kmw510

No glidescope capture when flying in level change

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I just started flying with vatsim. I was flying the star to SFO in LNAV and VNAV when atc instructed me to descend to an altitude and turn to  a different heading. I used level change to make the descent and used heading select to fly the new heading. I am now out of LNAV and VNAV. Atc continued to give me instructions to intercept the ILS approach. I engaged VORLOC and it activated. Upon this I engaged APP. The pfd showing the white g/s, however, the glidescope was never captured. Having never had this happen before I tried several flights trying to enter the ILS approach using heading select and level change. I was never able to get glidescope capture and a couple times couldn't get VORLOC. I always get VORLOC and G/S capture when approaching using LNAV and VNAV and when flying manually. Is there an issue using MCP autopilot to transition to VORLOC and APP?

 

Kevin Wilson

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Hello Kevin, welcome to VATSIM!

Take a look at the KSFO Runway chart (www.airnav.com) and you'll find the altitude you need to be at, for the position your aircraft is at, in order to capture the Glideslope.  Remember that the glideslope is a finite vertical beam (localizer is a finite laternal beam) that you have to be inside in order to capture it.  You should always capture the glideslope with your aircraft underneath and flying into the beam rather than descending into the beam (glideslope).

The bottom of the runway chart will help you visualize the glideslope as well as provide you with the altitudes you need to be at.

I hope this is helpful to you.

 

Best wishes.

 

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51 minutes ago, Chock said:

Did you engage both autopilots?


I don't believe this is necessary in order to lock onto the glideslope.

 

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Nope, it isn't, I am just trying to determine what the problem might be. :cool:

 

 

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The reason I'm asking that, is because Autopilot A uses the Captain's (i.e. left) Course selector and the number one (Nav 1) radio's frequency, but Autopilot B uses the Co-Pilot's Course selector and the Nav 2 radio's frequency, so if you initiate a dual channel approach and you don't have both course selectors the same and both nav radios the same, the autopilot will freak out and not perform an automatic approach, but you might think it still has the localiser if the aircraft keeps on flying straight.

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On March 26, 2017 at 1:44 PM, DaveCT2003 said:

Hello Kevin, welcome to VATSIM!

Take a look at the KSFO Runway chart (www.airnav.com) and you'll find the altitude you need to be at, for the position your aircraft is at, in order to capture the Glideslope.  Remember that the glideslope is a finite vertical beam (localizer is a finite laternal beam) that you have to be inside in order to capture it.  You should always capture the glideslope with your aircraft underneath and flying into the beam rather than descending into the beam (glideslope).

The bottom of the runway chart will help you visualize the glideslope as well as provide you with the altitudes you need to be at.

I hope this is helpful to you.

 

Best wishes.

 

Hello DaveCT2003,

The ATC directions did have me descend to an altitude low enough to capture the glideslope in that way. For some reason when I am in level change I can't capture the glidesope. All my approaches using VNAV work fine. 

 

Kevin Wilson

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23 hours ago, Chock said:

Did you engage both autopilots?

Hello Chock,

No I use only the pilot side autopilot and have performed hundreds of vnav approaches successfully doing this. Thanks for the help.

 

Kevin Wilson

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Kevin, you said "The pfd showing the white g/s, however, the glidescope was never captured," which leaves me with no idea of what the GS was indicating.  Were you level and below GS, level and above GS or level and at GS?

With either LOC or GS, capture can take place from hand flying or any mode of automated flight (with or without a coupled approach, the GS mode will be activated).  I have been at an acquired altitude reached via FLCHG and captured GS many times, this is probably not your problem so the question is what did go wrong?  And for that we need a better understanding of the circumstances and configuration.

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6 hours ago, downscc said:

Kevin, you said "The pfd showing the white g/s, however, the glidescope was never captured," which leaves me with no idea of what the GS was indicating.  Were you level and below GS, level and above GS or level and at GS?

With either LOC or GS, capture can take place from hand flying or any mode of automated flight (with or without a coupled approach, the GS mode will be activated).  I have been at an acquired altitude reached via FLCHG and captured GS many times, this is probably not your problem so the question is what did go wrong?  And for that we need a better understanding of the circumstances and configuration.

Hello Dan,

I was flying level below the GS expecting that as soon as I intercepted the GS then it would be captured thereby having the autopilot follow the glideslope. For some reason upon intercepting the GS nothing happened and I remained in the GS waiting to capture mode. It has always worked when approaching in VNAV or flying manually. Just doesn't work when flying in lvl change mode. Is that normal?

 

Kevin Wilson

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Did the FMA pitch show G/S in small white indicating that glideslope was armed for capture?  You are not mentioning details like this that are important.  FCOM 4.20.17 does not lists any specific pitch modes that must be active to capture the glideslope (except that there is an option to inhibit GS capture before LOC capture).  Your level change mode changed to altitude acquired mode when the glide slope came alive and began to descend to center... it should be captured about 1 1/2 dots high.  Maybe you didn't have glideslope armed?

