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Guest beans

vnav help.

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Guest beans

Hi I have the 747-400.Can someone please help me understand this nightmare.:-zhelpThe question that I have is:When vnav is engaged do I still have to adjust the speed on the MCP or should vnav be doing this automatically as per FMC speeds for various waypoints etc?Because at the moment it doesn't.I am still having to manually increase the speed and the alt to maintain climb and reach target speed/alt.I am sure vnav should be doing all this for me and the climb should be automatic as per the FMC,as should the increases in the speed.I look forward to your help.Tass :-zhelp

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Yes, when you engage VNAV, the speed window in the FMC should go blank.Have you completed your pre-flight programming, activated it and pressed the "exec" button in your FMC ?Jose Luis.


signed: José Luis

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Oh! mistake !, what should go blank is the speed window in your MCP, not in your FMC.Jose Luis


signed: José Luis

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Guest beans

>Yes, when you engage VNAV, the speed window in the FMC should>go blank.>>Have you completed your pre-flight programming, activated it>and pressed the "exec" button in your FMC ?>>Jose Luis.Hi JoseThanks for the reply.I complete the pre flight etc and press 'exec'. when I press vnav the speed window goes blank as well,the problem starts after this.The speed and climb do not change unless I do them manually.The leg screen shows the various speeds/altitudes.When I increase the alt to next ATC recommendation ,the climb starts but the nose dips down and than starts climbing -drop can be upto 2000ft before the climb starts,until the desired alt is reached the yo-yo effect remains.The FMC is in climb mode-but I have tried other modes too and the problem is same.If you have the time I would appriciate a step by step guide on how to set up vnav.I have printed lesson 4 but beacuse I am not at level one even it looks abit complicated at the moment.Tass

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Hi:Well, I fly the 737, not the 747, but I presume their FMCs are very similar.Sometimes VNAV automatically disengages if the aircraft is not able to follow the programmed vertical path (this mostly happens in descents). Search if you are "asking for too much" in your climb profile.If I understand you, the yo-yo effect (nose up and down)is often used by the autopilot to regulate speed (increase or reduce).I don't know if that helps you. I started flying the 737 in April this year, so I am still a rookie, but everyday I am learning more and more about this wonderful aircraft.Jose Luis


signed: José Luis

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Tass,You *do* need to place the MCP altitude knob at the cruise altitude (or as assigned by ATC) for a climb to occur. The speed window should blank out when you engage VNAV.Have you done the type rating courses? TRC #4 goes through the whole VNAV system in detail.


Ryan Maziarz
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Make sure that you have a departure airfield and a destination airfield entered on RTE page 1. You can also enter the planned route here or on the LEGS page. Activate and Execute. Go to DEP/ARR page and enter the departure runway and SID (if there is one). Check on the LEGS page that there are no discontinuities (breaks) in the route. You should have a Magenta coloured line going all the way from your departure airfield to destination with no gaps or double backs. You can check this by staying on LEGS and selecting PLAN on your EFIS control to the left of the MCP panel. If you now look at the legs page it has a STEP prompt at the bottom Right of the screen. This can be used to centre the ND display onthe selected waypoint. Each time you press it selects the next waypoint down and centres the Nav display on it. You will notice in plan mode that the Nav display is alligned North up instaed of Track up. You can adjust the scale to suit when you are checking. Go to the PERF INIT page. You need to fill in all the boxes here. Go to the TO REF page and enter on the left hand side a Flap accel HT of 20/1500 (This will let the FMC know that you will be taking off with flaps 20 and commencing acceleration for flap retract at 1500 ft AGL. Enter E/O ACCEL HT 1500 (This is the altitude the aircraft will climb to on 3 engines before accelerating. Some airfields have a higher setting due to close in obstacles. 1500 is a fairly standard figure to use). THR REDUCTION Enter either 1500 or 5 (the 1500 means the power will go from TO thrust to what ever Climb thrust you have set {THR LIMIT page} If you enter a 5 or 1 you will get climb thrust at this flap setting instead of an altitude. For most operations we use 1500). Go across to the other side of the page and look at the TO speeds. These will appear once you have put something in the Flap/Acceration box on the left side. If you are happy with them then select the key on the Right next to each speed. This will change the font from small to large. Make sure the V1 speed is a min of 126 (GE powered ac). If it is smaller than that then type 126 and enter it at the V1 position.So in summary a typical set up should see you have on the left side:20/150015001500and on the Right side:V1 126Vr 145V2 153or something similar.Enter the V2 speed in the speed window on the MCP. Select LNAV and VNAV. This will ARM them for TO and you will see this by their nmaes appearing in white on the FMA panel above TO/GA TO/GA.You are now all set up for a VNAV departure. At 400 ft agl LNAV will go green and start following the track to the first waypoint (active waypoint). At 1000 ft AGL VNAV will engage and at 1500 ft AGL will command the aircraft to accelerate to retract flap. At 1500 ft the thrust will also reduce to climb thrust.I strongly suggest that you go thru all the PMDG 747 Lessons. There are different ways to set up the TO REF page but the values I have given you will work just about anywhere and conform with all noise abatement requirements.CheersSteve


