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Problem with Glide Slope Capture

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I'm following the tutorial, and everything works perfectly up to the point where the glideslope should be captured.  Any ideas for troubleshooting this?  The only thing I can think of is that when I save the flight immediately prior to descent, the aircraft reloads with something missing.  The aircraft, aircraft , flight plan, and all switch settings match the tutorial.  Thanks.

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I'm following the tutorial, and everything works perfectly up to the point where the glideslope should be captured. Any ideas for troubleshooting this? The only thing I can think of is that when I save the flight immediately prior to descent, the aircraft reloads with something missing. The aircraft, aircraft , flight plan, and all switch settings match the tutorial. Thanks.

 

Hi, Dave,

 

Please give more information.  Are you seeing the glideslope (GS) and localizer (LOC) indicators on the ND (which should be switched to approach mode)?  Do you have the APPR button pressed on the MCP (autopilot)?  If you do see the GS indicator on the ND, are you above or below the actual glideslope?  What modes are showing on the FMA, which is the horizontal line at the top of the PFD that shows Autothrottle mode, horizontal mode and vertical mode? 

 

A screen shot would also help.

 

Mike

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Hi,

 

Can you please show a screenshot of the MCP and the PFD?

To capture the glideslope, you must be established on the localizer with the APP armed and below the gideslope.

GS must be displayed in blue white (tired) below the actual pitch mode on the FMA.

 

Edit: Mike you just beat me on this.

Edited by Budbud

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Edit: Mike you just beat me on this.

 

But you got right to the point!

 

 

 


I'm following the tutorial, and everything works perfectly up to the point where the glideslope should be captured. Any ideas for troubleshooting this? The only thing I can think of is that when I save the flight immediately prior to descent, the aircraft reloads with something missing. The aircraft, aircraft , flight plan, and all switch settings match the tutorial. Thanks.

 

Dave, please take a look at the tutorial, pages 80 and 81.  On p. 80 you can see what the PFD should look like just before you have captured the LOC and on p. 81 you can see what the PFD should look like after you have captured both LOC and GS.  Note the FMA indications across the top of the PFD.  In the first picture LOC is white because it is armed but the aircraft hasn't captured the localizer yet.  In the second picture both LOC and GS are green because the aircraft has captured both.

 

Romain's point should be emphasized: you need to be below the GS to capture it.

 

Mike

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you need to be below the GS to capture it.

 

That is usually the best practice but you can capture a GS coming down on it from above.  I've had to do that a few times and it does work.

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True, intercepting the glide from above technically works on the aircraft.

However it is way more tricky as you have to carefully manage the aircraft energy to be able to descent faster than the glide slope in order to intercept it.
For most of the modern commercial jets, it means that you have already slown down enough to get some flaps extended.
If you attempt to capture from above in clean config and then expect to slow down once you are established, good luck!  :smile:

 

I did also but I don't feel comfortable with that because you may never catch it and eventually would have to perform a go around.
There is no such risk if you capture from below.

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If you attempt to capture from above in clean config

 

Not this guy.  Been flying for four decades..., just pointing out that it can be done.  I've had ATC do it to me real world.

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That is usually the best practice but you can capture a GS coming down on it from above. I've had to do that a few times and it does work.

 

 


True, intercepting the glide from above technically works on the aircraft.

However it is way more tricky as you have to carefully manage the aircraft energy to be able to descent faster than the glide slope in order to intercept it.
For most of the modern commercial jets, it means that you have already slown down enough to get some flaps extended.
If you attempt to capture from above in clean config and then expect to slow down once you are established, good luck! :smile:

I did also but I don't feel comfortable with that because you may never catch it and eventually would have to perform a go around.
There is no such risk if you capture from below.

 

I've done it quite a few times as well, usually using VS.  But since 1) it is quite a bit more difficult than coming in level below the GS and 2) to me at least usually the result of poor planning -- coming in too high (and often too fast).  I, and I think Romain, were just trying to make it simple for someone who is most likely new to sophisticated heavy jet simulations.  AFAIK neither the 747 nor the 777 will capture the GS unless the aircraft catches up with it by descending.

 

Mike


Not this guy.  Been flying for four decades..., just pointing out that it can be done.  I've had ATC do it to me real world.

 

 

I suppose if you have full airbrakes and gear down. continually lower flaps to maximum allowable by given speed as speed decreases.  A few weeks ago I got to talking with a Delta 737 NG pilot who told me you can descend from 10,000 ft, 250K, 10 miles out and land OK.  She had been a military pilot so I don't know whether she ever tried this in a civilian simulator, but she had clearly done it in a military equivalent aircraft.   I told her about the NGX and she said  that if it's hard to slow down it's realistic.  Haven't tried this myself yet, primarily due to 747 release.

 

Mike

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10,000 ft, 250K, 10 miles out and land OK

 

That was a visual approach I hope. Gear down, speedbrakes. As much flap as able.  Hard to picture.

Sounds more like a HiTacan approach the military uses.

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That was a visual approach I hope. Gear down, speedbrakes. As much flap as able. Hard to picture.

Sounds more like a HiTacan approach the military uses.

