fix(gpws): fixed mode 4 logic

[LeechCZ]

Fixes #8134

Summary of Changes

Mode 4C logic has been changed so it can only be triggered during take-off and go-around and does not trigger warnings during approaches.
Mode 4A and Mode 4B logic has been changed so it can be triggered even when the FMGC is not in the Approach phase.
The general Mode 4 logic has been changed so that the Mode 4C can only be triggered before passing 2400 ft RA during a take-off or go-around. After that point, only Mode 4A and 4B warnings can be triggered to be available during an approach.

Screenshots (if necessary)

References

These pictures are from the A320 FCOM.

Additional context

Discord username (if different from GitHub): leech2188

Testing instructions

1. Check for normal GPWS operation during a flight (mainly no erroneous Mode 4 warnings, other modes should not be affected)
2. Test for normal Mode 4 warnings as shown in References:
   • Mode 4C warnings during a take-off or go-around
   • Mode 4A / 4B warnings during an approach

How to download the PR for QA

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2. Click on the Checks tab on the PR
3. On the left side, click on the bottom PR tab
4. Click on the A32NX download link at the bottom of the page

[tracernz]

Code style fixes.

[tracernz]

Formatting is good now. I haven't reviewed the logic against my refs at all.

[BlueberryKing]

Thanks for the PR! Apart from my suggestions, there is a small issue with the logic. Mode 4A is only meant to trigger if the gear is up and the flaps are not in landing configuration. Then, Mode 4B can also issue "TOO LOW GEAR" in the envelope where it would issue "TOO LOW FLAPS" if the gear is not down.

[LeechCZ]

Thanks for the PR! Apart from my suggestions, there is a small issue with the logic. Mode 4A is only meant to trigger if the gear is up and the flaps are not in landing configuration. Then, Mode 4B can also issue "TOO LOW GEAR" in the envelope where it would issue "TOO LOW FLAPS" if the gear is not down.

If you have any other refference, could you please provide it to me? As I understand it, from the FCOM provided in the PR, Mode 4A can only be triggered if the LG is not down. And the Mode 4B can only be triggered if the LG is down and the flaps are not in landing configuration. Althoug it also says in the FCOM that Mode 4B can trigger the "TOO LOW GEAR" warning, but that is at least to my understanding contradictory to the trigger conditions mentioned above in the document.

[GlideLeo]

Thanks for the PR! Apart from my suggestions, there is a small issue with the logic. Mode 4A is only meant to trigger if the gear is up and the flaps are not in landing configuration. Then, Mode 4B can also issue "TOO LOW GEAR" in the envelope where it would issue "TOO LOW FLAPS" if the gear is not down.

If you have any other refference, could you please provide it to me? As I understand it, from the FCOM provided in the PR, Mode 4A can only be triggered if the LG is not down. And the Mode 4B can only be triggered if the LG is down and the flaps are not in landing configuration. Althoug it also says in the FCOM that Mode 4B can trigger the "TOO LOW GEAR" warning, but that is at least to my understanding contradictory to the trigger conditions mentioned above in the document.

It's right, mode 4B can also be triggered when "flaps in landing configuration and gear not in landing configuration".In fact, the envelope diagram looks like this when gear up

Because when the landing flaps are set, the transition is made to 4B, even though the gear is in the up position.

Your FCOM seems a bit outdated, but even in the newer versions of the FCOM, the descriptions aren't entirely accurate. These details are sourced from Airbus specifications. Sorry for not being able to provide the original document.

outdated

[beheh]

@2hwk are you sure this RTT? Looking at the comments this PR seems to have some deficiencies that still need to be addressed.

[beheh]

Flagging this PR as "changes requested" due to the mentioned logic from the most recent comments.

stale

[beheh]

I'm happy with the code, but have not done an accuracy check.

[Aleloplt]

Quality Assurance Tester/Trainee Report

Discord : Alelo
Object of testing: 8136
Tier of Testing : (1/2)
Date : 31/07/2024

Testing Process:
Initial flight from EGLL - EGFF.
Full start up to pushback in normal time
Approach into EGFF and multiple go arounds to test different modes
First Test - Mode 4C

• AP disconnected
• TOGA thrust engaged
• Pitch reduced to minimise height gain - steady 100'RA flight
• "too low terrain audible"
• Pitched up to gain altitude and eventually GPWS call out disappeared
  -IGNORE VFE OVSPD - i did this myself

Second Test - Mode 4A

• Normal approach w/ AP on right down to MNM.
• Flaps full, LDG gear up, VAPP 140kn
• "too low gear" audible upon passing 490'RA
• Go around and tested again - including mode 4C test
• Descent towards terrain using FPA -3.0 at 195knots
• "Too low Terrain" only audible roughly at 600'RA

Third Test - Mode 4B

• Normal approach using FPA -3.0
• LDG down, Flap 3 160 knots
• "too low terrain" audible 250'RA
• "too low flaps" audible instantly at 240'RA

Negatives:
The exact call outs dont seem to match the FCOM document provided. I.e should be hearing too low terrain less than 1000'RA without the gear and at 196knots but that was coming in far later and im not sure if thats meant to be correct

Testing Results:
Mode 4C - Passed
Mode 4A - Gear call out - Passed
Mode 4B - Flaps call - Passed

Conclusions:
Overall working really well to what its needed fore in terms of FLAPS and GEAR comparable to the sims ive been in. Just needs more clarity on the 'too low terrain calls and whether not hearing them as per the FCOM provided is allowable.

Media:
Media files are too big to be sent here. If you PM me on discord ill send them across

[beheh]

Thanks for the QA! Merging this is then just pending an accuracy check.