Fix Wayline Cycling

[emerydc8]

This is because this new feature works only for approach legs, not for missed approach legs.

Just saw this (below) on the update page. Thanks, Hardy!

10.0.9b:

0.9.0079. Modification 0.9.0075 is now applied to missed approach legs too.

[Britjet]

Jon,
The inbound track is predicated on the legs page - it can't go the other way. If you give it a sensible intercept it will turn inbound when - (and if, as is being discussed) it captures in LNAV.
Peter

[Hardy Heinlin]

You mean inbound to the runway, right? Not inbound (back) to the unsequenced active waypoint?


|-|ardy

[emerydc8]

I don't understand how it could track away from the CF in 1L unless maybe the CF is viewed by the FMC as an anchor point, like an open-ended airway intercept where the anchor point is in 1L until it intercepts the airway, then it cycles and the "to" waypoint appears in 1L.

But in the case of an LNAV approach when you turn inside the CF wayline, I don't think that happens because the "to" waypoint would be the FF and we know that the CF stays in 1L during the entire approach. Definitely would be a good one to test in the sim, although it would probably be difficult to squeeze in.

Jon

[Britjet]

I think we are basically talking about the same thing here, that it won't turn and track (effectively the wrong way up the approach) to a missed waypoint once it engages in LNAV, it will engage the magenta track which still exists, but track the course that is in the legs page...?
As I understand it, although the leg won't cycle, the aircraft will still turn and track inbound to the runway, with the (uncycled) leg behind it.

[Hardy Heinlin]

Hi Peter,

I think so too. That's also how PSX works. The only new addition now is that the FMC won't sequence approach waypoints until the wayline has been crossed, and because of that addition, LNAV won't even capture the leg after the active waypoint. Outside the approach it will capture, but outside it will also sequence without the wayline crossing requirement.


|-|ardy

[Britjet]

Indeed, Hardy. As you know I'm not of the opinion that it won't lock on, but hopefully we will see.
Peter.

[emerydc8]

Hi Peter,

If it actually does track inbound to the runway with the CF in 1L and you do a missed approach, does it follow the missed approach route or does it take you back to the CF when you engage LNAV at 400?

Jon

[Hardy Heinlin]

Hi Jon,

my thesis: If it tracks (if), it will track the extended course line of the active leg; it can't track inactive legs.


|-|ardy

[emerydc8]

When you press TOGA, doesn't the missed approach route become active?

[Hardy Heinlin]

No, the missed approach will not start before the M.A.P. Imagine you were on an arc on the way to the runway; you can't leave the arc and go directly to the MAP.

[Britjet]

I can't test at the moment. But from my previous sim days, it is as Hardy describes...
Peter

[emerydc8]

Thanks, Peter. I'll check on this too and report back.

Jon

[emerydc8]

I think we are basically talking about the same thing here, that it won't turn and track (effectively the wrong way up the approach) to a missed waypoint once it engages in LNAV, it will engage the magenta track which still exists, but track the course that is in the legs page...?
As I understand it, although the leg won't cycle, the aircraft will still turn and track inbound to the runway, with the (uncycled) leg behind it.

Hi Peter,

I had a chance to test this in the sim today. LNAV will not capture if you turn inside the CF. I tried turning inside the CF while on a right base for 25L at LAX. What I thought was interesting was that as you got further away from the CF (in HDG SEL with LNAV armed), the VPP indicated that the aircraft was that much under the path. In this example, I am level at 3000', the CF (HUNDA) altitude is 3600' and the FF (LIMMA) altitude is 1900'. You can see that when I was nearly abeam LIMMA, the VPP showed me about 1500' under the path and increasing. https://www.youtube.com/watch?v=ABSFv99P_BE

Jon

[Britjet]

Yes, I queried this some time ago with a trainer friend and he told me that it wouldn't lock on. Sorry, I thought I had posted that somewhere...

Peter.