NDB holding with GNS430W

[achimha]

I am planning to fly my first NDB hold using the GNS430W instead of the ADF and I would welcome any input on whether I got things right. I tried before but didn't push all the right buttons...

To make things easier, I picked an approach for Frankfurt-Hahn EDFH, here's the approach plate (https://dl.dropbox.com/u/16258475/EDFH-IAC%20ILS%20OR%20LOC%20RWY%2003.pdf) and the STAR (https://dl.dropbox.com/u/16258475/EDFH-STAR%20RWY%2003_21.pdf).

I will arrive from the southeast via OLIVI to the HAN NDB. The GNS will drive the autopilot in GPS mode with GPSS and a flight plan. The OLIVI1R arrival and ILS 03 is selected in the GNS430. I want to enter the holding, make one complete hold and then start the approach as published.

I'm on the leg from OLIVI to HAN NDB on a track of 311°. As I'm in GPSS mode, the CRS pointer is pegged on the glass cockpit. Before arriving at HAN, I stop sequencing by pressing OBS. This should unpeg my course pointer and still show 311° as the selected course. The AP is now flying a course of 311° with the GPS as its source and it will not sequence to the next leg even when I pass HAN. Now at HAN, I choose to perform a teardrop entry. Therefore I change the course pointer to 330° and continue for one minute.

Is that correct? Will the course pointer on 330° do the right thing or do I have to disable GPSS and use the heading bug on 330°?

Next question: How do I perform the left turn and intercept the QDM 120 of the HAN NDB? I could disable GPSS, turn the heading bug left to an intercept course and the same time select 120° on the course pointer, watch the deviation bar and twist the heading bug to correctly intercept it. But maybe there is a more elegant method?

Now arriving over HAN NDB, I use the heading bug to turn left on 300° and fly outbound for one minute, using the map on the GNS430 to see when I am abeam the NDB (or does the TO/FROM flag work in that case?). Then again, a left turn and intercept of QDM 120 to HAN NDB.

At this point, I press OBS again to enable sequencing and enable GPSS. Per procedure, the AP should leave HAN DNB on a QDR of 090, go 4 DME out then left turn direct inbound HAN NDB, pass it and go outbound on QDR 227 until 12 DME, left turn and ILS intercept. From experience, I know that the GNS430 often only contains the waypoints but no information on what kind of manoeuvres to perform to get there. In the case of EDFH, there is an RNAV overlay for the approach and this is what the GNS430W will know and fly. However, in my example I don't want to do that, I want to fly the regular approach assisted by the GNS430.

When pressing OBS, the GNS430 sometimes asks for a QDM. Haven't figured out when exactly it will do that and what the exact effects are in combination with the autopilot and the course pointer.

Hope the GNS430 pundits can shed some light on this.

Thanks!

[peterh337]

There is a paragraph here (http://www.peter2000.co.uk/aviation/barcelona/) on two ways to fly a hold using a GPS.

They are the same for any "simple" IFR GPS - a KLN94 or a GNSx30.

The OBS/HDG method gives you the most control, and a totally accurate inbound track.

The HDG-only method is the simplest and frankly easily accurate enough in practice, and because it forces you to use your brain you don't get the standard "what the hell is it doing now" situation :)

With a GNSx30 coupled to an autopilot using ARINC roll steering (either directly, if the AP accepts ARINC steering, or via a roll steering converter which converts ARINC roll steering commands into a fake heading bug) and with a GPS database containing the holding pattern, you can fly the whole hold on the autopilot.

[achimha]

With a GNSx30 coupled to an autopilot using ARINC roll steering (either directly, if the AP accepts ARINC steering, or via a roll steering converter which converts ARINC roll steering commands into a fake heading bug) and with a GPS database containing the holding pattern, you can fly the whole hold on the autopilot.

From what I gathered, the GNS430 will fly the holding if it is a mandatory part of the procedure, not if it is optional. It doesn't even know about holdings that are not mandatory parts of approaches/departures.

I guess what you described in your article is probably the best thing to do. Use OBS with NAV (CORRECTION: with GPS, not NAV) for inbound and HDB mode with the heading bug to make turns and fly outbound legs.

