Aviation: Instrument training, Visual Descent Point?

Question

Hello Im an Instrument Student and I have a question. Why not all the Approach plates have a Visual Descent Point (VDP)? Im doing training in Opa Locka, FL and I was looking at the app plates and RWY 9L GPS approach has a Visual Descent Point (1.1NM) but GPS RWY 27R doesnt have one... why is that? Is there a way to determine it without having to look at it on the app plates?

thanks, jose.

Answer 1

A visual descent point is published for runways where the Missed Approach Point on a non-precision approach would put you in a position where you cannot make a normal 3-degree descent to the touchdown zone. The VDP is always located before the MAP and is a tip-off that you may need to execute a missed approach if you cannot see the runway or its environment when you get there. In fact, this is the policy of most, if not all airlines because if you try to make a landing from the MAP in a large or fast aircraft you would land long and possibly overshoot the runway unless it is an unusually long one. You can often get away with flying the approach all the way to the MAP in a smaller or slower aircraft and still make a safe landing, but it is not considered a safe or wise thing to do in an aircraft that is faster or heavier. Note that quite often the MAP is often over or close to the end of the runway, which is not the best place to be 300-500 feet high in anything other than an aircraft like a single engine Piper or Cessna.

FAA's official definition of VDP:

"A defined point on the final approach course of a nonprecision straight-in approach procedure from which normal descent from the MDA to the runway touchdown point may be commenced, provided the approach threshold of that runway, or approach lights, or other markings identifiable with the approach end of that runway are clearly visible to the pilot."

The operative phrase here is "normal descent to the runway touchdown point", which implies the standard 3 degree flight path to the touchdown zone painted on the runway. If you stray too far from that descent angle or touch down a long way past the touchdown zone on a short runway, it could be construed as careless or reckless operation for which you might get invited to an interview with the Feds.

Answer 2

HAA/10 gives the remaining time in seconds if you are timing the approach.  (E.g. if the HAA is 470 ft., subtract 47 seconds from the time you are expecting to fly from the final approach fix to the threshold).  

That works ok if the missed approach point is at the landing threshold.  It doesn't always work as well when the MAP is very far from the threshold.

It also assumes a groundspeed of 113 kts.  

If your groundspeed is much different from 113 kts, then adjust the time proportionately.

Or you can calculate where the VDP would be based on the gradient of a 3º slope;  that gradient is about 318 ft per nautical mile.  Just divide the HAA by 318.

Answer 3

It used to be that no approaches had VDP's.  Now some do, but I don't know how they decide which ones to include one on.  The easy way to figure one out is to divide the height above touchdown by 300 for distance, or take ten percent of the HAT for time.  That gives you the distance in miles, or time in minutes, depending on how you are determining the missed approach point.