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Thread: King KMA24 Marker Beacon problem

  1. #1

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    King KMA24 Marker Beacon problem

    I haven't built an experimental yet, but I am planning on building a kit helicopter. In the meantime I wonder if I can get some assistance. I own a Mooney that lived in Nevada for a long time under a shade hangar till I moved back to Peoria. The avionics have been plagued with the micro fine dust that blows all around there and now I am having different issues related to poor connections. I've got most of them sorted out, but am puzzled by my marker beacon indicator. I can receive some beacons, but not all of them. For example I take off on runway 31 and receive the middle marker and outer marker for 13 as I depart, but when I return for landing on 31 I do not receive the marker beacon tones or lights. There are no NOTAMS indicating there is an issue with the 31 marker beacons so I'm sure it is something in my plane. Do all marker beacons broadcast on the same frequency and channel and if so why can I receive some and not others? I have King avionics witha KMA24. I appreciate your comments.

  2. #2

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    Bump anyone know where I can post to get an answer.

  3. #3
    Mike Switzer's Avatar
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    I don't know the answer to your question, but if you end up getting it worked on we have had good luck with Bloomington Avionics.

  4. #4

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    I am a retired avionics shop owner and will give you the most likely cause for you 3LMB problem. All marker beacon signals at all airports transmit on a single frequency of 75.00 MHz. It is the frequency of the modulation tone that triggers whether the blue (OM), amber (MM)or white (IM) light flashes. The blue light frequency is 400 Hz, the amber light frequency is 1300 Hz and the white light frequency is 3000 Hz.

    The marker beacon antenna on the belly of your Mooney is most likely of the 'boat hull' type and depending on the brand and model of antenna, it probably has suffered a major loss of sensitivity. To test that theory, fly over both a OM and MM beacon at an altitude of 400 ft above ground. If you receive the tones and the lights flash normally, then fly over those same beacons at an altitude of 2500 ft. If the beacons work OK at 400 ft but not at 2500 ft, go to an avionics shop and have them first check the marker beacon receiver sensitivity of the KMA-24 on their test bench. If it bench tests normal, then you 'boat hull' marker beacon antenna needs to be replaced. This assumes of course that the antenna coax cable and associated connectors between the KMA-24 and the antenna are OK.
    Last edited by whemme; 10-20-2011 at 08:01 PM.

  5. #5

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    Thanks for your assistance. So if the antenna is weak or the connection is then I would receive signals at one end of the runway, but not the other since both ends have markers? The plane spent a lot of its life in Vegas where it was attacked by fine micro dust in the tuners and such so I'm fighting bad connections on KX-155 where the display is chopped off at the bottom and scratchy ADF reception and intercom so I assume this may be a case of poor connection?

  6. #6

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    Quote Originally Posted by Mike Switzer View Post
    I don't know the answer to your question, but if you end up getting it worked on we have had good luck with Bloomington Avionics.
    I'll consider that since I do not want to deal with Byerly. I wish there was someone around here that still did inexpesive traveling IFR instrument certs. Haven't had mine certfied since I was in Vegas.

  7. #7

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    lvflyer,

    I am not saying definately that your marker beacon antenna is weak. What I gave you was a way to determine if your antenna is most likely defective. Also, testing the marker beacon system does not depend on which end of the runway a marker beacon transmitter is located. What does count is your altitude above the marker beacon transmitter location as you fly over it.

    The marker beacon transmitter on the ground directs a signal upwards towards your airplane as you pass over its site. The signal is transmitted upwards in the shape of a ice cream cone with the signal spread getting wider (and weaker) the higher in altitude you are as you pass over the transmitter site.

    Typically the amber MM is almost always located 0.5 NM off of the end of an ILS runway and usually when you are centered on the glideslope as you pass of the MM, you will be 200 ft above it. The blue OM can be located anywhere from 3 NM to 7 NM off of the end of the ILS runway and the altitude when on glideslope as you pass over it can range from 1000 ft to 2200 ft typically.

    You need to fly over the MM and OM at your airport like I explained in my earlier post in order to trouble shoot your system to determine if the problem is your antenna or possibly the marker beacon receiver itself in you King KMA-24.

  8. #8

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    Thanks again, I'm not getting notified of answers by email so I just check in now and then. So I understand how they work somewhat, but what doesn't make sense is that I take off on say 13 and as I depart I get the MM tone and light even when turning off of the runway course for a few degrees and enter the pattern. When I make an ILS approach to missed approasch point and altitude on 13 I don't get any tone or light. Since it is a controlled airport I didn't have the opportunity to make an ILS on 31 yet to see if I pick up the OM an MM on an approach. So altitude would be the same on departure and approach. I assume the boat rudder looking antenna is the marker beacon one and it is only accessible by removing a belly pan so it isn't an easy access thing to look at. Getting to be winter here also so I don't know how long I have to take a look at it in an unheated hangar. I wonder is it possible the signal strength may be weaker at one end of the runway and my antenna connection is corroded just enough to keep it from being heard. If anyone gets a chance to fly by KPIA and check out the marker beacon on 13 let me know if it works for you.

  9. #9

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    lvflyer,

    At the Peoria, IL airport (KPIA), if you takeoff on runway 13 and proceed straight out, the only marker beacon off the end of that runway is the OM located 5.2 NM off of the SE end. There is no MM off the end of runway 13 so I don't see how it is possible that you can receive a MM light and tone off the end of runway 13.

    On an approach to runway 13, both an OM and a MM exist. The OM is 5.2 NM NW of the approach end of runway 13 and the MM is 0.4 NM NW of the approach end of runway 13.

    Look at the approach plates for both ILS Rwy 13 and ILS Rwy 31 to see what I am talking about.

    I would recommend that you go see Greg Vail at Bloomington Avionics since you are located closeby and have him troubleshoot your marker beacon system.

  10. #10

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    Quote Originally Posted by whemme View Post
    lvflyer,

    At the Peoria, IL airport (KPIA), if you takeoff on runway 13 and proceed straight out, the only marker beacon off the end of that runway is the OM located 5.2 NM off of the SE end. There is no MM off the end of runway 13 so I don't see how it is possible that you can receive a MM light and tone off the end of runway 13.

    On an approach to runway 13, both an OM and a MM exist. The OM is 5.2 NM NW of the approach end of runway 13 and the MM is 0.4 NM NW of the approach end of runway 13.

    Look at the approach plates for both ILS Rwy 13 and ILS Rwy 31 to see what I am talking about.


    I would recommend that you go see Greg Vail at Bloomington Avionics since you are located closeby and have him troubleshoot your marker beacon system.
    If you say so. I didn't pay attention to what light was flashing on departure, but I got a tone and flash and none on approach at same altitude. I also heard the tone as I left the departure heading for a while as I turned into the pattern as well so it was plenty strong. The mystery remains why at one end and not the other? Planes pretty much in bed for the winter so not sure if I'll get to Bloomington. Not rich either so that is a factor. If only I could find a partner.

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