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Salir

VNAV

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Hi guys,

 

I am having problems with my VNAV. It doesn't obey the instructions I set in FMC in LEGS (SIDs), although the VNAV, Flight Director and CMD are on. There's no problem with my LNAV. After I take off and switch the VNAV, LNAV and CMD on, the plane follows the route but descents and falls instead of climbing. What am I supposed to do?

And another question: where could I download the actual SIDs and STARs so the FMC displays them to me with correct altitudes and speeds? Is there any addon for this?

 

Thanks

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Did you roll the altitude up on the MCP? If it's not set high enough, the aircraft will not climb above it (though it wouldn't cause you to descend).

 

Do you have a trim axis assigned on your joystick? If you do, any spikes from the hardware could override the autopilot's commands and cause a disconnect.

 

Try and get a screenshot that shows your MCP (where the autopilot is). That would probably show us everything we need to know.

 

Welcome to the forums, by the way.

Just a head's up: One of the forum rules here is to sign your posts with your real name.

http://forum.avsim.net/topic/245586-you-must-sign-your-full-real-name-to-posts-to-use-this-forum-posts-without-names-will-be-deleted/

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Thanks, I tried these settings (like in the picture), but the VNAV starts to work like after 4 minutes flying 80 feet over the ground after take off. I have no idea how to make the VNAV work immediately after the take off.. The picture shows the settings of my MCP before take off. After taking off I switch the CMD on.

 

Stephen Geri

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I didn't think you could activate the CMD below 500Ft and I personally wouldn't even then. It is simply a personal preference and company policies vary but I use FLCH, SPD and Lnav to 10000ft then switch to VNAV, but VNAVshould work providing the FMC is setup correctly, above 500ft and next crossing altitude is higher than your current altitude. Often times when activating VNAV immediately on TO, the first waypoint crossing alt. will be lower than the actual altitude your at thus causing it to dive to that altitude when activating VNAV.

 

Sids and Stars are available through Navagraph. They are not "Free"

 

http://www.navigraph...www/fmsdata.asp

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VNAV is not available immediately after takeoff.

 

The picture shows the settings of my MCP before take off.

 

After departure, do you see an entry on the left side of the PFD (that's where any speed modes are displayed)? In your picture, it's blank. Also, your FMC says "ACT 181KT CLIMB" which to me says something is wrong in how the aircraft has been set up. I could be wrong, but that climb should say the planned 250 (or 250+ KT) climb. Since you have that same speed in the speed window, it's making me think you're overriding FMC controlled speed with what you've set, which could interfere with how things are working.

 

If you haven't tried them yet, I'd try the type rating courses (TRCs) from PMDG's downloads page. They explain how everything should be properly set up.

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, but that climb should say the planned 250 (or 250+ KT) climb

 

I don't think so. Not until CMD and VNAV mode is activated will it display the FMC speeds? At this point, it is displaying the correct speed, whats in the MCU airspeed window. Which is V2+20 or whatever it may be. Altitude will always display what is set in the MCU. The MCU alt setting trumps the FMC , it will not climb above or below the MCU ALT setting. The FMC speeds will override the MCU speed, in VNAV mode, unless there is"intervention"

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I tried to engage the autopilot after reaching 500 feet altitude and it worked. Actually it worked even without clicking on CMD (??) But it should be all right now..

Also, your FMC says "ACT 181KT CLIMB"

I entered there the V2 speed, which FMC had given to me - is there something wrong? I don't really understand you terminology guys :-)

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I entered there the V2 speed, which FMC had given to me - is there something wrong? I don't really understand you terminology guys :-)

 

Das good!! :Applause:

 

MCU=Mode Control Unit, Not really an "Autopilot" it controlls Automatic mode of flight your in or activating. AP is dumbed down MS name.

 

FMC=Flight Management Computer

 

CMD= Command, commands the MCU to performs a function.. AP on

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Yeah I know what FMC and CMD is - I use them :rolleyes: MCU was unknown to me.. However thanks guys for helping me. Oh one more question: are there on navigraph all waypoints and airways? What exactly should I download there?

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Some strange abbreviations kicking around in here today :lol: ......

 

I am intrigued as to how you managed to get the PITCH Flight Mode Annunciator (FMA) to show ALT (in GREEN) as the active PITCH mode whilst on the ground prior to take off?

 

Under normal circumstances when the Flight Director (FD) is switched on as part of the Mode Control Panel (MCP) set up prior to pushback the FMAs should - from left to right read:

 

*BLANK* |TOGA|TOGA

 

What MCP buttons did you press to make the FD PITCH mode go into an altitude hold mode instead of remaining in TOGA Mode?

 

I presume that 181 was your calculated V2 Speed that you took from the Take Off Page of the Control Display Unit (CDU) & that you have set this in the MCP Speed window on the MCP?

 

After a steady rotation rate of 2-3 degrees per second you should hold the aircraft at about 9-10 degrees nose pitch UP until a positive rate of climb is observed on the VSI at the right side of the PFD & confirmed by the standby altimeter, the rear of the aircraft will contact the runway if the nose UP pitch of the aircraft is increased beyond approximately 11 degrees whilst the main landing gear remains in contact with the runway.

 

The aircraft can then be rotated further to achive V2 +10 knots (up to a maximum of V2 +25 knots). Once airborne (as indicated by a positive rate of climb as already described)...so the aircraft is flown in pitch with 'speed on elevator' or speed controlled by pitch at this stage.

 

These two distinct phases will come together smoothly if the rotation rate is 2-3 degrees per second & so long as the STABilizer Trim has been set correctly,the flaps are in the take off range (10 - 20) & the level of thrust produced by the engines is appropriate for the aircraft weight, runway length & ambient weather conditions.

 

LNAV (if as in your case) will engage (if previously armed in white) in GREEN on the centre (ROLL Mode) of the FMA at 50 feet Above Airport Level (aal) & VNAV will engage (if previously armed in white) in GREEN on the right (PITCH Mode) of the FMA at 400 feet aal.

 

As VNAV engages the THRUST MODE of the FMA (left side) will change to THRUST REF & the MCP SPEED Window will close on the MCP.

 

Different companies have different SOPs about FD PITCH mode guidance, some advise following the FD Pitch mode command immediately after take off whilst others demand the aircraft is flown in pitch with 'speed on elevator' or speed controlled by pitch until passing 400ft aal at which time the PITCH should be adjusted (if necessary) to satisfy the FD PITCH commands.

 

An Autopilot (AP) channel (there are three to coincide with the 3 buttons on the MCP) can be engaged above 250ft aal. - provided an control surface pressures have been 'trimmed out' which is a normal technique for most Autopilot equipped aircraft.

 

At the Acceleration Altitude (aa) VNAV will command a lower PITCH attitude to accelerate the aircraft (flap retraction sequence) to the ECON CLB SPD which, in the 744 could be anywhere from 250kts up to VREF30 +100kts (approx 285kts) dependant on the aircraft weight.

 

In VNAV, the aircraft will continue to climb to the altitude set in the MCP ALTITUDE Window, or to that in the LEGS Page if it is a lower value than that set in the MCP ALTITUDE window. The altitude values that are in large font in the LEGs page are called CONSTRAINTS & are normaly asscociated with altitude restrictions present in SIDs & STARs.

 

To overide the ALT CONSTRAINTS set in the LEGs page all one needs to do is set a new (higher than the LEGs Page CONSTRAINT value) altitude in the MCP ALTITUDE Window & press the MCP ALT Button.

 

The CONSTRAINT will be erased on the LEGs page & the aircraft will continue to climb in VNAV. One press of the MCP ALT Button removes one CONSTRAINT so the MCP ALT Button will need to be pressed perhaps several times clear all of the LEGs Page CONSTRAINT values.

 

I can just see that there appears to be an ALT CONSTRAINT present on the Control Display Unit (CDU) - is looks like it is at 1000ft so you would need to press the MCP ALT Button to clear it once VNAV had become the active PITCH Mode to prevent an inadvertant level off at low level.

