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victorlima01

Still cannot perform dual channel autoland!

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Hi all, I have been having problems with autolands. When setting up the aircraft during descent for an autoland procedure in an ILS equipped airport, I proceed in the following way: I tune both nav radios to the ils freq, press the vor/loc button on the MCP and the aircraft faithfully captures the localizer. I then proceed with flap extensions speeding down to vref etc and when the Glideslope becomes alive I'm all set up and I press app on the MCP and then press the second autopilot command button (i.e if I were using CMD A for loc capture and descent I press CMD B as well for full autoland). The aircraft then flawlessly performs an autoland (better than my manual landings I might add). The problem is that I consistently get a yellow SINGLE CHANNEL message on the FMA when I press app and select the second autopilot. From what I know of the airplane that warning is inconsistent with a full autoland correct? If so, then how come the aircraft lands perfectly? Am I missing something to execute a dual channel autoland? BTW, what is the difference between the single channel and dual channel procedures?thanks for the help. Regards, Victorhttp://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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Guest glenb

Victor,The display will change at 1500 feet above the ground. It will flash on and off in yellow as a self test then will show CMD and the pitch mode will show flare below the GS indication. Flare will replace GS at about 40 feet above the runway. This change occurs at a busy time in the approach and you may have missed it. If that is not happening then there is a problem.

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Hello Glen! Thanks for the reply. BTW I just saw your email and will reply shortly. It's getting harder day by day to be able to work, study, fly and prepare for private pilot exam so responding to emails has become a low priority for the time being; but thank you so much for keeping in touch. I believe I am having some sort of trouble because I do not get a CMD on the FMA only the yellow ISNGLE CHANNEL warning. Other than that everythingoccurs the way you mentioned. I will try reinstalling the planes because I do not think it's pilot error on this one. Thansk for the Help. Keep in touch!Best Regards,Victorhttp://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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Guest jase439

I've never seen this. I see SINGLE CHANNEL (or 1CH) displayed all the way down to 1500' AGL, at which time the PFD cues flash yellow, at which time selection of the CMD B autopilot clears the SINGLE CHANNEL annunciation and arms FLARE mode.

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Now that is interesting. I'm almost sure that at some point in my life I've seen a green DUAL CHANNEL indication in the FMA a the point I engaged the second autopilot and pressed app. If this is not the case, then why are autolands ever referred to as "dual channel approaches" in the B737NG aircraft? From what I understood, dual channel means that there are two autopilots flying the approach in a coupled mode, making it possible for the GS to be followed down to the RWY. If I remember correctly, if the two autopilots aren't engaged or the two nav radios set, the aircraft simply will not capture and follow the GS - because a single autopilot is only "able" to capture and track the loc, not having been "taught" by Boeing engineers to perform a full ILS all by itself. ;)BTW, when performing such approaches, at which point do you guys switch from LOC to APP in the MCP and press the CMD B? Is the correct order to first switch to app and then press CMD B? What should I do if I wanna fly on full autopilot (LOC/GS/throttles) all the way down to for example 500 or 300' AGL? Should I set it all up like a dual channel full ILS approach and then disengage both autopilots? Thanks for the input. Cheers, Victorhttp://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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>RWY. If I remember correctly, if the two autopilots aren't>engaged or the two nav radios set, the aircraft simply will>not capture and follow the GS - because a single autopilot is>only "able" to capture and track the loc, not having been>"taught" by Boeing engineers to perform a full ILS all by>itself.Seriously :-hmmmI never heard such a thing. A single autopilot is capable of full ILS including auto-landing and the only reason you use two during autoland is for redundancy.You normally switch to APP when GS starts to "move". At least this is what I do. But you could probably do it earlier.Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2http://www.precisionmanuals.com/images/forum/747400.jpg


Michael J.

