Problem re-engaging LNAV in-flight

[xander787 0]

So I keep getting the error in the FMC saying that I'm not on an "intercept heading" when I'm trying to re-engage LNAV in the air after having to manually set the heading because of ATC. Once I want to get back to my flightpath and re-engage LNAV, it keeps spitting out this error no matter what. I read this in the Introduction pdf:

To arm LNAV in flight : Requires a valid interception point for

active leg, interception angle less than 90 degrees OR within 3

miles cross tracks error OR within 3 miles from active. LNAV will

stay armed until interception.

 

But I guess I don't understand what it's saying or perhaps I'm trying to re-engage it incorrectly because no matter what I do I keep getting the same error. I set the plane on a heading that will see it cross the course but still no dice. Any help with this? Thanks so much.

[Spin737 102]

It might help to make sure that the jet is navigating toward the active leg. If you have the jet pointing at the course as it goes from XXXXX to YYYYY, but the LEGS page says your next fix is AAAAA, then the FMC gets confused.

 

Also make sure you know if you're supposed to be proceeding directly to fix YYYYY, or if you're supposed to join the airway.

 

That's a start, anyway. Some pics will help get a better answer.

[xander787 0]

It might help to make sure that the jet is navigating toward the active leg. If you have the jet pointing at the course as it goes from XXXXX to YYYYY, but the LEGS page says your next fix is AAAAA, then the FMC gets confused.

 

Also make sure you know if you're supposed to be proceeding directly to fix YYYYY, or if you're supposed to join the airway.

 

That's a start, anyway. Some pics will help get a better answer.

 

Thanks for the advice, I'll check next time and make sure I am indeed pointing the jet at the active leg. I'll also try to get some screenshots should I get the error again

[pete_auau 1,163]

Another way is to line select the top waypoint and than select it again at the top than select lnav again

[Jackal. 25]

Use the HDG select mode to get you back onto the pink line then you can reengage LNAV. The post above should also give you the correct solution.

[photons 0]

You can't engage LNAV if you are 3nm outside the active route. You can intercept your route by using heading select initially by selecting a heading within 90 degrees of the path. Within 3nm of your path you can then select vnav and the aircraft will begin to re intercept the route.

 

If you are heading towards your route at an angle more than 90 degrees and within 3 nm of the route, vnav will not engage untill you are within the 90 degrees.

 

This is why you need to study the 737NG, be it CBT, manuals or videos before you begin to take it into the air. Recommended 3 weeks of study at least and it will be worth it in the end.

[Spin737 102]

You can't engage LNAV if you are 3nm outside the active route. You can intercept your route by using heading select initially by selecting a heading within 90 degrees of the path. Within 3nm of your path you can then select vnav and the aircraft will begin to re intercept the route.

 

Close, but no cigar.

 

In flight, the AFDS intercepts and tracks the active FMC route. Either of the

following capture criteria must be met:

- on any heading and within 3 nm of the active route segment

- if outside of 3 nm of active route segment, aircraft must be on an

intercept course of 90° or less and intercept the route segment before

the active waypoint

 

You can be 5 or 50 miles from the course as long as you're on an intercept heading with the wings level when you select LNAV (and intercepting before the active waypoint).

[falcon999 24]

Another way is to line select the top waypoint and than select it again at the top than select lnav again

 

Another way of saying this is select a waypoint and use the "direct to" function.

[photons 0]

Close, but no cigar.

 

 

 

You can be 5 or 50 miles from the course as long as you're on an intercept heading with the wings level when you select LNAV (and intercepting before the active waypoint).

 

I am still learning, although I've learnt a hell of a lot in the past 6 months with information I already had on the 737 since 2009. Mainly though CBT's intended to train cadets into 737NG type ratings.

[xander787 0]

Well I found the solution after flying today and it was indeed what Spin737 suggested, I probably wasn't pointing the aircraft at the active leg. I made sure I did today and all seemed fine, thanks so very much, it was really bugging me not being able to figure that out and after reading the manual I didn't think about checking that. Also

 

This is why you need to study the 737NG, be it CBT, manuals or videos before you begin to take it into the air. Recommended 3 weeks of study at least and it will be worth it in the end.

 

I did reference the manuals and such and have watched many tutorials online. I've been reading the manuals on and off and have flown both tutorials, this was just one problem that, even after referencing the appropriate documents, I was having trouble figuring out. Sorry.