What is the correct phraseology for a Terrain/Obstacle Alert?

The phraseology for a Terrain/Obstacle Alert accurately reflects the urgency and clarity required in such situations, which is why "Low altitude alert (call sign), check your altitude immediately!" is the best choice. This phrase communicates the critical nature of the alert while clearly identifying the aircraft involved with the call sign. The directive to "check your altitude immediately" emphasizes swift action, which is essential during a potential terrain or obstacle conflict.

In air traffic control, it is crucial to provide clear and concise information to pilots to ensure their immediate understanding and response. The use of "low altitude alert" is a standardized phrase that is recognized in aviation communication, making it less prone to misinterpretation during high-stress situations. This choice encapsulates both the concern for safety and the necessity for rapid corrective action.

Other options may lack the immediacy or clarity necessary for alerting a pilot about potential danger. For example, phrases that do not specify "low altitude" may not convey the same level of urgency, and those that suggest adjustments to flight paths without emphasizing altitude checks could lead to confusion. This choice effectively prioritizes the pilot's immediate response to a critical safety issue.