MD-11 glide capture logic

[Guest JaredA]

It might be me again, I hope it is :) but I noticed after seeing the ITVV Martinair video that my MD-11 will switch to the G/S, Land armed indication and climb up into the glide slope if approaching from below and capture when the glide becomes alive, has anyone else seen this?

[SetSpeed 22]

I noticed this same behavior with my fs9 MD-11. I was flying the ILS to runway 8 in KABQ. I was level at 8000ft inbound with NAV and alt HOLD engaged. Just before crossing the ABQ vor, I pushed the appr/land switch. At that time, LOC and GS engaged and the plane pitched up about 25 degrees with almost max thrust and climbed like a rocket until it intercepted the glideslope. After that, it performed as I expected.Adam

[Guest Totalbeginner]

I noticed this same behavior with my fs9 MD-11. I was flying the ILS to runway 8 in KABQ. I was level at 8000ft inbound with NAV and alt HOLD engaged. Just before crossing the ABQ vor, I pushed the appr/land switch. At that time, LOC and GS engaged and the plane pitched up about 25 degrees with almost max thrust and climbed like a rocket until it intercepted the glideslope. After that, it performed as I expected.Adam

I must admit I do find G/S capture on the MD11 a little disappointing. Especially if LOC capture occurs while ABOVE the G/S. In this instance, the aircraft takes on a suicidal dive! There are a few approaches in Europe that are surrounded by terrain and it is necessary to fly the Localiser while stepping down to platform altitude. But with the MD11 it's just not possible. If you're above the G/S by any value, it immediately captures and dives. I've tried using the LOC ONLY on the FMC, but when you want to arm the G/S, pressing the APPR/LAND button doesn't cancel LOC ONLY on the FMA and subsequently inhibits an autoland.On the Martinair DVD you can see that on their return to Amsterdam, the exact same thing happens. They must have been vectored in quite tight and they caputre the LOC while above the G/S. Instead, they wait until the aircraft is tracking the LOC and then selct FPA and simply capture the G/S from above. Not good practice, but sometimes necessary. It would be really nice if this could be fixed in a future update... hint hint :(

[Guest cfgarrod]

Assuming you are capturing the glideslope from below your FMA indication should typically be:160Thrust / LOC AP1 / Land Armed Hold 3000The aircraft should never climb out of altitude hold towards the glideslope. It should maintain level flight until about 1/3 dot below and then follow the 'slope.What does your FMA show during your pitch up?As for intercepting from above, I believe an option can be selected in a PMDG menu 'Allow G/S intercept from above' (if it's allowed by your airline). Can't remember if it's in the MD11 or 747 menus, standby I'll have a look...Chris

[saher52 0]

Same happened to me at VHHH runway 07R ( FS9 )I was at 5000ft captured only LOC and was about 17 miles to the runway, as soon as the GS become alive the aircraft pitched up to intercept GS

[Guest JaredA]

Chris, My FMA indicates exactly what you said and indicates correctly, its just that the autopilot doesn't hold the alt it climbs into the glide, I'll get a screen shot on my next approach.

[emvaos 13]

Chris, My FMA indicates exactly what you said and indicates correctly, its just that the autopilot doesn't hold the alt it climbs into the glide, I'll get a screen shot on my next approach.

Jared,This is one of those SHOULD NEVER EVER HAPPEN things. Just checked again. The GS arm to active transition occurs when the AFS calculates that the negative (repeat negative) vertical speed required would take less or equal time for the GS needle to centre but constrainted by absolute needle position (never more than half a dot).What's banging your FSUIPC memory when this happens ?Puzzled,Vangelis

[michal 44]

What's banging your FSUIPC memory when this happens ?

Cosmic radiation? :(

[Guest JaredA]

I don't know thats why I am posting :) Here I am on the 26R approach at ATL this shot is one second after the airplane started receiving the glide slope signal, clearly climbing up to the glide with everything stable. Here it is after it captured it. The only other things I run are my VAs ACARS, Active Sky, and Squawk box which you can see in the shots.

[Guest cfgarrod]

Can you confirm that you are in level flight Altitude Hold mode before this happens?Chris

[michal 44]

Can you confirm that you are in level flight Altitude Hold mode before this happens?

correct, but I would be rather skeptical of any confirmations :( , I would like to see what the FMA looked like 3 seconds before the first pic above.

[Guest JaredA]

Yes. I was level at 5, but if we need another picture I'll get one.

[Guest JaredA]

Alright I did see a difference and maybe a new problem, using maybe here as a true maybe, you can't see it in the pictures, BUT the climbing into the glide didn't occur as you can see in these shots, the difference was....... This approach was shot with no manual tuning of the ILS into the Nav/Rad page, the last one was with manual tuning The new odd thing I saw here was after asking the MCDU/FMS to fly the PIGLET STAR into MCO I had a speed and alt restriction of 250 and 11 at PIGLET as per the STAR then the wind shifted and I deleted the 250 speed restriction after that as by evidence in the pictures the autopilot would not hold the selected altuide, I hope that was due to weather changes within FS9.

[Guest JaredA]

Bump!

[A320driver 17]

It might be me again, I hope it is :) but I noticed after seeing the ITVV Martinair video that my MD-11 will switch to the G/S, Land armed indication and climb up into the glide slope if approaching from below and capture when the glide becomes alive, has anyone else seen this?

I am having the same issue as well.