a slow speed. Upon rolling off the asphalt I shut down the engine and contacted ground and had the aircraft towed to maintenance. No damage was noted on the aircraft or on any airport equipment.

Data retrieved from NASA's ASRS site 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.

A C-172 instructor reported the aircraft began veering right while taxiing while the student was under control of the airplane. The instructor took the controls and tried to turn to the taxiway but was unable and shutdown the engine as the aircraft exited the taxiway.