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VDP and MAP. Where MA decision should be made?

Asked by: 706 views FAA Regulations, Instrument Rating

Hello, instructors. I've got a question. When we have both a VDP and a MAP in a NPA chart, at which point between the two are we supposed to "decide" (not execute) our missed approach? I know we're expected to start our missed approach at the MAP, but I'm curious whether we're expected to make a decision to go missed or not when we're over the VDP, because after all the VDP is the point where "a descent to a landing on the intended runway can be made at a normal rate of descent using normal maneuvers (91.175)" and as such it would be against this regulation if we start our descent after the VDP.

Is my logic correct here? Or since the VDP is only advisory, and I'm the PIC, I can decide to land even though I'm aware I passed the VDP. Thank you.

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2 Answers

  1. Russ Roslewski on Jan 18, 2017

    The VDP does indeed indicate a place where a normal descent to landing can be made. It does not, however, indicate the ONLY point where a normal descent to landing can be made.

    A VDP is placed where the MDA intersects the designed glidepath of the procedure. Generally this is right around 3 degrees. This is actually pretty low for most small GA airplanes. I assume you are in training and using an airplane such as a Cessna 172 (but it doesn’t really matter).

    Think about a VFR pattern. You roll out on final at maybe 500 feet AGL, and are likely within a mile of the runway on final. That right there is about a 5 degree glidepath or steeper, and we do it every day. That’s a normal maneuver.

    So there is no problem delaying your descent until after the VDP. The VDP is merely a good guideline to say “if you reach this point and have the runway in sight, there will be no problem making the descent.” Waiting until after it won’t necessarily be unsafe either.

    Obviously the further you go past the VDP before seeing the runway and starting your descent, the steeper the descent becomes, until such point as you could no longer safely make it down to the runway. But that is up to you to decide.

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  2. John D Collins on Jan 18, 2017

    The VDP is mostly informational. One should not start their descent from the MDA after the runway is in sight until reaching the VDP. On some aircraft, they may not be able to safely make a descent to the runway using a normal descent, but that may not apply to other aircraft. My normal descent in VFR conditions in my Bonanza is closer to 6 degrees than to 3 degrees, so I have no difficulty descending using a normal descent well after the VDP. It can depend on the runway length, I need 1500 feet of available runway, so if the runway is 11,000 feet long, i can safely use the last third of the runway. Also, the approach is likely to have a circling option, many of which have the same MDA, in which case, I can spot the runway late and still circle to land, even on the straight in runway by going all the way around the pattern.

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