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Calculating Your Missing VDP During an Instrumental Approach Without One Provided

In the event that a Visual Descent Point (VDP) isn't present during your next landing approach, here's the suggested course of action.

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Calculating Your VDP Absent in Instrument Approach Methods
Calculating Your VDP Absent in Instrument Approach Methods

Calculating Your Missing VDP During an Instrumental Approach Without One Provided

In the world of aviation, understanding Visual Descent Points (VDPs) is crucial for pilots during non-precision approaches. These points mark the start of a visual descent from the Minimum Descent Altitude (MDA) to the runway.

The MDA for a non-precision approach is typically 500 feet Above Ground Level (AGL). However, the exact MDA can vary, and it's essential to know this height to calculate the VDP.

To find the approximate distance for starting a descent from MDA to the runway, you divide the MDA's AGL value by 300. For instance, if the MDA is 600 feet AGL, the VDP would be approximately 2 Nautical Miles (NM) from the runway threshold.

A VDP is denoted by a bold "V" on an approach chart. However, not every non-precision approach has a VDP published. In such cases, pilots can calculate an approximate VDP manually.

Here's how:

  1. Identify the MDA above runway elevation (in feet). This is the height at which you begin a visual descent.
  2. Use the standard visual descent angle of about 3 degrees.
  3. Calculate the horizontal distance from the runway threshold to the VDP using the formula: Distance to VDP (NM) = Height above runway (feet) / 300

For example, if the MDA is 600 feet above runway elevation:

Distance to VDP = 600 / 300 = 2 NM

This means the VDP lies approximately 2 NM from the runway threshold along the final approach course. Starting descent from MDA at that point following a 3° path leads you to the runway threshold in a stabilized descent.

However, it's important to note that the calculated VDP assumes a clear 3° glide path and does not guarantee obstacle clearance below MDA unless published. Approaches without a provided VDP have not been fully assessed for descent path obstacle clearance below MDA, so caution is needed.

The published visual descent angle (VDA), if shown, is advisory only and does not guarantee additional protection below MDA. When no VDP is published, pilots should exercise greater vigilance when descending below MDA visually to avoid obstacles.

Some operators or training recommend cross-checking the calculated VDP with other approach and terrain information for safety.

For instance, on the Crookston (KCKN) VOR/DME Approach to Runway 13, the lowest MDA is 344 feet above the TDZE, which when divided by 300 gives an approximate distance of 1.15 for starting a 3-degree descent to the runway.

In summary, you can estimate the VDP by dividing your height above the runway at MDA by 300 (feet per NM) to find the distance from the runway threshold to begin your descent on a 3° angle. However, always remain cautious as this is not an officially protected descent path if not published.

For more real-world flying tips and information, consider subscribing to the Boldmethod email service, which offers weekly insights. Additionally, the Instrument Procedures course from Boldmethod can help earn an instrument rating and master IFR flying.

[1] FAA and professional aviation guidance on non-precision approaches without published VDPs.

  1. In the realm of aviation, pilots must comprehend Visual Descent Points (VDPs) during non-precision approaches, providing a start for visual descent from the Minimum Descent Altitude (MDA) to the runway.
  2. The MDA for a non-precision approach is often 500 feet Above Ground Level (AGL), but this can change, requiring knowledge of the exact MDA to determine the VDP.
  3. To calculate the approximate distance for starting a descent from MDA to the runway, pilots divide the MDA's AGL value by 300.
  4. A VDP is denoted on an approach chart by a bold "V", but not every non-precision approach will have a VDP published.
  5. In such instances, pilots can manually calculate an approximate VDP using the MDA above runway elevation, a standard visual descent angle, and the formula: Distance to VDP (NM) = Height above runway (feet) / 300.
  6. Operators or training may advise cross-checking the calculated VDP with other approach and terrain information for safety.
  7. Approaches without a provided VDP have not been fully assessed for descent path obstacle clearance below MDA, so caution is essential.
  8. The published visual descent angle (VDA), if shown, is advisory only and does not guarantee additional protection below MDA when no VDP is published.
  9. For more guidance on real-world flying and information, aviation enthusiasts might consider subscribing to the Boldmethod email service or enrolling in their Instrument Procedures course to earn an instrument rating and master IFR flying.

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