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VNAVDescent

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I am trying to figure out a small problem i have in VNAV. When it comes time for me to descend I lower the MCP altitude to say 10000 ft where I have on the legs page to cross a certain waypoint. I get the message saying lower MCP altitude (after I already have). The 737 wont descend to the desired altitude in VNAV. I am almost positive I am doing something wrong. I wonder if any one can point me to where I can find the proper procedure or can you tell me what I am doing wrong.Thank youAndrew

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Andrew,Are you using the zoom panel ? There seems (;-)) to be a few issues with commanding the MCP from it.anthonyAnthony MertonPrecision Manuals Developmenthttp://www.precisionmanuals.com

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No I was in the main. I almost had it but it cut off at 10000ft because of speed. So I dont how to avois that problem since the VNAV was controlling the entire descent. Also anybody find that LVL change makes the 737 a rocket ship?Andrew

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Andrew,Am I understanding you that Vnav worked perfectly from flight level XXX down to 10,000 feet then disconnected with an overspeed message? Sound about right to what happened?One of the PMDG guys pointed out in another buried thread by now that Vnav kicks out with a greater then 15 knot overspeed.As you are coming down from lets say FL250, you are probably clocking around 300-315 knots, as you cross FL100, suddenly you have a speed restriction. Vnav looks and sees "I am doing 300+, that +15 of the 240 I now need to be doing and kicks itself off".Plan on levelling out at 11,000 or 12,000 and loosing the speed prior to crossing 10,000 feet. It should help you out and cut back on the ATC complaints filed against you for busting into their airspace at warp 3 ;)As far as your LVL CHG rocket ship, yep, it is. Level Change works by setting maximum power (N1) then controlling speed via pitch as I understand it (not completely sure). To return to sub-orbital speeds, de-rate your N1 levels to something other then full thrust on the N1 page of the FMC. The NG seems grossly overpowered (I presume that this is to get better efficencies out of the engines - ie: bigger engine running at lower power settings = better bang for the fuel buck)Ray

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Wow Ray,Thanks for the info. You pretty much solved my problems. It makes alot sense to level off then continue my descent. So simple yet I never thought of it. Also makes sense to derate. I did not know thats how the level change worked. I had read an earlier post about not using V/S for large changes in altitude. Not sure why because V/S really works well. Anyway Thanks againAndrew

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AH this is where flying ships like this and PIC come into a field of their own ;). Today I was testing and was going MAX RATE to reach my TOC sooner but thought "ummm my CRZ SPD is 295 but my MAX RATE SPD is 267 and am cimbing like a rocket with little fuel in the tanks, this is not going ot make the people in the back very happy when I hit the TOC!" so 1000' before TOC I set it back to ECON and it had time to speed up to ECON SPD of 295 and leveled off nice and smooth . The point is that I used judement and did not just sit back letting this beautiful beast fly for me. I am learning something everyday, not many others had this effect on me ;)[h4]Best Wishes,Randy J. Smithhttp://img.villagephotos.com/p/2003-8/196432/winglets_lg.jpg [h3] AMD XP 2200 |MUNCHKIN 512 DDR RAM |ECS[/b ][i] K7S5A MB[/i] |GF2 MX 32 MEG and still runs GOOD!|WIN XP PRO |MITSUBISHI DIAMOND PLUS 91 19"[/h3]

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You hit it on the head, sometimes we get so enthralled with the automation tools that we forget that we are still there to actually fly the plane ;)It is tough to step back from the automation when first learning it and remember that it is only there to help you, not replace you.Ray

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I think I have to make that my vice!!"Help you, not replace you" Grreetings from the FMS

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I agree with you Guys. I was flying the MAAM B25 alot after it was released and that was all manual flying. I got back to flying the PSS AB 3xx and the PSS Dash 8 and then the 737ng. They made me a little lazy just relying on the AP and FMS. I have to think about it and do a little more flying and not just letting the FMS do all of my thinking.Andrew

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