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captain420

What am I doing wrong on my approach? Please help

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I have done a few flights from KIAH to KDFW and about 75% of the time I am able to capture the LOC... I'm not sure why sometimes its not capturing. What am I doing wrong?

 

I am landing at 17C (ILS Cat II) AT KDFW.... Using the BEREE1 STAR and ILS 17C approach... at the last waypoint in the star which is HEDMN, I then vector myself to the next waypoint. So I turn the HDG SEL to 207 and press it, my plane starts banking left, I then precede to wait until the heading is around 300 or so then I hit the LOC button.... but it doesn't capture it.... I had to to manually turn the HDG SEL to the right and then it finally capture the LOC. Is my timing off, or is this a bug in the PMDG plane?

I can't explain why it would capture and sometimes it wouldnt... I am doing things pretty much the same, however the point in which i hit the LOC button may be off a little bit. Am I suppose to capture it with 90 degrees or something? So if my runway course is 176 degrees, should I hit the LOC button when the heading on my ND shows around 270 then?

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Which aircraft type?

To capture the localizer you have to actually intercept it (i.e. cross its path). The point at which the LOC mode engages is generally dependent on the closure rate with the localizer beam. If you have a very shallow intercept angle and therefore a very small rate of closure, LOC will not engage until you are more or less on top of the beam (i.e. the CDI is more or less centred). If you are intercepting at a very large angle and therefore have a very high rate of closure with the beam then LOC will engage earlier in an attempt to intercept without overshooting (which may not be possible).

You can arm LOC mode more or less any time you want once you are cleared to intercept the localizer -- the precise parameters will be type specific, but on the Airbus for certain LOC mode can be armed with the aircraft heading anything up to about 120 degrees from the ILS front course. However, the important thing is that you should not arm LOC until you are cleared to intercept the localizer by ATC (or cleared for the approach) as there are occasions when ATC may deliberately want to take you through the localizer for spacing reasons.

Note again, that although it may be possible to arm LOC mode, engagement is another matter and, as I said above, is dependent upon rate of closure with the localizer beam.

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Okay I am doing a flight from KIAH-KDFW and trying to practice my landing/approach techniques. I am landing on runway 17C at Dallas, following the BEREE1 STAR down to ILS 17C approach. I am trying to manually descend to the target altitude in time so that I can capture the GS but I keep missing it and end up being above the GS capture altitude. Could someone please help me and point me in the right direction on what I'm doing wrong and what I need to do to make this approach?

After the LOC is captured, I try to hit FLCH and dial my altitude to 2300 and push the button to initiate the descend, but by the time it reaches the IF at JIFFY, the plane is still too high. I have tried everything that I can think of and I'm stuck. I have attempted this approach more than 10 times now and really need some help. I have posted a video so you guys can see what I'm doing. 

 

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16 minutes ago, captain420 said:

Could someone please help me and point me in the right direction on what I'm doing wrong and what I need to do to make this approach?

Energy management. It is an equation of both height and speed.

You start off in VNAV. The box thinks you are getting below the path because of the 6000ft restriction, so it gives you an armful of thrust and the speed runs away. That big lump of thrust there is essentially what is killing you: it is throwing a whole load of energy in to the system that you don't need or want.

Computers, and especially flight management computers are dumb. They can't project ahead like a human, so they will do stupid stuff like that. As soon as those thrust levers started even thinking about coming forward, you really needed to boot it out of VNAV, pull the thrust levers back and take more direct control over the thing - either V/S or FLCH.

That said - the situation was recoverable after that but you needed to be more positive. As you became established you were just below the glide, but you were in effect high because of the extra speed: so what you needed to do was start getting the speed coming back whilst maintaining the glide. By staying in FLCH, every time you wound the speed back the aeroplane started to reduce the rate of descent, taking you back above the glide.

What I would have done in that situation is go to V/S (maybe around -1500fpm or so?) to get a nice consistent rate going down to get on the glide -- I don't have the 777 so I don't know its descent characteristics intimately, but I would imagine that with V/S -1500 ish and Flap 1 you should still be slowing down with idle thrust. You can start winding the speed back and getting some flap out, perhaps drop the gear early if you need more drag to slow down. The speedbrake is not a lot of good at low speed -- the gear is the one thing on the aeroplane that provides the greatest amount of drag. Use it if you need to!

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29 minutes ago, captain420 said:

Okay I am doing a flight from KIAH-KDFW and trying to practice my landing/approach techniques.

 

I merged this new topic into the same topic you started the other day. Please stick to one topic and not keep opening new threads on the same issues. It's much easier for people to help you in one thread than to start multiple topics on the same issue.

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Thanks, but I'm not sure why in that video the FMC started with a huge boost of thrust, that never happened before in my other attempts. That's the 1st time it did that, so that's kind of weird and unexplainable. 

I have this scenario saved so that I can load it and practice. But anyways, I was using FLCH to slow the plane down and also to make it go down to the desired altitude that was in my MCP... But it seems like no matter what I try, I can't get the plane to reach the desired altitude at the last few waypoints before I hit the runway in order to capture the GS.

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6 minutes ago, captain420 said:

Thanks, but I'm not sure why in that video the FMC started with a huge boost of thrust, that never happened before in my other attempts. That's the 1st time it did that, so that's kind of weird and unexplainable. 

I have this scenario saved so that I can load it and practice. But anyways, I was using FLCH to slow the plane down and also to make it go down to the desired altitude that was in my MCP... But it seems like no matter what I try, I can't get the plane to reach the desired altitude at the last few waypoints before I hit the runway in order to capture the GS.

