vnav help.

[cowpatz 243]

>Hi Loiosh>Thanks for taking the time to reply.I am enclosing some screen>shots>at 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.>>Tass>>sorry for the cropped pics-they were still bigger than 150kb>allowed.Tass I have had a look at your posted pics and evrything is indicating correctly for what you have entered. For some reason you have entered 250/10000 in the speed restriction on the VNAV CLB page. If you look above it you will see SPD TRANS 257/10000. This SPD TRANS is the 250 kts below 10000 ft. The reason it is 257 kts and not 250 is because below 10000 ft you have to be at either 250 kts or min manoeuvering speed ie. Flap up min speed. For the 747 this is VREF + 100. You can see in your second pic the UP symbol on the speed tape at 237 (This is VREF + 80) so adding 20 kts to this gives us the 257 kts. You can see at the top of the FMC VNAV CLB page it says ACT 257 kt CLB. In other words the FMC is currently commanding a climb at 257 kts. If you now look at the MCP panel you will see that you have got 10,000 ft set in the window. The aircraft will always level out when reaching whatever altitude is set here regardless of what pitch mode you are in (FLCH, VNAV, VS or TOGA). The only exception to this is when the aircraft is descending down the ILS glideslope. So when you reach 10,000ft the aircraft will level off and the pitch mode annunciation will change from VNAV SPD to VNAV ALT. If you do not want to level off at 10,000 ft then set the altitude to what it is you want to level off at before you get there. If you have already levelled off at 10,000ft and are in VNAV ALT the only way you are going to climb higher (using VNAV) is to wind the altitude on the MCP to the altitude you wish to climb to, or have been cleared, to and then press the Altitude setting button (the same knob you turn to change the MCP altitude setting). This MUST be PRESSED to release the aircraft from VNAV ALT. The pitch mode will change to VNAV SPD and the aircraft will then climb and accelerate to the FMC VNAV climb speed. As you are now above 10,000 ft the 257 kts no longer applies and the speed you entered of 350/.843 does. The aircraft will now climb at that speed until it levels off at either the next altitude set in the MCP window (if equal to or below cruise alt) or the next altitude constraint in the legs page. This type of altitude constraint will show up on the legs page as a large font entry next to a waypoint. These are commonly found on some SIDs and STARS. If there are no constraints then it will climb to the cruise altitude entered into the FMC. If the MCP window is set at the same altitude as this cruise altitude then the pitch mode will go from VNAV SPD to VNAV PTH as it levels out. Remember whenever the pitch mode says VNAV ALT the aircraft has captured either the MCP altitude or an altitude entry in the legs page. The only way you can get out of VNAV ALT is to either change the MCP ALT window (Up in CLB, Down in descent) and PRESS the MCP ALT button or select another pitch mode.I think this is where you are going wrong. You are not pressing that button.Hope this helps you out. Let me know how you get on or if something is not clear.CheersSteve

[Ralgh 43]

TassIf I understand your problem correctly you are saying when you level off at an intermediate altitude, lower than your planned cruise altitude, and then get cleared to a higher altitude the plane won't climb. In your sequence of pictures I see the FMA (the three boxes above your horizon display) in picture 4 shows THR REF|LNAV|VNAV SPD. In the 5th picture it shows SPD|LNAV|VNAV ALT. That means the plane is leveling at that altitude. The throttles are now controlling speed and are not set to the FMC computed N1. Once that has happened VNAV is going to hold that altitude, in your case 10,000ft. When you dial a higher altitude into MCP the light in the VNAV button should go out. You would then press the VNAV button. The light would come back on and the plane will start a VNAV climb. The FMA would then display THR REF|LNAV|VNAV SPD again. The PMDG 747 does not work properly in this situation (at least not for you and me.) The only way I have been able to get the plane to go back into VNAV climb is to select level change and then VNAV again. I have posted about this before but I think it got lost in the description of a problem I was having with VNAV descents. The descent problem was fixed with an update for the freighter. I haven

[Guest Loiosh]

As Mr. Steve replied above, once you have reached the altitude set in your MCP the 747 will level off and stay at 10,000. If you dial the MCP higher (say 15,000) the 747 will stay at 10,000 -until- you depress the altitude dial. It is difficult to understand when you do not have the actual device before you, but like your radio's power/volume control you can rotate left and right and -click- (depress) the button. You need to click (depress) the Altitude button to let your baby know it is time to continue your climb.When the ATC clears you to rise at your descretion dial the cruse / step cruse altitude and depress the Altitude button.That threw me for a loop at first when I got the 747. She's a very complex aircraft.

[Guest beans]

HiMany thanksSteve,Tom and Loiosh for the 3 emails regarding the vnav,or rather my, problem.As you guys have pointed out I wasn't selecting the new ATC altitude and depressing the alt button-I did not know you have to do that.I belived that the plane was under the complete control of the FMC and all the alts,climb speeds and decents were managed automatically as per the vnav and the leg pages of the FMC.With me doing nothing!!!Obviously I was wronge.I selected the next fl as per ATC.pressed the alt button and could not beieve that the queen started to climb.Many thanks guys.Now that one prob is resolved -have you got time to help resolve my domestic problem.....I am spending too much time on the computer.Thanks to everyone who wrote to help.Tass:-laugh1

[cowpatz 243]

Glad to see that you got things working well Tass. The VNAV does take a bit to get your head around and I still see real world pilots struggle with it at times. If ever the aircraft levels off unexpectantly when in the VNAV mode just look at your FMA to see if the pitch mode is VNAV ALT. You then know that either the legs page has a alt restriction in it that VNAV is complying with or the MCP alt has been reached and needs to be reset. Coming out of Heathrow in the London the SIDs have a hold down of 6000ft. This is coded into the SID so it comes up on the legs page as an alt restriction. The number of guys I have seen that forget about this and if ATC clear us higher than 6000ft before we reach it guys just wind up the MCP to the higher altitude but forget to press the button (Pressing the button in this case will progressively delete each alt constraint with each push). They are then most surprised when the AC levels off at 6000ft and great handfuls of thrust come off to keep the speed at 250 kts. There are 2 things that are very helpful when using VNAV. 1. Look at the FMA. Especially the pitch mode....it lets you know what is going on.2. Look at the appropriate VNAV page. If you are climbing then look at the VNAV CLB page. Here you can see all the info the FMC is using for the climb. It tells you at the top of the page what it is doing ie. ACT 257 kt CLB. VNAV is actively climbing the aircraft at 257 kts. When you get in the cruise have a look at the VNAV CRZ page. This also tells you what is happening ie ie ACT ECON CRZ. In this case it is flying the aircraft at the appropriate speed for the current weight and alt of the aircraft according to the cost index you entered.Once you get used to looking at these you will find it will greatly enhance your flying and understanding of the principles of VNAV.Happy flyingCheersSteve

[Guest beans]

Thanks for the encourageing words Steve,I have had excellent pilots helping me.I wish I could say this was the last of my problems-I am trying to master the decent now -and what a challenge that is proveing to be too.Some time the PFD shows 'idle' and decent is ok and sometimes it stays stuck onto 'HOLD' and nothing happens.Or some times the speed either overshoots with 'overspeed' warning.I am working through lesson 4-lets hope I can master it.Many thanks Tass

[Guest Loiosh]

Don't be afraid to pull your spoilers if you need to descend harder than you expect. Unlike the Microsoft Flight Simulator ATC, Real-Life ATC is much better at letting you descend at pilot's discretion. If you would like to update your ATC to something a little more realistic I would suggest Radar Contact. Though I do still get pushed to a faster descent than I would like at times RC4 will normally allow me some discretion.