Holds with the Garmin

I’m working on my instrument rating and my instructor and I want to know if there are any “tricks” to using the 430 when flying a published hold over an NDB. If the hold is part of a published missed approach procedure or if a racetrack is part of the procedure turn, the 430 is great at helping you follow the racetrack. But there seems to be a lot more guesswork involved in flying a published hold over an NDB. Any suggestions?
Thanks. Heath

Heath,

Can you provide a specific example of a published NDB hold that you’re attempting to execute with the GNS 430? This may make it easier to answer your query.

Thanks,
Roger Freedman

I agree with those who have advocated use of the OBS function on the 430–it is an extremely useful and convenient tool for many things, including holds.

Your inbound leg to the holding fix will work just fine because you are indeed trying to follow a track over the ground (represented by the magenta line drawn by the 430).

However if you are holding in a significant crosswind, don’t try to follow the depicted racetrack on the outbound leg. If you do this your downwind turn will need to be significantly greater than standard rate and your upwind turn will be significantly less! The autopilot with altitude hold can likely handle it with no problem, but if you do it flying manually it could be uncomfortable and/or bring a furrow to the brow of an examiner. Here the tried-and-true formula of applying twice the crosswind correction on the outbound leg as on the inbound leg should work well. On the inbound leg just observe the difference between the ground track on the gps and the compass or DG’s magnetic heading, then on the outbound leg make it twice that difference into the crosswind. Works like a champ.

Holds are easy with the 430!

To do holds here is what I do. Suppose you want to a right hand hold with inbound 210. Set up the autopilot on altitude hold. Enter direct to wherever you want to plant your imaginary beacon. Dial 210 with the HSI and press OBS: this will draw a line representing the inbound track. Now fly along this (or do whatever sector join you want to the “beacon”) - NAV APR. Suppose for instance you are doing a direct join along 210. Befor you get to the beacon set your heading bug about 90 degrees to the right. As soon as you get to the beacon switch to heading mode and the aircraft will turn right. As it comes about set the heading bug to your outbound heading. At the end of the outbound leg turn the heading bug to the right and let the aircraft follow round. Then switch back to NAV APR so that the aircraft recaptures the inbound. Keep repeating this as much as you want. I find this works extrememly well.

An example would be “hold east of the PVC NDB on the 270 bearing, left turns.”
Thanks. Heath 157CD

Thanks, I’ll try it out. But I’ll have to “hand” fly it, since the examiner doesn’t seem to be too interested in how the autopilot flies (at least not for the purpose of my check ride). I haven’t played around much with the OBS function; I need to start. Thanks again. Heath 157CD

The Garmin 430 OBS feature is a very powerful tool - essentially it turns any arbitrary waypoint into a virtual VOR, with the added benefit that the selected radial is graphically depicted on the 430’s moving map, so you can instantly see where you are in relation to the fix and the course line. This is one of the features that makes the 430 a better piece of kit than UPSAT’s GX-60 (it does NOT have the OBS feature).

Definitely something worth practicing, but in fact it’s not at all hard to use - way easier with the map display than if you only had the OBS indicator.

One point to note - last time I checked, the course line on the Arnav didn’t get updated correctly if you changed the track setting on the OBS - the 430 redrew the magenta line, the Arnav didn’t. You can force it to redraw by pressing the OBS button twice.

My GX55 has an OBS function, so I’d presume your GX60 has it too. Once you’ve selected and activated a Direct-To waypoint, press the Direct-To button twice and you’ll be prompted for the OBS course. (Mine has a VFR installation so it’s not hooked to a CDI or HSI so I don’t know if it would automatically “read” an OBS from them.)

The GX60 does has have an OBS function, but it doesn’t draw it on the map, but will deflect the CDI.

I had one in my 172 for a few years. However after flying a huge 5 hours with the new Cirrus and the Garmins, I can definitely say the Garmins are nicer.

Clyde wrote:
“One point to note - last time I checked, the course line on the Arnav didn’t get updated correctly if you changed the track setting on the OBS - the 430 redrew the magenta line, the Arnav didn’t. You can force it to redraw by pressing the OBS button twice.”

Aha! You’ve just salvaged the usefulness of the OBS for me. I’ve been trying to figure out why I couldn’t perform this particular “Stupid Garmin Trick” with the Arnav.

