ILS approach, what am I missing?

[jkmess]

I'm pretty new to MSFS and, while I've watched videos and read guides online, I cannot get a plane to fly the glideslope on autopilot. It will fly the approach route fine, hitting the waypoints in NAV mode (G1000). It will then automatically switch CDI to LOC and line up with the runway moderately well. However, nothing I've tried will get it to fly the glideslope. I've tried leaving it in NAV mode, I've tried putting it in approach mode. Please help!

[ZombieHunter]

Tune in the ILS and turn on LOC hold on the AP. You will have to fly the plane to the intercept point but once you are established on the localizer LOC will hold it and the glideslope. LOC is not a miracle worker. It isn't going to fix a shoddy approach.

[Caelib]

You have to hit the "APPR" button to lock on to the glide slope when you intercept it. Once the glide slope is locked, the G-1000 will read "GS" in the top near the other auto-pilot fields (such as "LOC", etc).

Once you are locked, you will need to manually adjust the throttle to maintain the correct airspeed. And don't forget your flaps :)

[Atomicdogg1]

some runways only have localizer and no glideslope

[minot]

As Caelib correctly pointed out, any autopilot has two separate functions, one being responsible for lateral navigation (HDG, NAV, etc), and one different for vertical navigation (ALT, VS, FLC, VNAV etc).

When it comes to approaches, NAV mode is fine for laterally flying an approach (i.e. aligning the aircraft with the localizer), but as to aligning the aircraft with the glideslope, you have to activate the APPR mode. Note that you always have to intercept the GS from below. Once the APPR button is pressed, the indication "GS" should appear on the PFD in white with the previous mode (e.g. ALT) still being green as it is active (white = armed, green = active). Once the glideslope is intercepted, GS should turn green and the autopilot will follow the glideslope.

Unless the aircraft has autothrottle installed and it is correctly configured, you have to manually adjust your throttle in order to maintain the correct speed. Configuration changes (flaps, gear) also have to be done manually. Real world procedures normally provide for the aircraft being already fully configured at the FAF (final approach fix), which is the point where the final descent starts according to the published procedure (glideslope intercept).

As Atomicdogg1 pointed out, you have to distinguish between ILS approaches (lateral and vertical guidance) and LOC approaches (only lateral guidance). From a practical perspective, LOC approaches are flown identically to VOR approaches with the only significant difference that a localizer (LOC) is more precise (sensitive) than a VOR. In both cases, there is no vertical guidance other than published step-down fixes (defined by DME or time) to a minimum descend altitude/height. Therefore, it is impossible for an autopilot to autonomously fly a LOC/VOR approach - it can only fly the approach laterally, whereas the pilot as system operator is responsible for flying the approach vertically (e.g. in VS mode by continuously adjusting the descend rate).

[John W]

MSFS 2020 has a few quirks when flying ILS approaches that P3D and X Plane 11 do not. One thing in particular is the distance at which the glide slope can be detected. Both P3D and X Plane 11 seem to be able to detect (lock on to) the glide slope from further out, say 20 miles. FS2020 on the other hand doesn't seem to be able to do that and it detect (locks on to) the glide slope closer in. What this means when flying an approach for me is that I cannot intercept the glide slope at a higher altitude. Instead, when flying an ILS approach in FS2020 I have to step the aircraft down to final approach fix altitude manually using the autopilot altitude setting.

Another quirk I have encountered when flying an ILS in FS2020 is the inability of some of the aircraft to fly the glide slope at speeds above approach speed. What I have to do is configure most aircraft well before the final approach fix, be at final approach fix altitude and in approach mode on the autopilot in order to intercept a glide slope. With those conditions met once the aircraft starts down the glide path I then adjust the throttle to maintain approach speed.

[Team Triss]

What are you missing?

The runway, apparently.