Quoting myself:
When pressing OBS, the GNS430 sometimes asks for a QDM. Haven't figured out when exactly it will do that and what the exact effects are in combination with the autopilot and the course pointer.

I think I figured that one out using the simulator. When it is in VLOC mode (i.e. using the tuned VOR), it will ask for the desired course to the station. When in GPS mode, it will use the course pointer on the HSI. When in VLOC mode, it seems to always ask for the course to the waypoint, no matter if the waypoint is a VOR or something else.

[peterh337]

The HSI/EHSI course pointer (CP) value is supposed to be fed to your GPS.

There are many installations of the GNSx30 where this connection was not made. One avionics chap was most suprised when I told him about it :)

If present, this then enables the HSI CP setting to instantly transfer to the GPS.

What I find is this:

1) If the GPS/NAV switch is in GPS, and no flight plan is active, the EHSI CP is held at 360 and cannot be moved.

2) If the GPS/NAV switch is in GPS, and a flight plan is active, the EHSI CP is held at the current leg's track and cannot be moved.

3) If the GPS/NAV switch is in GPS, and the GPS is switched to the OBS mode, the EHSI CP can be moved and its value is copied to the GPS OBS track value. This is really handy.

To fly holds as discussed, you never need to switch the GPS/NAV switch to NAV.

But if you do switch the GPS/NAV switch to NAV (e.g. because you want the HSI for flying an ILS with) then you can turn the HSI CP but it no longer transfers to the GPS. You have to use the knob on the GPS to set the OBS value from then on. I use this sequence to fly an ILS, which is obviously flown in NAV mode, but I set a DCT to the airport and set the OBS to the ILS LOC track so I have a secondary reference for the lateral path.

I would think some of the above is installation dependent but it is probably standard for late-1990s avionics such as this (http://www.peter2000.co.uk/aviation/sn3500/final-panel-big.jpg).

[Dan the weegie]

Seems like a lot of work for a hold :) the old fashioned way works just fine :D

[achimha]

Thank you Peter, I think I got it. I never got around to using OBS mode with GPS and none of my flight instructors knew more than the very basics with the GNS430.

I can confirm your observations under 1)-2) provided that I enable GPSS. I don't know yet whether I have to disable GPSS in order to do 3) , i.e. make the course pointer moveable. If I have to do so, then I would also have to switch the autopilot from HDG to NAV and use its (crappy 1970s analog) technique of intercepting the chosen course. Where is the GPSS portion hidden in your setup? In my case it's a feature of the Aspen EFIS, the AP remains in HDG mode all the time. In which situations would you disable GPSS?

I also like your method of using the GPS as a backup to the ILS localizer with OBS and a direct. Will give that a try next time.

[peterh337]

Seems like a lot of work for a holdNot really, given that even the crude HDG-bug method saves you about 90% of the workload. You use NAV to get to the holding fix (obviously ;) ) and then use HDG to fly the appropriate hold entry leg, and then twiddle the HDG bug to fly the hold. Two twiddles per hold.

I've even had a pee while doing that :) You have 1 minute.

I never got around to using OBS mode with GPSIt's brilliant. Trust me :)

What kit have you got? How do you enable/disable GPSS?

I don't have GPSS. All I have is the EHSI (http://www.peter2000.co.uk/aviation/sn3500/), whose CP flips to the next leg's track automatically at each waypoint, and enroute that is practically the same thing as GPSS because the resulting track deviation, when flying with the GPS set to 1nm full scale, is zilch.

It doesn't give you a mathematically perfect steer but then GPSS doesn't either in all situations (AFAIK even latest airliners don't fly mathematically perfect holds, computed perfectly for the wind aloft while flying exact 0.5 or 1.0-rate turns). What GPSS gives you is the ability to fly stuff like holds and DME arcs - IF the GPS has them in its database.

Regarding that "unpublished" LELL holding pattern, I have heard (not checked it) that it is published as a hold for LEBL. I thought that practice (using e.g. Le Bourget SIDs at Pontoise) was mostly French :) But the point is that no GA GPS I know of will fly an unpublished hold.

