King KMA24 Marker Beacon problem

[lvflyer]

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.

[lvflyer]

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

[Mike Switzer]

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.

[whemme]

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.

[lvflyer]

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?

[lvflyer]

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.

[whemme]

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.

[lvflyer]

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.

[whemme]

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.

[lvflyer]

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.

[lvflyer]

I got a chance to get out to the plane today so here is what happened and I'm still baffled. I checked the connections to the antenna and KMA24 and all seemed tight and clean. I took off on 13 asking the tower ot allow me to cross the OM(TUNGG) 31 approach at 1500 feet. No tone or light. I had them vector me directly over TUNGG several times because my ADF is old and think has bitten the dust. It is original one for 1968. Anyone know an ADF that will fit in a round instrument hole? Anyway I then had them vector me to ADLER which is OM for 13 and as I approached the airport environment I began to pick up first the MM tone then closer I got the MM light on my way to ADLER where I got the OM light and tone. I climbed to 6000 feet and made a pass over ADLER where I got tone and light on high Sens and none on low sens and passing by airport environment I got tone and light for MM on high sens and none on low sens and was vectored once again to TUNGG and no light or tone. I asked tower if anyone else had commented on this condition and the answer was no. Passing over TUNGG at 6000 yielded no other result. I am perplexed.

[Frank Giger]

I'd think that forty-three years is an outstanding life cycle for any electronic part.

[whemme]

lvflyer,

That ADF you have in your panel that fits in a round 3-1/8" hole is a King KR-80 ADF. It is the only ADF that I am aware of that was ever designed to fit in an instrument panel hole rather than in the radio stack. A newer replacement ADF that will fit in that hole does not exist and getting your present KR-80 ADF repaired is problematic due to its age.

I agree that it is a puzzle as to why your OM tone and blue light works on the ADLER outer marker but not at the TUNGG outer marker.

By the way, I would not necessarily expect your marker beacon receiver to receive a usable signal at an altitude of 6000 ft. You may or may not get the tones and light at that high altitude but the normal altitude to cross those marker beacons at KPIA is 2400 ft or 2500 ft depending on whether your are on the ILS 13 or ILS 31 approach. The received signal strength will be a lot less at 6000 ft versus 2500 ft.

[lvflyer]

Thanks. I am aware of the altitude, but I figured if I could pick up the signals at that altitude then the equipment is sensitive enough. As to the ADF I do have a non useable ARNAV Loran in the copilot side. I've seen some old ADFs that might fit in that hole, because I doubt if I'll ever have an IFR aproved GPS installed when the hand helds can do so much more for much less. So what models do you think would slip in there. Can't very well do an ILS where an ADF is required for waypoint identification.

[whemme]

lvflyer,

It is not clear to me if you are talking about the avionics rack space now occupied by your ARNAV Loran-C receiver or the 3-1/8" instrument hole now holding your existing non-working King KR-80 ADF receiver. If you are talking about the instrument hole, the only ADF ever designed that will fit there is the KR-80. So, if you want a working ADF in that hole, then you must find some avionics shop that can still possibly repair that old ADF.

You don't say whether you have a panel mounted GPS in your Mooney or not; but assuming that you don't then I have a suggestion if you want a GPS and a newer replacement ADF system. Remove the ARNAV Loran-C system (which I assume is probably a ARNAV R-20) which is probably mounted in the right side avionics stack. That R-20 I believe has a mounting height of 3.25". In that space, you should be able to mount both a used King KR-87 ADF Receiver (which is 1.3" high) and a 2.0" GPS receiver. The King KR-87 ADF system in my opinion was the best ADF system ever designed. It consists of the KR-87 ADF Receiver, the KI-227 ADF Indicator and the KA-44B Combination ADF Loop/Sense Antenna.

You existing KR-80 ADF system consists of the KR-80 ADF Receiver/Indicator, a seperate long wire sense antenna and a KA-42 or possible a KA-42A Loop Antenna mounted on the aircraft belly. All of that would have to be removed to install a good used KR-87 ADF system.

Now some possible choices for a 2.0" high GPS receiver follow:

1) Garmin GPS-150 or GPS-150XL - these units are VFR only GPS receivers
2) Garmin GPS-155 or GPS-155XL - these units are IFR approach recertifiable GPS receivers but are not WAAS capable.
3) King KLN-94 - this unit is a IFR approach recertifiable GPS receiver, non-WAAS capable.

I recommend avoiding either the King KLN-89 VFR or King KLN-89B IFR units due to a history of very expensive display problems.

If you choose one of the IFR systems, then remember it must be installed with it an associated CDI (Course Deviation Indicator) which will need to be mounted in an available 3-1/8" instrument hole - you may or may not have an such a hole available. If not, and depending on what brand and model CDI you already have in your panel acting as your existing #1 VOR/ILS or #1 VOR/LOC, you may be able to share that CDI with an IFR GPS using a NAV-1/GPS switching system.

Just some ideas to consider. I love spending other people's money!

[lvflyer]

Thanks for your suggestions. Since the plane is pretty much a hangar queen and is only used when needed, rarely, I am not able to justify an in dash GPS. Since the LORAN system was decommisioned I purchased an Anywhere Map GPS that does everything the Garmin does except being certified as IFR and cost about a third of the Garmin. So I'm not any worse off than with the LORAN. My concern is with the ADF. I think all my KR-80 needs is cleaned since I can pick up radio stations, but the tuning is scratchy and I can't pinpoint which signal is the ADF. I know it is ancient, but in this day and age the ADF seems to be disappearing like the LORAN system. I would love to spend the money on a complete glass cockpit, but I am pretty sure I would never get that money out of it when/if it sells. In addition I know, for example, the G-1000 system in the CAP planes raised the annual expense to almost $20,000 a year. I certainly cannot justify that for a 68 Mooney. As to the Marker Beacon I am still perplexed. Sent a message to Bloomington Aviation with no response so not sure of my next step. The only thing I can think is the marker beacon frequency are within a tolerance that does not coorespond to the tolerances of the KMA-24 and thus one of th ebeacons is outside of the reception tuning of the indicator. If that is the case then the indicator needs to be recalibrated.

[Bill Greenwood]

I have a King KR 80 ADF, non working. I don't know of any shop that repairs these. I bought it from one of the big shops that sell used avionics and advertise a lot. After going to some trouble and expense to get in installed in my cockpit that is pretty short on room for avionics it would not work and the co would not take it back and give a refund, claimed too much time had expired, and they could not get parts.
I'd like to know if anyone has parts and can repair it. It is a neat looking package.