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.
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.”
A Non-Precision Approach is also known as a step-down approach.
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.
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.
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.
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:
As always, please share your comments and experience about this topic in the section below!
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