- Fixed a rare issue in LNAV calculation that could cause the aircraft to become unstable on a route leg that lies along a north-south longitudinal meridian.

 

It seems I´m having this problem. In certain long transatlantic flights the plane goes crazy and starts doing u turns in mid flight. Cant get the plane back on LNAV.

 

I wonder if this happens to every body or just a few people and if there is a way around it till the service pack comes out.

 

My 777 is grounded till I can fix this because long flights take too long to plan for them to screw up mid flight, and the 777 was pretty much made for this type of flights so I´m screwed!

 

Thanks,

This sounds more like the turbulence induced s-turns caused by a weak modeling of turbulence. You can turn off turbulence to solve the problem. Active Sky Next weather can simulate turbulence without this problem appearing.

I have had this happen departing NZAA going west and RJAA departing west also. Using ASN. It also happens with no weather. I put it down to the lnav bug or corrupted FP, maybe.

Luckily I've never had this issue

- Fixed a rare issue in LNAV calculation that could cause the aircraft to become unstable on a route leg that lies along a north-south longitudinal meridian.

 

It seems I´m having this problem. In certain long transatlantic flights the plane goes crazy and starts doing u turns in mid flight. Cant get the plane back on LNAV.

 

I wonder if this happens to every body or just a few people and if there is a way around it till the service pack comes out.

 

My 777 is grounded till I can fix this because long flights take too long to plan for them to screw up mid flight, and the 777 was pretty much made for this type of flights so I´m screwed!

 

Thanks,

It's unlikely that you will ever have a route leg along a north south meridian when flying transatlantic. So I would say you aren't suffering from this rare issue.

 

 

Sent from my iPhone using Tapatalk

This issue is present mainly on the polar routes. I have never experienced it in normal transatlantic routing

Now that i think about it this happens flying from asia to europe...last time it was aflight from narita to heathrow

I mostly fly from europe to thailand and never had a problem with LNAv

I mostly fly from europe to thailand and never had a problem with LNAv

I mostly fly from europe to thailand and never had a problem with LNAv

I mostly fly from europe to thailand and never had a problem with LNAv

It happens going west not east.

 

It is random. I could do 10 flights ex RJAA, but the 11th might do it.  It has only happened twice to me since the T7 was released. At least I don't have the freeze issue, which is worse

:mad: ive never had that issue my pc freezes after a few hours into the flight

I think you are missing a point on your route legs.

 

This happens when you take manual control of the aircraft for example, get wayoff the path (missed going through a point) and when you continue going forward to the the next point using LNAV the airplane will take a U turn because there is point on the legs that you have missed. 

Solution to the problem is update your FMC legs page to the next point forward.

thanks for the tip but i never go off my lnav course, i engage autopilot shortly after take off and lnav ' vnav shortly after and then let the plane fly itself, however i will try skiping a leg forward next time it happens.

I think you are missing a point on your route legs.

 

This happens when you take manual control of the aircraft for example, get wayoff the path (missed going through a point) and when you continue going forward to the the next point using LNAV the airplane will take a U turn because there is point on the legs that you have missed. 

Solution to the problem is update your FMC legs page to the next point forward.

I have had it happen on a SID. Second leg  of Tetra4 departure RJAA. As I posted earlier, totally random. In fact I have just departed Narita using the same SID, and no problems.

Not sure if you fully read my post above about this issue only occurring going west ? From RJAA and NZAA only ( so far).

This issue really has nothing to do with what you describe, as you are talking about deselecting Lnav, and doing a sightseeing tour, this is about Lnav losing the plot when it is being used, even on a sid.

And as the OP wrote it happened to him  going west as well, from asia.

Nothing to report so far. I flew very close to the Pole (but not over it) without issues, and I also flew a max range flight of 22 hours between HK and Santiago without issues, crossing the IDL.

 

It is very specific that it occurs along a NORTH/SOUTH LONGITUDE MERIDIAN, meaning the leg itself must follow said meridian, so I highly doubt this is the problem you are experiencing given the direction of flight.

 

If you fly North/South then you could encounter it, but not East/West (the meridian of the track in E/W is N/S which makes it a Latitude meridian).

 

Best regards,

Robin.