What must be done if a flat spot of 4 inches or greater is found on a wheel?

If a flat spot of 4 inches or greater is found on a wheel, the correct action is to remain stopped. This is crucial because a flat spot of that size indicates a significant defect that could compromise the integrity and safety of the vehicle. Continuing operations with a wheel in such condition could lead to further damage, increased risk of failure while the vehicle is in motion, or hazards related to stability and braking.

Remaining stopped allows for a thorough inspection and assessment to be made regarding the condition of the wheel and allows for the guidance of appropriate maintenance procedures to be followed. Taking immediate action to halt operations can help prevent accidents, ensure the safety of personnel, and maintain the overall operational integrity of the rail system.