Bob_Z

Turning Off Heading Select

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I'm flying with Heading Select engaged and now I want to fly to a waypoint. Since I'm not sure of the heading to the point, I presume I would engage LNAV after programming the route into the FMC.  When I engage LNAV, the PFD still shows Heading Select in green with LNAV below it in white.  Pushing the SEL button does nothing.  I'm ding something wrong, but not sure what.

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2 hours ago, Bob_Z said:

When I engage LNAV, the PFD still shows Heading Select in green with LNAV below it in white.  Pushing the SEL button does nothing.  I'm ding something wrong, but not sure what.

This means HDG SEL is active, LNAV is armed to take over when all of the proper conditions are met. My bet is that you're not on/near the track for it to take over just yet. Don't try to outsmart the AP logic. You'll lose.

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6 hours ago, Bob_Z said:

I'm flying with Heading Select engaged and now I want to fly to a waypoint. Since I'm not sure of the heading to the point, I presume I would engage LNAV after programming the route into the FMC.  When I engage LNAV, the PFD still shows Heading Select in green with LNAV below it in white.  Pushing the SEL button does nothing.  I'm ding something wrong, but not sure what.

Make certain that the waypoint you want to fly to is the first waypoint on the ACT RTE 1 LEGS. Left double click the waypoint, press execute, press VNAV immediately. The aircraft will now fly to the waypoint. Forget HEADING SELECT it has been disarmed.. You do not need to be on an intercept heading if you press LNAV immediately after clicking on the execute button.

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On 11 January 2018 at 0:27 AM, scandinavian13 said:

This means HDG SEL is active, LNAV is armed to take over when all of the proper conditions are met. My bet is that you're not on/near the track for it to take over just yet. Don't try to outsmart the AP logic. You'll lose.

Absolutely what he says.

Conditions have to be met for LNAV to be allowed to "take over" Lateral Navigation.

Examples include: angle of intercept of active waypoint, (similar to ILS intercept), speed of aircraft and angle of intercept - indeed, the FMC calculates whether the selected LNAV Waypoint is a viable target for its present heading and speed - if it is not, it will reject the command; which means back to you and a less aggressive course/speed plan onto your selected LNAV Waypoint intentions and onward journey.

You can't just tell it to "go here, and do this, by here" - It won't have it; You might want exceed the airframes performance but it will refuse to go long with your insane plan. And rightly so - it's watching your back.

The correct way is to fly manually, a route that intercepts your intended LNAV Waypoint at an acceptable height, speed and, crucially; angle of intercept to allow both you and the 777 to "join" seamlessly with the LNAV route.

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3 hours ago, ganter said:

the FMC calculates whether the selected LNAV Waypoint is a viable target for its present heading and speed - if it is not, it will reject the command; which means back to you

Try it the way I have outlined and you will find out it works. I just did it on a takeoff that has no SID out of FNLU. After several vectors I was cleared direct to OPAPO. Rather than try to get on a intercept heading, I double clicked OPAPO, executed, pressed LNAV. The aircraft turned to OPAPO and that was it.

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