Preconditions of HGS approach modes

[SinusJayCee 38]

Hi all,

 

I wasn't able to activate one of the HGS approach modes (AI, AII, AIII) yet. I set the RW length and elevation as well as the glideslope angle at the HGS control panel, I'm in APPR mode (nav source FMS), LOC and GS have been captured, and FD is on.

 

The manual (Vol 5) is saying on page 132:

Zitieren

Please bear in mind that some modes require some pre-conditions to be met before it can be activated.

 

So I assume that one or more preconditions are not met.

 

Does anybody know what I'm missing?

 

Thank you in advance for your help!

[remarck 2]

Hello you can try this (extract from the HGS Pilot guide)

 

 

 

AIII Mode Requirements and Conditions

These AIII conditions are necessary to arm AIII Mode:

• The runway elevation is set.
• The G/S angle is set.
• IRS #1 and IRS #2 are in NAV mode.
• All reversion selections (ATTD HDG, AIR DATA, EICAS, DISP
CONT, MFD reversion) are in NORM position.
• Basic attitude (pitch, roll, heading) data are within limits.
• All sensors/input data are valid.
• There are no HGS BIT faults.
• #1 and #2 VHF Navigation Receivers are tuned to the same localizer
frequency.
• FCS armed lateral and vertical modes are LOC and GS.
• The aircraft is above 800 feet AGL.
NOTE: AIII Mode can be selected on the STBY line before some of the
conditions necessary to arm the mode are met. “AIII” (with no
question mark) shows on the HCP STBY line, but does not
show as an armed mode on the Combiner display until all of
the conditions necessary to arm the mode are met.
Before AIII can become the active mode, FCS captured modes must be
LOC and GS.
AIII Mode Selection
Use this procedure to arm AIII Mode:
NOTE: AIII must be armed above 800 feet AGL.
1. Push the ACT pushbutton.
2. Push the STBY pushbutton until “AIII?” shows.
3. Push the ENTER pushbutton.
The AIII Mode is now armed. “AIII” shows on the HCP STBY line. When
the FCS captures LOC and GS modes, “AIII” flashes in the upper left
corner of the Combiner display, and the HGS changes to AIII Mode.

 

I don't know why nobody answer in this forum about HUD problems ?

I also had a question with no response about the management in descent with the HUD (why is the snowflake absent when using the HUD ?)

[SinusJayCee 38]

Thanks for your answer!

 

vor 4 Minuten, remarck sagte:

• #1 and #2 VHF Navigation Receivers are tuned to the same localizer frequency.

I guess this was my problem. I at least didn't set both receivers to the same frequency myself and I don't know whether autotuning does so. All other preconditions were met iirc.

 

vor 6 Minuten, remarck sagte:

2. Push the STBY pushbutton until “AIII?” shows.

Is the part with the question mark implemented? I can't remember seeing it before pressing ENTER. I will check this next time.

 

vor 7 Minuten, remarck sagte:

I don't know why nobody answer in this forum about HUD problems ?

My only explanation is that not that many people are using the HGS. I use it quite rarely myself as well.

 

vor 7 Minuten, remarck sagte:

I also had a question with no response about the management in descent with the HUD (why is the snowflake absent when using the HUD ?)

I did see your question, but don't know the answer. I've to say that for me the HUD is rather for takeoff and approach. For descent, the PFD is sufficient for me. But would of course be nice to have it fully functional.

[remarck 2]

3 hours ago, SinusJayCee said:

4 hours ago, remarck said:

 

I did see your question, but don't know the answer. I've to say that for me the HUD is rather for takeoff and approach. For descent, the PFD is sufficient for me. But would of course be nice to have it fully functional.

 

Thank you too for your answer. 

It will be nice to get this vertical information for RNAV approach for example, this will allow me to keep the focus on the runway through the HUD instead of changing every second the view in the cockpit.

I asked this question in my post because of the HGS guide that say that it is possible to see a snowflake or a vertical target speed like on the PFD.

[SinusJayCee 38]

On 27.8.2021 at 23:19, remarck sagte:

 

Thank you too for your answer. 

It will be nice to get this vertical information for RNAV approach for example, this will allow me to keep the focus on the runway through the HUD instead of changing every second the view in the cockpit.

I asked this question in my post because of the HGS guide that say that it is possible to see a snowflake or a vertical target speed like on the PFD.

That's true, for RNAV approaches this feature would be handy. But I've to admit that I don't now how precise the vertical guidance of the CRJ is anyway. For enroute descent this is fine, but for approach I do my own estimations and corrections. At LNAV minimus (usually around 500ft), you need to fly visually anyway. Here I really like the HUD, because you can track the runway  and PAPI lights through the window while having your speed, attitude, altitude and vertical speed in sight.

