Second RMI needle points 180° in wrong direction

[HOCHWALDSPRUDEL]

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

[Runaway Gun]

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.

[NSEU]

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

[411A]

Thanks for possible solutions
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.

[HOCHWALDSPRUDEL]

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.

[411A]

Obviously its been decades since I've seen an L1011 ...

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.

[Graybeard]

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

[FlapsFive]

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

[Deep and fast]

Flaps5

I had that prob in an Embraer too.

D and F

[Centaurus]

from that day on the ADF pointed exact 180 degrees out!!

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.:)

[FlapsFive]

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

FF

[411A]

Are you suggesting the L1011 has a comparator warning light

Not at all.
You might prefer to read again.
...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.



Obviously its been decades since I've seen an L1011 ...



Yup, therein is the problem, alright.:ugh:

[737Jock]

Your story is not very clear 411A

Normally, a loop/sense antenna problem, however, on the L1011, it normally is a comparator problem. Change one box, problem solved.
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.


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?

[L-Band]

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

[411A]

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.


Yup, you've got the picture.

[Checkboard]

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! :)

[411A]

...on one of the ADF boxes is U/S.



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.

[737Jock]

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

[411A]

can you please explain to me what reversed sensing in an ADF system is


As explained previously, 180 degree opposite indication.

Also what does the legend say on this "reversed sensing" flag on the Tristar RMI or is it the normal power failure flag?

Normal OFF flag.

What resolver is this, is it located in that box you mentioned earlier....?


Yes, on those aircraft so modified.

Can you explain the interface between the comparator and the ADF (that you mentioned) on the Tristar, what exactly does it monitor and how does it indicate a mis-compare, how many degrees of error must there be before you get a warning...?



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...
Obviously its been decades since I've seen an L1011 ...


...that may well apply.:ugh:

[411A]

So when a "reversed sensing" condition is detected "in the comparator" the pointers continue to indicate 180deg out but the 'OFF' flag appears in the ADF indicator to "warn you of this reverse sense" condition....?


Exactly.

I am an "avionics tech" and I don't know what you're talking about .


Quite possibly so.:rolleyes:

Funny that, you're the one thats "current on type"


Yes, flew one just yesterday.

I've admitted I haven't been on one for years, yet its me thats correcting you.....


Hardly the case.:ugh:

[411A]

What....they're still flying....?.......:rolleyes:


Absolutely.
Two will be placed in central America shortly, for ad-hoc charters.
Plenty of business, contrary to what some might think, starting January.
In the meantime, Umruh and Haj are calling.
High dollar business, make no mistake.

Small airlines that operate older aircraft have a definite advantage.
They have long retired manufacturer trained guys who positively know how to maintain these older airplanes and are paid accordingly.
Tax free, with a large bonus at the end of the contract.

No room for ASFKAP, as you might expect.:rolleyes:

[minimany]

Superb forensic probing ASKFAP. 411A 's loose claims and bluster needs to be exposed.

[411A]

The ADF system is so notoriously inaccurate you'd be getting a warning every time the aircraft turned never mind when subjected to the normal coastal, night and thunderstorm effects etc that cause errors in the system.


Perhaps for the younger guys it is a mystery, not for older folks whom have used one for many years....night/coastal effects notwithstanding.:}

a) Sadly deluded
b) Grossly misinformed
c) Deliberately trying to mislead anyone reading this thread.



None of the above.

Any further questions?:rolleyes:

[Gulfstreamaviator]

How long before both of these guys get tired, and the game is declared a draw.

Seriously as may states are withdrawing ADF, (sorry NDB) facilities, then the ADF receiver will only function as a base ball / football score receiver.

Can the BBC on 199 still be received when the lowest digital receiver suggests 200 is the lowest frequency.

Incidently my first ADF receiver was a coffee grinder.
Worked very well, only got lost one or two times.

The public need to know........glf

[HOCHWALDSPRUDEL]

Checkboard said: You can't set both needles to the same ADF box, there is no need to design in this functionality.Sure you can set both RMI needles of each RMI (LH and RH) to one ADF, if there is only one ADF installed in the aircraft and both RMI's are connected to that ADF, which is the case in our aircraft!

