Calculating Your VDP in the Absence of an Instrument Approach's Designated Value
In the world of aviation, navigating an instrument approach can sometimes be challenging, especially when a Visual Descent Point (VDP) is not published on the chart. This article will discuss a method for calculating a VDP in such situations, as well as some important factors to consider during a non-precision approach.
Before starting a descent down from the Minimum Descent Altitude (MDA) to the runway, it's crucial to ensure you have enough visibility to see not only the runway, but also any obstructions that might be in your path. However, not every non-precision approach has a VDP published on the chart.
When an approach has a VDP, you shouldn't descend below MDA prior to reaching the VDP. A VDP is denoted by a bold "V" on an approach chart and is defined as a point on the final approach course of a non-precision straight-in approach procedure from which normal descent from the MDA to the runway touchdown point may be commenced. VDPs are only published for straight-in instrument approaches to specific runways.
In the absence of a published VDP, extra caution is advised because obstacle protection below MDA may be less certain. To manually calculate the VDP using the MDA, runway elevation, and a 3-degree glide path, you can follow these steps:
- Determine the height above runway threshold at the MDA by subtracting the runway elevation from the MDA.
- Use a standard recommended descent angle, typically 3 degrees.
- Calculate the horizontal distance from the runway threshold to the VDP by dividing the height above the runway by the tangent of the desired descent angle.
Mathematically, this is:
[ VDP\ Distance = \frac{MDA - Runway\ Elevation}{\tan(3^\circ)} ]
This gives the distance from runway threshold to where you should begin your descent from the MDA to maintain a smooth 3° descent path to the runway.
For example, on the Crookston (KCKN) VOR/DME Approach to Runway 13, the lowest MDA is 344 feet above the TDZE. By using this method, a pilot can establish a safe visual descent point on a non-precision approach when the chart does not provide one.
It's essential to remember that the VDP is advisory and does not alter the requirement to maintain obstacle clearance or minimum altitudes, but it helps ensure a stabilized final approach descent and reduce excessive sink rates.
In some scenarios, a pilot might encounter clouds at 500' AGL, forcing them to go-around due to insufficient visibility. Intermittent ground contact can also make it tough for the pilot to find the runway, necessitating extra vigilance and careful navigation.
For those seeking to master IFR flying and earn their instrument rating, the Instrument Procedures course from Boldmethod can provide valuable guidance and support. By understanding the principles behind calculating a VDP and applying them in various flight scenarios, pilots can enhance their safety and confidence during non-precision approaches.
- In the absence of a published Visual Descent Point (VDP), it's crucial to exercise extra caution during a non-precision approach as obstacle protection below the Minimum Descent Altitude (MDA) may be less certain.
- To calculate a VDP manually when one is not provided on the chart, the height above runway threshold at the MDA should be determined by subtracting the runway elevation from the MDA.
- Using a standard recommended descent angle, typically 3 degrees, and the height above the runway, the horizontal distance from the runway threshold to the VDP can be calculated by dividing the height by the tangent of the desired descent angle.
- During a non-precision approach without a published VDP, a pilot should start their descent from the MDA at the calculated VDP to maintain a smooth 3° descent path to the runway.
- A VDP, denoted by a bold "V" on an approach chart, is defined as a point on the final approach course from which normal descent from the MDA to the runway touchdown point may be commenced.
- VDPs are only published for straight-in instrument approaches to specific runways and are advisory, not altering the requirement to maintain obstacle clearance or minimum altitudes.
- For pilots seeking to master Instrument Flight Rules (IFR) flying and earn their instrument rating, the Instrument Procedures course from Boldmethod can offer valuable guidance and support.
- The aerospace industry, including finance, business, education-and-self-development sectors, relies heavily on pilots who are skilled in navigating various flight scenarios, including non-precision approaches and calculating VDPs.
- In navigating an instrument approach, a pilot must consider not only the published procedures but also various factors such as cloud cover, ground contact, and visibility to ensure a safe and successful landing.
