![]() It too, mounts in the nose radome, but is less than half the width of the N9 Series. In this case, the N1 antenna satisfies this need perfectly. Some users prefer this concept but require glide slope. In addition to excellent localizer and glide slope patterns, many users utilize the localizer output for forward-looking VOR as well. The N9 Series is a balanced bent-back dipole antenna, which renders it immune from the nose radar motion. When dual receiver installations are used, appropriate couplers are available for dual localizer and dual glide slope receiver operation. Simultaneous localizer and glide slope signals will be provided for single receiver installations. The N9 Series has been designed to conform to radome curvatures providing minimum installation area and access for radar installations. In some cases, reinforcing ribs provide structural rigidity and mounting adaptability to the bulkhead for mechanical attachment and electrical grounding to the airframe. The antenna is designed with the radiating elements attached to a single curved dielectric window to provide support. After getting on course, a deviation out to the first dot means it's time to go missed.The design incorporates common radiating elements into a single monolithic structure for mounting on a bulkhead within a radome or to the radome directly. Getting the needle inside the outside dot means you've captured the signal. For example, RVR 300 takeoff operations may continue if a glideslope or Approach Lighting System (ALS) outage restricts ILS approach and landing operations and if the following requirements are met: (a) The localizer meets class III/E/4 requirements, and air traffic control (ATC) protects the localizer critical area to support CAT III operations. The 2 dot display puts a dot at that point and at full scale. My suspicion is that flight standards (and airline op specs) typically call for a missed approach if the deviation exceeds half scale. In over 20 years of working in avionics, I've never found anyone who could say definitively why 2 dot displays became standard. And to be even more confusing, many of the new RNP deviation displays don't have any dots, just a bar with a center and end marks with the steering line on top. But the GA aircraft I learned to fly in all had 4 dots on the CDI at full scale. I would agree this is common on air transport aircraft. You identified a generic convention of 2 dots at full scale. The requirement is that the pilot can discern the center, the limits, and that the indication is linear within a few percent. And after installation they have to be tested to show they work together within the spec.īut what about the dots? The MOPS don't specify what the display looks like. The display - even if it's part of a glass PFD - has to meet the MOPS. In this case (which is common today), the radio is tested to comply at the "output to the display" and must have an interface spec to allow a display to be interfaced. Even if the display isn't part of the ILS receiver it's bound by the MOPS. The MOPS has a standard for display of deviation in terms of centering accuracy (0.0 DDM) and linearity of the display out to "full-scale". There are minimum and maximum angular widths, so very short runways (<~3000 ft) will all have the same maximum width and very long runways will have the minimum width.īack to the ILS MOPS (DO-192 and DO-195). ![]() This standard means that shorter runways will have a wider LOC beam than a longer runway. With the LOC antenna at the other end of the runway, this sets the angular deviation guidance for the approach. The significance of 0.175 DDM is it defines the value at the limits of the course deviation display (full scale).Īnnex 10 requires the installation of an ILS requires (for most runways) the radiation pattern of the localizer to place full scale at the threshold of the runway at +/- 350 feet. It's also in DO-195 for localizer.īut what is 0.175 DDM and why is it referenced as "full-scale"? DDM is the Difference in Depth of Modulation of the 90 and 150 Hz audio tones that comprise the LOC and GS signals. ![]() There are various standards that come into play and I'll try to explain how they fit together.Īs you noted +/- 0.175 DDM is specified as "full-scale deflection." This is in Annex 10 and, as mins noted, DO-192 for glideslope. The problem you're having is that there is no standard definition of dots. ![]()
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