How many lights are required to set up an inverted 'Y' light formation?

• A. 4
• B. 3
• C. 5
• D. 6

Answer: (A)

Readability of ground-light patterns at night is essential for pilots to recognize the signal quickly and correctly. An inverted Y shape is formed by a single stem that splits into two branches, so to reproduce it clearly with lights you want four distinct points that define the shape: one light at the top of the stem, one at the fork point where the two branches diverge, and one light at the tip of each branch. This arrangement gives a clear, unambiguous outline from various angles and distances.

If you used only three lights, the fork area wouldn’t be as well defined and the pattern could be misread as a different signal. Adding more than four lights would clutter the silhouette and potentially confuse approaching aircraft or crews.