Definition about “establish localizer”..

7 Answers

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   John D Collins on Apr 29, 2015

   There isn’t a formal definition of established on the localizer course, but the IFR Practical Test Standard uses a criteria of +/- 3/4 scale. Most instructors use +/- 1/2 scale and I have seen this is in unpublished guidance that has been proposed for inclusion in the AIM. From a technical point of view, anything other than full scale deflection provides the pilot with positive course guidance, but I would recommend using half scale.

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   Russ Roslewski on Apr 29, 2015

   What I teach for any time you need to consider yourself “established” on a course (such as descending from a procedure turn, intercepting an ILS, turning onto a GPS final approach course, etc.) is that you are “established” when two conditions are met:

   1. You are within 1/2 scale deflection.
   2. Your heading (or ground track if available) is basically along the final approach course.

   #2 is important. If you’re intercepting a course at 45 degrees (like a procedure turn), just getting in to half scale deflection isn’t enough – you’re still pointing 45 degrees off the course and haven’t actually intercepted it yet. You could easily be through the course quickly if you get distracted.

   But once you turn the airplane so that it’s following the final approach course and are just trying to bracket the course, then you know that you’re “safe” and can descend to the next altitude.

   As John says, this isn’t published anywhere and there is no formal definition. But this is what I use, and what I teach, and I think it is the safest reasonable definition. (If you had to have the needle exactly in the center, now how precisely would you define “center”?)

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   Mark Kolber on Apr 30, 2015

   What “established” means is one of those great debates. From the Pilot/Controller glossary, we can see it simply means “To be stable or fixed on a route, route segment, altitude, heading, etc.” In other words, simple, plain English (which is IMO why it gets debated so much! How dare the FAA use English! :D).

   Even the PTS isn’t really helpful. Yes, the Instrument PTS requires maintaining less than 3/4 scale deflection but that doesn’t tell us anything about what it means to become established to begin with. Besides, the ATP PTS standard for the same maneuver is 1/4 scale deflection, so it’s a testing standard, not a definition.

   The only official metrics are the one in the ICAO Document 8168 “Procedures for Air Navigation” and out AIM. The ICAO procedures document lists half deflection for an ILS and VOR and withing 5° of the required bearing for an NDB. The AIM talks about being established on course for RNAV – “within 1 times the required accuracy for the segment being flown.”

   Bottom line is that, in the US, it’s English but a good guideline is the one John mentioned when the needle deflection is 1/2 scale or less and your heading is aligned with the desired course (remember – the needle will be absolutely centered at come point as you cross a course by 90 degrees – that’s hardly “established” by anyone’s definition).

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   Kris Kortokrax on May 01, 2015

   The question addressed ILS/LOC approaches.

   A typical clearance might contain language like “Maintain 5000 till established”.

   The question at hand appears to be “What would be the consequences of descending before the needle is centered?”

   There would probably be no legal consequences as I doubt that the controller is sitting at his scope waiting to detect that we have left 5000 feet before being exactly on the centerline of the localizer on his scope.

   That leaves terrain/obstacle clearance as the big consideration. I’m sure John can weigh in on what obstacle clearance is guaranteed in the design of an approach. I’m guessing that we have adequate margins for the entire course width since we are not necessarily able to exactly maintain the centerline for the duration of the approach.

   I did a little simple math. The course width on the localizer is from 3 to 6 degrees, depending on the length of the runway. That means that from full deflection to centerline is 1.5 to 3 degrees. At ten miles from the antenna (which should put us comfortably outside most final approach fixes), the distance from centerline to full scale deflection would be 1518′ – 3036′. At a 90 knot approach speed, we cover 152 feet per second. Using a more realistic 30 degree intercept, we would converge on the centerline at a rate of 76 feet per second (sin 30 * 152). That means it takes only 19-39 seconds to cover the distance from full scale deflection to the centerline.

   I have always considered myself established if the needle is no longer fully deflected (needle movement). Never had a controller chide me for descending too soon. Never hit any obstructions.

   Now consider, we do regular VOR checks. This only checks the VOR. It does not check accuracy of the localizer. How do we know we are on the centerline with a centered LOC indication? When was the last time anybody had their radio bench checked to make sure the localizer and glideslop indications were accurate?

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   Tyler Herbst on May 04, 2015

   At UND we are taught that as soon as we see the CDI begin to move in we can report established and or descend lower if need be.

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   Mark Kolber on May 05, 2015

   Tyler, I sure hope UND also requires your heading also be aligned somewhat with the course!

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7. 
   

   
   

   mccluredave1 on Mar 04, 2019

   I also looked in AIM etc. Nothing:
   ATC “maintain 5000 until established”
   Perhaps knowing what to avoid might be a reasonable approach also. So… you identify and listen to I-xxx. Obviously, what you don’t want to do is descend before the localizer CDI needle is moving, just because you hear morse code, or in an effort to “stay ahead” of aircraft, you “think” you saw needle move.
   Confirmation of CDI movement while cross-checking and not fixating is key. First look, yeah I think it’s moving, needle over outermost dot, second look, needle over 2nd or 3rd from outermost = confirmation = 3/4 – 1/2 deflection start descending.

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