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Strange autoland behaviour

Controlling your aircraft, using the autopilot etc.

Re: Strange autoland behaviour

Postby V12 » Tue Mar 05, 2019 8:58 pm

Illustrated short demo flight from LZIB to LZPP :

Throttle position for managed speed :

Image

Climb to cruise level 5000 feets :

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At cruise level :

Image

Descent and deceleration (throttle still in position from first image) :

Image

Activated LOC, Bus in the left turn to capture localizer :

Image

Glide Slope signal detected, activated APP mode for autoland

Image

On the Glide Slope, both AP, plane configured for landing - 145 kts, full flaps, lights, gear down, autobrake Medium, etc. :

Image

17 kts gusty crosswind, AP off for manual approach, I don't want risk autoland in that strong wind :

Image

Split second before touchdown :

Image

Some seconds after touchdown, still in 1 piece :

Image
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Re: Strange autoland behaviour

Postby kwanza » Tue Mar 05, 2019 9:52 pm

The fault is probably mine. I tried the other planes to check if I was totally confused. Two attempts were miserable failures for me, both of which were using autoland. I actually managed to to land the MD-11 manually - what a relief! Now the two failed attempts were rather interesting:
    - In auto-flight, the IDG-MD-11X follows the flight path faithfully maintaining its own speed and altitude. In fact, it sticks stubbornly at 7000ft even when AUTOLAND is engaged. Needless to say, it did not land.
    - The IDG-A33X has interesting characteristics. it kept climbing even with the throttle at 0%. I was desperately trying to get it to descend. Surely, in this case it should nosedive? No? To be clear, it was slowing down but not enough for it to make the runway.

My take is that I must have a major misunderstanding of the controls in Auto mode. I probably need to spend more time in manual before graduating to auto-pilot.

Thanks.
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Re: Strange autoland behaviour

Postby it0uchpods » Tue Mar 05, 2019 11:27 pm

Hi Kwanza:
The IDG A33X probably did that because you approach stall AoA. So the A.FLOOR (Alpha floor) function turned on, which puts TOGA power. Once the AoA is low enough, this changes to TOGA LK (Takeoff/go around lock). (these are shown on the upper left of PFD), and you need to switch the A/THR off to clear it. (then you can switch it on again). In A.FLOOR and TOGA LK modes, the throttle is ignored, hence why it is called "TOGA LOCK".

In regards to the MD-11, the MD-11s autoflight is different to Airbus and Boeing. You must pull the speed/altitude/heading knobs before it follows your command. AUTOLAND first arms Localizer, then Glideslope. Glideslope is not armed until LOC capture. Remember, that unlike generic planes, the Glideslope only captures if the diamond is near the center (about one half dot away). So you're glideslope was below you, and you were at 7000 ft, it won't capture. Same with the Airbus'.

I model the autoflight systems in my planes to extreme accuracy (including pilot reports of real life pilot's reports of it behaving odd in certain conditions :mrgreen:). Hence there is also a learning curve. The following may help you out:

PMDG's MD-11 Autopilot Guide: https://support.precisionmanuals.com/kb ... md-11.aspx

BAA Training Airbus Autoland Guide: https://www.youtube.com/watch?v=LIaMALJjOEc

Kind Regards,
Josh

PS: @V12, disconnect autopilot with SHIFT D (sidestick button, or AP DISC in dialog) instead of the AP1/2 buttons. This is the "correct" way to turn off the A/P, and will prevent the red ECAM warning. (2 clicks of button). Same with A/THR and CTRL D.
Last edited by it0uchpods on Wed Mar 06, 2019 5:32 am, edited 1 time in total.
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Re: Strange autoland behaviour

Postby V12 » Wed Mar 06, 2019 5:15 am

Thx for advice.
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Re: Strange autoland behaviour

Postby kwanza » Wed Mar 06, 2019 7:00 pm

Josh, thanks a lot for the useful pointers. The videos certainly helped to clarify a awful lot of things for me - they really improved my understanding. The good news is that I have finally achieved a level on control over the A32X albeit still imperfectly. Indeed, I was able to land it somewhat, but very messily. As I speculated before, the key to my partial success was getting a grip on the speed controls. I have a few questions:
    - Does the plane default to a speed on 100kts? When I plan my route, I had to set the cruise speed to 250+ before takeoff. Otherwise, I could never get the speed above 160kts regardless of my throttle level.
    - According to some tutorial i saw, I should able to use managed speed. So if I push the speed button, the FMGS should set the speed itself and the indicator should show "---". On the other hand, when I pull it, I should be in control of the speed. Is this correct? I certainly cannot get it to do the former.
    - After several attempts, I got the plane to "intercept" the ILS, On the PFD, the vertical indicator (diamond) was below the optimal level. It then shot right up above the centre. Then it dropped right down below the centre. Finally, it disappeared and I aborted the flight.
    - My best attempt got the vertical indicator spot on in the middle. This showed that it had fully captured the GS - the PFD showed SPEED and GS as green. However, at exactly 10ft, something triggered a panic - it turned right and landed at an angle (45 degrees) to the runway. I got the RETARD callout and the auto-brakes engaged. Why would it veer from the runway when it had the GS set?