[SinusJayCee 38]

@remarck FYI, activating AIII mode using the preconditions posted by you worked perfectly fine. I set everything up as described and after LOC and GS were captured, AIII activated automatically. It was in fact quite necessary, because the weather was really bad and I wasn't able to see the runway until a few feet above minimums

[KuntaKinte 210]

@SinusJayCee  Could you do me a favour and make a video of that same approach?

[remarck 2]

4 hours ago, SinusJayCee said:

@remarck FYI, activating AIII mode using the preconditions posted by you worked perfectly fine. I set everything up as described and after LOC and GS were captured, AIII activated automatically. It was in fact quite necessary, because the weather was really bad and I wasn't able to see the runway until a few feet above minimums

Can i ask you a question ? I don't know what is the use of the AIII manual mode for approach, is it not better to leave the autopilot for AIII approach ? What does it change when you set AIII in the HUD instead of PRI mode ?

[remarck 2]

I quote the manual :

 

"AIII Approach Mode

NOTE: Obtain operational approval from the appropriate regulatory
authority before conducting HGS low-visibility operations.

The HGS AIII Mode is specifically designed for manual ILS approach and
landing operations to CAT III minimums"

 

Usuly i let the autopilot managed the descent until the minimums, so i don't know what is the benefit of manual AIII  approach ?

[SinusJayCee 38]

vor 18 Stunden , KuntaKinte sagte:

@SinusJayCee  Could you do me a favour and make a video of that same approach?

I always fly with live weather, so that is hard to replicate. What exactly do you want to see? Maybe I can make a video that shows that.

 

vor 13 Stunden , remarck sagte:

Usuly i let the autopilot managed the descent until the minimums, so i don't know what is the benefit of manual AIII  approach ?

 

The point is the CAT III part here. At CAT I conditions, you can let the AP fly the plane to the corresponding minimums, establish proper visual reference to the runway, disconnect the AP and land the plane manually. But if the RVR is below CAT I, this is not longer possible. In order to land a plane at CAT II or CAT III conditions, some additional technical systems are required because the visual reference to the runway is established too late for a safe landing.

 

Modern airliners like the A320 and 738 have autoland systems, where the AP can land the plane automatically (CATIIIa) and can even perform the rollout (CATIIIb). The CRJ however has no autothrottle, and as a consequence, no autoland system can be implemented here. Because of that, the CRJ wouldn't be able to operate at CAT II or CAT III conditions. To overcome this limitation, it is equipped with the HGS allowing for manual CAT II or CAT III (a) approaches. So instead of having the AP landing the plane at bad visibility, you need to disconnect the AP not later than CAT I minimums and land it manual, while the reference to the runway is not established visually but using the HGS.

 

Here is a Wikipedia article about ILS CAT II and CAT III operations:

https://en.wikipedia.org/wiki/Instrument_landing_system#Special_CAT_II_and_CAT_III_operations

 

With that said, one has to add that the HGS is not fully implemented in the Aerosoft CRJ. It is supposed to display the terrain as well the position of the runway, which is not the case in the sim. In addition, it is not collimated, i.e., when you move your head in the sim, the data on the HUD moves as well instead of being fixed with respect to the environment. Both are limitations of MSFS I believe.

 

Here are two videos how it looks like in the real plane:

 

 

vor 13 Stunden , remarck sagte:

What does it change when you set AIII in the HUD instead of PRI mode ?

The main difference between PRI and AIII is that the latter is decluttered and only shows the information required for the approach but nothing else.

[remarck 2]

Thank you so much for your answer it is very clear, I didn't know that the CRJ wasn't ables to fly Cat 2 and 3 automatically. 

[KuntaKinte 210]

1 hour ago, SinusJayCee said:

I always fly with live weather, so that is hard to replicate. What exactly do you want to see? Maybe I can make a video that shows that.

 

It's not about the weather - in fact CAVOK would be even better   I would be interested in the airport and runway of your approach, the setup of the HUGS (control panel) and the symbology displayed on the combiner.

[SinusJayCee 38]

vor 3 Stunden , KuntaKinte sagte:

 

It's not about the weather - in fact CAVOK would be even better   I would be interested in the airport and runway of your approach, the setup of the HUGS (control panel) and the symbology displayed on the combiner.

All right, I'll try to make video when I find some free time.

[SinusJayCee 38]

Here's the requested video:

 

I set up the plane and everything quick and dirty, so please don't complain if not everything is done by the book I for example forgot the set the DH and at some point I loose too much speed. But all in all in shows setup of the HGS and everything quite good.

 

I guess I also found a bug, which I noticed earlier already: When pressing APPR, the AIII mode is enabled already, which is not correct I believe. It then reverts back to PRI and finally correctly engages when GS is captured.

[KuntaKinte 210]

Thank you very much for the video! And I appreciate you flying into my home base

 

You are right: AIII is only activated with GS capturing. I wasn't aware that you could re-engage AIII once it reverted to PRI mode. But still, this is not correct.

As for the symbology, there are several flaws I have yet to report.