Cheers

Steve Hall

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Guest beans

Many thanks Jose,Ryan and Steve for taking time to help.I do put the ATC advised speed in the alt on MCP but I thought the FMC should be conrolling the cliam-I have press the levelchnge knobto get climb.I am doing everything upto E/O ACCEL HT 1500 ,as Steve explains.I did not put these figures in the FMC or set the lnav and vnav before takeoff.Tomorrow I will follow exactly as Steve suggests and let you know how I get on.I have printed the lesson 4 but because this is my 2nd week of using the 747-400,I used to fun fly the 747 RFP,I find it a bit beyond me.Maybe in six months I will have mastered it.Tass:-)

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Guest Loiosh

Could you provide us a screen shot of your display when this happens, Tass? It would greatly help us with discovering your problem.If you cannot get a screen shot, a description of what your PFD displays would give us a clue to what your baby is thinking.Ex:HOLD - TO/GA - TO/GAor:BLANK - HDG SEL - VSNormally with a screen shot we can pick out what's happening.

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Guest matey

Tass, you can arm VNAV and LNAV before take off, also arm the Flight Director (FD) and the Auto Throttle before take off! Press the upper left MCP screw, that will simulate pressing Take off/Go away button. When you are 500 ft above the runway press CMD button. You will get auto throttle, Lnav and Vnav engaged in that moment. Thats all supposing you have input everything correctly in the FMC during the preflight.The MCP speed window will be blanked because FMC will guide speed and altitude. The plane will stop climbing when reaching the planed cruising altitude or the MCP displayed altitude. If the latter occurs you must select higher altitude and press the MCP altitude knob in order to restart the ascent.Bye

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Guest beans

>Could you provide us a screen shot of your display when this>happens, Tass? It would greatly help us with discovering your>problem.>>If you cannot get a screen shot, a description of what your>PFD displays would give us a clue to what your baby is>thinking.>>Ex:>HOLD - TO/GA - TO/GA>>or:>>BLANK - HDG SEL - VS>>Normally with a screen shot we can pick out what's happening.HiAs requested I have done few screen shots of the various FMC screens and also of the PFD just before starting on the runway for take off and one during climb.The flight atl is 26000,with ATC saying maintain runway heading and climb to 10000.I think my problem is due to either me thinking that the climb and the speed should be adjusted AUTOMATICALLY as per the leg screen of the FMC-with me doing nothing,or I think the leg speed/alt info is for guidance only and I have to decide the speed/alt and programme the FMC accordingly.If you could please clarify this than may be you can have some peace and quite from me. I have just found I can not send the files as they are cose they are larger than 150kb restriction-I have used paint to chop and compress them-if they don't open please let me have your email and I'll forward them.Tass

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Guest Loiosh

For future posting you may wish to save your files as JPEG-Photo format. It will reduce the size significantly. What I see there looks generally correct; however, PDU2-bmp doesn't show me the far right side of the autopilot console. I need to see if you have one of the three autopilots enabled and make sure the autopilot is engauged.I need to see the upper EICAS (I believe?) screen. The one that shows you the engine N1 power. That would tell me what your FMC is thinking. (CLB, for example).

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Guest beans

>For future posting you may wish to save your files as>JPEG-Photo format. It will reduce the size significantly. What>I see there looks generally correct; however, PDU2-bmp doesn't>show me the far right side of the autopilot console. I need to>see if you have one of the three autopilots enabled and make>sure the autopilot is engauged.>>I need to see the upper EICAS (I believe?) screen. The one>that shows you the engine N1 power. That would tell me what>your FMC is thinking. (CLB, for example).Hisorry don't know how to do j-peg,but here is another file showing what you asked for.The 1st botton of auto pilot is armed .Tass

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Guest Loiosh

Here's a picture showing how to save a file as a JPEG image so that we can view it. Also note the red circles which indicate areas where I cannot read what the screen is saying.Could I request that we get two shots next time. One of your entire display and a second showing your FMC?http://forums.avsim.net/user_files/151841.jpg

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Guest beans

Hi LoioshThanks for taking the time to reply.I am enclosing some screen shotsat the various stages of the cimb to 10000ft.The problem starts after this-the plane does not climb to the next level as per ATC request.This is 16000ft ,22000ft and finally 26000ft.I do put these numbers in the MCP.BUT nothing happens.I than go to manual climb by using 'flch' button.Tasssorry for the cropped pics-they were still bigger than 150kb allowed.

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