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Guest JaredA

MD-11 glide capture logic

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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?

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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

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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 :(

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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

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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

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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.

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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

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What's banging your FSUIPC memory when this happens ?
Cosmic radiation? :(

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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. UAL-2009-jan-9-001.jpg Here it is after it captured it. UAL-2009-jan-9-002.jpgThe only other things I run are my VAs ACARS, Active Sky, and Squawk box which you can see in the shots.

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

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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.

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

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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.......UAL-2009-jan-9-003.jpgUAL-2009-jan-9-004.jpg This approach was shot with no manual tuning of the ILS into the Nav/Rad page, the last one was with manual tuning UAL-2009-jan-9-005.jpgUAL-2009-jan-9-006.jpgThe 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.

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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.

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I have only done a few flight, but I've have not seen this behavoir. Two flights from a transition point put me below the G/S and the MD did not climb to capture it. I wonder if something esle is going on?

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Jared,I think your problem based on the pics you provided is that you are **never** truly in altitude HOLD state while approaching the GS capture. You are not in altitude hold because your "3000" is in white, if you were truly in hold it would have been in magenta instead. In fact your altitude seems to be all over the place, always significantly below 3000, no wonder it is not in hold. I don't know what is going on but from the pics it looks like extremely messy approach. So if there is no valid vertical mode and then GS comes around - the aircraft may in fact climb since this is the only vertical mode known to it that it can 'grab onto'. I don't know what messes your approach so badly - I would try to repeat it with NO weather and see how it goes but it is entirely possible your procedures are not exactly textbook.

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I have never had this problem either, my aircraft has never climbed to intercept the GS, and when I do select it above the GS it smoothly decents to intercept never have dive problem either.Jay V

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Maybe it helps if we have a look at the colour coding of FMA modes:White: manual control or pilot entries.Magenta: FMS calculated commands/values.Green: fail operational autoland functions.Cyan: AP engagement.Amber: cautions and failures.Red: warnings.Your FMA shows HOLD 3000 in white so you selected this altitude yourself. In the 4 screen shots the aircraft is not holding this altitude, it's at 2420, 2170, 2350 then 2590ft. Are you inadvertently overriding the autopilot with your control yoke?Chris G

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Nope when the autopilot is engaged I never touch my yoke plus I turned the sensitivity all the way down to the lowest setting to help prevent exactly that inadvertently overriding the autopilot and wouldn't the AP trip off if I were overriding it that much? I could tell it was trying to recapture 3,000, but it couldn't. In the second set of pictures it was in profile up till, as I stated in the other post, I deleted the 250 speed restriction then the autopilot couldn't capture the alt, it flew through it, but didn't capture as you see there so I switched to LVL change to see if it would recapture and as you can see it never did, I'm at a loss myself on the recapture deal. The only thing I saw a true difference in, as stated before, is the climb up into the glide didn't occur with auto tuning of the radios, but IT DID WITH MANUAL TUNING. Maybe, I should start another thread, but something else I saw, which it hasn't done till then, is the plane was on a 272 heading coming out of ATL to fly the PNUTT departure off 27R I preselected 250 as a heading and when the autopilot was engaged and I pulled the heading knob the autopilot commanded for a right turn to 250 instead of a left turn to 250 and after passing 10 in the climb, the FMC did not command the plane to accelerate above 250 knots, it did once it was past the second fix on the SID, but by then with the right turn instead made me fly over the airport and delayed the on course turn. Very strange indeed, I hope that the recapture thing and this wrong turn and not accelerating above 250 knots is FS just telling me it didn't want to work and needed a rest.

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The heading and speed deal must have been FS complaining cause I'm in flight now and performed the same produce and this time the autopilot did both the turn and acceleration above ten correctly, FS can be odd sometimes.

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but didn't capture as you see there so I switched to LVL change to see if it would recapture and as you can see it never did, I'm at a loss myself on the recapture deal.
So here you go .. until you master the "capture" stuff your ILS approaches will be hit-and-miss. This is a common misconception among armchair pilots that you can punch numbers into autopilot and the rest will be taken care of, - autopilot can only capture course, altitude, GS, speed, etc. if conditions are right, it is responsibility of the pilot to make sure that capture conditions are satisfied. By the way Chris is correct about the colors - my mistake.

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Yea, I know its the pilots job to monitor the system, but in this situation I wasn't in a high traffic area or there wasn't a lot of traffic so I made ever attempt to allow the system to correct itself, but it didn't thats why this thread was started in the first place, to see if it was just my learning curve to the MD-11 or a possible logic error. I haven't seen an FS add-on that is "perfect" upon release.

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For those reporting that the MD-11 suddenly climbs to reach G/S, if you think about it critically you've almost solved your problem.Its better to already have your final approach alititude held with PROF mode, as Michal was mentioning earlier on, your ALT should show up on your ND in magneta The reason why your MD-11 choses to climb @ G/S live; I believe is no logic fault. It sounds to me as though you have your approach altitude held in manual AP mode (white on your ND) then you're hitting PROF once the G/S comes alive. If you're doing this then you're commanding the AP VNAV to follow vertical instructions in magneta. Depending on where the G/S vertical bug (coloured in magneta) is on your ND, is where PROF AP will follow.Obviously if the G/S comes alive and the magneta bug appears at the top of your ND then it's representing that the glide path is above you so AP will climb to lock on to it as you've rightfully commanded it to do so.If you prefer to use manual AP ALT HOLD on approach then you're better off waiting untill the G/S bug on your ND comes down to at least level with your FD. Then once you hit PROF, the AP will follow the G/S bug which will be level with you at your alitiude or slightly below depending on when your press it.I agree with Michal, it's down to misconception of the autopilot usage, no development bug involved here.I could be wrong but that's my personal understanding from reading the manual bit by bit.

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Then why, assuming Micheal and Keiron are right, if you watch the Martinair video from ITVV on the demo of an CAT 3A approach wasn't the sim set up so the airplane was already coming in on the glide if the logic both talked about is true, look at the video at time 145:47 it was in PROF when APP/Land was pressed and the aircraft is on neither the LOC or glide and its holding 2,000 then it captures the LOC now why isn't it racing to catch the glide?????? based on what both of you are saying it should, but it doesn't and it shouldn't matter how the ILS was tuned manual or automatically and whether or not PROF was used till approach or not. No I press APP/Land not Prof on an approach, can't speak for others.Note: I didn't start this thread to start a war on who is right and who is wrong, I was hoping for folks to see my point of view on this.

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