[Atomicdogg1]

If the runway has ILS then you need to know the runway altitude and the ILS frequency to put in NAV radio. Once you have the right frequency in NAV 1 radio you can pick up the beacon at about 25 miles out. Once you have the beacon if your auto pilot is using GPS you need to switch to NAV 1 use localizer so it will track the runway beacon. Once you have the localizer beacon you can switch the autopilot to approach mode "CTRL A" you want to be about 2000ft above runway altitude before 10 miles out and you will intercept the glideslope just after you are 10 miles out. It works for me everytime. You can intercept the glideslope a little farther out if you are at a higher altitude but my general rule of thumb that works is 2000ft above runway altitude.

[yorran]

I don't get something here. Atomic and Minot, you're talking about NAV (gps) mode when aligning with the runway LOC (radio).
I understand some planes do switch modes by themselves, I can think of DA62 iirc, but not exclusively. I also understand that you shouldn't align to a LOC if you're more than 30° in your NAV heading. But for the sake of arguments, isn't it more precise to switch to LOC in approach as soon as it comes possible, and then to APP to include the glideslope as it starts to come about ?

Not a critisism by any means, I'm only a simmer and wish to understand how NAV would align you better to the runway than LOC. Feel free to speak your mind as you see fit.

[jkmess]

Publicado originalmente por LoR Team Triss:

What are you missing?

The runway, apparently.

:D

[whitbymermaid]

Publicado originalmente por jkmess:

I'm pretty new to MSFS and, while I've watched videos and read guides online, I cannot get a plane to fly the glideslope on autopilot. It will fly the approach route fine, hitting the waypoints in NAV mode (G1000). It will then automatically switch CDI to LOC and line up with the runway moderately well. However, nothing I've tried will get it to fly the glideslope. I've tried leaving it in NAV mode, I've tried putting it in approach mode. Please help!

I read your post a couple of times because it's easy to launch in to an answer without really understanding what the author is really asking for.

You say you're new to MSFS, are you also new to flying, and specifically instrument and IFR flying?

You're using the G1000, you're also using GPS as the Nav mode on your route with the autopilot engaged. You also confirm the Nav is switching from GPS to the navigation radio number one to display the localiser for the selected ILS at the end of the route.

What you haven't stated is anything to do with the planned or actual altitude, either along the route or at the approach stage?

As others have said, you must be at or below the published ILS glideslope altitude at the final approach fix for the autopilot to capture it and follow the beam down towards the runway.

One of the biggest problems with trying to fly an IFR approach with the sim is that most users seem not to be using a/the chart for the specific approach as they're not provided with the sim. That leads to those users having no idea as to the position of the final approach fix or its altitude, so not much chance of being on the glideslope at the correct point for the AP to lock on to it. The localiser isn't such a problem because it's generally pointing within a few degrees of the runway heading and spreads out to up to 35 degrees either side.

[Atomicdogg1]

I stated to switch to localizer as soon as you have the beacon then switch to approach but in order to capture the glideslope you have to be within the correct altitude range.

[minot]

Publicado originalmente por yorran:

I don't get something here. Atomic and Minot, you're talking about NAV (gps) mode when aligning with the runway LOC (radio).
I understand some planes do switch modes by themselves, I can think of DA62 iirc, but not exclusively. I also understand that you shouldn't align to a LOC if you're more than 30° in your NAV heading. But for the sake of arguments, isn't it more precise to switch to LOC in approach as soon as it comes possible, and then to APP to include the glideslope as it starts to come about ?

Not a critisism by any means, I'm only a simmer and wish to understand how NAV would align you better to the runway than LOC. Feel free to speak your mind as you see fit.

Thank you for your input and just for the sake of completeness: "Nav mode" is the autopilot mode which basically follows the (primary) navigation source, be it GNSS/RNAV (magenta) or raw data such as VOR or LOC (green). NAV only refers to the AP mode (even if the PFD indicates LOC when following the signal of a localizer).

