DME help Please

[aprewett]

Hello,
I am doing some net based lessons. Currently on LOC approaches.
I am instructed to, at different times use the DME, with NAV 1 and 2.
Using it with NAV 1 is simple, have it on RMT.
My problem lies with showing it for NAV 2 with the LOC frequency.
If I understand correctly, I should be able to input a frequency in the FREQ setting and then switch to GS/T to recieve that frequencies info.
I don't seem to get anything.
So I must be doing it wrong, as I can get LOC DME info by using NAV 1. But sometimes I also need NAV 1 to show other info like FAF's etc
Thanks
Allan

[Great Ozzie]

Hi Allan,

Afaik, the DME cannot be used with NAV2. RMT for NAV1 DME display, and FREQ / GS/T for DME display of the frequency dialed into the DME unit.

An example of what I would do when needing two DME's... using the KMFR LOC/DME BC-B approach (direct download link using the FAA Terminal Procedures Basic Search).

I am going to put the I-MFR freq (110.3) in NAV1 and the OED freq (113.6) in both NAV2 and the DME. After flying e.g. to WISEP (the IAF) I can use NAV2 and the DME set to either FREQ or GS/T to fly the OED 24 DME arc. Then, when the 147° radial centers, I can start my turn inbound to KMFR and switch the DME to RMT to obtain the necessary DMEs (off of the localizer in NAV1) for the stepdown fixes for the backcourse approach into KMFR.

So I must be doing it wrong, as I can get LOC DME info by using NAV 1. But sometimes I also need NAV 1 to show other info like FAF's etc

Would you mind giving me an example approach where you are having this problem?

-Rob

[aprewett]

Thanks Ozzie,
Quick reply as I am at work.
I am using this excellent tutorial;
http://www.navfltsm.addr.com/index.htm
In the ILS section tutorial he often advises using NAV 2 combined with DME for the LOC approaches (I am only up to that part).
I will need to digest your answer as initially I could not follow what you are advising.
From the info on the DME, it sounded like I should be able to us 'FREQ', to put the LOC frequency in and switch to the right to get the DME info but I was getting nothing.
I did not need two DME's, but as I could only get DME info via NAV 1. I was supposed to be using NAV 1 for obtaining other info, like intercepting another VOR signal, so as to triangulate my position. So I was having to us NAV 1 for both.
If you have a look at his info, maybe I am doing it wrong.
Thanks
Allan

[Great Ozzie]

Ok... sry about the brief explanation on the above approach... just disregard it unless you have some interest in it.

I see what you mean about the DME display. I'd imagine you are going to have to "flip" his instructions for the C172. I see his reasoning for using NAV2:

NOTE: Fly the Instrument Approach portion with your Nav-2 Receiver for better needle visibility.

As an Instrument Instructor, I confess I chaffed a bit when I saw that. Reason is... I (typically) set primary navigation in NAV1 and secondary navigation info in NAV2. Also, the radio stack is set-up to fly this way... the Glideslope only in NAV1 - how the autopilot uses the radios (NAV1 is source) and how the KN 62A (the DME unit) is wired in.

Two ways for DME readout (as you know):
1) From the active frequency in NAV1 when the DME is switched to RMT mode
2) From the DME unit itself when switched to FREQ or GS/T mode

Certainly acceptable to fly the approach the way he describes if one so desires... it isn't "wrong", but the C172 isn't setup to this way to display a DME for NAV2. Some DME displays are setup to display NAV1 / NAV2 DME... for example, the default Mooney Bravo uses one of these type of DME displays.

This is my suggestion for the Localizer 16 approach to Beverly...

•NAV1 Active freq 112.5 (LWM) | Standby freq 110.5 (I-BVY)
•NAV2 Active freq 110.5 (I-BVY) | Standby freq 116.5 (PSM)
•DME FREQ: 116.5 (PSM)
•DME set to RMT Mode
•NAV2 OBS Head: Set to 157°

Fly to LWM using NAV1 (I think the initial instruction Fly the first leg with Nav-2 is a typo).

After his - Begin your descent to 1800 ft.:

•Switch NAV1 Active freq to 110.5 (I-BVY) and fly NAV1 (verify needle with NAV2 OBS needle)
•Rotate NAV1 OBS to 157° (a reminder of the Localizer Inbound course Heading)
•Rotate NAV2 OBS to 210° (Holding Radial course Heading for the Missed Approach)
(RW... I'd most likely have you fly the approach at 90kias - but 75kias no problem here)

Reasoning for my setup:

•As I said, I prefer my main navigation in NAV1 - secondary in NAV2.
•I have DME when I need it for the approach without switching the DME switch (to LWM and I-BVY).
•I have a backup Localizer in NAV2 in case NAV1 were to fail.
•NAV1 & NAV2 Localizer (110.5) - I will do an IDENT before LWM for both Radios (will re-ID I-BVY when switching NAV1).
•I can rotate the NAV2 OBS to 210° *if I wanted to* to prepare for the Missed. Note that since this is a Localizer course (unlike with a VOR), the OBS change does not effect the needle.
•DME ready to be switched to the PSM VOR to locate WITCH intersection (Missed Approach holding fix)

Sound good or?
-Rob

Edit: I should mention that... before descent to 1800', I would verify I am at or beyond LADTI intersection (so check before descending after switching to NAV1).

[aprewett]

Great, Thanks Rob.
Will give that a fly.
Thanks again for your help and the detailed reply.
Allan

[aprewett]

Hello Rob,
Work kept me away from Simming. Just had go at your proposed approach and it was great. Easy work load in the cockpit.
Thanks again
Allan

[Great Ozzie]

Glad to hear that worked out Allan,

Yeah.. it really helps to stuff as many freqs in the NAV / COMMs as possible to be prepared for "what's next".

Welcome btw.
-Rob