VDP on An IA
Should You Go Missed If You Fly Past The VDP On An Instrument Approach?
By Swayne Martin|
Live from the Flight Deck
You've passed the VDP on an instrument approach, and you start to see the runway, but you're high. What should you do?
Visual Descent Point (VDP), Defined According to the AIM, "the VDP is a defined 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, and if your approach has one, you shouldn't descend below MDA prior to reaching the VDP.
When you reach VDP, you'll typically be able to follow a 3-degree glide path to the runway, which is the same glide path as most precision approaches.
So how do you know if your approach has a VDP? It's denoted by a bold V, like the image below.
What To Do If A VDP Isn't Published
When instrument procedure designers survey land during the creation of an approach, they'll analyze what obstructions penetrate safety clearance tolerances. If obstructions are present, a VDP might be denied during the creation of the instrument approach. This is why you won't find a "V" published on every non-precision approach, like the image below.
If that's the case, you can use a rule-of-thumb to find the approximate distance where you would start a descent from MDA to the runway: Take the AGL value of the MDA and divide it by 300.
For example, on the Crookston (KCKN) VOR/DME Approach to Runway 13, the lowest MDA takes you to 344 feet above the TDZE. Divide this by 300, and you'll get 1.15, which is the approximate distance from the runway where you can start a 3-degree descent to the runway.
Remember that the resulting value is NOT DME. It is the VDP's distance from the runway. You'll need to add or subtract this from DME readings to properly locate your descent point.
And there's another thing to keep in mind. In many cases, the VDP wasn't published because of terrain or obstacles. Before you start your descent down from MDA to the runway, be sure you have enough visibility not only see the runway, but also see any obstructions that might be in your path (more on this in a bit).
What Is "Continuous Position To Land"?
VDP does not define a point necessary for a "continuous position to land" under FAR 91.175. A variety of descent angles can provide you with a stabilized approach, which is important for a safe descent below MDA.
You Just Flew Past VDP. Now What?
If you flew past VDP because the required items for descent weren't met, but you're not to the missed approach point yet, you're faced with a decision: Should you plan to go missed? Should you continue to the MAP?
The closer you get to the missed approach point at MDA, the higher the descent angle you need to get to the runway. However, if you see the runway environment past VDP, you may still be able to make a safe descent to landing.
Whether you can safely make a steeper than normal descent comes down to what kind of airplane you're flying, your configuration, and the speed you fly the final approach segment at.
In something like a light, single-engine piston, you'll have a lot more leeway than a jet. The faster you fly, the faster descent rate you'll need to make the same descent angle work. Because of this, many pilots plan to go missed if the runway environment isn't in-sight by the VDP.
No matter what you fly, you don't want to put yourself in a situation where you need a rapid descent to make the runway. If you're not used to flying steep, high descent-rate approaches in clear weather, attempting one when you're shooting an approach in poor visibility isn't a great idea.
That said, the VDP isn't a required decision point (the required decision point is the missed approach point). The VDP is a great way to fly a stabilized approach from MDA to the runway, but it's not a legal requirement for going missed.
No hay comentarios:
Publicar un comentario
Espero atento tus comentarios