What is the correct phraseology for a terrain/obstruction alert?

The correct phraseology for a terrain/obstruction alert is essential for ensuring that the flight crew responds promptly and effectively to potential hazards. The phrase "Low altitude alert (callsign). Check your altitude immediately" conveys a clear and urgent message that emphasizes the urgency of the situation. This statement alerts the crew to the fact that they are flying at a low altitude, which is critical for their awareness and safety.

By instructing the crew to "check your altitude immediately," it draws their immediate attention to their current flight parameters, allowing them to assess their position relative to terrain and potential obstructions effectively. This type of phraseology is standardized so that it is easily understood by pilots, ensuring that they can react swiftly to prevent an accident.

In contrast, other options may not convey the necessary urgency or specificity regarding altitude concerns. They might instruct actions that aren’t as direct in addressing the imminent threat posed by terrain or obstacles. Thus, the clarity and directness of the phraseology make choice C the best option for a terrain/obstruction alert.