If ____ is visible on the nose gear tire, the aircraft should not be accepted.

The visibility of red cord on the nose gear tire indicates that the tire has worn down to a critical level, which compromises the tire's structural integrity and performance. Tires are designed with a tread that provides traction and stability during takeoff, landing, and taxiing. The red cord acts as a warning indicator, showing that significant wear has occurred. When this red cord is visible, it suggests that the tire has reached its safety limit and should be replaced to ensure the safety of the aircraft and its operations.

This is crucial because operating an aircraft with worn tires can lead to reduced performance and an increased risk of failure during critical phases of flight. Therefore, the presence of red cord dictates the necessity for immediate action to either replace the tire or defer acceptance of the aircraft until it has been properly serviced.