HDG SELECT problem 744

[Sekkha 15]

On my last flight I had a strange issue with HDG SELECT mode

First leg on the SID was a VECTOR, so after initially having selected LNAV  I changed it to HDG SELECT during taxi out. On climbout  the FD suddenly commanded a right turn away from the selected HDG of 11°....

Sorry, screenshot has low resolution to see details, but current heading is 12°, selected HDG is 11° , active roll mode is HDG SEL  and FD is comanding a right turn......how can that be?

Am I missing anything ?

 

best regards

 

 

 

[Samany69 41]

Hello 
In a vector type SID, an armed F/D will attempt to guide through next active waypoint after final departure course.

Best Regards.


Edit: Do not mix it up with RNAV Navigation + A/P. They are totally other things. F/D tries to guide you through the next active waypoint while LNAV is a function of your route. An active Vector SID with LNAV plus A/P will make your bird fly straight on final departure course ( LNAV Function ) while the F/D alone will aim at the next active waypoint.

Edited January 31, 2019 by Samany69

[nitsaw 3]

1 hour ago, Samany69 said:

Hello 
In a vector type SID, an armed F/D will attempt to guide through next active waypoint after final departure course.

Best Regards.


Edit: Do not mix it up with RNAV Navigation + A/P. They are totally other things. F/D tries to guide you through the next active waypoint while LNAV is a function of your route. An active Vector SID with LNAV plus A/P will make your bird fly straight on final departure course ( LNAV Function ) while the F/D alone will aim at the next active waypoint.

I don’t believe he is mixing anything, the image he provided the FD should not be commanding a turn to the right! He is in Heading Select on the FMA and his heading is synced up with the heading he’s flying! LNAV is not active or armed so this doesn’t seem right to me.

Best Regards,

Austin MacDaniels 

[Jetlinker 13]

I agree it doesn’t look right. For what it’s worth though, when using assigned headings in the real world we will bug the assigned heading but takeoff with no lateral mode selected.  At 400’ AGL we then engage HDG SEL. I’m not sure if that would have prevented your situation or not but it isn’t typical to perform the takeoff while in HDG SEL mode. 

Edited February 1, 2019 by Jetlinker

[nitsaw 3]

25 minutes ago, Jetlinker said:

I agree it doesn’t look right. For what it’s worth though, when using assigned headings in the real world we will bug the assigned heading but takeoff with no lateral mode selected.  At 400’ AGL we then engage HDG SEL. I’m not sure if that would have prevented your situation or not but it isn’t typical to perform the takeoff while in HDG SEL mode. 

It looks like he would have been okay if he stayed in LNAV on the takeoff. I can’t really make out the legs page on the right CDU but it appears it’s a vector on the runway track although I may be wrong?!? I have never had this happen to me as I only arm VNAV on takeoff if I’m going to use HDG SEL to vector to the initial fix. I would be curious to see if he could replicate what is shown in his screen shot. 

Best Regards,

Austin MacDaniels 

[Jetlinker 13]

2 hours ago, nitsaw said:

It looks like he would have been okay if he stayed in LNAV on the takeoff. I can’t really make out the legs page on the right CDU but it appears it’s a vector on the runway track although I may be wrong?!?

I agree, it looks like an initial heading is in the FMC and is separated from the first fix by vectors. LNAV would have worked fine too.  

Edited February 1, 2019 by Jetlinker

[Sekkha 15]

thanks for your replies everyone !

I luckily had saved the scenario just before hitting the TOGA button, so I now could recreate exactly this takeoff, and this time FD just commanded straight ahead as I was expecting. 

The only difference between both takeoffs is the fact that on the first one which gave me this surprising FD command I had LNAV activated during taxi  and then switched to HDG SEL before entering the runway   (I normally always use LNAV also for vectors, but this time I dont know why I wanted to go with HDG SEL), meanwhile on the second takeoff the plane was already loaded with HDG SEL active....so , dont know..

 

This is the legs page:

[scandinavian13 5,192]

6 hours ago, Sekkha said:

This is the legs page:

Welcome to the Baltimore Washington area! (How sad is it that I can tell just by the fix names?)

[vc10man 732]

Even I recognised them🤣

[scandinavian13 5,192]

9 minutes ago, vc10man said:

Even I recognised them🤣

Good to know I'm not alone 🤣.

Also: anyone here remember the thing the other year where people were debating whether or not a sound clip had Yanni or Laurel in it?

I got a good laugh out of it (without even watching the video), mostly because these fixes have been in this area for literal decades before that internet thing became a thing:

https://skyvector.com/?ll=39.22352996152355,-76.81022643401427&chart=301&zoom=3&fpl=YANNI LURRL

Edited February 1, 2019 by scandinavian13

[30K 72]

Well, I know all the fixes around EDDL F and M so I know that feeling lol. It's crazy