LNAV Problems

So I’m flying on a long haul and I tried to switch LNAV (GPS Source) on, but every time I do it switches to a different heading on which none of my waypoints are.

Make sure that in the NAV menu (above the A/P menu) - that the SOURCE is set to GPS - it should follow the active leg in your flight plan if set this way.

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Sorry I’m ind of new to IF so I don’t know all the switches and things. My bad.

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And about the GPS source I set it and it still goes to heading 238 instead of 263

If set to GPS and LNAV is on - it will attempt to fly towards the active leg of your flight plan (the part highlighted a magenta colour) rather than directly to the next waypoint.

Are you able to share a screenshot if possible?


Ok for starters you are flying way too fast - the B777 cruises at ~M0.84-85. You are just wasting fuel by trying to fly at .92.

The reason why the HDG is different in your FPL is because of the Earth’s curvature - it will only show the initial HDG in your flight plan.

The initial HDG from KSFO to KABTO would’ve been 297° but because of the long leg length and the earth’s curvature the actual heading will change over time.

Also not sure why you have a waypoint 7.2NM from your destination set for 32000ft…


o the heading changes

Yeah just leave LNAV on and it will follow your flight plan just fine.

Be careful though when having waypoints too close together. Try and not have waypoints with drastic heading changes less than 15-20NM apart, otherwise there is a chance the autopilot will overshoot and then fly in circles trying to capture the second waypoint.

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ao i could just use heading 238 instead of the 263 which my autopilot says right?

Just have LNAV on and then leave it - it will be fine.


K thank you!

No problem! Any other questions - feel free to send me a message!

Have a great rest of your day!