Vector SID- Direct to First Waypoint

[emerydc8]

He took off with LNAV armed. At 50' it went active. On the climbout, he was cleared direct VTU. He pressed HDG SEL twice (didn't touch the LNAV button) and it took him direct VTU.

[Britjet]

I am back to my sock-eating promise (and Christmas stockings at that!) if this would even be an option.
What about vectors at the end of an intermediate approach procedure? Would you think that pressing HDG SEL twice would send you in LNAV to the CF? No way...
This doesn't stack up at all for me - I can't see any way that one mode selection would engage another. It just isn't logical or even safe, just to save a bit of button-pushing for the crew.
However I will dutifully test it out in the (non BA-specific - GE version) sim on Tuesday in addition to my previous tests which were negative.
Peter.
Edit: I see on your original post Jon that there is no mention in the ATLAS text that you originally quoted, of HDG SEL activating LNAV. It says that pushing HDG SEL removes the vectors condition (tested negative in BA sim) and then it says you have to push LNAV -  no mention of a second push of HDG SEL.

[emerydc8]

I agree that the double-push of HDG SEL sounds strange to me too. The original check airman's manual had you pushing HDG SEL then LNAV. That makes more sense to me because, like you said, one mode selection shouldn't engage another. I haven't seen either of these work in practice. I'm trying to see if my friend at Atlas can come up with a video of this. Neither alleged feature is printed in any official manual. No surprise there. Thanks again for checking.

Jon

[Hardy Heinlin]

Do we agree that the rest of that option is a nice feature? -- I mean that second HDG SEL push which removes the VECTORS leg (like an MCP ALT push removes a constraint).


|-|ardy

[Britjet]

To be honest, Hardy, not really, in my opinion. The vector (which could be bearing-specific, of course) is a useful reminder of what the SID expects. Then, if for any reason you decide not to use LNAV...e.g...
To give one example where this happens -  being slightly off-course while asymmetric is a pain in LNAV (real aircraft) because the system is very active with LNAV roll/tracking demands while you are still struggling to get the beast under control, and guys will sometimes press HDG SEL to give them less confusing guidance) - if you have pressed HDG SEL you have just lost the overlay of where you should be going...
Although it sounds like a labour-saver I think it potentially confuses things. I note of course that in the vertical mode a push on the ALTSEL will change the FMC, but I don't think this would be a good idea In the lateral mode.
I think that unless there is direct evidence of this, then even if it sounds "like a good idea" it shouldn't be introduced. I'm sure you don't want to invent a 7H7...;-)
Peter.

[Hardy Heinlin]

Understood -- as far as the initial push of HDG SEL is concerned. There should be no effect, and -- I assume -- there is no effect.

But who will push the HDG SEL button when HDG SEL is already engaged? You will just turn the knob for new headings, and everything will work as usual.

Only when ATC gives you a direct, you will push the HDG SEL switch a second time, and only that action will remove the VECTORS from the FMC. You would do this anyway (head down on the CDU). And if you are aware of this option, you will expect this effect.


|-|ardy

[emerydc8]

Hi Peter,

My friend at Atlas did a trip down to South America last night with one of your former co-workers on-board (Ian C.), who is now a sim instructor there. They discussed this issue extensively. According to Ian, the original illustration that I posted above in post #1 is correct! Now my friend is totally confused because he was convinced that he got it to work using the double-push of HDG SEL. I told him that Hardy would want to see some hard evidence now in the form of either a video or your confirming it for us in the big sim. So, he's going to try to get a video either in the airplane or possibly in the sim this month, since he's flying out of MIA. I know you already tried it (unsuccessfully) in one sim, but maybe it's worth trying it in another. Thanks.

Jon

[Britjet]

I should get chance to try the VTU7 out of LAX tomorrow.
Peter.

[emerydc8]

Thanks, Peter.

Jon

[Britjet]

I tried a couple of departures in the GE sim last night, and while it is fair to say that the socks are back in the drawer it did throw up one surprise..

Dep JFK 13L with a generic Kennedy 6? SID. To enable a possible LNAV I also put ENE in the legs. It looked something like this..
1L - 130degs or so for the initial airborne segment
2L - VECTORS
3l - ENE.

I got airborne in TOGA with LNAV armed. LNAV engaged at 50R, (I think) but nothing changed in the LEGS page.
I pressed HDG SEL, and VECTORS was removed, and ENE moved to 2L.
I then pressed HDG SEL again - no effect.
Pressing repeatedly made no change, and pressing LNAV again merely armed LNAV. no change to the LEGS.
So it seems something IS going on here with the VECTORS line.


