The highest obstacle on the approach end of your LZ is 14 meters tall. Setting up the LZ for night operations, what is the unusable obstacle ratio on the approach end of your LZ?

• A. 98 meters
• B. 196 meters
• C. 14 meters
• D. 392 meters

Answer: (B)

The concept being tested is how to size the unusable obstacle area on the approach end for night LZ operations. In this scenario, the rule uses the square of the highest obstacle height (in meters) to determine the unusable distance on the approach end. This creates a conservative buffer to maintain clearance when visibility is reduced at night.

With the tallest obstacle at 14 meters, the unusable distance becomes 14 squared, which is 196 meters. This means that on the approach end, 196 meters of the LZ would be unusable for landing due to obstacle clearance requirements in night conditions. The other options reflect different multipliers or direct heights, which do not follow the night-operation rule.