What does a solid yellow light indicate on the exterior of a PA5 car?

A solid yellow light on the exterior of a PA5 car indicates that the Powered Equipment Heating Unit (PEHU) in that car has been activated. This is an important signal for train engineers and crew because it provides information about the operational status of the car's equipment, particularly in colder weather conditions where heating may be necessary to ensure the comfortable operation of passenger amenities.

Understanding the significance of the PEHU activation is critical for safe train operations, as it allows the crew to monitor and ensure that necessary heating is functioning properly. This activation helps maintain a safe and pleasant environment for passengers. It may also be linked to the overall performance of the train, especially during winter months, when equipment can be negatively affected by cold temperatures.

The other options do not accurately reflect what the solid yellow light signifies. For example, a malfunctioning engine would typically warrant a different indicator, and the approach to a station would be marked with different lighting signals. Emergency stops would require an immediate response and different alerting mechanisms. Hence, recognizing the specifics of the yellow light is crucial for train operations and safety protocols.