When should you issue a terrain/obstruction alert?

Issuing a terrain/obstruction alert is essential for ensuring the safety of the aircraft, especially in critical flight phases. The correct choice is justified as alerts must be issued anytime an aircraft is at an altitude that presents an unsafe situation concerning terrain or obstructions. This approach underscores the need for constant vigilance regarding the aircraft's altitude relative to the surrounding terrain, regardless of the phase of flight.

For example, if an aircraft is cruising at an altitude that is too low compared to the terrain or obstructions in the vicinity, a terrain warning is necessary, as it alerts the crew to the risk of a potential collision. This safety protocol is not limited to specific operation phases, such as approach; instead, it applies uniformly whenever the aircraft's altitude poses a danger.

In contrast to this, other options suggest scenarios that might limit the issuance of alerts, which could compromise safety. Therefore, the requirement for alerts is broad and focused on ensuring that any risky altitude situation is communicated to the flight crew effectively.