1. What is Visual Descent Point (VDP)?

The Visual Descent Point (VDP) is a critical point on a non-precision instrument approach procedure that allows pilots to begin a normal descent from the Minimum Descent Altitude (MDA) to the runway when visual references are acquired.

2. How Does the Calculator Work?

The calculator uses the VDP formula:

Where:

• \( VDP \) — Visual Descent Point (nautical miles from runway threshold)
• \( HAT \) — Height Above Touchdown (feet)

Explanation: The formula calculates the distance from the runway threshold where a normal 3-degree glidepath descent can begin from the MDA.

3. Importance of VDP Calculation

Details: Accurate VDP calculation is crucial for safe instrument approaches, allowing pilots to transition smoothly from instrument to visual flight and establish a stable descent profile to the runway.

4. Using the Calculator

Tips: Enter the Height Above Touchdown (HAT) in feet. The HAT value is typically found on instrument approach charts and represents the minimum altitude above the touchdown zone.

5. Frequently Asked Questions (FAQ)

Q1: Why is the divisor 300 in the VDP formula?
A: The divisor 300 represents the descent gradient for a standard 3-degree glidepath (approximately 300 feet per nautical mile).

Q2: When should VDP be used?
A: VDP should be used during non-precision instrument approaches when the pilot has acquired sufficient visual references to continue the approach visually.

Q3: What if the calculated VDP is beyond the MAP?
A: If the calculated VDP is beyond the Missed Approach Point (MAP), use the MAP as your descent point and be prepared for a steeper than normal descent angle.

Q4: Are there limitations to this calculation?
A: This calculation assumes standard atmospheric conditions and a 3-degree glidepath. Actual descent angles may vary based on aircraft performance and wind conditions.

Q5: How does VDP differ from FAF?
A: The Final Approach Fix (FAF) is where the final approach segment begins, while VDP is the point where visual descent can begin from the Minimum Descent Altitude.