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Guest gilbnx

Autothrottle at cruise alt problem with 744X... Pls help

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Guest gilbnx

Hi,I have a problem to maintain the indicated speed on my FMC.Whenever I level off (FL330 in my case) and Thrust limit changes to CRZ, it seems that N1 is set for 101.7 as max. This is not sufficient to maintain the CRZ settings which was inidicated in my FMC VNAV page (CRZ ALT = FL330, SEL SPD = .842, OPT alt = 341).In these settings I'm loosing speed slowly and the only way I could maintain speed at about .808 Mach was by selecting the CON thrust limit (or turning off AT and maintain higher N1 of about 109 or so).If FMC is recommending the Optimal alt and speed, why the thrust limit is not sufficient to maintain speed at that (or lower) altitude?Never had a problem like that with the FS9 PMDG version, this is new issue for me with the B744X

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Guest dt1951

Maybe a dumb question, but is your weight such that you are too heavy to be at that altitude? What is the recommended FL for the weight?

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Guest gilbnx

Well, OPT altitude is the "Optimal altitude" for my weight at any given time of the flight. This is why I mentioned it in my posting.I was flying at an altitude that should be OK for the weight I was carried at that time (at least per the FMC).Gil.

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GIL,Go to PROG page 2 and check your outside air temperature (termed as SAT : static air temperature).For standard atmosphere should be (15 - altitude x 2) up to aprox 36000. If the actual value is greater by more than 5-10 degrees (ISA deviation) you are flying through a heat wave and engine performance is seriously affected. Some external programs tend to set +20 or more temperature deviations. Vangelis===================================== E. M. Vaos Precision Manuals Development Group www.precisionmanuals.com=====================================


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E M V

Precision Manuals Development Group

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Guest gilbnx

Thanks Vaos,I am going to check the temp. in my next flight. (I used FSinn which captures weather updates to fly in VATSIM)In the meantime, I saw this post with a similar description of the problem. This time, there was no external weather update... You can look at: http://forums.avsim.net/dcboard.php?az=sho...d=139098&page=3Gil.

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Guest Mnarboe

I also had this problem on a flight, the speed was set to 100knots on the PDF, even though the correct speed for the fix was displayed in the FMC pages. I just had to override it with the IAS/MACH selector, or we'd have fallen out of the sky. There was no engine performance problem, and to be frank, I don't see why going through a hot spot would make the plane want to self-destruct :DAfter another half an hour of flight, I tried to let the FMC control speed again, and now it worked....Another thing is that engine power sometimes goes down to 0% for all engines, just to gradually climb to 80+ again, and LNAV/VNAV are disabled, even though the lights for their buttons are still lit, so you can't see that they're disabled (except for on the PFD). I then click VNAV/LNAV (lights still lit), and everything works again. This has happened after things like saving a flight, but also unprovoced.

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Guest AJ

>I also had this problem on a flight, the speed was set to>100knots on the PDF, even though the correct speed for the fix>was displayed in the FMC pages. I just had to override it with>the IAS/MACH selector, or we'd have fallen out of the sky.>There was no engine performance problem, and to be frank, I>don't see why going through a hot spot would make the plane>want to self-destruct :D>>After another half an hour of flight, I tried to let the FMC>control speed again, and now it worked....>>Another thing is that engine power sometimes goes down to 0%>for all engines, just to gradually climb to 80+ again, and>LNAV/VNAV are disabled, even though the lights for their>buttons are still lit, so you can't see that they're disabled>(except for on the PFD). I then click VNAV/LNAV (lights still>lit), and everything works again. This has happened after>things like saving a flight, but also unprovoced.One other possibility, especially if you are using FS online weather, is a sudden shift in wind directions or speed. This has been a problem for years with FS online weather as it gets weather from different reporting stations, sometimes these statiosn can report radicaly different winds at the smae altitude. Thus you might suddenly go from a strong tail wind to a strong head wind (or vice versa) which woudl cause the autopilot to react in an extreme way and would also explain why everything was normal when you tried it later and the winds were mroe moderate. The commercial version of FSUIPC has a wind smoothing feature that helps with this a lot.Andrew

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