I also like your method of using the GPS as a backup to the ILS localizer with OBS and a direct

Do remember to use a DCT waypoint which is on or close to the runway. At some very big airports, a DCT [airport name] may get you the centre of another runway. IIRC, it is supposed to be the centre of the principal instrument runway, but it may be the centre of the airport. I tend to look on the plate and use some navaid which is obviously next to the runway. But it won't ever be as accurate as the localiser. It may pick up a mis-set ILS though, and should pick up a mis-set HSI CP (which in extreme cases, with an EHSI, can cause you to fail to intercept the LOC).

[Dan the weegie]

Ok, peeing while in the hold is fairly impressive, would be more so in my crate but I guess then it really would be the "wet dream 31" :D not having autopilot I know not of these bizarre things you speak of.

[tmmorris]

Even on my Garmin Aera 500 the OBS/twiddle method is a damned sight easier than ADF holds (monitored on the ADF, naturally ;) ). As the Aera allows you to type the OBS selection directly on the touchscreen the sequence is

Inbound to the holding fix: switch to Panel mode and from from flightplan mode to DCT mode, enable OBS mode but leave the OBS alone

On arrival at the hold fly the appropriate outbound heading to join the hold* while entering the hold inbound track on the OBS

Fly the hold as if it was a VOR hold (using the HSI purple pointer to indicate abeam)

*OK, if picky, for teardrop entry use the OBS to fly the 30deg offset if you must...

Tim

[Pugilistic Animus]

Holding in general...turn the Shortest way back around to the beacon/way point on the Non-holding side..don't worry if you aint too exact...fly the correct holding timing or leg length on the Holding side...wind? double the crab angle obtained on the holding side in and fly it opositely on the Non-holding side...:zzz:

[peterh337]

Indeed; holds are trivial once you can see where you are :)

[achimha]

OK, I tried the OBS method and it appears to work. Once I press OBS in GPS mode, the GNS430 will ask me for a course, offering the current course as the default. After that, the course pointer on the EFIS becomes moveable.

However, when asking for a course, the GNS430 decides whether this is a FROM or a TO course. It was not possible to change the TO/FROM. I wonder what the exact criteria are for it to show TO or FROM. Probably it will apply the VOR radial logic and the TO/FROM toggles as I adjust the course. Didn't try that, just noticed that once it was TO and in the other case FROM.

What I basically ended up doing was driving the AP with the heading bug all the time and watching the course pointer / deviation bar with the OBS inbound radial set for adjusting the heading bug. When supposed to go inbound a fix, I used the handheld Garmin with its projected track line.

As soon as I set the autopilot to NAV mode, it will perform its standard intercepts to center the deviation bar and that is not always what you want to do when you're rather close to the fix. So I haven't found a good way to actually use the OBS/GPS information to drive the AP in a sensible way.

[peterh337]

That's a different OBS functionality to what I have seen previously but I have never flown behind a GNSx30 and actually done something nontrivial with it.

Normally, you would specify TO for the OBS value, because that is how it is used. You use the OBS function to fly to the "DCT" waypoint.

It's also best to keep the procedure simple. For example a hold may be defined on a VOR radial, and that radial will obviously be from the VOR (being a "radial" :) ). But I would still use the TO mode. Especially as you are more than likely to be flying to the holding fix from some random place, not from overhead the VOR.

As soon as I set the autopilot to NAV mode, it will perform its standard intercepts to center the deviation bar and that is not always what you want to do when you're rather close to the fix. So I haven't found a good way to actually use the OBS/GPS information to drive the AP in a sensible way.

I wonder if perhaps you are seeing the famous "Honeywell functionality". I discovered this right away in 2002 but everybody denied it.

Basically, if tracking a GPS track, you must not press NAV unless the HSI bar deviation is at least 3 divisions (3/5 of full scale). If you fail to obey this, the AP turns onto the current CP track and then gradually adjusts the heading to reduce the error. Usually, this is really crap. There are two workarounds. One is to do the intercept in HDG mode and switch to NAV only when right on track (but even then the AP usually does some wiggles and confuses radar ATC) and the other one is to set the GPS sensitivity from the enroute default of 5nm FS to 1nm FS or even 0.3nm FS; this obviously increases the HSI deflection...