 

Unfortunately didn't get to talk further -- had to get on flight (I think she was deadheading and sat in the jump seat -- I sat in coach)!  She described it as an emergency procedure to get down fast.

 

Mike

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I worked further on this and I noted that the waypoints as programmed in the CDU starting at DYAMD through CEPIN have "at or above" restrictions on the lowest permissible altitude at the waypoint (with the exception of ARCHI).

 

The IFR charts at the end of the tutorial document specify specific altitudes starting at FRELY through AXMUL I understand the reason for the at-or-above restrictions (I'm a pilot in the real world).  I believe that what is happening in the sim is that the at-or-above restrictions keep the aircraft above the glideslope.  I removed the at-or-above restrictions, and changed the altitude at waypoint values to 100 feet below the chart values on ZILED GIRR, DUMBA, and CEPIN, and now have no trouble with glideslope capture.  The glide slope is above the aircraft and it is captured as the aircraft flies through it in the descent.

 

 A second issue is that the tutorial (correctly) states that the MDA be set to 1800 feet.  The AXMUL waypoint specifies an altitude of 1800 ft.,  but the preceding waypoint (CEPIN) has an at-or-above restriction, so the aircraft enters the CEPIN - AXMUL leg on a path above the glide slope, and appears to never capture it (at least for me).  When the aircraft arrives at AXMUL, GS hasn't been captured, so the FD uses the 1800 ft MDA and flies over the airport at 1800 ft.

 

Does anyone know if the simulation is limited to glide slope capture from below?  I have not been able to capture the glideslope from above. 

 

My impression is that the limited GS capture range in P3D, combined with the at-or-above restrictions in the CDU waypoints, can cause issues.

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Posted Today, 06:03 PM

I worked further on this and I noted that the waypoints as programmed in the CDU starting at DYAMD through CEPIN have "at or above" restrictions on the lowest permissible altitude at the waypoint (with the exception of ARCHI).



The IFR charts at the end of the tutorial document specify specific altitudes starting at FRELY through AXMUL I understand the reason for the at-or-above restrictions (I'm a pilot in the real world). I believe that what is happening in the sim is that the at-or-above restrictions keep the aircraft above the glideslope. I removed the at-or-above restrictions, and changed the altitude at waypoint values to 100 feet below the chart values on ZILED GIRR, DUMBA, and CEPIN, and now have no trouble with glideslope capture. The glide slope is above the aircraft and it is captured as the aircraft flies through it in the descent.



A second issue is that the tutorial (correctly) states that the MDA be set to 1800 feet. The AXMUL waypoint specifies an altitude of 1800 ft., but the preceding waypoint (CEPIN) has an at-or-above restriction, so the aircraft enters the CEPIN - AXMUL leg on a path above the glide slope, and appears to never capture it (at least for me). When the aircraft arrives at AXMUL, GS hasn't been captured, so the FD uses the 1800 ft MDA and flies over the airport at 1800 ft.

Does anyone know if the simulation is limited to glide slope capture from below? I have not been able to capture the glideslope from above.

My impression is that the limited GS capture range in P3D, combined with the at-or-above restrictions in the CDU waypoints, can cause issues.

 

I just flew part of the approach.  The VNAV vertical path is very close to the glideslope path.   One thing to note is that you need to set the MCP Altitude window well above the 1800 ft altitude at AXMUL before you get there.  This is mentioned in  the tutorial.  It is standard to set the altitude to the Goaround altitude, 3000ft for this runway and approach.  If you are well below the goaround altitude (I believe at least 300 ft below), here 3000 ft, VNAV will continue the descent even though the altitude is above your current altitude. The plane wouldn't have stayed at 1800ft; it would have continued the descent.  If you are just missing GS capture you can use VS to "catch up" with it.

 

Mike

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I flew that arrival too during testing and had no problem following the steps in the tutorial exactly and intercepting glide slope. No need to modify the arrival constraints. 

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I had this problem twice now approaching both RWY25L and RWY25R at EDDF ( Aerosoft Mega Airports Frankfurt V2).

I descend in VNAV until where Glideslope capture should occur.

The VNAV path brings me very close to G/S Capture (Only missing less than ½ a dot before being aligned) at 4000 ft for RWY25L and 5000 ft at RWY25R ( I know RWY25R isn´t meant to be used by B744). The autopilot engages Altitude Hold just before Glideslope capture and I need to lower the MCP altitude below 4000/5000 ft in order to capture the Glideslope. So maybe in VNAV MCP altitude should be reached just a short time before reaching the Glideslope intercept point.

The better, and maybe more realistic way, is to use V/S mode below 10.000 ft., but I still think that VNAV should work too.

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7 minutes ago, Wothan said:

The better, and maybe more realistic way, is to use V/S mode below 10.000 ft., but I still think that VNAV should work too.

Not the better.  Not realistic either.  You will find the use of FLCH better suited to accomplishing this.  This pitch mode assures you of speed protection. In FLCH you use your thrust to modulate your descent rate, and pitch is automatically adjusted for the set speed.  This gives you total control of the aircraft.  V/S does none of this.

The vertical path ideally should lead you down to a smooth GS intercept but realistically there are times where you have to become the pilot.

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