What must happen when using HF for communication between controllers and pilots?

When using HF (High Frequency) communication between controllers and pilots, it is essential that all instructions are read back by the pilot. This practice enhances safety and ensures clarity in communication, particularly because HF communication is often susceptible to interference, static, and other quality issues that can lead to misunderstandings. The read-back process serves as a confirmation mechanism, making it clear that the pilot has understood the instructions accurately and is aware of the requirements set by the controller.

The requirement for read-back is especially critical in complex or safety-related instructions, such as clearances, altitudes, and routes. By requiring pilots to repeat back what they have been instructed, it reduces the risk of errors that might occur due to miscommunication, which is particularly valuable in the less-reliable HF communication environment. This protocol is a fundamental part of aviation radio communication standards and practices, aimed at enhancing the safety and efficiency of flight operations.