Welcome Guest. Sign in or Signup

1 Answers

Localizer Approach and Timing to MAP Safety Concern

Asked by: 2430 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? 

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

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.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.