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Airway-to-exit-point-reroute

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Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
Has anyone experimented with the airway-intercept-to-exit-point described on page 367 of the PSX manual?

One of the favorite maneuvers a certain airline here in the U.S. loves to test on check rides is a re-route to intercept a different airway to an exit point (VOR) , similar to what is described here (scroll down the page to the highlighted headnote):

https://drive.google.com/file/d/0B-WRh0Hf7VdZRW9HbTNLMll6ems/view?usp=sharing

I have tried this scenario in PSX and have only been able to get it to partially work, but only if there is no airway at all in the RTE page. So, I don't know if PSX is set up to do this, or maybe I'm just doing something wrong. It may very well take too much code-writing effort on Hardy's part for something that most pilots who fly the airplane aren't even aware of.

In PSX, if there is already an airway installed on the RTE page, when I try to enter a new airway in 1L, it says INVALID ENTRY. Likewise, when I try to enter the exit point (VOR) in 1R of the RTE page it says INVALID ENTRY. So, for purposes of attempting this scenario in PSX, I set it up so that my RTE page would be blank prior to entering the new route:

Depart JFK RW31L using the SKORR 3 Departure to SKORR (nothing after that).
RTE is KJFK to KJFK.
Initial altitude is 5000'.
Arm LNAV and VNAV for takeoff.

After takeoff, as the aircraft passes SKORR, you will get an END OF ROUTE message. The aircraft will remain on the same course when the route ends. The RTE page will be clear.

As soon as you see the END OF ROUTE, ATC instructs you to fly a heading of 290 to intercept J77 to PTW (Pottstown). As noted in the attached document, for the FMC to auto-sequence this properly, you must wait until you are within 25 miles of an "anchoring waypoint" along the airway. In this case, BWZ (Broadway) will be the anchoring waypoint. In my scenario, waiting until 21 miles west of CRI (it should be auto-tuned in VOR 2) will put you within 25 miles of BWZ.

Once you are within 25 miles of BWZ, go to RTE 2/2 and insert J77 in 1L and PTW in 1R. For orientation purposes, I would strongly encourage you to look at this map. https://drive.google.com/file/d/0B-WRh0Hf7VdZTHRMdmMzUXVSWHM/view?usp=sharing

On a 290 heading, you will plan to intercept J77 south of BWZ then to PTW.

What PSX Does:

When you execute J77 to PTW on the RTE page, it will draw a route directly to BWZ (the anchoring waypoint), then correctly draw the segment of J77 between BWZ and PTW. If you look on the LEGS page, you will see the course directly to BWZ (approx. 312) and if you select LNAV, the aircraft will turn directly to BWZ and then track J77 down to PTW.

What the Airplane Does:

In the airplane, you need not have the RTE page blank to do this exercise. It will accept a new airway by simply typing over the existing airway in 1L of the RTE page. When you enter the new airway (J77), you will get blank boxes in 1R where you can enter the exit point (PTW).

When you execute J77 to PTW in the airplane, it will identify BWZ as an anchoring waypoint (just as PSX does) and bring that to 1R in the RTE page and 1L in the LEGS page (just like PSX). But the airplane will put dashes above BWZ on the LEGS page -- not the course direct to BWZ like PSX does. If you arm LNAV, it will stay armed on a 290 heading until you intercept J77 south of BWZ. Then it will capture J77 and turn left to PTW. Once J77 is intercepted, BWZ will automatically be replaced by PTW in the LEGS and RTE pages and LNAV will navigate toward PTW.

Keep in mind that the anchoring waypoint will never be over-flown even though it will appear in 1R of the RTE page and 1L of the LEGS page until you intercept the airway; then it drops out and is replaced by the "to" waypoint which in this case is PTW.

So, in the airplane, if you are on a heading to intercept J77, the FMC automatically determines the segment of the airway closest to your present position and all you need to do is (1) type in the new airway, (2) type in the exit point, (3) execute, and (4) arm LNAV. The FMC will automatically sequence it, intercept J77 south of BWZ and fly to PTW. This will work as long as your present heading will intercept the airway somewhere between the anchoring waypoint and the first fix after the anchoring waypoint (in this case PTW). If it doesn't, refer to the attached two-page document above for how to deal with this.

