LNAV and VECTORS waypoints

[Peter Clark]

Hi,

When flying a procedure in LNAV/VNAV that contains a VECTORS waypoint, what's the normal(correct?) AFDS mode behavior when that waypoint becomes active? Stay on LNAV with current heading, or drop to HDG HLD waiting for HDG SEL or a new direct-to LSK 1/re-enable LNAV to be commanded?

Thanks!

[Hardy Heinlin]

Hi Peter,

the AFDS remains in LNAV mode and keeps the last heading.

As far as I recall, in order to continue the route with LNAV you need to enter a waypoint in 1L (or re-enter it in 1L if it's already there) to make a direct-to or an intercept-leg-to, and then execute.

I think LOC capture is the only navigational condition that forces an automatic mode change away from LNAV. LNAV also remains engaged when flying past the route end or a route discontinuity. Otherwise, only system failures or manual switch actions can  disengage LNAV.


Cheers,

|-|ardy

[Peter Clark]

Hi,

Cool, thanks. I was thinking that for situational awareness at least the system would revert down to HDG HLD and annunciate that instead.

[Mariano]

Hi guys,

This might be obvious, but it doesn't hurt to point it out anyway.

For the 767, Boeing recommends to avoid using LNAV to intercept the localizer since the A/P might not switch from LNAV to LOC. The airplane might end up paralleling the localizer with LNAV engaged and LOC still armed. I have seen this happen.

I recall reading the same suggested procedure in the 744 FCTM a while ago.

Mariano

[Hardy Heinlin]

The airplane might end up paralleling the localizer with LNAV engaged and LOC still armed

May also happen in PS :-)

[Mariano]

Hardy,

Yes indeed. It has happened to me before intercepting the LSZH runway 14 localizer from TRA VOR segment of the arrival. Talk about realism!

Mariano