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Guest lbb

VNAV questions

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Hi guys,For flap retraction I often use the VNAV chosen speeds to guide me. That started me wondering about how these speeds are determined. On the CLB page you can see the speed restriction change as you select different flap settings, which, as I understand it, are the speeds the bug on the ASI will move to.With a Vref 40 of 128 I get the following numbers:flaps 15: 158 = Vref + 30flaps 5: 168 = Vref + 40flaps 1: 198 = Vref + 70Now, in my original Boeing FCTM for the NG, the flap maneuvring speed schedule indicates the following:flaps 15 = Vref + 20flaps 5 = Vref + 30flaps 1 = Vref + 50Can anyone enlighten me as to why there is a difference between these two tables? At first I thought that perhaps the bug goes to the speed for the next flap setting, but since Vref + 40 is not mentioned anywhere in the FCTM table that can't be it. And it can't be placard speed either, see the placard.Then, during ECON PATH descent into EGKK I wanted to get rid of an altitude constraint in the TIM2E arrival, downloaded from Navdata. I found I could only do so in the LEGS page. In the real thing you can also delete the constraint from the DES page.But then, when I had deleted the constraint, the aircraft (or perhaps just me :-)) got quite confused. Obviously, there was now suddenly a different path, and the aircraft slowed down from a commanded speed of around 280 to around 260, without the speed bug moving, in an effort the capture the path. Is that what is supposed to happen? I would assume that there is a maximum speed deviation, somehow 20 kts difference seems rather large.Leo Bakker

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Hi guys,And some more questions. I know VNAV is a tough cookie, but that's what makes it all the more interesting :-)Below a screenshot where you can see two vertical profile points which are obviously not on the route, but rather in between the aircraft and the active waypoint. What are these points? Deceleration points? But then why are there two? Plus, I'm already below 240kts. And shouldn't they be displayed on the route?Also there is a profile deviation scale showing. But as you can see, I'm not in VNAV. (In fact, I had accidentally chosen the ENG OUT option and after that VNAV wouldn't engage). Is it correct for this scale to be there when not in VNAV? And if so, what does it do, since I'm not on VNAV and LNAV? What kind of profile is it showing then?Any VNAV experts out there?Leo Bakkerhttp://forums.avsim.net/user_files/54916.jpg

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Hi! Me again. Look at the FMC showing confusing information on the vertical bearing and vertical speed. I suppose it shows a V/B of 18.3 and a V/S of 13,021 and in fact I think that these figures might well be true, since there's only 3.7 nm to go and quite some height to lose.However it did make me wonder if in the real thing there are limits to these numbers. If you go ever closer, mathematically the V/S would approach infinite, right?Leo Bakkerhttp://forums.avsim.net/user_files/56386.jpg

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If you can find a NG pilot who engages VNAV prior to flaps up I will be shocked. I am not sure about the FCTM (I have that too) as regards to the current weight of your aircraft for the FMC calculations for flaps retraction. Anthony can maybe answer that. Those green donuts are, er well leftover information,. The ND is not *perfect* and that is only one example although a very small issue...[h4]Best Wishes,Randy J. Smithhttp://www.precisionmanuals.com/images/betaimg.jpg

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