KX155 problem determination help

[N3322G]

Our #2 radio is a KX155. The ILS frequencies and glide slope work great however the VOR part appears to not be receiving the stations. Is there a way of diagnosing whether it is in the unit vs connection to antenna for a non-mechanic?

Would anything done during an IFR static check impact operations?

[Charles Schefer]

Hi Pat,

Sorry to hear of the difficulty. My #2 is also a KX-155

By IFR Static check I assume you mean the 24-month Pitot-Static check (i.e. 14CFR 91.411)? If your problem occurred immediately following any maintenance I'd be suspicious that something was knocked.

If I understand correctly it sounds like glideslope works but lateral nav (VOR radial / Localizer) does not? The VOR/LOC antenna is separate from the glideslope antenna. On my bird, the VOR antenna consists of two antenna angled 45-deg rearward either side from the top of the vertical stabilizer (right where the read beacon is). The glideslope antenna on the other hand; looks like a wing or boomerang mounted atop a stand. I think it was originally mounted on the roof of the cabin but now it's actually mounted in the front of the nose cowl section (which surprised me when I bought the plane but hey - it works well and is not in the airflow to cause drag).

Perhaps if maintenance was just performed the VOR antenna connection was disconnected inadvertently. At any rate I would first check antenna connections before anything else. An allen key can be used to remove the KX-155 from it's tray (small hole right in the front of the unit). From there you may need to get back in to the back of the tray to check the connections. You may also be more quickly be able to see by laying on the front floor and look up behind the panel. I've done that many times. Easiest way is to sit on the wing and "lay back" onto the front cabin floor with the front seats all the way back. You have to be a little bit of a contortionist

Beyond that you could take the access panel off the tail cone area on the left side of the fuselage forward of the stabilator and look in there for a wiring disconnect. You could also perhaps take off the cap at the top o the tail where the beacon is and look in there. With a multimeter you could Ohm out the antenna wires. I doubt the wires are broken. My first bet is it's just disconnected at one end or the other.

Good Luck,

- Charles

[N3322G]

thanks Charles - that was very helpful. I'll be doing some more checking.

The Localizer guidance works perfectly as does the GS. Matches the 530 stuff exactly.

We just don't use the #2 VOR that often so I can't say exactly when it failed.

[Charles Schefer]

Ah... well if the localizer works that should be the same antenna as the VOR so if that's the case perhaps the antenna is not the issue... or perhaps it is. I think it's still worth checking the connections as step 1 and if possible Ohm out the wires. I've often found that connections can be good on the ground but not in the air due to vibration so sometimes "jiggling" the wires during an Ohm / continuity test can reveal problems that you might otherwise not find.

Beyond checking the wires you might need to have an avionics shop bench test the KX-155.

Here's another idea... do you know anyone else with a KX-155? If so would they be willing to lend you their unit to test? It's just one allen screw in the front to remove it from the tray. Swap the two KX-155s and if the problem "moves" to their plane and no longer exists in yours then the unit is the issue. If the problem stays with your plane then it must be wiring.

- Charles

[Charles Schefer]

I don't mean to insult by asking but.... are you sure the VOR was in service when you determined the KX-155 was not working? I know you said it was working on the Garmin 530 above but... if you accidentally left the 530 in GPS mode vs VLOC via the CDI button then you would be getting guidance off the GPS. Using the CDI in GPS and pressing OBS you can slew in any course just like a VOR.

FWIW - I've been tripped up by things like that. Once I could not get my autopilot to track and was perplexed. Finally I realized the little "NAV 1 / NAV 2" D2DP selector switch was centered so neither Nav 1 nor Nav 2 was a source!

Just a thought....

- Charles

[N3322G]

Charles,

No insult taken about the VOR in service. I have checked it on multiple flights - hoping that it would magically repair itself. UKW has had work done recently so that was my very 1st thought. I figured I would garner ideas here and then do some more testing in flight. Do have to regularly run those engines around and the pilots too.

Going to have some downtime coming up with husbands hip parts being removed, replaced and signed off. I get some nice solo time and won't be doing any practice approaches without my favorite safety pilot. If I have to ship the 155 off, it would be a fine time to have it be absent - not that I need it or the 530 or the 496 or even a map for the keep us current route.

Thanks for the advice and thoughts. As we chatted over lunch, husband laughed at the butt on the wing and contort to see under the panel as I am not that tall - plus, I might get in but not be able to get out ... just things we newly Medicared folks laugh about

[N3322G]

Forgot to mention that UKW, my favorite test VOR is one of the arrival gates for DFW - odds that it consistently out of service or having a problem is small IMHO.

[Charles Schefer]

Ah, I'm sure the DFW VORs are kept in good shape . It was just a thought. Glad I at least brought some lunchtime humor . Good luck with it Pat. Seriously I'd see if someone has a KX-155 you can swap in the tray for testing. That would tell you if its the unit or the wiring.

- Charles

[N3322G]

Too funny. When threatened with owner maintenance, the 155 performed perfectly.

If both of us hadn't seen the problem multiple times, I'd say it was me ... Ken flew today and it was flawless, so he claimed full credit for the correct operation.

...maybe it really was the VOR itself - here's hoping.

[comancheeflyer]

Check and see if you here a station identifier over the #2 radio nav and if you hear it then I think the radio is good. If loc works then the radio is good and you have a indicator problem if it is a KI208/209. Would not be the first time I have seen this.
Thanks Commancheeflyer

[N3322G]

We've determined that the power connection is loose. We can fix the problem every time by pushing the unit 'back' into its slot. There is no discernible movement but it restores the function. Will be addressed when we put in ADS-b as it is only 1 of 2 back up units.

Thanks to all who provided advice.