Instrument Tip: Going visual

It seems that for forever, the advice was to chop the power at the final approach fix and dive for the minimum descent altitude, with the goal of seeing the runway as early as possible, and then starting a descent.

The visual descent point (VDP) is a tool to stop the madness and bring some stability to nonprecision approaches. Missed approach points are often near the end of the runway. This gives you the latitude to drop down to the minimum descent altitude and then drone along until the bitter end. If you don’t see the runway, the decision to start the missed approach is easy. But what if you do see the runway? Now you have to decide if you want to dive down in order to make it. In a slow, draggy airplane, this might not be a problem. But as you step up to bigger and faster airplanes, it’s easy to see how you could skid off the end of the runway in such a scenario.

The VDP is a marker on the approach from which a normal descent and landing can be made, and in certain applications takes away the needs for such a hasty last-minute decision. It generally reflects the intersection of a 3-degree glideslope with the missed approach altitude.

When you arrive at the VDP you have three options:

1. Ignore it. The VDP isn’t the missed approach point. There’s no requirement that you do anything at the VDP, so you have the option to keep buzzing along until you reach the MAP.
2. Start a descent. The VDP does not give you a clearance to descend below the minimum descent altitude before seeing the runway. It’s not a license to ignore the requirements of FAR 91.175 (the conditions by which you’re allowed to descend below the minimum descent altitude). But, if you’ve already broken out of the clouds and the visibility is good enough that you can see the runway, the VDP is a good point from which to begin the final descent to the runway. Even though it isn’t regulatory, it’s also good to think of the VDP as the absolute initial point of the final descent. As the Aeronautical Information Manual says, “The pilot should not descend below the MDA prior to reaching the VDP.”
3. Go missed. Although we’re trained to continue an approach to the missed approach point, there’s nothing that says we can’t break it off early. Doing so could be the safest course of action. If you think of the VDP not as a point from which a decent can begin, but instead as the primary missed approach point, you’ll never be faced with the choice of whether or not to dive for the runway at the last moment. Rather, when you don’t see the runway at the VDP, begin the missed approach, knowing that you can’t make a normal stabilized approach beyond that point.

Not every nonprecision approach has a VDP. If an obstruction rises into the visual segment of the approach, a VDP won’t be published, for example. In these cases you can mentally create your own VDP by taking the difference between the minimum descent altitude and the touchdown zone elevation and dividing by 300. This will give you a general point at which to begin the descent or go missed, but remember that the absence of the VDP may mean there’s an obstruction to avoid. Also keep in mind that for this calculation you are looking for distance from the end of the runway, not the GPS center point or DME of the airport. Usually these are in the middle of the airport. You may need to subtract this distance from your VDP to make sure you end up with a stabilized approach to the runway and not a phantom marker in the middle of the airport.

With the VDP there’s no longer a reason to dive for the runway at the missed approach point. Especially in instrument conditions, stability is the goal, and a VDP offers just that.

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