1. What is a Visual Descent Point (VDP) Calculator?

Definition: This calculator determines the Visual Descent Point (VDP) for aircraft approach, which is the point where a normal descent from the Minimum Descent Altitude (MDA) to the runway should begin.

Purpose: It helps pilots plan their approach and descent when flying non-precision instrument approaches.

2. How Does the VDP Calculator Work?

The calculator uses the formula:

Where:

• \( VDP \) — Visual descent point (nautical miles)
• \( D \) — Distance to runway (nautical miles)
• \( h \) — Height above runway (feet)
• \( \theta \) — Glide path angle (degrees)

Explanation: The formula calculates the point where a stable descent at the specified glide path angle would intercept the runway surface.

3. Importance of VDP Calculation

Details: Proper VDP calculation ensures safe approach procedures, stable descent profiles, and helps prevent controlled flight into terrain (CFIT) accidents.

4. Using the Calculator

Tips: Enter the distance to runway in nautical miles, height above runway in feet, and glide path angle in degrees (default 3°). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What is a typical glide path angle?
A: Most instrument approaches use a 3° glide path, though some may vary between 2.5° to 3.5°.

Q2: How do I determine the height above runway?
A: This is typically the Minimum Descent Altitude (MDA) minus the runway elevation.

Q3: When would the VDP be negative?
A: A negative VDP means the aircraft is already inside the normal descent point, indicating an unstable approach.

Q4: How does runway length affect VDP?
A: The calculator assumes touchdown at the runway threshold. For longer runways, pilots may adjust the VDP slightly.

Q5: Is this calculation used for all approaches?
A: Primarily for non-precision approaches. Precision approaches (ILS) have published glide paths.