ILS missed app point vs LOC missed app point

3 Answers

1. 
   

   
   

   John D Collins on Oct 01, 2015

   When you are flying a vertically guided approach such as an ILS with a GS, your aircraft is moving both forward and continuously descending at the same time on the GS. When you reach the Decision Altitude (DA), you are close to the ground, maybe only 200 feet above the threshold and roughly 2/3 of a mile away from it. The point that the GS crosses the DA is where you must make the decision to continue or to initiate the missed approach. Momentum of the aircraft is going to continue to carry the aircraft towards the ground, and you must immediately initiate the missed approach climb. Even so, you will still sink some distance beyond the DA location and the design of the ILS and obstacle protection allows for this. However, it does not allow for dilly dally, so if you don’t want to plant the airplane in the ground you need to add power, pitch, obtain a positive rate of climb, raise the gear, and follow the missed approach procedure.

   When you are flying the localizer version of the same procedure, you don’t have a means of determining the missed approach point that is defined by the GS and altitude. So another means, a missed approach point (FAF), is used to determine its location. It can be a DME distance or a time as measured from a known point at the FAF. With a localizer approach, the aircraft is expected to level at or above the Minimum Descent Altitude (MDA) and fly at this altitude until the pilot decides to miss the approach. The pull up for a non precision approach with an MDA starts from level flight and there are no equivalent provisions for a sink thru as there is with a DA. Also, the MDA is typically at a higher altitude than the DA. The pilot can decide to miss the approach before reaching the MAP or can wait until reaching the MAP. Regardless where the pilot begins the climb, they may not make any turns until past the MAP, because the obstacle protection for the turns only exists after this point. So even though the aircraft may be established at the MDA well prior to the MAP, they must continue to the MAP before following any of the lateral portion of the procedure. Note also that the purpose of the MAP is to define where the missed approach procedure begins, and is not the last point on the approach segment from which a straight in landing can be effected. To land straight in, one must typically spot the runway well before the MAP if a safe landing is to be conducted. The MAP might be the last point before a circle to land, but even in this case, one typically has to spot the airport before reaching the MAP.

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   Kris Kortokrax on Oct 01, 2015

   There is no difference. The missed approach segment of the approach is begun at the MAP.

   Arrival at the DH/DA on a precision approach is the MAP.

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3. 
   

   
   

   Mark Kolber on Oct 01, 2015

   I agree with Kris’ short answer. And John’s longer explanation ultimately say the same thing.

   In both cases you initiate the missed at the MAP, the only difference being that, on an ILS, DA =is= the MAP for that approach, just like on an ILS, glideslope intercept is the FAF for that type of approach.

   It’s not any more complicated than that.

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