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MSFS Flying ILS approach on autopilot

E

eric_marciano

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531
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france
Hello experts,

I am developing an aircraft that has the ability to fly an ILS approach using the autopilot. The LOC mode guides the aircraft on the lateral axis (localizer) and the APR guides it on both lateral and vertical axis (approach mode, handling both localizer and glideslope).
To engage the LOC mode, I use the K:AP_LOC_HOLD_ON event, and when the glide slope comes active, I turn the LOC mode off (K:AP_LOC_HOLD_OFF) and I engage the approach mode that manages both, using K:AP_APR_HOLD_ON. It used to work perfectly, but the latest sim update broke it all... The LOC mode still works fine, but not the approach mode, which means the aircraft does not descend to follow the glide slope guidance when it is intercepted.

Do you have any idea about the way to make it work as before?
I posted a question on the dev forum but I have no reply yet...

Any help is welcome,
Eric
 
Hi Eric

I do not have MSFS , but in FSX you need to select the NAV/GPS mode switch to GPS , could that be the Problem ?

Cheers
Karol
 
You're right, this might be the explanation, I didn't think about this...
I don't change this mode, but if it was set to GPS during a previous usage of the sim, it may remain and the ILS guidance does not work anymore.
I will check this ASAP.
 
No, this is not the reason. I checked my code and I already had a function that prevent GPS DRIVES NAV1 to be engaged.
Another test flight showed the aircraft started the descent when intercepting the glideslope, but it went down so strongly that it crashed into the ground, as if the PID settings of the autopilot were ignored.
This made me think that they were in the ai.cfg file, maybe they should now be in systems.cfg in [AUTOPILOT] section?
 
"......... the aircraft started the descent when intercepting the glideslope, but it went down so strongly that it crashed into the ground ......"
Your description sounds familiar .

At this thread

Heavy Jet ILS Glide Slope Problem

Whenever I fly a large jet such as a C5 Galaxy, the aircraft engages the ILS OK but the autopilot approach hold has trouble adjusting to the slope. After entering the slope, the plane is slow to react and then will have to take a rather deep dive to get down to the slope, then it overshoots and h...
www.flightsim.com www.flightsim.com
the OP described similar on the 20 JUN 2019 while attempting an ILS approach .

I responded on the 23 JUN 2019 that his airspeed [160 kts ] was too fast and resulted in failed glideslope capture , and suggested that he try a lower airspeed at time of ILS engagement.
He reduced the airspeed considerably and the ILS worked and successfully captured and followed the glideslope .

Might be worth a try at a lower engagement airspeed .

Cheers
Karol
 
I agree, speed is important. I think I manage it correctly, going down from 230 to 140 in final.
The problem is that is used to work fine, and it doesn't work any more.
I made some changes and now it seems to work again, but I don't know why... So I don't know when it may fail again. Very strange...

In fact, I have adjusted the PID settings for the LOC and GS guidance (lateral and vertical) in ai.cfg, and they were good. After these failures, I thought the PID settings should be in systems.cfg instead (in the [AUOTPILOT] section), so I moved them here. It was working, but the PID settings were completely wrong, even though I kept the exact same values.
So I reverted back to the initial, with all PID settings in ai.cfg and nothing in systems.cfg, and now it works like a charm.
I don't know if I am perfectly clear here, but my main question is: where should the PID settings be? In ai.cfg or systems.cfg?
I'm afraid nobody has the answer to this question...
 
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