Vector SID- Direct to First Waypoint

[emerydc8]

Are you saying that LNAV won't engage immediately upon selecting it and go direct to the first waypoint after VECTORS?

[Hardy Heinlin]

LNAV never engages immediately when the MCP LNAV switch is pushed. The switch arms LNAV.

The armed LNAV will engage when the usual conditions are met (2.5 nm etc.).


The trick that your friend observed (HDG SEL push makes direct-to and arms LNAV) apparently does not work in the BA sim. I haven't included that trick. Just implemented Peter's observation.

[emerydc8]

Maybe I'm misunderstanding what you are saying. If you are on a vector SID with VECTORS active and you press HDG SEL, then LNAV, won't LNAV go active right away and take you to the direct-to waypoint?

I'm not talking about the trick my friend observed with the double-pump of HDG SEL --  I'm talking about the training guide excerpt I posted back in July.

[Hardy Heinlin]

I quote my comment again. Which part exactly is not clear? :-)

It's like making an airway intercept with the first fix being the anchor and the ensuing fix providing the target for the course of that initial leg that is to be intercepted. Within 2.5 nm abeam of that leg, and past the anchor in route direction, LNAV will engage.

That's how I understand the system. It will be in the next beta.


|-|ardy

You press HDG SEL.
VECTORS disappears.
The next waypoint is active and it is an anchor with ---° on LEGS page in 1L title.
The next leg you want to intercept goes from that anchor to the next waypoint.
You arm LNAV.
You're approaching that leg ...
LNAV will engage within 2.5 nm abeam of that leg ...

[emerydc8]

On Peter's example, would ENE be the anchor? The anchor is usually behind you.

[Hardy Heinlin]

Yes.

[Britjet]

Jon,

As I said, the video "expired" as I was pressing LNAV to see what happened, but I can say that when I pressed LNAV, it merely re-armed the LNAV, but it did not engage.
The clincher for me here is that there is no course available in the FMC to enable it to go direct - UNLESS you reinsert ENE at 1L (which is the way it was always used by me) when a direct course will appear in the FMC and THEN you can execute and LNAV in the normal way...
Personally I don't think the 2.5nm "rule" applies here until you get to ENE - but I could be wrong about that..Is that what you mean, Hardy?
Peter

[Hardy Heinlin]

Personally I don't think the 2.5nm "rule" applies here until you get to ENE

These two things don't exclude each other. Both things say: "engage LNAV when you intercept that leg".

When you are at ENE, you are at that leg.
When you are within 2.5 nm, you are at that leg.

Of course, you need another waypoint after ENE to have a leg to intercept. If the route has only one waypoint, the journey is over at ENE. There is literally no point then.


|-|ardy

[Hardy Heinlin]

I'll have to undo a recent modification:

In the current update, if a VECTORS line is preceded by a turn, the ND only shows the turn, not the straight vectors line thereafter. (Example: KLAX 06L CHATY3 SID.) The line should be displayed.

Question:

Say, a VECTORS leg requires an initial 090° HDG. The current aircraft HDG is 060°. When this VECTORS leg is active, a magenta line starts at the aircraft symbol. Will this entire line be straight or will there be an initial magenta turn segment from 060° to 090°, with a straight line only starting after that turn?

I think a turn segment should start at the aircraft nose. Only thereafter the straight line should start.

Edit: Now available in PSX 10.1.1-beta6 http://aerowinx.com/board/index.php?topic=4020.0


|-|

[Hardy Heinlin]

Another question ...

Here's an old photo I shot on the real aircraft in YSSY, with the FMC ORIGIN set to KLAX and the ND showing the CHATY3 SID from Rwy 06L. After 530 ft there is a VECTORS leg. The third and last waypoint in the route is CHATY. The ND shows a line to CHATY with an undefined starting point, although CHATY is the anchor waypoint for the vectors; there is no course defined in the database for this line to CHATY. The course of this line is equal to the course from the 06L threshold to CHATY. I'm wondering if this line is removed when a SID transition is attached after CHATY. None of the SID transitions start with a course that is equal to the course of this line; in other words, this line is not the extended leg line of the first SID transition leg.

Peter, if you read this, do you remember whether there was such a line to ENE when you made your video in your last sim session?




|-|

[Britjet]

Hi Hardy,
No, I don't remember anything like that. It's a strange one....
Peter.

[emerydc8]

Jon,

As I said, the video "expired" as I was pressing LNAV to see what happened, but I can say that when I pressed LNAV, it merely re-armed the LNAV, but it did not engage.
The clincher for me here is that there is no course available in the FMC to enable it to go direct - UNLESS you reinsert ENE at 1L (which is the way it was always used by me) when a direct course will appear in the FMC and THEN you can execute and LNAV in the normal way...
Personally I don't think the 2.5nm "rule" applies here until you get to ENE - but I could be wrong about that..Is that what you mean, Hardy?
Peter

Thanks, Peter. I may have access to the big sim next week. If I can, I'll check this out.

