Hi all,I apologise if this has been asked previously, I have had a hardtime trying to find it.I've came across a strange problem with my T/D calculation presumably done by the FMC. The T/D marker (enroute, the green one) is fluctuating quite fast between two points approximately 10nm apart. This is apparent on both the ND, FMC, and when the aircraft gets close the closer point when it fluctuates, the FMC ALT Reset message and the FMC warning button on the main panel would illuminate on and off to the frequency of the flashing.Anyone had experienced this problem before and might have some solutions to this?Cheers,BrendanPS.Excuse the typo in the title.

Edited March 4, 201214 yr by Brenchen

Brendan,I remember Ryan saying that this happens under certain circumstances and actually happens in the real thing also. Don't worry about it, the aircraft will still fly properly.

Thanks for the reply, that's quite interesting

This is because the FMC is right on the "edge" between two different placements of the T/D point in terms of the path solver's equations. We have seen video of the real thing doing this in certain cases, so you can rest assured our solver is working exactly like the real one does. You can get the same effect with the magenta curve predictions too. Basically the solution is right on the line between being drawn in two different ways - the actual value for where T/D will start is the same, but the drawing part of the solution jumps.

This is because the FMC is right on the "edge" between two different placements of the T/D point in terms of the path solver's equations. We have seen video of the real thing doing this in certain cases, so you can rest assured our solver is working exactly like the real one does. You can get the same effect with the magenta curve predictions too. Basically the solution is right on the line between being drawn in two different ways - the actual value for where T/D will start is the same, but the drawing part of the solution jumps.

Now i'm curious to see this video... can you send us the link?

It's something from our development archive taken by one of our test pilots - it could potentially identify him and his airline, can't do that sorry. I do recall a youtube video somewhere that showed the magenta line jumping though - definitely don't remember the exact link though.