 

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25 minutes ago, downscc said:

Did the FMA pitch show G/S in small white indicating that glideslope was armed for capture?  You are not mentioning details like this that are important.  FCOM 4.20.17 does not lists any specific pitch modes that must be active to capture the glideslope (except that there is an option to inhibit GS capture before LOC capture).  Your level change mode changed to altitude acquired mode when the glide slope came alive and began to descend to center... it should be captured about 1 1/2 dots high.  Maybe you didn't have glideslope armed?

 

Hi Dan,

I am confused now. In my original post I state that upon Vorloc capture I engage APP and see the white G/S in the pfd. Does that not answer your question or is there something else. Based on your statements there should not be any reason that a VNAV approach should be any different from a lvl change approach. Something must be haywire in my sim software.

 

Kevin Wilson

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Yes Kevin the GS armed is clear to me at least. At this point could you replicate the situation and post a screenshot of your Pfd and mfd indications ? VORLOC was engaged in green right ? 

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1 hour ago, kmw510 said:

In my original post I state that upon Vorloc capture I engage APP and see the white G/S in the pfd.

I interpreted that to mean you saw the white glide slope deviation indicator on the PFD, which is why I asked about the FMA indication.  Let's go down this path, did you see both a white small letters G/S on the FMA and the white glide slope deviation indicator?

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Two myths I'd like to dispel: it is not required to capture the GS from below and it is not required to capture the LOC before arming APP. Throw those out of the equation. 

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I think that the OP is annoyed that he is convinced that there is nothing wrong with his techniques and advice provided on a wrong assumption. So I will go the other way and think that this is probably due to a panel state. Can you try to do a flight with a fresh airplane and panel state and not from an old ? Looks like you are doing everything right and the ILS is not engaging properly. Also, are you using the Virtual Cockpit MCP or other hardware ? still even with the latter if the G/S arms in white letters it should later engage to green letters.

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11 hours ago, Spin737 said:

Two myths I'd like to dispel: it is not required to capture the GS from below and it is not required to capture the LOC before arming APP. Throw those out of the equation. 

Matt, the PMDG product does have a company option to inhibit GS capture before LOC and it is mentioned as an option in the FCOM.  You are correct about the above/below capture and I've done both with this product without unexpected problems.

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I think what Matt is saying is you can arm both VLOC and GS through APP without having to arm VORLOC first and capture in order to arm APP. Different than capturing VORLOC first in order for GS to engage. But it can still arm.

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Hi All,

There is a problem with my sim. I flew the exact same flight on a friends sim and was able to capture glideslope. So thanks for the help but I don't want to waste your time any further. What fun I am going to have tracing this down.

 

Kevin Wilson

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10 hours ago, kmw510 said:

There is a problem with my sim. I flew the exact same flight on a friends sim and was able to capture glideslope. So thanks for the help but I don't want to waste your time any further. What fun I am going to have tracing this down.

Kevin, if possible, copy exactly your friend's options setup for the particular aircraft you flew on your friend's system and use it for the same type of aircraft on yours.

 

Mike

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On 3/29/2017 at 8:17 AM, downscc said:

Matt, the PMDG product does have a company option to inhibit GS capture before LOC and it is mentioned as an option in the FCOM. 

 

On 3/29/2017 at 11:22 AM, ALF1 said:

I think what Matt is saying is you can arm both VLOC and GS through APP without having to arm VORLOC first and capture in order to arm APP. Different than capturing VORLOC first in order for GS to engage. But it can still arm.

I think the LOC before G/S is the most common option. Which is the default in the sim? If you had the cap G/S before LOC option selected, and you didn't want to follow the G/S, then capturing the LOC first and then arming the APP would make sense.

 

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On 3/29/2017 at 2:23 PM, kmw510 said:

I flew the exact same flight on a friends sim and was able to capture glideslope. So thanks for the help but I don't want to waste your time any further. What fun I am going to have tracing this down.

Not at my FSX computer right now, but there should be an aircraft-specific profile in FSX or P3D)/PMDG/737 NGX/aircraft (or airplanes).  The file names have specific tail numbers for each livery.  You could copy that file from your friend's computer to your computer in the same location, rename it to correspond with the tail number of one of your liveries (after backing up the similarly named file that already exists) and see if that fixes the problem for that aircraft.

You can also see the specific options for each livery in the OC.  Don't know whether you can copy them from the OC window to a file to compare your friend's settings with yours.  Remember that the settings, including GS capture options, are aircraft specific.

Mike

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5 hours ago, Spin737 said:

 

I think the LOC before G/S is the most common option. Which is the default in the sim? If you had the cap G/S before LOC option selected, and you didn't want to follow the G/S, then capturing the LOC first and then arming the APP would make sense.

 

I wouldn't even dream of engaging a GS profile without being in the LOC first, is that not super unsafe ? I admit I follow it for guidance and when on a feeder route to a fix where its published minimum altitude permits it, but unless it is an RNP approach with a G/P angle I try to stay away.

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22 minutes ago, ALF1 said:

I wouldn't even dream of engaging a GS profile without being in the LOC first, is that not super unsafe ? I admit I follow it for guidance and when on a feeder route to a fix where its published minimum altitude permits it, but unless it is an RNP approach with a G/P angle I try to stay away.

I wouldn't, either. I've seen the GS do some pretty funky things when not on the LOC. Heck, I've seen it do funky things she you ARE on the LOC. 

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