Calculating Your Personal VDP When No Approach Waypoint Provided for Instrument Landing
In a recent incident, a flight approaching Runway 13 at Crookston (KCKN) encountered a situation where the Visual Descent Point (VDP), a crucial point in a non-precision approach, was not published on the chart. This article outlines the steps a pilot can take to estimate a VDP in such circumstances.
When a VDP is not available, pilots must determine the optimal location to begin descent from the Minimum Descent Altitude (MDA). The MDA for the non-precision approach at KCKN is 500 feet Above Ground Level (AGL).
## Steps to Estimate a VDP
1. **Determine the Expected Descent Angle**: For non-precision approaches, a typical descent angle is around 3° to 5°. A standard of 3.5° can be used if specific guidance is not available.
2. **Calculate the Distance from the Threshold**: The VDP is typically located at a distance from the runway threshold that allows a descent at the chosen angle to reach the threshold at the desired height.
- **Formula**: \[ \text{Distance} = \frac{\text{Descent Altitude above Threshold}}{\tan(\text{Descent Angle})} \] - **Example**: If the aircraft is at 344 feet above the runway threshold (the MDA at KCKN) and using a 3.5° descent angle: \[ \text{Distance} = \frac{344}{\tan(3.5^\circ)} \approx 1.15 \times 344 \approx 398.4 \text{ nautical miles} \]
3. **Convert Distance to a Location**: Once you have the distance, you can use visual references or landmarks along the approach path to estimate the VDP location.
4. **Consider Obstacles and Clearance**: Ensure that the chosen VDP does not lead into obstacles or areas with insufficient clearance.
5. **Operational Considerations**: Remember that a VDP calculated without official publication may not provide the same level of obstacle protection as a published VDP. Pilots must remain vigilant and adjust as necessary to ensure safe descent.
In the case of the flight at KCKN, the runway suddenly became visible at the 12 o'clock position, but the flight was too high and elected to go-around. If the VDP had been calculated and the flight had started its descent from MDA to the runway, it might have avoided the need for a go-around.
In conclusion, while the absence of a VDP on the chart can present challenges, pilots can estimate a VDP using the steps outlined above. It is essential to remain vigilant and follow all applicable safety guidelines, especially when potential obstacles are present.
- In the absence of a published Visual Descent Point (VDP), pilots must determine the optimal location to begin descent from the Minimum Descent Altitude (MDA).
- For non-precision approaches, a typical descent angle is around 3° to 5°, with a standard of 3.5° when no specific guidance is provided.
- To calculate the distance from the runway threshold, divide the Descent Altitude above Threshold by the tangent of the Descent Angle.
- Using this distance, convert it into a location using visual references or landmarks along the approach path to estimate the VDP location.
- When choosing a VDP, consider potential obstacles and ensure there is sufficient clearance for a safe descent.
- Operational considerations are crucial: a VDP calculated without official publication may not offer the same level of obstacle protection as a published VDP.
- In such circumstances, pilots must remain vigilant and adjust as necessary to ensure a safe descent.
- The aerospace industry relies on advancements in navigation, technology, and proper training to enhance flight safety during non-precision approaches.
- Effective financial management and industry-standard procedures play a vital role in ensuring that airports like KCKN provide accurate information for safe flying.
