737 RDMI ADF Dip?
 

Hi,
Have a sim ride coming up and just wanted to check with the experts to see if the 737 RDMI has Dip on the ADF or whether it is cancelled out?
Many Thanks
VC10

Hi...
It's a long time since I've done my tech stuff...but what's "Dip" ?

I didn't want to say anything and admit to my ignorance, but I'm fascinated! How did I fly 38 years and not know what that was? Hundreds of NDB approaches too! And 8 years on the 737. Must have been a danger to someone! So what the hell is it when it's at home?

In the -700 I haven't see it. On the -200 sim no, but that's the sim. I think it's scrubbed out. Last time I saw dip was in a PA34!

MK

many thanks

ADF...?? Is that the thing your looking at when it gets dark after both your IDG's quit? :E

...don't tell me - I know where it is...right at the tip of my tounge...I've seen it somewhere...

Doh! :\

BamThwock et al;
The ADF has two main receiver errors as you turn onto a track (ignoring general lack of accuracy:eek: ).
Quadrantal error is caused by signal reflections off the airframe, and should be calibrated out in any self respecting transport aircraft.
Dip, on the other hand, is a geometric fact of life that is a function of range, altitude and bank angle. The ADF needle points at where the transmitter is in relation to the nose of the aircraft. If you imagine flying towards the beacon with 90 degrees of bank (briefly!!), the needle will point at an angle that depends on your altitude and range. When turning onto a course, the needle has a tendency to point towards the lower wing by a few degrees, how much is a bit of guesswork. I don't know of any system that is able to correct for this!
In the real world, it is rarely an issue these days as most approaches are flown by positioning the aircraft using the FMS, with the ADF being used to confirm we have no map shift. I don't know about the 737, but in the Challenger we're even allowed to do it this way on an OPC!
VC10 - Good luck with the sim.

It's been awhile.....

In addition to error indication due to a turn.... there is also the "Shore Line Effect". If I recall this can be apparent when approaching an NDB (on land) from over the water.

I am sure there are some bright minds out there that explain exactly the cause of this.:)

Yes, and there is night effect that approximately halves the useable range and of course our old friends thunderstorms. I was concentrating on the errors in the actual ADF receiver to save on space....

No.

Dip error is not exhibited on the ADF RMI needles of the 737-300-900 or the B757/767.

We may have lost contact with VC10's question which was whether the "dip" is apparent in the simulator. I have flown a bunch of simulators and never did see the effect presented, nor have I ever seen it in simulator fidelity check schedules. I would think we can take it as read that the simulator computor hasn't been taught about this, and therefore works as though the ADF loop is always level and therefore there is no dip.

I would suggest you can ignore the real world in the sim and watch the track come up on RMI as you progress round base turn, with the ability to fiddle your bank/rate of turn to roll out on track and earn a piggy stamp.

In an aircraft if you do this you will find the ADF is indicating an underturn, you apply more bank, exacerbating the effect which becomes apparent when you roll the wings level and the needle mockingly crosses to the outside of the turn. For my part I always ensure being right on the intermediate track before the turn, fly the turn at the recommended angle of bank, then roll level to read the outcome before getting the tracking process under way. (Oh all right, if you know the crosswind, there are things you can do)

It would be of interest to know whether there are any aircraft in which attitude is fed to the ADF loops, otherwise and as said by BizJetJockey, this characteristic exists by virtue of irrefutable geometry. It is certainly present in all of some twelve transport aircraft I have flown, from Dove to 747, including 737 and 767.