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Thread: Navaids

  1. #1

    Default Navaids

    I am steadily working my way through the learning curve and can occasionally land on or near the runway and sometimes the right way up - however.
    737 NG.
    I am trying to understand tuning the localiser, glide slope and beacons.
    I am flying short hops between EGGD and EGFF generally at half light and it is possible to see each airport from the other following take-off.
    When I set the nav radios, I understand the ILS frequency but how do I set the localiser frequency? I have discovered there is not a set relationship between the two frequencies. The glide slope frequency offered in the FMC works effectively and the localiser also (not that I can land using them solely!).
    Then there are the beacons. Where do or can I set the VOR frequencies?

  2. #2
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    Default Navaids

    When you tune the appropriate ILS frequency, you will be tuned to both the localizer ( indicating you're on the correct path to get you to the runway) and the glideslope. This ensures your vertical navigation i.e., when you "capture" the glideslope, your plane will follow the signal down to the runway. Typically, you, the pilot, will take over at the last few seconds.

    For *both* the localizer and the glideslope, the "capture" point must not be too shar of an angle. If you're way off to the left or right when you try to acquire the localizer you have a better chance to miss it altogether.

    On the glideslope, you'll typically need to be somewhere around 1,500 feet AGL or you'll miss the capture.

    If I were you, I'd look for YouTube videos that show your airplane capturing both the localizer and the glideslope. Once you've seen it a few times, it becomes pretty much old hat.

    Good luck.

    Art Burke - N4PJ
    Leesburg, FL

  3. #3

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    Thanks for the response.
    I know how to use the GS and the LOC. What intrigued me is that there are two frequencies involved, one for each.

    Taken from Wiki;
    "Two signals are transmitted on one of 40 ILS channels. One is modulated at 90 Hz, the other at 150 Hz. These are transmitted from co-located antennas. Each antenna transmits a narrow beam.

    Localizer (LOC) and glide slope (G/S) carrier frequencies are paired so that the navigation radio automatically tunes the G/S frequency which corresponds to the selected LOC frequency. The LOC signal is in the 110 MHz range while the G/S signal is in the 330 MHz range.[2]
    LOC carrier frequencies range between 108.10 MHz and 111.95 MHz (with the 100 kHz first decimal digit always odd, so 108.10, 108.15, 108.30, etc., are LOC frequencies and are not used for any other purpose)."

    I set the LOC frequency (either manually on the centre console or in the FMC) but I didn't understand how to set the GS frequency. If there was a direct mathematical relationship between the two, I could understand how the GS signal could be set from the LOC frequency but there isn't. It would be interesting to know where the second frequency is derived from. (I know it doesn't matter but I like to understand.)

    I am still trying to land completely manually using the PAPI and am improving (Honestly - to self).

  4. #4
    Join Date
    Feb 2016
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    Leesburg, FL
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    Default Navaids

    I think maybe you're trying to read a bit too much in this! You don't have to tune a separate frequency
    to get both the localizer and the glideslope. As you fly more and more, you'll discover many, many
    situations where there is no glideslope - just the localizer. The localizer lines you up for the runway,
    and the PAPI (or equivalent) help you figure out the slope - TWO WHITE YOU'RE TOO HIGH. TWO RED, YOU'RE DEAD.

    As a side point: when you tune a VOR, it's somewhat like tuning an ILS - it's pretty specialized.
    The ILS gets you both components (if they're both there) without you having to worry about the
    technicality of how they're tuned. On the "standard" VOR, it's kind of a rotating signal - each radial is
    "broadcast" on an offset so you, the pilot, can tell one radial from another. But you don't have to
    worry about all the specialized frequency and such - tuning the navaid for a specific radial happens
    more or less automatically as you're tuning the NAV frequency.

    For your ILS practice, set up a scenario - i.e., the plane at such-and-such an altitude, such-and-such a
    speed and a specific distance from the runway threshold - preferably a mile or two minimum, but not
    too far away. Keep practicing that same scenario, but fly the plane a little too far left, then maybe a
    little too far right, etc. Identifying where your plane goes and where the needles react will tell you a
    lot and the more you do it, the easier it is to realize what makes it tick.

    The key is for the system to guide you to the ground at the proper glideslope. But you, as the pilot,
    do have to help somewhat!

    I had a friend years ago who was a pilot for a large airline. He flew 747s. He stressed numerous times
    that if we could have a working autopilot, most of us flight simmers could probably land his 747
    without scaring the beejesus out of the paying public. If the autopilot is on the blink we'd better be
    looking hard for some parachutes!

    It doesn't stagger my mind that you and I could maneuver such a beast, but it's got to make one
    feel pretty good to know you could possibly do it.

    Practice, practice, practice!

    Art - N4PJ
    Leesburg, FL

  5. #5

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    I find the PAPI really great although the gentleman with the voice keeps shouting "Pull up, PULL UP,PULL UP" even when I have two reds and two whites!
    The same one who wants to ban candles.

  6. #6
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    Default Navaids

    I'm not aware of any "real life" audio-warning-coupling of the PAPI lights and an airplane cockpit. I suspect you're using some kind of add-on and it's not functioning properly. It doesn't truly matter, but it probably is somewhat annoying to have it there to help you and all it does is complain!

    Art Burke - N4PJ
    Leesburg, FL

  7. #7

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    Quote Originally Posted by Art Burke View Post
    I'm not aware of any "real life" audio-warning-coupling of the PAPI lights and an airplane cockpit. I suspect you're using some kind of add-on and it's not functioning properly. It doesn't truly matter, but it probably is somewhat annoying to have it there to help you and all it does is complain!

    Art Burke - N4PJ
    Leesburg, FL
    The "PULL UP" is presumably flying too low and is a height warning. I thought there would be an awareness in the system that I was approaching a landing. The fact that there is also a "GLIDE SLOPE" warning suggests some confusion.
    One of the runways I use starts very close to the water's edge and is significantly higher than the water. In that situation, the radio height is misleading.

  8. #8
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    Default Navaids

    A "standard" VOR is tuned via the NAV radio. The standard C172 has a radio (and dial) for VOR1 and VOR2. You can tune these VORs with the published frequency. When you are close enough to the VOR for your receiver to know that, the "needle" will become active and you can tune the appropriate radial.

    When the VOR you tune into is "slaved" as an ILS, you will have two needles that will eventually be active - one of them (vertical) for the localizer and the other (horizontal) for the glideslope. You don't have to tune separate frequencies for both the glideslope and localizer. They both work on the same frequency.

    When you write "beacon" I assume you're referring to an NDB (Non-Directional Beacon). These are apparently being slowly phased out. The utilization of GPS technology probably has a lot to do with this.

    Imagine you walk into a dark room. There is no light, but voices can be heard. "Where are you?" you ask. Suddenly, off to your left, a voice says "I'm over here." Well, the magic question now is , "...where is over here?"

    Now let's alter the scenario slightly and replace the voice with a light. Even a candle will work. In a dark room a candle can appear to be quite bright.

    So now, the candle and the sound are coming from the same place. Slowly turn your body until you're directly facing the light from the candle. Where the light/sound is coming from has a "relative" bearing. With some minor arithmetic, you can determine the actual bearing required to get to the beacon (the candle).

    Here's one in its most simplistic form. Let's say you are flying due North (360/0 degrees). You have to turn left 40-degrees to face the signal/light. That means you will need to fly a heading of 320-degrees to fly directly to the beacon.

    Now let's say you were flying 350-degrees when you started turning toward the beacon, but it's still 40-degrees "relative bearing" to the beacon. Thus 350-40 = 310 and you need to steer a heading of 310 to get to the beacon.

    To add just a little to the complexity, keep in mind that many (most?) of the NDBs are also used as an "outer marker" to help you find your way around the sky. The "outer marker" is often your FAF (Final Air Fix) on an approach to an airport so you get the warm fuzzies about where you are and where the airport/runway is.

    Snoop around on YouTube and you can very likely find some far better examples for VORs, NDBs and the like. They have to be plentiful - the "ground school" stuff is just chock full of issues dealing with them.

    Good luck.

    Art Burke - N4PJ
    Leesburg, FL

  9. #9

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    That was really helpful as before. I appreciate it is difficult not to talk down to enquirers but doing so ensures that the picture painted is complete. Better to assume nothing!

    I have been a lifelong yachtsman so am pretty happy with two dimensional navigation. I grew up in a world of Decca, Loran, Omega, DF radio fixing, DR, buoyage, compass bearing fixing, visual range finding, sextant, and eventually, GPS.

    Three dimensional navigation is very similar except that there is a strong incentive to get the third one right! Up to a point, when sailing, you can stop (or at least slow down or hold safe position). I understand that is generally frowned upon in flight.

    I wonder how the move towards GPS is viewed in the professional pilots' world. The various yachting forums I subscribe to, carry not infrequent reports of local GPS outages. Not disastrous in sailing (with forewarning and contingencies) but if air radio navaids are discontinued, that could be concerning.

    Flying tuition is burdened with a huge list of abbreviations which are, initially, a block on assimilation of new skills. As an old git, that is a bit of a struggle!

    The audio warnings are presumably a Boeing thing. Our holiday flights have nearly always been in 737 NGs and the local (static) simulator is based on that (approved for commercial training). That is why my "flying" is with this aircraft. I am fascinated much more by the technology than actually flying.

    I believe it was Smiths Industries (my previous employer) who introduced auto land in association with BLEU (WIKI last line refers to SI although the link doesn't work!). The technology was frightening by modern standards. The autopilot used electro-mechanical switches (whose cute name I can't remember) and the "clicking" was both worrying and reassuring!

  10. #10
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    Here is a text that explains the basic GPWS (Ground Proximity Warning System.)
    link:
    https://www.google.com/amp/s/uniting...rning-systems/

    (basic) GPWS goes off when:
    part of text from link:
    Mode 1 – High rate of descent
    Mode 2 – High rate of closure with the ground
    Mode 3 – Loss of altitude after take-off
    Mode 4 – Proximity to the ground when not in the landing configuration
    Mode 5 – Descent below the Instrument Landing System (ILS) glideslope
    ((These parameters are also what cause the Pull-Up warning in the sim.))


    When GPWS sounds your response should always be to go around immediately.
    (In most planes that means to:
    Immediately Add thrust, then pull up and climb.h wings level for maximum lift.
    And later, when positive climb is established retract gear. (Then perhaps retract one step of flaps only.).)
    [That order may be slightly differ in other aircraft types.]

    Always assume the warning is correct. Figure out why the warning sounded later.

    (of course in a simulator it is less pressing to go around.)

    il.
    Last edited by il88pp; 04-08-2021 at 04:32 PM.

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