One work-around I found in PSX is to note the segment where a 290 heading will intercept J77. In this case it would be between BWZ and PTW. The LEGS page will correctly show a 237 course from BWZ to PTW. Then, bring PTW up to 1L and insert that course (237) into 6R. This will extend the centerline of J77 out from PTW. Then you could fly a 290 heading with LNAV armed to intercept the 237 course to PTW (J77).

Of course, the problem with this work-around is that with any existing route installed in the RTE page, I have been unable to overwrite it with a new route.

I need to do some more experimenting with this, but it seems that there are two issues I am finding:

(1) PSX doesn't seem to allow me to overwrite an existing airway with a new airway. The RTE page has to be empty to do this.

(2) PSX correctly identifies an anchoring waypoint, but it goes directly to the anchoring waypoint (in this case BWZ). The real airplane knows what segment of the airway it is closest to and plans to put the anchoring waypoint behind it when it finally does intercept. So, the real airplane puts dashes above the anchoring waypoint on the LEGS page instead of the course directly to the anchoring waypoint like PSX.

I sure hope this doesn't cause anyone to want to lie down in a dark room. Thoughts?
Moderator
Registered: May 2009
Posts: 5140
emerydc8 wrote
Has anyone experimented with the airway-intercept-to-exit-point described on page 367 of the PSX manual?

Yes, me, about 500 times.

And it worked all the time :-)


Regards,

|-|ardy


P.S: What document is that? It displays FMC altitudes without a trailing zero, e.g. 10802 instead of rounded 10800. The real FMC doesn't show a 1 foot resolution. Can we trust this documentation?

« Last edit by Hardy Heinlin on Wed, 15 Jul 2015 02:49:20 +0000. »
Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
Hi Hardy,

Are you able to get it to do something different than the results I am getting?
Moderator
Registered: May 2009
Posts: 5140
I haven't checked it yet. Looks like a very long story :-)
Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
It came from the training department at Atlas Air/Polar Air Cargo. They do operate a few 747's.
Moderator
Registered: May 2009
Posts: 5140
Also, in this document, the leg distances in the middle of the LEGS page have decimals. Normally, this is 737 FMC style (Smith's). Unless there has been a software update recently ...
Moderator
Registered: May 2009
Posts: 5140
« Last edit by Hardy Heinlin on Wed, 15 Jul 2015 04:00:50 +0000. »
Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
That's pretty much what I'm getting on my example -- PSX wants to go direct to the anchoring waypoint when LNAV is selected, rather than having the dashed lines above the anchoring waypoint (on LEGS page) and continue on the selected heading to intercept with LNAV armed until it intercepts the airway and puts the anchoring waypoint behind it.

My work-around was to do as you suggest by bringing the next waypoint to 1L on the LEGS page and using 6R to insert the inbound course. But it still has to be an empty RTE page.
« Last edit by emerydc8 on Wed, 15 Jul 2015 05:42:08 +0000. »
Member
Registered: May 2009
Posts: 131
Location: Reutlingen, Germany (near EDDS)
> Also, in this document, the leg distances in the middle of the LEGS page
> have decimals. Normally, this is 737 FMC style (Smith's). Unless there has
> been a software update recently ...

to me, it is quite obvious - the diagrams of the ND and MCDU are screenshots from the PMDG 747-400 add-on for MSFS. (Compare the pixel patterns of the MCDU with sceenshots on the PMDG homepage).

So that would explain the differences to PSX in terms of FMC distances and altitudes.

That a training department would use the PMDG 744 for training amazes me.

Markus
Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
This is an excerpt from a 144-page training aid written by some Atlas check airmen as a supplement for their own pilots. So, it's not an officially-sanctioned Atlas Air publication, but it is coming from experienced line and simulator check airmen. And they probably did use PMDG for the screen shots. But wouldn't it be better to focus on the veracity of the procedure presented, rather than be appalled by their use of PMDG to aid in the presentation?