Sometimes you just have to take over and fly the plane. I fly this route in the 737, T7 and 747 quite a bit since it's a nice short flight and I live in Dallas and use KDFW a lot.

Rather than relying on the VNAV all the time or using FLCH, I use VS and airspeed control if needed. Sometimes you might need to extend the spoilers as well, no crime doing that of your too fast. 

Fly the plane, rather than having it fly you, if you know what I mean. You're the pilot in command not the FMC and autopilot.

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16 minutes ago, captain420 said:

Thanks, but I'm not sure why in that video the FMC started with a huge boost of thrust, that never happened before in my other attempts. That's the 1st time it did that, so that's kind of weird and unexplainable. 

I've explained to you the reason it gave you a boost of thrust: you were low on the VNAV profile (check the VNAV profile pointer indicating a few hundred feet low) and approaching a 6000A restriction, perhaps because you were lower at that point than in your previous attempts.

In any case, the reason it put the thrust in is irrelevant: it did! As soon as it did, you needed to take some action to stop it from doing something undesirable -- that is part of your monitoring responsibility. Before you fly the approach, you need to have thought through in advance where you want the aeroplane to be, at what speed and in which modes. Then, if when you fly it as soon as it starts to diverge from that pre-planned model, step in and take action to get it back to where you wanted it. The earlier you step in the better: it is better to make a small correction early than a large correction late.

16 minutes ago, captain420 said:

I was using FLCH to slow the plane down and also to make it go down to the desired altitude that was in my MCP... But it seems like no matter what I try, I can't get the plane to reach the desired altitude at the last few waypoints before I hit the runway in order to capture the GS.

Did you read my post? FLCH is not the optimum mode for what you are trying to do here, precisely because the one thing FLCH will not do is "slow down and go down". It will do one or the other, but not both.

You have options here: you could either have stayed in FLCH at 220kt with Flap 1 out until you were well below the glideslope, then levelled out at 2300ft and slowed down in level flight, or you could have done as I suggested -- change to V/S mode and go down (consistently) whilst slowing down (gradually). Winding the speed back in FLCH will just result in the problem you had here: you catch up the glide, so you wind the speed back a bit, FLCH reduces the rate of descent in order to slow down (quickly) and you lose the glide again. Even so, if you had got some more drag out (like extended the landing gear, and/or the speedbrake) you could probably still have coaxed it down.

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I cannot see the video, it won't load :-(

But I see that you are using the 777. Are you pressing APP after capturing the LOC?

In APP mode the plane will follow the glidepath, no matter what your speed is. Then you just stick out the flaps, speedbrakes, gear, etc. Whatever will slow you down. :-)

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I just saw the video: Press APP at 1:45 and your problem is solved ;-)

You are under the glide at that moment and with APP you will intercept the Glideslope. After that you can brake as mentioned above, with flaps, speedbrakes, gear. And the plane will hold the vertical path / glideslope. It will try to reduce the speed, but most of the time the drag with flaps 1 or 5 is not enough. Then apply speedbrakes or gear down, this will help you destroying energy.

 

 

While in FLCH mode the plane will do this: Hold the altitude until it reaches the target speed and THEN starting to pitch down to maintain the speed.

 

Edit: At the moment that you press APP you are already above the glideslope. Intercepting the glideslope from above is much more complicated than intercepting it from below. You would have to apply massive speedbrakes and have a V/S of way more then -700 feet/s (most of the time the "default" vertical speed for ILSes).

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Thanks for the tips, I managed to finally get it to work without applying speedbrakes at all. I'm not sure why in first few initial attempts of mine it was very difficult to slow down the plane. But I recently tried it again and it was all quite easy. Not sure if it has to do with any strange behaviors from loading from a saved state in the PMDG or what not, but all seems to be quite normal now and the plane seems much more controllable than I had thought. 

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On 21/06/2017 at 9:59 PM, skelsey said:

You start off in VNAV. The box thinks you are getting below the path because of the 6000ft restriction, so it gives you an armful of thrust and the speed runs away. That big lump of thrust there is essentially what is killing you: it is throwing a whole load of energy in to the system that you don't need or want.

 

Ah!  Thanks.

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The Flight Mode Annunciators (FMAs) are what you should focus on as the tell you what mode the aircraft is in at any point in time. They are at the top of the EADI display.

In VNAV mode and when in VNAV PTH in effect the elevators are attempting to maintain the computed path. The aircraft can only stay on this path by increasing or deceasing speed. It will do so until it either requires drag (going too fast) or needs thrust (going too slow). When it gets to the point that it cant stay on the path the pitch FMA changes to VNAV SPD and the elevators will now maintain a speed and no longer maintain the path. This will usually be accompanied by a drag required message if too fast and thrust application if too slow. The thrust application might be brutal and cause an overshoot of your required speed. You can prevent this by watching the speed during the descent and if you see it start to go below the magenta bug (especially if accompanied by a green speed trend vector pointing down and you are in Thrust Hold mode on the autothrottle), by applying manual thrust to stop the deceleration. Likewise if getting too fast apply a little speed brake to help control the speed. Most heavy jets will struggle to maintain speed or slow up with just flap 1 selected and going down the glideslope. Select flap 5 and around 180 -185 kts when manoeuvring close to the LOC and GS capture zones.

In your video if you had selected APP after LOC capture you would have picked up the GS fine, however, you would have been fast and needed to use the speed brake and a higher flap setting to get back on a stable profile.

Have a good read up of the manual on the FMAs and get a good understanding of each FMA mode and it will help enormously.

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