Final answer:
Surveillance approach guidance can be discontinued when the pilot reports 'c) Improved visibility'. This allows pilots to safely navigate without additional assistance, which is mainly provided during poor visibility conditions.
Step-by-step explanation:
The question pertains to a scenario in air traffic control where surveillance approach guidance may be given to pilots. This guidance is typically provided when pilots require assistance due to various factors such as poor visibility or heavy traffic. The question asks at what point this guidance can be discontinued.
Among the options provided, surveillance approach guidance may be discontinued when the pilot reports 'c) Improved visibility'. This is because better visibility allows pilots to navigate more safely without the need for additional assistance from air traffic control. Therefore, once visibility has improved beyond a certain threshold that is deemed safe for visual flight rules (VFR), pilots can continue without surveillance approach guidance.
It's important to note that arrival delays, unfavorable wind conditions, and increased air traffic may actually necessitate the continuation of surveillance approach guidance to ensure safety and efficiency in the control of air traffic.