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2 Answers

Missed procedure below MDA/DA/DH

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FAA Regulations, Instrument Rating

Let's say you continue below the DA/DH on an IAP because you have the APL insight; and of course no lower then 100 ft above TDZE.

Now you arrive and don't see any required visual cues to continue to land.

  1. When would you decide to go missed on an ILS? since you already descended below your DA? 
  2. If you were to execute a missed procedure below the DA/DH on the same scenario above are you assured obstacle clearance? (my thoughts are no, obstacle clearance is only assured if its executed at the MAP, at or above MDA or DA/DH with a 200ft/nm climb)

2 Answers



  1. John D Collins on Jul 21, 2018

    It is not prudent to put yourself in a box that does not have options. So before you descend below the DA/MDA using only the approach lights, you should review the missed approach procedure and determine that your actual climb performance will put you quickly above the 200 feet per NM slope. As you point out the 200 feet/NM climb gradient begins at the DA on a vertically guided procedure or the MDA beginnning at the MAP. There are too many possible situations to cover all of them, but generally if the reported surface visibility is at or above minimums, at 100 feet you should be only 0.35 mile from the threshold if you are following a 3 degree GS, so it should be in sight. One exception might be a ground fog layer that you descend into. If this is the case, a brief climb is likely to put you in visual conditions where you can visually avoid obstacles.

    These kinds of scenarios occur also while circling or when the approach ends at a MAP where you proceed visually to the runway if you have the required visibility.

    So to answer your questions,

    1. Immediately.

    2. No you are not assured obstacle separation on the missed approach procedure until you have climbed back to an altitude above the 200 ft/NM slope on the missed approach path and from that point continue to climb at or greater than the 200 ft/NM or other non standard gradient for the procedure. The airlines have to deal with this kind of issue when they lose an engine on takeoff or go around and have lost an engine. They need to work out an alternate path that matches the worst case scenario or they can’t operate into that airport.

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  2. KDS on Jul 21, 2018

    The other situation that happens with regularity in simulators is that just before you arrive at the threshold an airport vehicle or a wide body jet pulls onto the runway. It’s so frequent that when you see flashing lights at the hold line you can count on it happening. Fortunately, real life is less problem plagued than simulator life although the problems can have much grimmer consequences.

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