Second RMI needle points 180° in wrong direction
 

Has anyone ever had this strange curiosity?

We were flying with both RMI's and both RMI needles set to ADF1. Normally, all 4 needles, 2 in each RMI (Left RMI and Right RMI) should point toward the ADF. But instead only one needle in each RMI pointed to the ADF which was in front of us, and the other 2 needles pointed 180 in the wrong direction, behind us. Also when we chanded our heading , the 2 wrong indicating neeedles kept completely aligned with the two good working needles, but just with the tail up instead of the head up. Pretty strange thing. We re-selected the ADF/VOR buttons on the RMI to VOR, which was then correctly indicated on all 4 needles......reselecting the 4 needles to ADF, one in each RMI was then again pointing exactly 180° in the wrong direction.
Later on ground, we tried again and only after selecting a different ADF frequency, all 4 needles finally pointed in the same direction again. Then we selected the original frequency again, where we had these problemes, and all 4 pointed in the right direction.
Can it be possible, that these two wrong pointing needles were some kind of stuck but kept perfectly aligned with the 2 good indicating ones, also during heading changes...so they moved as well...so they couldn't really be stuck???? What might have been the reason for those problemes?

Thanks for possible solutions.....pretty strange thing.
Regards

Yes, it's very possible, and a known phenomena. I'm not qualied to go one, but I thought I'd put your mind at ease.

Sensor loop aerial detects null value phase shifts etc... or something like that.. meaning the ADF needles can point 180 out - but shouldn't.

It sounds like the Sense Antenna for one of your ADF's is faulty.

I've been told that the Loop Antenna can df without the Sense Antenna, but only if the signal is good.

You didn't specify what type of aircraft you have. For each ADF system, some aircraft have separate sense and loop antennae. Other aircraft have combined sense and loop elements in the same antenna.

On our Classic 747's, the sense antenna connection was a single black wire attached to an antenna embedded in the wing to body fairing panels. It was easily broken.

Did your maintenance department correct the problem?

Rgds.
NSEU

Occasionally noted on a variety of airplanes that I have flown over the years.
Normally, a loop/sense antenna problem, however, on the L1011, it normally is a comparator problem.
Change one box, problem solved.

Thank you very much so far.....aircraft flown was a King Air C90B. We have only installed one ADF.

Maintenance said it might be a construction problem, that it was not constructed to point with all 4 needles to an ADF and that there could be a problem with the electrics and a phase shift could occure......we are supposed to try it again next flight.

Quite likely the problem, then...:rolleyes:

Newer build aircraft and those so modified via service bulletin incorporated a comparator/resolver in the ADF system, to indicate a reversed sensing condition.
It caused a flag to appear in the respective RMI indication.
However, it did not resolve another problem that is common with ADF receivers in general.
If the broadcast signal 'goes away' due to equipment failure on the ground, no flag will appear, so it is quite necessary to have one crew member monitor the audio continuously, during an NDB approach.

Greetings Saarlander.

I did extensive avionics work on a C-90 a couple of years ago, but all we did with the ADF was to remove it, and remove the single RMI...

You presumably have a single AC source in that plane, so no phasing conflict should be expected. If you want to go into this deeper, you will need to know the model number of the ADF receiver, RMIs and VOR receivers, and whether there is a separate module for driving the RMIs. You may contact me offline if you want.

We lived in Jaegersburg, bei Homburg, in 1966-7, and it was idyllic.

GB

On one of our club C152's (probably slightly different type of aircraft to what you are refering :ok:) the aircraft was struck by lightning and from that day on the ADF pointed exact 180 degrees out!!

FF

Flaps5

I had that prob in an Embraer too.

D and F

Hopefully the aircraft was not permitted to fly from that day on, with that known defect; or at the least the ADF labelled with an inoperative sticker until the defect was rectified.:)

'Twas, but thought I'd fiddle with it as I was going past an NDB at the time :}

FF

Not at all.
You might prefer to read again.
Yup, therein is the problem, alright.:ugh:

Your story is not very clear 411A

What I understand you mean is that the comperator will cause a flag to appear on the respective (180 degree off) RMI.
But in that case how can replacing the comperator solve the problem of a needle pointing 180 degrees in the wrong direction? Seems like you are just trying to remove the flag.
Isn't the problem on the L1011 that the comperator is flagging an RMI, that is in fact in perfect working order?

Right then time to put this right!!

Hockwaldsprudel's post was -- BOTH RMI NEEDLES IN LH AMD RH WERE SELECTED TO ADF 1. which does mean one ADF displaying on all four needle, one needle each side was displaying 180 out, now that says to me that the follow up resolver is u/s in the 360 quadrant however ok in the 90/270 quadrant.
Tune in the same station and do a 360 and see what happens.

Cannot in no way be an ADF problem!!!

L

Yup, you've got the picture.

You can't set both needles to the same ADF box, there is no need to design in this functionality. You can only set both needles to ADF (where they will display their respective ADFs - needle one to ADF one, needle two to ADF two) and then set both ADFs to the same NDB frequency. As this is the only set-up possible, this is what is assumed from the first post, and the situation explained by the sense antennae (or modern equivalent) on one of the ADF boxes is U/S.

Speaking so much of needles, ASFKAP - keep needling, I'm enjoying it, at least! :)

No, not necessarily.
If audio station ident is heard, the ADF receiver is functional.
If the ADF pointer is 180 degrees to the desired direction, it is the resolver, not the receiver.

Now, if one has installed one of the older Collins ADF sets, where manual direction finding was possible (many 707's for example), then proper pointer orientation can be determined without the resolver.

:EThanks for your answer 411A! It's all clear to me now!

As explained previously, 180 degree opposite indication.

Normal OFF flag.

Yes, on those aircraft so modified.

No, I fly 'em, not maintain 'em
You will have to ask an avionics tech about this.

This is all quite elementary, I'm surprised ASFKAP is not informed...then again, due to...
...that may well apply.:ugh:

Exactly.

Quite possibly so.:rolleyes:

Yes, flew one just yesterday.

Hardly the case.:ugh: