https://soaneemrana.org/onewebmedia/AUTOMATIC FLIGHT CONTROL BY PALLET.pdf

Excellent book on all aspects of autopilot historic and current. Page 177 on deals with autoland systems specifically. It's worth understanding the principles before implementing them imo! 

8 hours ago, Christopher Low said:

You need to have VOR/LOC engaged before pressing the APP button. If I am conducting a circuit at an airport, and I want to fly a race track pattern in the 737, I usually press the VOR/LOC button when I am turning onto base, and then the APP button when I am turning onto final. That always results in the VOR/LOC capture during the final turn, followed soon after by G/S.

Not really though - you can arm VOR/LOC first if you want to but there's no advantage, and perhaps the disadvantage of forgetting to arm APP subsequently (two steps instead of one step). On an ILS, APP is armed straight away and you're set, unless in specific cases. Arming APP accomplishes the same thing arming VOR/LOC does plus arming G/S at the same button press too.

I am sure that I read somewhere (it may have been the PMDG 737 Tutorial #1) that VOR/LOC has to be armed first before APP.....

6 minutes ago, Christopher Low said:

I am sure that I read somewhere (it may have been the PMDG 737 Tutorial #1) that VOR/LOC has to be armed first before APP.....

That's not necessary. Arming APP arms both VOR/LOC and G/S at the same time, whereas arming VOR/LOC arms only VOR/LOC. The reason VOR/LOC exists is for cases where you have no glideslope like on a VOR approach or intercepting a VOR radial when not using LNAV. But it's not a prerequisite for arming APP on an ILS, because APP arms VOR/LOC anyway (plus G/S).

8 hours ago, Christopher Low said:

You need to have VOR/LOC engaged before pressing the APP button. If I am conducting a circuit at an airport, and I want to fly a race track pattern in the 737, I usually press the VOR/LOC button when I am turning onto base, and then the APP button when I am turning onto final. That always results in the VOR/LOC capture during the final turn, followed soon after by G/S.

Probably almost 1,000 approaches in the 737, and I have never done that. I just hit the App button when LOC indicator  becomes active. 

Edited March 31, 20242 yr by Bobsk8

Page 84 of PMDG 737 Tutorial #1 (for the 737NGX in P3D). That is where I picked up that little nugget of information

Edited March 31, 20242 yr by Christopher Low

58 minutes ago, Christopher Low said:

Page 84 of PMDG 737 Tutorial #1 (for the 737NGX in P3D). That is where I picked up that little nugget of information

I don't have the P3D version anymore so I can't check what it says. However, it's definitely not required to arm VOR/LOC first before arming APP unless in specific cases, for example when you're not yet receiving a glideslope signal but want to intercept the localizer. In most cases you'll have both signals though and you can just press APP straight away without the VOR/LOC detour.

I believe that there is a specific circumstance under which it is important to activate VOR/LOC prior to arming APP mode that involves whether or not the glide slope signal has been captured. Ideally, it should be possible to simply activate APP, intercept the localizer signal and then capture the glide slope for the descent. Indeed, that's the way ILS approaches are performed on most aircraft including most RW Boeing 737 family models. However, PMDG 737 variants are all equipped with Integrated Approach Navigation (IAN), something that's been discussed at length on the PMDG forum.

With IAN-equipped aircraft, one can also simply activate APP and fly the guidance (or have the AP do it for you), but you have to be certain that the glideslope signal is active before pushing the APP button. If the GS signal is not being received, guidance for that approach will be based on the internal RNAV system, not the ground-based GS component of the ILS system. This is subtly indicated by the color of the FD needles, green for the conventional ILS vs. magenta for the RNAV computed by the FMS. The approach minima for those two systems can differ significantly, so one does need to be aware of which approach is being flown. In addition to the color of the FD needles, the FMA will display different modes for the two case, GS for the ILS, and GP for the RNAV.

It is my understanding that relatively few 737 aircraft in the real world are equipped with IAN, but PMDG's all are. To my understanding, this is not an option that can be disabled as so many others are. So unless you're sure that the GS signal is being received at the moment that you want to press the APP button on the approach, the more certain protocol would be to activate VOR/LOC first, establish position on the LOC, and then when certain that the GS is active, press APP prior to GS capture.

For a much more authoritative explanation, watch this

 

Edited March 31, 20242 yr by jrw4
indicated by strikeout in two places. corrected below

I know this thread is about autoland in the PMDG 737. But if you really want easy and nearly flawless autoland capability, try the default Asobo 787 Dreamliner. All you need do with the 787 is select the APP button when intercepting the glideslope at your destination airport. Once you're below an altitude of about 1800 feet, you'll see a "Land 3" indication on your main panel -- indicating that the plane will indeed land itself for you. If this particular airport doesn't support autoland, you'll instead see a message saying "No Autoland." If the airport supports autoland, and if you set the autobrake before touching down, you can literally have a cup of coffee and watch the plane land itself, and then come to a stop on the runway center line. Over this past weekend, I landed once in Halifax, Nova Scotia, and again in Gander, Newfoundland. At both of these airports, the fog was so thick that the runway came into view only a 100 feet or so above the ground. In real life, the airports might have been restricted in their operation. Using autoland, "I" made two perfect landings.

Edited March 31, 20242 yr by David Mills

1 hour ago, jrw4 said:

This is subtly indicated by the color of the FD needles, green for the conventional ILS vs. magenta for the RNAV computed by the FMS.

What do you mean by FD needles? The FD doesn't change color, it's always magenta.

2 hours ago, Christopher Low said:

Page 84 of PMDG 737 Tutorial #1 (for the 737NGX in P3D). That is where I picked up that little nugget of information

I followed the same manual but for FSX! It helps with my flow and situational awareness whether it's essential or not.

DECEL: Flaps 1(to 5)

APPROACHING FF: Flaps 10

SELECT VORLOC

LOCALIZER ALIVE: Gear down/flaps 15

SELECT APPR

GS ALIVE Flaps 25

GS ACTIVE Approach flaps

None of this is IRL official I just it WORKS well with the 737 for me (and 777 in FSX) . 

The Boeing FCOM for the 737-800 states both VORLOC and APPR intercept localizer from the same lateral modes (HDG SEL, LNAV, or CWS R) but as APP is performing TWO functions it needs more prep before selecting. That's me summing up there's a page of info for each!

@threexgreen is correct. I was conflating the 737 with some other aircraft with regard to the display colors. Sorry. More correctly, it is the FMA indications that are important. In an IAN approach, the FMA reads FAC and G/P, while in ILS it reads VOR/LOC and G/S. The FD needles are always magenta. I can attest to the fact that it is possible to inadvertently get into the IAN mode by pressing the APP button before the glide slope is being received. It's the consequence of there being two functions assigned to the APP button in the design of this aircraft's control systems.

I have corrected the original post by striking over the two sentences regarding color.

I feel like this is getting a bit too convoluted, when in reality it's pretty simple.

• If flying a conventional ILS: Arm APP when cleared for the approach and both localizer and glideslope signals are being received (magenta diamond outlined or filled for both on the PFD). APP is the default approach mode. Use VOR/LOC only if the glideslope signal is not yet being received but the localizer needs to be intercepted right away. If no immediate capture of the localizer is required, just wait until the glideslope is alive and go for APP.
• If flying in IAN: Arm APP when cleared for the approach (or when close to the approach if no ATC is used in the sim).

That's it. You can of course arm VOR/LOC first if it's a preference, but this is not a requirement at all for APP. You'll just end up having to press two buttons at different times each to accomplish the same thing that pressing APP once does, meaning there is more workload and a higher risk of mistakes like forgetting to arm APP afterwards if you get distracted.

9 minutes ago, jrw4 said:

I was conflating the 737 with some other aircraft with regard to the display colors

No problem. I think you thought about the Airbus.

The PMDG autolands very realistically; even gives you the choice between fail passive and fail operational (most operators use fail passive, but you can switch it to fail operational and have full automatic centerline tracking during rollout.

As others have said, there is no reason to arm VOR / LOC before approach.  If that guidance exists in a PMDG tutorial, it's wrong - that, or it's their way of helping you avoid the pitfalls of their always-IAN-equipped sim.  The aircraft behavior of capturing FAC and/or GP instead of LOC and GS if you arm approach before receiving a valid loc and glideslope IS correct, it's just unexpected considering most 737s do not have IAN.  Many of us have been asking PMDG for quite a long time to make this optional.  While it exists in limited use in reality, IAN is functionally a useless mode.  It was originally designed for airlines to be able to fly satnav approaches without needing to train another approach profile, but the use cases are pretty limited (straight in approach etc.). In reality these days, almost everyone simply uses the more capable LNAV / VNAV modes.

Now if you want some fun, dispense with the autoland altogether and just hand fly the Cat III approach 😉.

https://www.twitch.tv/stearmandriver/v/1592372849?sr=a&t=102s