DME ARCs

[ark 1,288]

I know how to fly a DME VOR arc using standard steam gages by repeatedly adjusting the heading and resetting the OBS while monitoring the course needle as it swings from "2 dots on one side to 2 dots on the other". But how are DME arcs typically handled in a/c like the T7 or 737 NGX? Similar to the above, in the 737 I could see constantly resetting the course in the course window and monitoring the CDI on the ND VOR mode display, but I would think there is a better way.

Thx,

Al

[Continental737 7]

DME arcs in an airliner can be flown two ways. First, the DME arc can be coded in the FMC data base if it is part of a published instrument approach procedure. Then the crew just uses LNAV and follows the ARC which was loaded from the data base. Second you can creat your own unpublished DME arc by using the format ABC010/10 and insert it into the legs page to create your own arc. ABC being the reference VOR, and 010/10 being the radial and distance. For example if I wanted to start a 10 DME arc from the LAX VOR on the 040 radial and exit on the 090 radial I would enter LAX040/10, LAX050/10, LAX060/10...LAX090/10 in the FMC, then use LNAV to fly the arc.

[Avantime 81]

IIRC You can also put in range arcs in the FIX page. Just enter the navaid ident and specify a range.

[Alpha Floor 237]

FIX page is extremely useful and so many people don't know it.

 

I'll do a tutorial video on flying arcs on the 777.

[evanbanalian 8]

I don't think any airline will be allowed to fly a non published DME arc.

[Fabo 213]

 

 

I know how to fly a DME VOR arc using standard steam gages by repeatedly adjusting the heading and resetting the OBS while monitoring the course needle as it swings from "2 dots on one side to 2 dots on the other".

 

Wait, what?

[Alpha Floor 237]

Wait, what?

 

I think he means the technique of not flying an actual arc, but rather a polygon. You fly straight segments and do your turns so as to keep the plane within two circles that are of radius +/- 0.2 NM to the actual DME arc...

[Don t moderate me this way 882]

That's how they teach it in GA planes for your instrument rating.

[ark 1,288]

I think he means the technique of not flying an actual arc, but rather a polygon. You fly straight segments and do your turns so as to keep the plane within two circles that are of radius +/- 0.2 NM to the actual DME arc...

Yes, the method I briefly described above is a "bare bones" technique for a minimally equipped IFR a/c. It only requires a VOR  & DME capability (no AP, GPS, etc) and keeps a relatively slow (100+ kts) a/c well within the +- 4NM protected area around the arc (should keep you within +- 1 NM). So this technique works for a typical basic GA single engine or light twin a/c. However, a heavy, well equipped a/c flying the arc at 200+Kts is another story and thus my original question.

Al

[willywonka 36]

 

 

However, a heavy, well equipped a/c flying the arc at 200+Kts is another story and thus my original question.

If you're flying DME arc in the 737 you're probably well under 200 kts. Anyway, the ways to draw the magenta arc has already been described. You can also draw a green arc from FIX page and follow that.

 

Or, why don't you just tune the VOR and display the bearing on the ND in CTR, and fly it exactly like you learned in a Cessna?

[ark 1,288]

Or, why don't you just tune the VOR and display the bearing on the ND in CTR, and fly it exactly like you learned in a Cessna?

 

Yep, I mentioned that in my original post. However, the main motivation for my question was just to learn how the airlines typically fly DME arcs, although I'm beginning to think they don't have to do it very often -- probably get vectors instead.

 

Appreciate all the comments and info.

Al

[Meese 5]

Well, RNAV is taking over the world. The FAA is still a bit on the analogue side, but you'll have to search far and wide to find medium and greater sized airports in the JAA countries that is not equipped with RNAV/P-RNAV STARs and approach procedures (and of course the CATII / III ils) . Well, that might be a bit of an overstatement, but the old procedures are fleeting more and more with each cycle. The fact is that, in my experience, the pilots too use the modern precision systems rather than cranking up the VOR/DME and ADF. It's just that much more convenient. I'm not saying there isn't any ol' stick 'n rudder flyers around, but at the end of a 8-10-12 hour shift, on your 4th, 7th or10th year on the job, I'm guessing a lot of people opt for the comfy straight in (more or less) STAR to ILS or GNSS/P-RNAV procedure.

I myself still light up with joy when I get to do some real work in the sim. Flying arcs, I prefer to bring up the cirular map and use continous HDG adjustment to keep the directional needle at my 90* until it's time to turn onto the inbound. This does indeed increase the work load considerably, keeping up with the published altitudes, speed restrictions, and conducting the approach checks of the plane itself, but that's where I find the most joy in the sim.

 

[willywonka 36]

 

 

However, the main motivation for my question was just to learn how the airlines typically fly DME arcs, although I'm beginning to think they don't have to do it very often -- probably get vectors instead.

Yep. It's easier to get vectored around. But as it's been said, flying it on raw data is probably the most convenient option. 

[Alec 370]

With a RMI instrument flying an DME Arc is much easier, keep that needled on the 90degree angle, from that you correct for wind using your DME.

[Fadamor 6]

It seems the DME arc is going the way of the dodo.  Based on the NextGen document put out by the FAA last year, the only reason the VOR's are still around is there is still GA without RNAV/RNP capability. Once that changes you can expect most of the old VOR/DME stations to be decommissioned.