[SinusJayCee 38]

Vor 1 Stunde, KuntaKinte sagte:

And I appreciate you flying into my home base

I actually fly to and from EDDH pretty often

 

Vor 1 Stunde, KuntaKinte sagte:

You are right: AIII is only activated with GS capturing. I wasn't aware that you could re-engage AIII once it reverted to PRI mode. But still, this is not correct.

As far as I know, the first engagement is not correct, but the second engagement when capturing GS is when it actually should have activated.

 

Vor 1 Stunde, KuntaKinte sagte:

As for the symbology, there are several flaws I have yet to report.

I've to admit that I don't fully understand the symbology of AIII. Must crucially is the lateral deviation. It is supposed to be indicated by the vertical line, but how do you read it? Is it supposed to be centered?

[KuntaKinte 210]

The vertical line (lateral deviation line) indicates the lateral deviation from the localizer. When it matches the conformal selected course (uppointing arrow at the compass scale) you are on the localizer. There should also be a horizontal line (glideslope deviation line) which indicates vertical deviation from - you have guessed it - the GS. You are on the GS when this line overlays the GS reference line (the one with the label "- 3.00" = 3° glidepath as on your approach plate). Ideally both lines (which have a gap in the middle) form a crosshair at the GS reference line with the flightpath symbol (big circle) and the guidance cue (small circle) in the middle.

[CRJay 428]

On 8/30/2021 at 11:18 AM, SinusJayCee said:

The point is the CAT III part here. At CAT I conditions, you can let the AP fly the plane to the corresponding minimums, establish proper visual reference to the runway, disconnect the AP and land the plane manually. But if the RVR is below CAT I, this is not longer possible. In order to land a plane at CAT II or CAT III conditions, some additional technical systems are required because the visual reference to the runway is established too late for a safe landing.

 

Modern airliners like the A320 and 738 have autoland systems, where the AP can land the plane automatically (CATIIIa) and can even perform the rollout (CATIIIb). The CRJ however has no autothrottle, and as a consequence, no autoland system can be implemented here. Because of that, the CRJ wouldn't be able to operate at CAT II or CAT III conditions.

 

With the right training and approvals you can definitely fly the CRJ700/900 down to CAT2 minima on autopilot. Lowest height you can disengage is 60ft and CAT2 minima are not lower than 100ft RA. So in that sense, the only benefit of the HGS is CAT3a manual approval. You'd need to operate into CAT3 weather afflicted airports a lot to get a return on the investment of the HGS. That is one reason why many CRJs do not have it (but annoyingly, do have the provision for it above the left seat, source of many head bumps getting in and out of that seat).

[FlyByWire128 42]

1 hour ago, CRJay said:

You'd need to operate into CAT3 weather afflicted airports a lot to get a return on the investment of the HGS.

 

Now I'm wondering what airport(s) would have this type of weather frequently (i.e. where are you most likely to have to fly an approach to CAT II or CAT III minima?)...  

[CRJay 428]

4 minutes ago, FlyByWire128 said:

Now I'm wondering what airport(s) would have this type of weather frequently (i.e. where are you most likely to have to fly an approach to CAT II or CAT III minima?)...  

 

Airports in climates that experience somewhat cold weather and situated in valleys, or near large-ish bodies of water are usually pretty decent candidates. 

[SinusJayCee 38]

vor 13 Stunden , CRJay sagte:

With the right training and approvals you can definitely fly the CRJ700/900 down to CAT2 minima on autopilot. Lowest height you can disengage is 60ft and CAT2 minima are not lower than 100ft RA.

Thanks for information! I always thought you need have some kind of additional equipment to do an approach at CAT II conditions.

[SinusJayCee 38]

vor 22 Stunden , KuntaKinte sagte:

The vertical line (lateral deviation line) indicates the lateral deviation from the localizer. When it matches the conformal selected course (uppointing arrow at the compass scale) you are on the localizer.

Thanks for clarification! I missed the small arrow to determine the lateral deviation. However, the indication doesn't seem to be very precises. For example at 10:20 in my video, I see no significant deviation from the localizer according to the FD and HSI, but the lateral deviation line is a few degree right of the arrow.

 

vor 22 Stunden , KuntaKinte sagte:

There should also be a horizontal line (glideslope deviation line) which indicates vertical deviation from - you have guessed it - the GS. You are on the GS when this line overlays the GS reference line (the one with the label "- 3.00" = 3° glidepath as on your approach plate). Ideally both lines (which have a gap in the middle) form a crosshair at the GS reference line with the flightpath symbol (big circle) and the guidance cue (small circle) in the middle.

There is a horizontal line at -3°, but it seems to be fixed at this position. So I guess this is the reference line. But I cannot spot the glideslope deviation line. There is of course also the GS diamond on the right side.

[KuntaKinte 210]

Yeah, a lot of the symbology is missing ...