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Guest Jonno_S

A curious problem flying my PMDG 747

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Guest Jonno_S

I'll cut to the chase. TOGW - 380T. OAT 28c.CoG within limits Departed WSSS for EDDF and initial cruise was FL300. Everything looking good. Just before reaching that FL, ASv6 was doing it's thing with wx and threw some nasty storms at me.Quite some turbulence. Aircraft getting thrown around. Fun to watch! Then I noticed something strange. The AoA was increasing and the speed slowly bleeding off. The stick shaker was coming on and off quite a bit. The only way to increase speed was to disable the A/T and manually apply full throttle up to about 117 N1 and only then would the speed very slowly increase. In fact, barely at all. Perhaps 1 knot gained every 15-20 seconds at that high power.I thought perhaps icing? On went the anti-ice/wing ice. But didn't make a differnce. Even when it attained cruising speed the N1 was WELL above normal causing high fuel flow. AoA was around 7 degrees. Stayed like this for an hour or so. This was all around midnight and I just had to go to bed, but sometime around 0530 - pee stop - I checked again and it was fine. Everything running fine again all within normal parameters.So what was the problem? A little glitch between PMDG, AS and MSFS perhaps? Or it really was a wx issue? More annoying then anything really because it chewed through the fuel. Anyone experienced something like this before? Any help would be VERY appreciated!Jon.

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Jon,Sounds like the famous outside air temperature problem to me. If the temperature at altitude rises over the standard ISA temperature the aircraft engines will have to work harder and harder. Eventually the temperature is high enough to make the aircraft stall. Only remedy is to descent to lower altitude where you either have a lower OAT or where the engines can cope. This happens in real life as well.Hope it helps,


Mats Johansson
PMDG Flight Test Dept
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Guest Jonno_S

Ahh. There ya go. Have to keep an eye on that one for next time.Thanks, Mats.Jon.

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