Which of the following would indicate a need for immediate attention to the air brake system?

Unusual noises or vibrations during braking are clear indicators that the air brake system may have a problem that requires immediate attention. These signs suggest that there may be an underlying issue with the components of the brake system, such as air leaks, worn parts, or mechanical failures. Ignoring such symptoms can lead to severe consequences, including complete brake failure, which can pose significant safety risks while operating the train.

In contrast, consistent pressure readings may indicate that the air brake system is functioning as expected, while gradual increases in braking distance could suggest a developing issue but might not require immediate attention compared to evident mechanical issues like strange noises or vibrations. Regular maintenance schedules being met demonstrates a proactive approach to maintenance but does not, in itself, indicate that the system is free from potential problems. Therefore, when unusual signs are present, they should always be addressed promptly to ensure the safety and reliability of the braking system.