Hey guys,I swear, these things must come looking for me. There seems to be a problem with me (or the FO's FMC) when GPS is disabled via the options menu.Everything is fine until the AT engages to set TO power. I immediately get an amber CHK POS on both ND's, and the FO's map disappears. The FO's FMC reset's it's position to S00E00. I also get 2 scratchpad messages- CHECK POSITION and FMC POSITION MISMATCH.The pictures have the FMC1 on the left and FMC2 on the right. These are taken after I reject the takeoff.Pic 1 shows the captain's ND. FMC1 is at the correct position, while FMC2 is ai the other side of the Atlantic.Pic 2 shows the FO's ND after I stop It displayed normally before the start of the takeoff roll. Note that all 3 IRU's show the same position, but FMC2 position error has exceeded the display limits.Pic 5 shows POS3/3Interestingly, if we continue the takeoff, FMS2 resets to the correct position as shown in pics 3 and 4, which display his NDNote that in pic 3, IRU2 seems to have no drift error.The aircraft was loaded with the cold and dark cargo setup. I tried to see if perhaps I needed to select INITIALIZE IRS on both FMC's, but sa I suspected, selecting it on one FMC cleared the message from the other.Another thing I noticed is that no performance calculations (optimum altitude, altitude predictions etc.) are done until the IRU's have aligned (GPS disabled). Is this normal?PaulEDIT: The forum messed up the attachment order a bit, so I've edited the post to read correctly.

I confirm this as well

I also can confirm this, happens to me most the time but now I just ignore it and continue the takeoff, fixes itself shortly after.Jay V.

nudge

Once you advance throttles for take-off fmc position is updated using the nav database coordinates of the take-off runway. Obviousloy something goes wrong here for the FMC2 position. When airborn position is calculated using radio updates and the problem is corrected. I will have a look into that and let you know why this is happening.