We still didn't really find the problem....:-) I think I will follow L-Bands advice, which seems to me to be the most convincing answer "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".
Anyway thank you all...maybe someone has had the same problem and really knows about the answer.

Cheers....

[411A]

Sure you can set both RMI needles of each RMI (LH and RH) to one ADF, if there is only one ADF installed in the aircraft and both RMI's are connected to that ADF, which is the case in our aircraft!


The slight problem some folks have, HOCHWALDSPRUDEL, is that...because they have never seen a particular avionics arrangement, they therefore apparently make up their minds that it could not possibly exist.

I would call this....closed minds.
And yes, there must be a resolver in any ADF system, as otherwise manual direction finding would need to be used...and yes, I've done that, too....long ago.

Going further, some folks think that an ADF cannot be used for reasonably accurate navigation.
They would be quite wrong, of course...perhaps because they have not been taught properly about NDB navigation in the first place.

[One Outsider]

Forget it ASFKAP.

The man is a foghorn. He knows it, you know, I know it, everybody knows it.

[411A]

how do you know which of the two ADF signals which may be displayed in that indicator is faulty, what specifically does your ops manual say about this situation...?


There are three flags in each RMI...two signal condition flags, and one PWR flag.
If the RMI fails, the PWR OFF flag appears.
If the VOR receiver should fail or the VOR not be operable on the ground, the respective fail flag will appear, if VOR is selected.
If reversed sensing (IE, 180 degree ambiguity) is sensed, the respective fail flag will appear, if ADF is selected.
If the ADF transmitter on the ground should fail, a fail flag will not appear in the RMI, so audio monitoring is needed. In addition, on some installations, the ADF needles will be driven to the nine o'clock position.
If the ADF receiver fails, the respective fail flag will appear if ADF is selected.

I know you "only fly 'em" but is it possible you could ask one of your "highly experienced, long retired, manufacturer trained" hot shots to explain it to you and then you can come back here and tell us all about it...?



If I remember, will do.
Keep in mind these folks didn't design the system, they only fix it when necessary.

[411A]

You quite clearly stated the normal 'OFF' flag appears when a "reversed sensing condition" is detected, now you're saying its the respective (ADF) fail flag....?



Yes, the normal flag when the respective ADF receiver either fails, or the 180 degree ambiguity is sensed.
The legend on this flag is...OFF.

There are, however, different variations, depending on original customer option...in fact, those aircraft ordered by TAP had a separate RMI for the ADF indications...IE: two RMI's on each pilots instrument panel.

Many of the aircraft delivered originally to BA had a completely different ADF display...IE: the respective ADF pointers were placed on the HSI...which caused this instrument to look like, as one pilot described it...a pin ball machine.:}

And, yes, I've flown this varient as well, complete with its 'ground pointer' on the ADI.

[411A]

Quite frankly, ASFKAP, I really have no idea what you are on about.:rolleyes:

To repeat.
Two ADF receivers installed on the airplane.
Each receiver drives its respective pointer on both pilots and copilots RMI.
Number one receiver drives number one pointer, number two receiver drives number two pointer on each respective RMI instrument.
With me so far?:rolleyes:
IF the pilots (or copilots) RMI power fails, the sharks fin OFF flag appears.
IF the number one ADF receiver fails, each RMI instrument will show an ADF OFF flag to appear, on both RMI's
Conversely, IF number two ADF receiver fails, the respective ADF pointer will show an OFF flag in both RMI instruments.
Following now?:}
In addition, on those aircraft so modified, IF number one or number two pointers shows a 180 degree ambiguity, that respective pointer is flagged on both RMI indicators.
That flag has a legend that says OFF...on both RMI instruments.
The remaining ADF receiver that is properly functioning will still display correctly, provided the ADF receiver is tuned correctly, and ADF is selected on the respective RMI.

It is entirely possible that BA had their ADF indicators (as previously described) on the HSI wired entirely differently, and therefore the display was different...ala, pin ball machine...as indicated previously.

IF you would like to transport your good self down to JED during the Haj, I will be pleased to demonstrate.
You can even ride with us to Ouagadougou or BoBo Dioulasso to see how it is all done, and quiz our avionics guys about the system, to your hearts content
Just remember to ontain the necessary visas and don't forget your (retired) crew ID.

Deal...or no deal?:hmm: