If brakes on a car fail to apply, how long must they remain applied during testing when retesting?

When retesting brakes that have failed to apply, it is necessary to have them applied for a duration of 3 minutes to ensure they are functioning correctly and safely. This time frame allows for a thorough assessment of the brake system's performance and reliability. By holding the brakes for this specific duration, technicians can confirm that any issues have been resolved and that the brakes will perform effectively in real-world conditions. This practice is critical for maintaining safety standards within the railway system and ensuring that all components are functioning as intended before the car is returned to service.