When you select a new waypoint on top (legs page) and execute, you are going DIRECT TO it (if Lnav is engaged).

 

Before you execute you have the possibility to choose ABEAM.

ABEAM Still creates a direct course to the waypoint you had just put on top on the legs page.

But for other waypoints that you are now not overflying anymore (you are passing abeam them), new waypoints are created in the FMC. Called ABEAM waypoints.

The reason to do this are various.

Some like to have ABEAM points so they can keep track on their paper flight plan where they are.

Sometimes you need an abeam point to be able to do and write down a planned fuel check on the paper flight plan.

Also, going direct deletes all waypoints in between here and there, and with that, all forcast wind forcasts the FMC had for those points!

If you get a 600nm or more direct (not uncommon in USA/Australia), choosing ABEAM points, inserts the forcast winds at those abeam points which is better for time and fuel estimates.

 

When you select a new waypoint on top and BEFORE executing you type a course in the right hand bottom of the CDU, then you have created an INTERCEPT COURSE TO.

This way you can put for example a VOR (or any other waypoint) on top, type 360 in the right bottom, execute.

Then with heading select take up a heading that will intercept the magenta line somewhere.

Then arm Lnav (click the switch, Lnav will stay white).

And watch how Lnav becomes magenta (egaged) and the airplane intercepts and track towards your VOR with a 360 inbound course.

This is the explanation what i waiting for  ^_^

 

It appear more clearly now.

 

 

Thanks a lot to spend time to make a good answer.I will test that on my next flight this week-end Mexico(MMMX) to Bruxelles(EBBR).

You are welcome ;-)