Hi all,

A problem that's been annoying me for a while, any help would be great.

I'm flying on LNAV and have a STAR and ILS all set up in FMS. Annoyingly and for some random reason LNAV puts me on a very acute interception course on the ILS, so much so that if I left it alone I would basically intercept the localiser at the runway threshold. Obviously this makes pushing the LOC or APP switches irrelevant as I'm not on an intercept course.

There are fixes and waypoints plotted in but the LNAV seems to just ignore these even though they are in the FMS.

Hope I've been clear enough.

Any help?
Cheers

Mark,

This is indeed a common problem. In the ATC environment the controller would never let this happen. They would vector you for a reasonable intercept angle. Most times YOU are the controller so make it happen!

Since you are most likely flying in just YOUR simulator, you have the ability to vector your aircraft to whatever heading you want. In the example of the ILS to RW 12R in KSTL you can alter your flight plan in the CDU to make the approach better for you. Let's say the CDU or STAR heads you at the end of the runway. All you need to do is add a few points to make the angle better.

If in this case, the STAR had you from FTZ to some point close to the end of the runway, you could add PAULY after FTZ or even NAIRN or the OM OBLIO. All would make the approach angle smoother.

Does that make sense?  

Lou



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connoan wrote on Jul 26^th, 2013 at 8:07pm:


Have you solved your problem? If not, please post the flightplan including departure/arrival airports with runways used and I will see if there is any additional help that I can provide.

Michael Cubine

connoan wrote on Aug 2^nd, 2013 at 5:17pm:


Hi Michael or anyone.

Below is my flight plan. I've also taken 4 screenshots to show the problem as it occurs but am not allow to post images yet

The problem is that the waypoint DME12 is ignored by LNAV and instead heads straight for the next waypoint, UW which because it is at the runway threshold, means I don't intercept the localiser until I'm pretty much at the edge of the runway.

Any thoughts?
Cheers


FLIGHTPLAN

EGLL (Heathrow) 27L DEPARTURE

SID CPT3F

LEGS INCLUSIVE OF SID AND STAR

-D25BB
-D258G
-D262K
-WOD
-CPT8
-CPT
-TNT
-POL
-RIBEL
-SHAPP
-MARGO
-TAR35
-ESKD0
-TLA10
-TLA
-D323K
-D323O
-D323U
-DME12
-UW
-RW06

STAR TWEED1A TRANSITION TLA

EGPH (Edinburgh) ILS06

What AIRAC cycle are you using? The SID out of EGLL is associated with another runway. Probably 27R and not 27L. I don't even see a DME12 in the approach to runway 6 at EGPH. The attached image shows the last the last four waypoints before the runway and cover a distance of 32 miles. So I would think DME12 would be in there. However, you are correct about the plane not following the flight plan.  The plane is heading to the northwest based upon the first two waypoints. Prior to those two wapoints it turns to the northeast and flys directly to the airport and doesn't intercept the ILS LOC. So it's land by manual flight or nothing. I could use the same runways and try a different route. How would that be?

Michael Cubine

When you select ILS Rwy 06 you are presented with two IAFs - TLA and UW. Select UW and then you can use LNAV. Once you are on inbound course, press LOC, dial 40 degrees in heading window, right click center select button and the plane should capture the localizer. When localizer is captured press  the APP buttton. Set your altitude to 2000 feet. 4000 is too high. By the time you capture the localizer you will be above the glideslope. Don't rely on VNAV for any of this. You need V/S to control the rate of descent to 2000. And go slow because you are doing all this in 12 miles.

Michael Cubine

LNAV works ok at other airports but I don't think there is anything wrong at EGPH. The 752 is just turning too soon and rolling out of the turn before it should. The turns must be precise if you are going to intertercept a localizer as soon as the turn is completred. The LNAV in the 752 is too sloppy to execute a precise turn. A 90 degree turn to intercept a localizer is difficult. However it can be done. I flew an additonal flight maybe two nights ago from EGLL-EGPH in the 737 NGX. Following the route, the turn to final, intercept, capture, and landing went like cllockwork. So there is nothing wrong with your home airport.

If you want to waste your time you could report this to CS support. The 752 has flown like this for the four versions that I have had. You just have to be ready for anything at anytime.


Michael Cubine

Edit – One of the things I find helpful is to draw a line on the HSI that shows the airport and the runway headings per the attached image. I can use this as a reference point if I end up doing a go around because of missing the localizer or glideslope. I fly parallel to this line on the outbound leg and follow it inbound. This can be tricky at large airports because the line runs thru the center of the airport and is not in anyway tied to a particular runway so you are going to be a hair to the right or left of the line but you will still intercept the localizer of the runway.

i rarely use Vnav to intercept  usualy atc sends me vectors using flight chg and heading select to intercept once localizer captures arm app and sends me down the correct glidescope no problems,