For most pilots, the most difficult part of flying is executing a safe landing. To help you, there are several tools you can use, the Visual Descent Point, or VDP, is one of them. But what exactly is it, and how can you use it?
Table of Contents
- Why Is It Important to Know About the Visual Descent Point?
- Why Is the Visual Descent Point Not Published?
- What Happens if I Miss a VDP?
- Is the VDP Mandatory?
- Is It Possible to Go Below the Minimum Descent Altitude Before Getting to the Visual Descent Point?
- What Are the Criteria for Descending Below the Minimum Descent Altitude?
- Does a VDP Guarantee Obstacle Clearance?
- What Is the Difference Between a Precision Approach and a Non-Precision Approach?
- What Approaches Have a Visual Descent Point?
The Visual Descent Point (VDP) is a point that tells the pilot when to descend below the Minimum Descent Altitude (MDA), even if they can’t see the runway. It is typically displayed on the profile view section of the approach chart with a “V”.
Brought about to improve pilot safety, the VDP is designed to prevent a pilot by descending too quickly and hitting an obstacle of some kind by remaining at the MDA until they have acquired one of the approved visual references.
Why Is It Important to Know About the Visual Descent Point?
A visual descent point is an important tool in aviation and it is something every pilot needs to know about. It is a point on the approach chart where the pilot begins their final descent towards the runway. It enables the pilot to know when to start descending instead of using the usual “dive and drive” concept.
According to the FAA and the National Transportation Safety Board (NTSB), most accidents while making a non-precision approach are linked to an unstabilized landing process. This is why every pilot should know how to use the VDP.
It is also calculated based on the aircraft’s rate of descent and it is indicated on the chart so that pilots can easily find it.
Why Is the Visual Descent Point Not Published?
Knowing how to calculate the visual descent point is also an important factor to consider while flying because sometimes it is not called out on the approach chart and pilots will have to calculate it themselves.
Use the equation below to find the visual descent point if it is not published on the chart.
- What we are trying to identify with the visual descent point is where the pilot will leave the MDA to be able to have a stabilized gliding of three degrees.
- Visual descent point (VDP) = height above touchdown (HAT)300 feet
- If the HAT is 562, divide it by 300, and you will get 1.88NM. This means that while descending from the final approach fix, you will get a three-degree glideslope to the runway when you get to 1.88NM.
- Keep in mind that the above equation is a “rule of thumb.” This means that it is not based on the exact calculations. The accurate calculation is HAT divided by 318, but we use 300 because it is easier to understand.
It is important to know that if the VDP is not published, it is because there are obstacles like terrain that could interfere with a safe descent.
In this situation, calculate your visual descent point, but make sure you have enough visibility to see any potential risks before you begin your descent from the MDA.
If there are obstacles, the chart will display “visual segment obstacles,” indicating that you may need to change your approach to avoid risks.
What Happens if I Miss a VDP?
You can continue to fly when you miss the VDP at the minimum descent altitude till you get to the missed approach point.
But if you still lack visibility, or you are unable to pick up at least one of the visual reference points and begin your final descent by the time you reach the missed approach point, then you must turn around and execute a missed approach procedure.
Never start your descent from the minimum descent altitude (MDA) and go beyond the missed approach point (MAP) because it is prohibited and your touchdown point will be shifted too far down the runway for safety.
Keep in mind that some pilots like to use the visual descent point as a missed approach point. By deciding to call a missed approach if they do not have enough visibility or they are out of position, pilots give themselves enough time to abort the landing attempt before crossing the missed approach point.
Finally, it is up to the pilot to call a missed approach at the visual descent point or the MAP. If they are unable to descend at the visual descent point because they initially failed to meet the necessary criteria, but conditions changed and they met the criteria before arriving at the MAP, it is within the pilot’s decision to continue landing.
Given that any aircraft starting a descent before the visual descent point will not meet up to the standard three-degree glideslope, pilots must consider the type of airplane they use, its configuration, speed, descent rate, and runaway length before making a choice.
Is the VDP Mandatory?
The visual descent point is not a legal requirement; however, it is a good way to fly a stabilized approach from the MDA to the runway.
There are three options for you when you get to the visual descent point and they include:
- Ignore it: The visual descent point is not the missed approach point and there is no rule that you do anything at the VPD. So, you have the option to keep moving until you reach the MAP.
- Start descending: The visual descent point does not permit you to go below the minimum descent altitude before you can see the runway. It is not legal to disregard the rules that guide you before descending below the MDA.
However, it is a suitable point to start your final descent to the runway if you’ve gotten through the clouds and you have enough visibility to see the runway.
- Go missed: Although pilots are trained to continue an approach to the missed approach point, no rule says they can’t break it off early. It is possible that doing this might be the safest course of action.
If you think of the visual descent point as the primary missed approach point and not as a point from which a descent can begin, then you will not have the problem of choosing between diving or not diving for the runway at the last moment.
Is It Possible to Go Below the Minimum Descent Altitude Before Getting to the Visual Descent Point?
The question of whether you should wait until you get to the visual descent point before descending below the MDA has sparked much controversy among pilots. Or if it is only a guideline that pilots can ignore whenever they want.
According to the rules from the Code of Federal Regulations (CFR), pilots are only allowed to descend when they’ve met the necessary conditions for descent below the minimum descent altitude. It does not state anything about how that relates to the visual descent point.
However, while describing how to descend in a recent publication, the FAA states that you should not descend below the MDA before reaching the visual descent point.
What Are the Criteria for Descending Below the Minimum Descent Altitude?
You must meet the following conditions before you are eligible to descend below the minimum descent altitude.
- Must have the necessary visibility to descend safely
- Aircraft must be in a continuous position to make a normal descent and land on the intended runway
- Must have the runway environment insight
You can start your descent when you reach the visual descent point if you meet all the above criteria. But if you did not, you must drop below the MDA until you meet all the criteria.
If you did not meet up to the criteria by the time you reach the visual descent point, it is referred to as missing or flying past the VDP.
Does a VDP Guarantee Obstacle Clearance?
Any approach with a visual descent point ensures a pilot’s safety from obstacles below the MDA to the runway threshold. While anyone without a visual descent point gives no assurance of the pilot’s safety from obstacles once they descend below the MDA.
What Is the Difference Between a Precision Approach and a Non-Precision Approach?
A precision approach uses a ground station and they send information about your position and your final approach. The benefit of flying a precision approach is that you have instant information about your position during the last part of the descent.
This is crucial because you get close to the ground and terrain in the last part of your final descent, so it helps maintain a stabilized landing procedure.
A non-precision approach on the other hand doesn’t have all the information that helps the pilot. What happens in a non-precision approach is that the pilot has close information.
For example, they might have a localizer that tells them if they are moving to the left or the right but they do not receive any information on their final approach.
The main challenge of flying a non-precision approach is that because you get so busy on the final stage of your flight, where you have to configure the plane, make sure you put the terrain and weather into account, you might get overloaded with work and this can lead to a major crash.
It is more challenging to descend while using a non-precision approach compared to a precision approach where you have all the information you need.
What Approaches Have a Visual Descent Point?
A visual descent point is a point on a straight-in, non-precision approach. It does not provide more value to other approaches because they have enough information that tells the pilot how to proceed at any time.