When is it appropriate to approach a helicopter?

The correct choice highlights the importance of situational awareness and the specific conditions that necessitate approaching a helicopter. Approaching a helicopter is generally governed by safety protocols, which dictate that personnel should only approach when there is a legitimate reason to do so, and it is essential to ensure that it is safe at that time.

In many scenarios, it may be necessary to approach a helicopter for reasons such as assisting with an operation, aiding emergency services, or engaging in training exercises. However, this must be balanced with ensuring that the helicopter is in a safe state, such as being stationary, with rotors not in motion, and after assessing any communication signals or instructions from the crew. Thus, the term "when necessary" captures the essence of recognizing one’s duties as well as fostering an understanding of the protocols in place for approaching aircraft safely.