Which of the following is NOT an example of OS'ing?

The correct option is based on understanding what constitutes "OS'ing," which refers to "on-scene" communications or reports that ensure various aspects of train operations are being monitored and communicated clearly. In this context, OS'ing involves confirming the status or location of the train relative to signals, stations, or other control mechanisms.

When the EOTD (End of Train Device) indicates that the train is moving and the engine has passed three miles beyond the limits, this does not directly represent OS'ing. Instead, it reflects a state of the train's movement after it has already passed a certain point, without the incorporation of critical updates or confirmations that would typically be communicated in OS'ing. OS'ing usually involves confirming positions or statuses as trains pass critical points, such as signals or stations, rather than documenting an ongoing status after certain thresholds.

In contrast, the other options clearly relate to active monitoring and communications. The approaching engine to the next station, the train stopped at a signal, and monitoring the track ahead all directly correlate with proactive checks and reporting that are essential components of OS'ing.