You are referring to a mode of the respective avionics unit (such as the G1000): Referring to the G1000/G3000, GNS430/530 GTN650/750 and so on, there is always a button named "CDI" which switches between raw data (i.e. tuning in the frequency and - very simplified - using the aircraft's antennas and arrays in order to find the direction to the selected station - needles are green) and satellite-based navigation (RNAV, where all navigation is derived from the aircraft's position above the underlying WGS84-model of the earth as determined by the satellite-based navigation equipment of the aircraft - needles are magenta).

You are correct: NDB, VOR, LOC, ILS etc approaches have to be flown raw-data and some avionics do automatically switch modes when arriving at the IAF (or the FAF at latest IIRC).

As to the correct procedure to align with final approach course and intercepting glide slope: Published procedures always dictate (at least) one point before the final approach fix (which is the point where descend starts). Even if ATC clears you a shortcut, they must not give you a "direct" to the FAF itself but only to the last fix before the FAF, so you end up aligned correctly with the approach as defined by the published procedure.
For a simple example, see https://eaip.austrocontrol.at/lo/211203/Charts/LOWG/LO_AD_2_LOWG_13-1-2_en.pdf: Depending on the direction you are coming from, you would be cleared to GRZ VOR in 4000' or to VAGIL in 3500'. From GRZ you would finally end up on final approach course in 3300' and intercept the glide slope at 6.8nm DME from OEG (which is the localizer for this ILS approach). From VAGIL, you would remain in 3500' until the FAP (which in this case is slightly earlier, namely at 7.4nm DME from the localizer).

Intercepting a glideslope before reaching the FAF does not make any sense if flown correctly:
Firstly, you are only allowed to intercept a glide slope from below (otherwise there might be a risk to intercept and follow a false signal).
Secondly, it is a common procedure to be fully configured for landing when intercepting the glide slope. One reason therefore is that some high-performance aircraft might have difficulties to decelerate during the descend in order to further lower the flaps etc. Another reason is that any configuration change results in significant performance changes, so you would have to significantly correct power setting and trim during your approach to the runway. Especially during IFR approaches (assuming no sufficient visibility), you should be free to exclusively concentrate on maintaining track and glide slope / descend rate / check altitudes.

[ZombieHunter]

LOC will not hold the glide slope. That is approach. But even then you can't just set things and forget them. Even with auto throttle you cannot do this. A select few aircraft are CAT 3 autoland and are required to perform such landing every so often to make sure the system is working. But most approaches in most aircraft are hand flown with guidance. Relying too much on automation in such a critical phase of flight is a recipe for disaster. Also APs in the aircraft I have flown have specific instructions as to when they should be used and when they should not be. There are also different types of GPS. And some are only certified for VFR only flights and/or cannot be used as a primary navigation source.

I've also never intercepted a glide slope 20 miles from the runway and have no idea why you would ever do this. My experience with glideslope intercepts has been what Minot suggests. But I am not doing IFR training at the moment so someone who is IFR certified would know way more than I. I do know 100% though that you do not rely on automation or some system in the aircraft to get you on the ground in 99% of aircraft. You are the one flying the plane and it is your responsibility to be in control of it at all times. Fly the plane is the number one priority.

The best approaches are stable and in control. Even if you are a bit high or a bit low that can be fixed. An unstable approach is a go around or risk bending the aircraft. As for IFR there are published minimums that you must meet in order to land. Once you break out it pretty much becomes a VFR approach.

[yorran]

Thank you both for answering.
I fly mostly IFR, and include approaches before final in my plans, something I didn't say in my initial question. This means my flightplans do include a complete pattern before final, and I usually intercept the ILS at 2500 / 3000 ft from the runway altitude at the right distance, and under the glide slope.

What I thought I read was, when you are ready, at the right time, to switch to APP, you stay on GPS. That didn't make sense to me (unless you're flying RNVAV approach of course). That NAV definition redefined and answered my question.
I appreciate the time you took to answer.

[jkmess]

Thanks for all of the helpful replies. Yes, I'm reasonably new to this sim and flying sims in general. It would be helpful if the sim had a manual, but very little does these days. Anyway, I'm slowly learning and enjoying almost every minute.