Jon D.
Member
Registered: May 2009
Posts: 131
Location: Reutlingen, Germany (near EDDS)
Hi Jon,

> But wouldn't it be better to focus on the veracity of the procedure presented,
> rather than be appalled by their use of PMDG to aid in the presentation?

you're right. (Note that I am amazed, not appaled. ;) ). It was more a word of caution, that is, check PSX vs. the real airplane (and not on PMDG 744, unless checking whether PMDG744 is correct with respect to a certain functionality).

Markus
Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
Hi Markus,

Understood. If I recall, the PMDG 747-400 willl not do as the publication describes. I can't remember why, but I remember years ago that I couldn't get it to do as advertised.

I was given the very re-route depicted on the (linked to) map on my -400 type ride, except I was told the exit point would be SAX instead of PTW. I'm pretty sure the Level-D sim I was in (I think it came from NCA or ANA) does as the publication describes.

I sent an email to one of the check airmen who wrote the training aid, asking him if he has verified this in the real airplane.

Jon D.
Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
From the FMC User's Guide:

Quote
[T]he FMC automatically determines the segment of the airway closest to your present position -
GLACO - in the example and displays this anchoring wpt in 1R. It is the wpt located immediately prior to the intersection of the airway. Even though the active wpt is the beginning "anchor" point of the airway segment, LNAV will not navigate to this wpt, nor will the FMC display course guidance. However, once the course is intercepted, the active wpt will automatically cycle to the next wpt along the airway, and LNAV will navigate in the proper direction.


https://drive.google.com/file/d/0B-WRh0Hf7VdZdnY0UVkxcWdnaUE/view?usp=sharing

Also, from an email I just received from an Atlas check airman who wrote the training aid:

Quote
Hi Jon: Yes this does work. If you are within 25 miles and are on a heading to intercept the route between the anchor point and the first fix, all you have to do is arm LNAV. As a sim instructor, I demonstrate this to the crews. If you are heading to intercept anywhere beyond the first fix after the anchor point, you must perform a course intercept to the fix you will be flying towards. When this fix is entered into 1L the inbound data base course is displayed in 6R. Make the course big by selecting 6R. Execute and arm LNAV.
Moderator
Registered: May 2009
Posts: 5140
Re anchor point automatically being the last waypoint instead of the active:

I think this software change will be "relatively easy". When the airway stuff is found and constructed as usual, the FMC simply autosequences the anchor point. The ND shows the modified route in white, but the LEGS page -- in this special case -- starts its list at the last waypoint instead of the active, i.e. the last waypoint (the anchor point) will be the first list item, and its course-to indication is dashed. -- This is "relatively easy" because the FMC has always two last waypoints in its memory; the active waypoint is always number 3 on the list. So I just need to shift the list for the LEGS page display. There are no changes on the ND; the ND displays the last two waypoints as usual (the oldest one without a symbol; that's just to draw a line or curve to the last waypoint).


Re 25 nm rule:

Does that mean the current PSX version behaves correctly if the anchor point is farther away than 25 nm?

Should the anchor point be the last waypoint only if the anchor point lies within
25 nm? -- That is, "within 25 nm" in the moment when the pilot has made the route modification?


Cheers,

|-|ardy
« Last edit by Hardy Heinlin on Wed, 15 Jul 2015 14:44:37 +0000. »
Member
Registered: Jun 2015
Posts: 103
Location: Tucson, AZ USA
Quote
Re 25 nm rule:

Does that mean the current PSX version behaves correctly if the anchor point is farther away than 25 nm?

Should the anchor point be the last waypoint only if the anchor point lies within
25 nm? -- That is, "within 25 nm" in the moment when the pilot has made the route modification?


Let me see if I can find out about this, Hardy. I'm not sure what it should do outside the 25 nm point. Anyone here have access to a Level-D sim?
Moderator
Registered: May 2009
Posts: 5140
Here's another trick:

In PSX too you don't need an empty RTE page.

Enter the exit point in the LEGS page in 1L instead of the RTE page in 1R.

Then go to the RTE page and enter the airway in 1L. -- Bingo :-)

(I've learned that the RTE page should not be used for route edits; i.e. build the route on the RTE page, edit it on the LEGS page. A wrong edit on the RTE page may delete multiple waypoints by a single button push.)


Cheers,

|-|ardy

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