Upon receiving a hot bearing detector defect notification, how many axles must be checked?

When receiving a hot bearing detector defect notification, it is essential to conduct a thorough check to ensure the safety and integrity of the train's operation. The correct choice indicates that both the axles ahead of and behind the detected defect must be checked within a range of 20 axles. This comprehensive approach helps to identify any potential issues that may be caused by a rising temperature in bearings on not just the axle where the defect was detected but also on adjacent ones, which may also be affected.

Examining 20 axles ahead and behind allows for adequate assessment of the performance of the entire train and ensures that any issues related to other axles are identified and addressed promptly. Conducting inspections within this wider range helps to prevent further complications or failures that could arise from undetected hot bearings, thereby enhancing overall safety and operational efficiency.

Options that suggest a narrower scope of inspection, such as limiting the check to five or only to the indicated axle, may miss critical signs of bearing failures elsewhere on the train. This could lead to unsafe conditions or operational disruptions if other issues are present but not identified because they fell outside the checked range.