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Localizer Approach and Timing to MAP Safety Concern

Asked by: 921 views Instrument Rating

Unless you are equipped with fancy avionics, you're probably not able to determine the exact GS that you are descending at on a LOC approach. Assume two scenarios for a LOC approach with only a time-based MAP: you reach your calculated MAP earlier than the actual MAP or you reach your calculated MAP after the actual MAP. The first scenario seems dangerous since you will execute the missed prior to the runway threshold/actual MAP; the second, not as much as long as it's not a significant difference that will put you outside of obstacle clearance range. In the second scenario, tower can advise you that you flew past the runway threshold, but in the former, it may be too late for ATC to correct you. Obviously, the FAA established this estimating method knowing that it will be an approximation (right?), but is the consequence of a MAP miscalculation a valid safety concern? 

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1 Answers



  1. John D Collins on Jun 18, 2016

    When time is the only means of determining the location of the MAP, you are expected to begin the miss when the time expires. The TERPS designers have taken into account normal errors introduced by GS errors. You are not expected to make any turns until you have reached the MAP as determined by time.

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