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Didn't the old Dreamfleet 737-400 say Dual channel when you had both autopilots connected?Anyway, if you are in Single Channel autopilot approach mode the plane is not able to flare automatically and you don't have autopilot go-around, you have to follow the flight director instead.Autopilot landning is only available in Dual Channel Autopilot Approach, not single channel. In single channel "the autopilot must be disconnected before you reach 50 feet radio altitude".Or to quote the CBT:- - - - - DUAL CHANNEL AUTOPILOT APPROACH - - - - -Before the approach - Set courses on the CMP - Tune and identify frequencies on the navigation radiosArm the approach - push APP - verify VOR/LOC and G/S are armedAfter approach is armed - Push CMD for the second autopilotAfter localizer capture - Verify VOR/LOC has engagedAfter glideslope capture - Verify G/S on the FMA - Verify G/A on the TMD - Set missed approach altitude on the MCP - Verify FLARE is armedAfter touchdown - Disengage the autopilot manually- - - - SINGEL CHANNEL AUTOPILOT APPROACH - - - -Before the approach - Set courses on the MCP - Tune and identify frequencies on the navigation radiosArm the approach - Push APP - Verify VOR/LOC and G/S are armedAfter localizer capture - Verify VOR/LOC has engagedAfter glideslope capture - Verify G/S On the FMA - Verify G/A on the TMD - Single CH stays illuminated - Set missed approach altitude on the MCP - No FLARE, you must land manually


Krister Lindén
EFMA, Finland
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Ok, so I can see I made a couple mistakes regarding single vs. dual channel landings. I thought that if I only had one autopilot armed the airplane did not follow the GS. Sorry for confusing everyones' heads. But the fact still remains that after doing everything correctly so as to perform a dual channel autoland and verifying that both autopilots are on and doing what they're supposed to (via the FMA) during final approach; I still get the single channel warning on the PFD. What's even more strange is that the plane is still able to flare and touchdown all by itself. I'm starting to think I don't have an autopilot problem but rather a display problem on the PFDBest Regards,Victor http://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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Guest jase439

The only problem I see with this is that you can't arm the second autopilot until you are at or below 1500' AGL (after the PFD cues flash yellow). Toggling the second autopilot above this altitude will disconnect CMD A and connect CMD B - and you'll have to recapture the localizer by rearming APP mode.

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Guest glenb

Victor,Are you saying the even after descending through and below 1500 feet you still have the Single Channel on the PFD?I know that above 1500 feet it is single but at 1500 feet the display flashes a couple of times yellow then changes to CMD and flare shows in the pitch section below the GS indicator.

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Victor,Some screenshots might help us guide you.I don't think this is a display problem though, I'm afraid. ;-)In real life the autopilot is able to flare with one A/P. It is the rules of redundancy and fail-safe mechanisms that requires the dual channel approach. So you can do a single channel autoland but you are not premitted to do it. If you get the difference. Regarding your problem. Check you have NAV 1 and 2 set to ILS freq. Be sure to arm APP when heading towards the ILS LOC. Check either A or B is active on the MCP and that you have LOC and G/S armed (in white) on the FMA. When LOC capture (green on the FMA, active mode) press the remaining A/P CMD button on the MCP. Check you have both A and B active on the MCP and that you have SINGLE CH on the FMA as well as the FLARE armed. At 1500 ft radio height you will get the yellow flashing deviator bars which is a confidence test of the automatic flight system and if both A/P CMD buttons are activated you should now see CMD in the FMA. And you are on 2 CH AUTOLAND!Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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| Asus Z270-A | Intel i5-7600K @ 4.8 GHz OC/H2O | nVidia Geforce GTX 1070 8GB OC/O2|

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Oops. The problem might be in my head rather than on my plane because after reading Mats' reply I came to the conclusion that everything is working fine and I was misled to believe there was a problem. The thing is I could swear that at some point in my life I saw a green DUAL CHANNEL display on my PFD below the FMA where there's usually the green CMD. And one day when all of a sudden I realized that I was getting a yellow SINGLE CHANNEL above 1500 AGL I thought something was amiss.Mats, the airplane is behaving just like you said it should be: with both CMD buttons armed and APP armed as well I get a green GS and LOC on the FMA and a yellow single channel which is substituted by the good old grrenish CMD when passing 1500. After that the plane proceeds flawlessly and lands beautifully. So I guess there's no problem after all.I would like to thank all of you guys who helped me and apologize as well for wasting your precious time looking into something that wasn't there in the first place - yet another case of the dude who didn't read the manual thoroughly. Won't happen again!I just have one question left: will the PMDG flare with only one autopilot like in real life or won't it? And BTW, to disarm the autopilot prior to landing when not performing a full autoland but using th a/p to take as almost all the way down will just touching the yoke suffice or will that put the plane in CWS mode? If it does enter CWS I would say that this isn't the smartest design feature of the 737, but a rather dangereous one right? Just my two cents.Thanks once again guys.Regards,Victorhttp://www.precisionmanuals.com/images/forum/800driver.jpg


Cheers,
Victor M. Lima
 

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