What must be done when a route or altitude in a previously issued clearance is amended?

When a route or altitude in a previously issued clearance is amended, the correct action is to restate all applicable instructions. This ensures that pilots have a clear and unambiguous understanding of the current flight instructions, including any changes made to their route or altitude. By restating all applicable instructions, it reinforces the complete picture of the clearance, helping to prevent any misunderstandings or errors that could arise from partial information.

In aviation operations, clarity and accuracy in communication are crucial for maintaining safety and efficient air traffic management. By clearly stating all parts of the amended clearance, controllers help pilots comply fully with the new routing or altitudes specified. This practice also serves to confirm that pilots are aware of and understand both the changed parts and any other pre-existing instructions that remain in effect.

The other choices do not align with the procedural requirements for handling such amendments. Issuing a new clearance could lead to confusion if not all elements are properly reviewed, while notifying affected pilots or asking for pilot confirmation alone does not fulfill the need to clearly communicate all instructions, which is essential for operational safety.