Jon

[emerydc8]

I tried this four times in the sim today and got it to work every time, as long as I installed a subsequent waypoint after the direct-to waypoint. So, off of LAX RW25L on the VTU7 departure, after VTU was RZS. Sorry about the shaky video. I had to pull the gear and I was operating solo on this.
https://youtu.be/ZsB5r7-hLKA

Cheers,
Jon

[Hardy Heinlin]

Great. Thanks, Jon!

From your video I'm learning:

• The dashed "---°" leg line title after VECTORS only occurs if that leg is the last one in the route.
• RTE page VIA line after VECTORS is dashed "-----" even though the VIA name to the exit point is known.
• The course to the fix after VECTORS is shown on the ND (in the video 277°)

You coincidentally pressed LNAV in that moment when the predefined 277° course also was your optimal direct-to course. So it's not clear whether it intercepts that predefined 277° course or changes it for a more suitable direct-to. There's also a turn segment at the aircraft nose. It would have been interesting to see what it would have done if LNAV was pressed when the 277° course line was behind the aircraft. I guess it either had drawn a turn segment back to the 277° line, or created a direct-to course of something like 285° (clockwise away from 277°).


Cheers,

|-|ardy


On the LEGS page, the course to VTU is 277° when VTU is the 3. fix, then 276° or 278° when it's the 2. fix, then again 277° when it is the active fix. Might be a rounding error. But it suggests that this course is not a database course.

Theory:
In your video at 2:48, it doesn't exactly make a direct-to. When LNAV engages, the aircraft is a fraction of a mile past the magenta turn segment. If it was the LNAV engagement which would set a direct-to course, that magenta turn would start directly at the aircraft nose. But it doesn't. It's very close. Because it's very close it gives the impression of LNAV setting a new direct-to. But it's just that same fixed 277° course that has always been there even before take-off. But this is just a theory!

[emerydc8]

Hi Hardy,

Here's another video I did of the exact departure. Maybe you can get something out of it that wasn't in the previous video. The course to VTU was originally 277, then it went to 279 and then back to 277. I'm not sure how the logic works on this.

I noticed that there is a few-second delay between the time I press HDG SEL and the time I see VTU move up to 1L in the CDU. Maybe it's just the slow processors that CAE used.
https://youtu.be/oWIE_AvPIh0

Also, I can confirm the three dashed lines (- - - ) above the direct-to waypoint and no LNAV engagement (only arms) when no subsequent fix is entered. I did the Kennedy departure off 13L using ENE, as Peter did, and got the same result with nothing after ENE.

[Hardy Heinlin]

Hi Jon,

I see no difference to the previous video. It flies that 277° course again which is indicated before take-off.

That little sequencing delay in the FMC is certainly normal. Nothing happens instantly. These delays also occur in PSX.

I would suggest that 277° course is the course that goes from the VECTORS starting point to the next fix. But this can't be a general rule; on the photo below the course to CHATY refers to the runway threshold (approximately):

[emerydc8]

What I need to do is let it go further out on the 250 heading before pressing HDG SEL. Hopefully I will get a chance soon and report back.

[Hardy Heinlin]

A quicker method, and to see even more effects, would be the CHATY3 departure from Rwy 06L like on my photo above :-)


I just noticed that our Navtech database has another fix 1 nm after CHATY, and the course to that fix is exactly equal to that open intercept course to CHATY displayed on the photo. I guess this 1 nm leg after CHATY just exists to generate that intercept course. (I don't know if Jeppesen uses the same trick.)

[torrence]

Hardy and Jon,

I'm not sure I'm following all this discussion with all the conditional logic etc.  I am interested in the way SID's with Vectors work however.  I set up one of my standard flights from KLAX to KSFO in PSX with the VTU6 departure (VTU7 is not in current database) with RZS transition and route to BSR arrivals to SFO.  So plenty of legs after VTU.  However, I get the ------o Heading line after VECTORS no matter how I construct the route.  To go direct to VTU after Vectors sequences I have to downselect VTU and put it back in 1L to get the heading to show up.  Not sure this is totally consistent with what you guys are looking at.  Situ with my take-off set up is here:

https://www.dropbox.com/s/ymc3g29ooh6fkf4/KLAX%20TO%20VTU6.situ?dl=0

Cheers,
Torrence

[Hardy Heinlin]

Hi Torrence, I noticed this also. I'll try to change a few things in the next update ...

Cheers,

|-|ardy

Great. Thanks, Jon!

From your video I'm learning:

• The dashed "---°" leg line title after VECTORS only occurs if that leg is the last one in the route.
• RTE page VIA line after VECTORS is dashed "-----" even though the VIA name to the exit point is known.
• The course to the fix after VECTORS is shown on the ND (in the video 277°)