Post SP1b LNAV Issue?

[hollins.t 0]

Hello -I'm not sure if this is really a problem with the NGX or if I completely missed something. I flew into KMCO the other day, no problem at all. Last night I updated my NGX to SP1b and departed KMCO this morning. I departed runway 36R and set up to turn left direct to RSW. After completing the turn I tuned on my Autopilot then my LNAV, then VNAV like I usually do. I had to click all three buttons twice each before they would engage (Yoke was centered and no control inputs were being put in at all). It continued to climb me up to FL360 like it was supposed to, and I am currently at FL360 and cruise speed. However my aircraft is not tracking direct towards RSW but flying at heading 195 (my heading selector is 000) and about 5-8 NM off of what my course should be.I just went back in to the FMC > Legs Page and clicked next to RSW and re-entered it as the current "waypoint" and it seems to be working now. But why did it not pick up like it was supposed to out of the "gate"? Everything in the cockpit checked out, no warning lights or anything like that. Nothing in the failures page either.Anyone else want to give that departure a shot and see if the same thing happens to them? KMCO, 36R, direct to RSW (No SID), FL360.Any imput would be appreciated!

[mcair01 3]

Also having a problem with Sp1b LNAV. First flight after installation of patch: KGRB-GRR-LAN with an ILS28L approach selected. Everything running normally until GRR, next waypoint is Burye and LNAV loses the plot. The course line disappears from the ND, LNAV/VNAV and CMDA still engaged, the aircraft meanders in a lazy r/h turn.

[hollins.t 0]

Very weird.

[Jeff_B 8]

I get the LNAV/VNAV lights turning off after TOGA. but otherwise LNAV works like it should.

[Tabs 2,790]

I get the LNAV/VNAV lights turning off after TOGA. but otherwise LNAV works like it should.

That's completely normal - it's letting you know you're locked into the TO/GA modes during the takeoff sequence and can't disengage them with the MCP buttons. Same thing happens during autolands.

[Jeff_B 8]

Thanks RM.

[Tabs 2,790]

I just tried the situation from the original post several times and saw no problems.Couple ideas:1. Are you positive your yoke isn't out of calibration or spiking - that's what the inability to engage modes+AP sounds like to me.2. I think you may be misunderstanding how a direct leg works - when a leg is direct, the plane's nose keeps turning until it's pointing directly at the waypoint - this is continuously updated, the magenta curve and course drawn after you exec it is an initial prediction, but when the speed of the airplane is changing during the turn as it is here, the plane is always going to end up off the magenta line. Direct to with a big reversal like this isn't a course intercept where it's going to go and intercept that prediction line - it will turn the nose directly at the waypoint and this could be off the magenta line easily if the speed is changing while the turn happens. When this happens in real life they do exactly as you did there, just line select the waypoint into 1L again and it'll redraw.

[hollins.t 0]

I just tried the situation from the original post several times and saw no problems.Couple ideas:1. Are you positive your yoke isn't out of calibration or spiking - that's what the inability to engage modes+AP sounds like to me.2. I think you may be misunderstanding how a direct leg works - when a leg is direct, the plane's nose keeps turning until it's pointing directly at the waypoint - this is continuously updated, the magenta curve and course drawn after you exec it is an initial prediction, but when the speed of the airplane is changing during the turn as it is here, the plane is always going to end up off the magenta line. Direct to with a big reversal like this isn't a course intercept where it's going to go and intercept that prediction line - it will turn the nose directly at the waypoint and this could be off the magenta line easily if the speed is changing while the turn happens. When this happens in real life they do exactly as you did there, just line select the waypoint into 1L again and it'll redraw.

Hey Ryan,Thanks! I rechecked my calibration and everything seems fine. I also hadnt changed any hardware (even unplugged anything). It was weird because it looked as though it was going directly to my second leg "MARCI" but even that seemed a little off. It looked as though i should have been at least HDG 210 or a little greater to be even close to RSW and at least 200 or greater to be close to MARCI. I forgot to mention, there were no abnormal messages in the FMC and no "BYPASS" messages. I'm pretty sure this is on my end since you arent having that problem, I'll redo the same flight in the morning to see if I get the same results or not.Thanks!

[jgcomp1 0]

Also having a problem with Sp1b LNAV. First flight after installation of patch: KGRB-GRR-LAN with an ILS28L approach selected. Everything running normally until GRR, next waypoint is Burye and LNAV loses the plot. The course line disappears from the ND, LNAV/VNAV and CMDA still engaged, the aircraft meanders in a lazy r/h turn.

I had today a problem navigating from CYOW to CYUL that resemble very much to what you described. Course line disappeared after reaching HOKKE enroute to EBMOK. Aircraft began swaying left to right and back. Reactivating EBMOK solves the problem. Course line reappears then and aircraft stabilize on course.