Please pardon my ignorance.

Thanks.
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Re: Strange autoland behaviour

Postby it0uchpods » Wed Mar 06, 2019 8:41 pm

Hi kwanza:
Yes, by default the FMGS powers up with the speed knob at 100kts. You have to change it yourself. For Managed speed (push), you need to setup the MCDU computer.
If the diamond behaves weird, you are too high or in the wrong place.

As I said, at 10ft, that means the LOC signal was lost. G/S only does vertical, LOC does lateral.
I just checked that rw. The ILS signal is lost over the threshold. This is a bad thing in the scenery. I can't fix that. Autoland needs the ILS signal to work. Try KSFO 28L.

Here it is in signal:
Image

And here it loses signal at 70ft:
Image

I have no protection for this yet. I guess I should make it keep wings level.

Kind Regards,
Josh
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Re: Strange autoland behaviour

Postby Thorsten » Wed Mar 06, 2019 8:48 pm

This is a bad thing in the scenery. I can't fix that. Autoland needs the ILS signal to work.


You could if you really wanted - you could remember the last ILS-determined threshold position that was good and fall back to a virtual ILS signal in case the actual signal goes bad. It wouldn't be overly difficult even.

Shuttle uses 'its own' TACAN signals because they're supposed to be picked up from 400 miles out (which works at the altitude), but FG doesn't let TACAN propagate that far. And 'its own' MLS signals because there's no MLS in FG.
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Re: Strange autoland behaviour

Postby it0uchpods » Wed Mar 06, 2019 10:12 pm

Thorsten, Good idea. I look into that.

Kind Regards,
Josh
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Re: Strange autoland behaviour

Postby it0uchpods » Sat Mar 09, 2019 6:06 pm

I am working on updating IT-AUTOFLIGHT to V4.0 -- which is a complete rewrite of the logic controller to correct various minor issues it has (such as performance impact, lots of getprop, etc)

Until I figure out something better, the A/P will trip off if signal lost during autoland, and revert to HDG and V/S if lost during approach. (this behavior may vary slightly in the MD-11 or A3XX implementation of ITAF, as they use custom versions that have the changes needed to act like they should.)

Kind Regards,
Josh
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Re: Strange autoland behaviour

Postby kwanza » Sun Mar 10, 2019 10:51 pm

Great stuff. I downloaded a newer version of the A33X today and flew the Voyager model to SEA, where I was able to autoland successfully (for the first ever) without any issue. I am not sure if this was v4.0, but I saw no glitches. Thanks a lot for everything.
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Re: Strange autoland behaviour

Postby it0uchpods » Sun Mar 10, 2019 11:08 pm

Hi kwanza:
Glad to hear! Nope, this is not a V4.0 yet. Once the generic framework is done, then I will begin to customize it and update the rest of the Autoflight system in the MD-11 and Airbus families as they use a customized system and controller.

Kind Regards,
Josh
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Re: Strange autoland behaviour

Postby kwanza » Thu Mar 14, 2019 5:41 pm

Thanks Josh,

This latest observation might be connected to the ILS signal issue. On the MD-11, I have twice landed on different runways at KSEA (i.e. 34L and 34R). On both occasions, I intercepted the glide slope and touched down successfully, but the plane failed to align with the runway. The only way I could control its direction was by disengaging the AUTOLAND and using the right brakes. I had got all the correct alerts: DUAL LAND -> FLARE -> ALIGN -> ROLLOUT. For some reason, it assumed the wrong bearing of the runway (I had used 345).

Regards,

Kwanza
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Re: Strange autoland behaviour

Postby it0uchpods » Thu Mar 14, 2019 6:11 pm

Hi kwanza.
Good DUAL LAND
Image

ALIGN ok:
Image

right after FLARE, signal is lost from the ILS, so the old one would go into the abyss, the V4.0 controller I just added now does what the real one does and trips the A/P off, and goes to HEADING and V/S
Image

So again, use a runway that has ILS going down the runway and it will work. If problem, its the fault of whoever made that scenery.

Kind Regards,
Josh
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Re: Strange autoland behaviour

Postby kwanza » Thu Mar 14, 2019 8:17 pm

OK, now I understand. It seems to me that most runways have faulty data. I tried a runway in KDTW and lost the signal again. At least now I know when I need to retake control.

As an aside, what keys will show different views (besides V and Shift-V)? For example, "6" does not show the AFS Panel View on my system. Neither does "3" show the Overhead View, etc.

Thanks.
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Re: Strange autoland behaviour

Postby it0uchpods » Thu Mar 14, 2019 8:55 pm

Hi kwanza,
Yes. It is a sad thing. Any plane with the V4.0 controller will drop back into HDG/VS if lost during LOC/GS, and disconnect A/P if in Align/Flare when signal lost. Behavior may vary by aircraft.(MD-11 vs A3XX vs Generic)

For view - make sure keyboard mode is off, and use the number row not the numpad.

Kind Regards,
Josh
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