An instrument landing system (ILS) critical area sign has what color combination?

The correct answer is that an instrument landing system (ILS) critical area sign features a white inscription on a red background. This color combination is specifically designed to alert pilots and ground personnel of the critical area associated with the ILS. The white text on a red background creates a high contrast that ensures visibility and quick recognition, which is essential in aviation environments where timing and clarity are crucial for safety during landing approaches.

By using these colors, the sign effectively communicates its importance, indicating that entry into this area must be managed carefully, especially in conditions where guidance systems are in use.