How can you identify the highest obstruction on an approach plate, and is it in MSL or AGL?

• A. The bold arrow; it is MSL
• B. The bold line; it is MSL
• C. The dotted line; it is AGL
• D. The shaded area; it is AGL

Answer: (A)

The highest obstruction on an approach plate is identified by a bold arrow. That symbol is the quick visual cue for the single tallest obstacle along the instrument approach. The height of that obstruction is expressed in feet MSL (mean sea level), not AGL. Using MSL provides a universal reference that stays consistent regardless of the airport’s elevation. Other symbols like a bold line, dotted line, or shaded area do not indicate the tallest obstruction, so they aren’t the correct cue for this detail.