Hi,

 

Had a little problem with LNAV.  After takeoff I selected a heading that intercepted the track on the ND.  However when I selected the LNAV, it didn't come on and I got a message in the FMC that said not on interception track.  I tried several different angles to the track, from 5 degrees to 45 degrees but kept getting the same problem.  This is the first time I have had this problem and am wondering if it was just a glitch in this flight or I'm doing something wrong.  Any ideas?

 

Thanks

 

Rob

Check and see what the active leg is on the FMC. Either that, or your procedure files have said vector and you have failed to connect the two, and have just flown off the vector rather than to the point.

 

For example, the CHINS7 Arrival into SEA will take you to an intersection named AUBRN, where you will either fly 340 or 160 to bring you south or north of the Seattle airport. In the NGX, if you aren t making an active leg or flying vectors to said leg, you will just fly on the last vector assigned, and it will cause your FMC to say not on intercept heading. You don t want any offset, you want your heading on the MCP to make a straight line as possible to your intended waypoint. The LNAV mode will be in standby while the HDG mode is engaged, and once the aircraft picks up on the LNAV track, it will then swap over and you can continue on.

 

Easiest way to do it if you absolutely have to. Eliminate the little elevation waypoint on the procedure files, make a heading directly to your first waypoint intersection, and fly it from there.

If the worst comes to the worst, go to Legs page, Select a waypoint, Put it up the top like you were going to direct-track-to, then maybe enter a course to that waypoint you want to intercept in the scratchpad and enter it into line select bottom right. Execute. Then select LNAV.

 

1: Legs Page

2: Select waypoint in front of you "Next waypoint"
3: Line select this waypoint to the Top Left of page 1 of the legs page.

 

Optional a: type in the course you want to track to this waypoint

Optional b: Line select the course into bottom right

 

4: Press Execute

5: LNAV engage.