The Mysterious Visual Descent Point (VDP)
July 18, 2018
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By:
Thomas Peeters
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Airline Interview Prep Series 1 – The Mysterious VDP

1. Introduction

During Airline Selection Procedures a candidate’s theoretical knowledge is put to the test. 

In general this involves in-depth questions concerning ATPL topics such as Airlaw, Meteo, Power Plants, Principles of Flight, etc. However, often a candidate is faced with questions of a more operational nature. For example the calculation of climb gradients and TOD’s, the meaning of certain symbols and abbreviations used on approach plates and enroute charts, cold temperature corrections to barometric based minima, rate of descends required to maintain typical 3 degree glide slopes, etc. 

At first glance several of these operational questions might seem rather complex. Even more, some questions will lure the applicant into performing brain breaking calculations while easy rule-of-thumbs will do the job!

In the weeks to come EuroPilot Center will discuss several challenging Airline Assessment topics to assist the ab-initio pilot in passing his/her theoretical interview with flying colors.

2. Let's talk about the VDP

In today’s blog we will discuss the use of the Visual Descent Point (VDP) during a classic, dive-and-drive, non-precision approach.

According to regulations a Visual Descent Point can be defined as a defined point on the final approach course of a non-precision straight-in approach procedure from which a normal descent from the MDA to the runway touchdown point may be commenced provided visual reference is established.

Source: Aeronautical Information Manual (AIM)

3. The purpose of VDP during step-down approaches

A Non-Precision Approach is also known as a step-down approach.

Source: Jeppesen

Between the Initial Approach Fix (IAF) and the Minimum Descend Altitude/height (MDA/H), several intermediate points can be found which need to be crossed prior to continuing the descend down to the minima. 

This requires a technique whereby the pilot will continuously re-adjust power to facilitate the level-offs and subsequent descends. More commonly, this procedure is known as a ‘Dive-and-Drive’ technique.

Upon reaching the MDA/H, a final level-off takes place and the pilot continues towards the Missed Approach Point (Mapt). If adequate visual references can be established, a descend towards the runway will be made. Lack of these visual references will result, at the latest at the Mapt, in a go-around! 

However, there is a pitfall! Even though an aircraft acquires visual references at or prior to the Mapt, a stabilised descend at a (comfortable) 3 degree angle towards the runway threshold, might have become impossible. After all, the closer to the Mapt, the steeper the angle of descend required! This would force a high-speed aircraft into maintaining a (very) high rate of descend. 

To resolve this issue, commercial pilots will calculate the latest point on the approach from which a stabilised descend at a 3 degree slope can be made. This point is known as the Visual Descent Point or VDP.  If a pilot has not established visual contact upon reaching the VDP, a go-around might be initiated despite the fact that the Mapt has not yet been reached.

4. Let's calculate our VDP

Some chart providers will include Visual Descend Points on their approach plates. If you are using Jeppesen, the VDP is indicated by a letter “V”, printed in bold on the approach plate.

Source: Jeppesen

If the VDP is not indicated on your plate, it is possible to calculate the approximate position of this reference point by an easy rule-of-thumb.

  • Divide the Minimum Descend Height (MDH) by 300 and you’ll find the distance of the VDP from the runway threshold (nautical miles). 
  • Furthermore, by multiplying the Minimum Descend Altitude (MDA) by 6, you can calculate  the required visibility (in meters) which would allow for positive identification of the runway threshold at the VDP.

5. Step-Down versus Continuous Descent Final Approaches (CDFA)

Nowadays most of these classic step-down approaches are flown as Continuous Descent Final Approaches. From the Final Approach Fix (FAF) onwards, a continuous descend towards the minima is performed. 

The minima of these types of approaches are commonly referred to as ‘Decision Altitudes’ (DA) and the descend profile is optimised in such a way that the MDH will coincide with the Visual Descend Point. 

The benefits associated with CDFAs are numerous: 

  • Increase in safety. 
  • Increase in situational awareness and a reduction in pilot workload.
  • Optimisation of  fuel efficiency. 
  • Reduction of noise pollution. 
  • Streamlining the way precision approaches ,approaches with vertical guidance and non-precision approaches are flown. 

As always, please share your comments and experience about this topic in the section below!

We'd love to hear from you!

Thomas Peeters
Thomas was the former Deputy Head of Training at EuroPilot Center and full time Flight Instructor. He loves the privilege of sharing knowledge, training young pilots and helping them achieving their goals. Amazing flight-deck views, soaring through blue skies, the elements of freedom and adventure all lead up to completing his childhood dream of becoming a professional pilot.
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