NOSEWHEEL STEERING, PEDAL DISCONNECT AND TOWING
Nosewheel steering combines command inputs, electronic processing, hydraulic power and a permitted ground configuration. Tiller and pedal inputs do not have the same steering authority. The reference architecture processes these requests through the braking/steering control system, with speed and flight/ground conditions shaping the available response. Rudder movement and nosewheel steering must therefore remain distinct observations even when one physical simulator device supplies both inputs. A correct-looking pedal animation is not proof of the expected nosewheel command. [87, PDF pp. 87, 92] [21, PDF pp. 107–116]
The tiller’s pedal-disconnect function concerns the relationship between rudder-pedal steering input and nosewheel control. It is not the same function as the towing disconnect arrangement. The towing state allows the ground operation to handle the nosewheel and is associated with its own cockpit indication. Before self-powered taxi, establish that the tug/pin arrangement is resolved and steering is available. A cleared indication should be correlated with the actual ground handover rather than used as permission to move through servicing equipment. [90, Rudder_Tiller_PED DISC with Block2; input interpretation] [23, PDF pp. 1048–1050]
The older Airbus briefing depicts Green hydraulic steering. Current Fenix configuration documentation also exposes a Yellow-steering option, so a universal Green-only dependency would be wrong for the simulated option set. Identify the configured source before predicting the consequence of a hydraulic loss. Preserved braking, alternate-brake pressure and functioning rudder do not by themselves establish retained steering. The relevant electronic, hydraulic and towing/flight-ground conditions must all support the function. [87, PDF p. 92] [70, Available Options: fnx_yellow_hydraulic_steering]
Geometry then determines what the successful command does on the ground. The main gear follows inside the cockpit/nose path through a turn, particularly on a long A321. Steering input, cockpit sightline and clearance of the whole airframe need to be assessed together. In a hardware investigation, keep the reference airframe, speed and command source fixed, remove conflicting assignments and compare cockpit/nosewheel response. This separates a control-mapping problem from the different wheelbase/oversteering technique required by another family member. [21, PDF pp. 108–110] [75, Published flight-control calibration] [90, Pedal/tiller input configuration]