Hi everyone. Since the recent B747 update I’ve been experiencing a couple of issues as follows:-
- Discontinuity in the route is now always showing after selecting the flight route from World screen and needs to be manually deleted.
- LNAV doesn’t engage if the runway T/O heading is significantly different to the track to the first WP. I have to turn the aircraft using HDG SEL to intercept the route after which LNAV kicks in.
Neither of these issues were present in the older version. Are these ‘real world’ changes, am I doing something wrong, or are these bugs? My flights have all started at the runway threshold and not from cold.
Would really appreciate thoughts/solutions please.
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Yes. You’re doing nothing wrong.
If your current heading is not within a certain range of the LNAV path, you have to fly to intercept it, as you’ve discovered.
These are realism implementations. If you look up “discontinuities” throughout the forum you’ll find out reasons why they exist IRL.
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Thanks buddy. I’ve had to do a lot of digging to get to where I’m now in dealing with these issues. What a pain.
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You’re not alone. Many of the deeper systems depth improvements to base aircraft and avionics have thrown a number of people off.
Once you understand them, though, it’s generally no big deal to become adjusted to them.
Sure! I didn’t even realise there had been an update and thought the program had become unstable.
Thanks for the heads-up
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Expect some more new features coming to the 747 with SU13 releasing soon, too.
Most of the time your LNAV and VNAV shouldn’t be engaged on the ground. These are real world procedures and I am glad these are implemented now. I assure you, once you learn this the “right way”, the adjustment is minor and it’s not a big deal. It actually gives you something to do on an airliner… if not for these things, it would be a total bore to fly. 
Agreed that it mustn’t be boring! The problem was I didn’t know the update had happened. Just for clarification, I only engage LNAV after TO. Thanks for your response.
I always enable LNAV and VNAV on the ground before takeoff to insure the flight plan is going to work. If either doesn’t light up, then there is a problem I need to fix and I prefer fixing things on the ground instead of in flight. I suppose they then can be turned off before takeoff.
When flying away from the airport and the flight path or any possibility of being on the flight path, it is possible to use HDG to attempt to intercept the flight path. But the 747 seems to take miles to turn and when the turn is finished, the heading no longer points to an intercept.
It is easier with LNAV engaged, on the LEGS page to press LSK1 to put the first waypoint into the scratchpad, then press LSK1 again to paste the waypoint over itself. Press the lit green EXEC button. The FMC plots and flies a direct course to the first waypoint to intercept the original flight path. No turning or enabling HDG necessary. The FMC does all the hard work for you!
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Oh brilliant. Will give this a try. 
Just to be clear, is this done on the ground and the LNAV then disengaged or just after TO?
I think it is okay to leave LNAV on while the autopilot is off. I usually leave LNAV on and enable the autopilot somewhere between 500 and 1000 ft. I know some pilots prefer to leave the autopilot off and manually fly the aircraft until reaching 10,000 or 12,000 ft. Some pilots prefer to disengage the autopilot at 10,000 ft to fly the arrival and approach manually. For me there is too much activity with checklists, making sure the engines and systems are behaving, and responding to ATC to fly manually without the autopilot. I always end up going way off course.
LNAV can be easily activated on the ground, I can’t confirm about the 747 but for the 737 the first track after the runway should be within 5 degrees to be able to activate LNAV.
This is even nice to have so you can fly FD after take off.
Regarding VNAV this one should be switched on after take off. Somewhere after 1000 feet.
Although I was reading forums where airliners accepted / required to have it switched on prior to take off.
-Bram
Yes, you are correct about the RL airliners having the VNAV on prior to take off. I was watching RL TO U-Tube, and it was on.
That will depend on the airline. They all have their own specific SOPs when it comes to things like VNAV and LNAV being enabled prior to takeoff. Some allow it, others don’t.
For what it’s worth, all planes are like this to some extent. I fly the much smaller CJ4, and also have to manually adjust the heading bug as needed to ensure it turns enough to intercept. If 1/2 bank is active, it’s like that old song, “give me 40 acres and I’ll turn this rig around.” It’ll get there, but it’ll take a while.
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