How many lights are required to mark a code letter at night with flanker lights?

To mark a code letter at night using flanker lights, 11 lights are required. This quantity is established in aviation lighting procedures, which specify that the positioning of flanker lights must be sufficiently visible to indicate the designated code letters in low-visibility conditions.

The use of a specific number of lights ensures that the code can be clearly distinguished from other signals and visual clutter, allowing those in the aircraft to identify the letters reliably. This is particularly important during night operations when visibility is limited, making proper illumination crucial for safety and navigation.

In the context of this question, the answer reflects the standard practices in aviation signaling and emphasizes the importance of adhering to established guidelines for effective performance during night operations. The other quantities provided do not conform to the established requirement, highlighting the critical nature of following protocols in aviation situations.