Departure 2..
From KLAX 25L VTU 7 SID.
LEGS page looked something like this..
1L 251
2L 251/SMO 154r
3L VECTORS
4L VTU

LNAV engaged at 50R, and I pressed HDG SEL at 400ft or so.
HDG SEL on FMA (of course) but no change to the LEGS.
I then waited until the SMO radial crosscut was satisfied and pressed HDG SEL repeatedly after that to see if it would remove the vectors, but no change at all in the LEGS.

I'm puzzled by this. After seeing VECTORS disappear on the JFK departure I would have expected the same thing, but it didn't happen.
Also, in both departures, the fix after the VECTORS never made it to 1L. At no time was there an EXEC light.

I am wondering if there might be something in the SID coding that enables the removal of VECTORS, or where it appears in the LEGS sequence.
As usual my test was pretty unscientific as I was dealing with guests flying skills or lack therof at the same time, and I couldn't film it because my phone was out of memory!
I will try and get another opportunity in the next couple of weeks to test further.

Peter

[Hardy Heinlin]

Thank you, Peter!

I pressed HDG SEL, and VECTORS was removed, and ENE moved to 2L.

I don't understand. Wasn't ENE at 2L already when VECTORS was at 1L? What was at 1L when VECTORS was removed? Dashes?


Cheers,

|-|ardy

[Britjet]

No, as per my little "diagram", ENE started out at  3L and moved to 2L when the VECTORS disappeared. As far as I recall, nothing changed at 1L.
I don't think you will get VECTORS at 1L because there will always be a runway initial climb out (I think).
It really needs a video....;-)
Peter

[emerydc8]

Thanks for testing, Peter. I agree -- a video would be helpful.
Jon

[Hardy Heinlin]

This is what I expected:


Take-off position:

1L - Initial airborne segment
2L - VECTORS
3L - ENE


When initial airborne segment is sequenced:

1L - VECTORS
2L - ENE



This is what Peter saw in the BA sim, as far as I understand him:


Take-off position:

1L - Initial airborne segment
2L - VECTORS
3L - ENE


When initial airborne segment was not sequenced yet, and HDG SEL was pushed:

1L - Initial airborne segment
2L - ENE


I can't believe that! :-)

I don't think you will get VECTORS at 1L because there will always be a runway initial climb out (I think).

Sure, but later in flight the initial climb out will be sequenced; that's the phase I mean.

You mean when the initial legs before VECTORS are sequenced, and VECTORS becomes active, VECTORS will be instantly sequenced as well and the next normal leg will move to 1L and stay there forever until you manually sequence it? This makes no sense ... -- unless the CRS line title in 1L is dashed and the ND keeps a moving vector line on the aircraft symbol; these features would indicate that a manual path termination is required. Is this true?


Cheers,

|-|ardy

[Hardy Heinlin]

I can't believe that! :-)

Meanwhile I can :-)

From another subject I just learned that an altitude terminated hold is not flown if the altitude is reached before entering that hold; I conclude the hold is then removed from the route even if it sits beyond the first waypoint.

The FMC is full of hidden wonders.

Inspired by this, I can now also imagine a VECTORS leg is removed from the route when the pilot engages HDG SEL before reaching the VECTORS leg.

(Once the VECTORS is active, the control logic may be different.)


Regards,

|-|ardy

[Britjet]

I took a video last night. It is a standard JFK SID from 22R using LNAV. As you can see the initial segment sequences by itself and pushing HDG SEL after that removes the VECTORS line and engages HDG SEL.
I was about to push the LNAV again when the video halted (out of memory) but I do know that LNAV was re-armed as would be expected, and that there was no change to the FMC presentation. LNAV did not engage.

https://youtu.be/BBkyLdRxe7w

Hope this helps..

Peter

[Avi]

Interesting.

Is there a possibility that this is an airline specific?

[Hardy Heinlin]

Thank you, Peter.

I think it's not airline specific.

I'll implement this effect. My plan is this:

When the FMC detects that VECTORS and HDG SEL are active at the same time, VECTORS will be sequenced and the next waypoint becomes an anchor waypoint with ---° dashes in the line title of L1 of the LEGS page.

The waypoint after VECTORS is always an anchor point; the dashes ---° in the LEGS line title are always displayed after VECTORS on the route waypoint list. When HDG SEL is engaged while VECTORS is the next or active leg, the waypoint after VECTORS becomes active.


|-|ardy

[emerydc8]

Thanks for testing, Peter.

So, just to verify that on a vector SID, when VECTORS is active and you want to go direct to the first waypoint listed after VECTORS, all you have to do is push HDG SEL, then LNAV, as I described in my July post? http://aerowinx.com/board/index.php?topic=3695.msg38118#msg38118

Jon

[Hardy Heinlin]

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