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xkoote

B748 VNAV descent

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Hello,

maybe someone can clarify this for me. I have flown two different aircraft types in my life that are fully VNAV capable, and countless in the FS world. Is it just me, or does the B748 remain endlessly in SPD | xxx | VNAV PTH when initiating a descent? Maybe this is specific to the B748? From what I know, the Boeing VNAV will;

- Calculate a ToD point using as much information it has at its disposal ( e.g. descent winds, gross weight, descent speed and crossing restrictions )

- Once that point is reached, VNAV will initiate a sequence that without variation will reduce the thrust to idle. IDLE is displayed during this time. When the throttle reaches idle, thrust mode changes to HOLD.

- ONLY when current airspeed drops below a preset value, does thrust mode change back to SPD to re capture the speed before going back to idle.

As I am experiencing for a few flights now, VNAV will stay in SPD | xxx | VNAV PTH at top of descent, and thrust will keep managing speed during the descent. I kept it in VNAV for about 2 minutes to see if it finally changes to idle. It never does. Am I missing something? Or is this maybe a known issue?

 

Cheers,

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The -8 FMC calculates an "off-idle" VNAV descent, so it's normal behavior AFAIK.

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Interesting ! Thanks. I’ll go find some reading material ...

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