The 747 since the last update is acting strange. I can never reach my cruise altitude of between 41k and 44k. It gets to about 40k and then the engines go to idle and then it suddenly goes nose down to around 35k then throttles up and attempts to climb again and repeats the process. This happens in VNAV and in FL CH modes. Altering the payload weight, speed and vertical speed modes does nothing either. It never did this before. Hiting NAV and VNAV got you to your cruise altitude without any problems and it’s driving me nuts now.
Anyone else notice this? 
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Is there any chance there’s a live weather data problem again, like very high outside air temperatures above FL400? Such problems have occurred before, and are not happy for your engines.
Weather seems fine. Clear and no strong winds.
No sign of a high OAT on your instrument panel? That’s what would be relevant.
I suspect it has something to do with the weight and CG tbh. I’ve just generated another transatlantic crossing but this time I fully loaded the flights fuel and payload and adjusted the CG when I got the red warning. I manage to get to cruising altitude of 42k if I use FL CH instead of VNAV at Mach 0.90. Whilst on cruise, if I hit the VNAV button though it immediately begins to drop at a rapid rate. It’s not a stall but an actual nose-down dive.
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I’d say the 747 AP is buggy. This problem has caused me headaches on most my 747 flights. At this point I just fly a320 with unlimited fuel as a “representative substitute aircraft” until they sort out the god awful 747. Between the lighting and AP issues it’s unusable for transoceanic work.