-Curt

Re:

Here the tried-and-true formula of applying twice the
crosswind correction on the outbound leg as on the
inbound leg should work well.
At the risk of starting a war, I’m going to have to point out that, according to the FAA, the double-the-angle technique is actually tried and false, and the proper correction is to TRIPLE the angle!
I first encountered this triple-the-angle theory on my ATP ride in 1979. The designee that I rode with, Jim Richter, had a big thing about it, and he told me he was pestering the FAA about it. His theory was that during the 4-minute holding pattern 3 of those minutes are subject to the drift that youÂ’re trying to compensate for. Makes sense when you think about it. You are being skewed during the 2 turns as well as the outbound leg. At that time, the FAA still published a recommendation of doubling the angle on the outbound leg.
But Jim must have finally got to ‘em. If you look up section 5-3-7 (j)(6)© in the AIM it reads:
“Compensate for wind effect primarily by drift correction on the inbound and outbound legs. When outbound, triple the inbound drift correction to avoid major turning adjustments; e.g., if correcting left by 8 degrees when inbound, correct right by 24 degrees when outbound.”

(If you are a registered AOPA member you can click http://www.aopa.org/members/files/aim/chapter_5.html#5-3-7here to view this section.)

After trying it both ways, I have to say that I think Jim was right. Triple works better than double. Someone adept at physics and calculus (Roger – are you listening?) with a little time on their hands can probably prove what seems intuitive – double is not enough, triple is too much, but it is closer to triple than double.

> I had one in my 172 for a few years.

Derek,

I also had the GX60 in my previous airplane – also a 172. When I had it, I described it as “Great”. Now, I’d call it “Nearly Adequate”. I wonder what will come along next, to demote my beloved brace of Garmins?

  • Mike.

In reply to:


The GX60 does has have an OBS function, but it doesn’t draw it on the map, but will deflect the CDI.


True, but to use the OBS function, you have to enter the desired course into the GPS - the GX60 does not read the OBS setting from the indicator itself. Sufficiently un-ergonomic to justify pretending it’s not there [:)]

No doubt we’ll be complaining about the high cost of replacing our antiquated panel in our Cirrus airplanes in 10 years. Whenever you start getting into computer type functionality and technology you’ll see a substantial improvement and speed of evolution.

I’m sure just after we decide to get a satellite weather system, the second generation will be far superior for less money and be available 6 months after it is installed. The same for collision avoidance. Oh well. Savor the moment.

You’re correct that it isn’t as simple as spinning a single knob, but I successfully used it for both holds and intercept victor xx or radial xxx.

No doubt though the Garmin’s connected to an HSI or a CDI with an OBS are a MUCH better interface.

Triple works better than double. Someone adept at physics and calculus (Roger – are you listening?) with a little time on their hands can probably prove what seems intuitive – double is not enough, triple is too much, but it is closer to triple than double.

Gordon,

Alas, having excess time on my hands is not one of my problems!

Maybe I’ll assign this to my freshmen honors physics students… Quite by coincidence, they actually have a related problem on this week’s homework. They have to find the formula for the wind correction angle for an airplane subjected to a wind blowing at an arbitrary speed in an arbitrary direction. (Evil, aren’t I?)

Cheers,
Roger

Having taken my checkride 3 hours ago I will agree with triple. As an example, if flying the inbound without a wind correction you would be blown “X” feet downwind but a crosswind correction of 5 degrees for the 1 minute inbound will prevent the X feet of downwind drift, Then you will be blown X feet downwind during each turn and the outbound. Since you can’t correct the downwind drift in either turn, you have to make all three corrections during the 1 minute outbound. Now if there is a headwind or tailwind component that makes the outbound and inbound “times” unequal all bets are off. If your outbound is extended then a little less than triple, a little more than triple if your outbound is less than a minute.

They have to find the formula for the wind correction angle for an airplane subjected to a wind blowing at an arbitrary speed in an arbitrary direction. (Evil, aren’t I?)
Roger,
That IS pretty evil. Especially because every knows the answer:
Wind Correction Angle (Aircraft traveling at arbitrary speed, arbitrary direction, with wind coming from arbitrary degrees at arbitary knots) =… ARBITRARY!
I’ve flown that way for years. As long as you’re not too particular about your destination, you never get lost. [;)][;)][nudge][nudge] (Oh, there’s no symbol for that? There should be!)

  • Mike.