 

Finally some info on the various PITCH Modes available, clearly in manual flight the pilot will follow the FD PITCH comands & in automatic flight one of the three autopilots will do likewise. So the aircraft could be stalled or 'overspeeded' in any mode by a pilot who does not follow the FD PITCH or ROLL commands in manual flight without an autopilot channel engaged.

 

VNAV - the safest mode - it provides both FLAP Limit Overspeed protection & SPEED Protection - this means it will not provide PITCH mode guidance to fly the aircraft at a speed exceeding the maximum for the current flap setting as depicted on the SPEED Tape on the left of the PFD - in effect it will provide PITCH UP guidance (speed on elevator) to do this.

 

It will also provide PITCH mode guidance to fly the aircraft within the maximum/minimum speeds identified by the yellow buffet onset indications as displayed on the SPEED Tape on the left of the PFD dependant on weight & ambient conditions.

 

FLCH (Flight Level Change) - provides SPEED Protection only.

 

So in effect you could still 'bust' through the flap speed limits & damage these surfaces.

 

V/S - (Vertical Speed) - Seems to be the simmers favourite - it provides neither FLAP Limit Overspeed protection or SPEED Protection & it can fly you away from the MCP Altitude & it could kill you very easily by stalling you - even with an autopilot channel engaged.

 

It is normally only used for subtle changes in altitude through all phases of flight.

 

Some clearer shots of the LEGs Pages, Take Off Page & VNAV CLB Pages of the CDU, the MCP & PFD/ND, would be handy to see more clearly what is going on.

 

As this is a commercial forum there are a few simple rules regarding you signature (which requires your full name) - its worth spending a few minutes reading the sticky:

 

http://forum.avsim.n...ill-be-deleted/

 

Anyway, get back to us & I am sure we can get you sorted out in no time.

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Thanks Steve, such a great 'exhausting' explanation. I am sorry for the missing signature, I am always forgetting it! About the MCP settings, I pushed these buttons in this exact order:

F/D on

Autothrottle on

Put the altitude in the MCP (usually 10000f) (without pushing ALT Hold, but it reacts the same as if I pushed it)

LNAV on

VNAV on

--after takeoff--

CMD on when VNAV PATH appears

 

Then it works all right.. but could you rather help me with downloading those SIDs, STARs and other waypoints from Navigraph?

 

Regards

 

Stephen Geri

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I am sorry for the missing signature, I am always forgetting it!

 

You can set your forum settings to automatically insert a signature.

 

but could you rather help me with downloading those SIDs, STARs and other waypoints from Navigraph?

 

http://www.navigraph...www/fmsdata.asp

 

They're installers, so installing the data is no more difficult than installing your aircraft was. Just click on the download link for the aircraft you wish to update.

 

Navigraph is a paid service, just so you know. It takes a good bit of effort to get the data that they have (thus the fee). It used to be more public, but the source took it down citing security reasons.

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Thanks Kyle. Just a few more questions:

 

What are the OVRD pumps good for?

 

How do you configurate XFEED pumps?

 

While approaching an airport, when I extend flaps too prematurely, VNAV path suddenly extinguishes, so does the SPD sign, instead of which IDLE and then HOLD appears.. What is this caused by?

 

However, thank you all guys for helping me!

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Hello,

 

I'm new to AVSIM and I thought this would bbe a great place to seek help on FSX.

 

The PMDG 747-400 for fsx is giving me a sprawling headache when it comes to taking off and climbing.

 

During climbing, it suddenly pitches up (as fast as 3500fpm) then, a couple of seconds it nosedives .

 

This repeats itself to the pont of the plane stalling.

 

It has become (virtually) impossible to fly the PMDG 747 on my laptop, yet, earlier this year, it was ok.

 

I would greatly appreciate it if someone could help me with this issue.

 

Thanks.

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I would greatly appreciate it if someone could help me with this issue.

 

Hi Anderson,

 

Welcome to the forums. It's definitely recommended that you create your own thread when you're having issues (unless they're the exact same issues, which it doesn't seem that they are). You'll end up getting more help that way. Posting like this also derails the main help issue with the original poster. Just a note for next time...

 

It sounds like you have a trim axis assigned on your hardware (joystick/throttle/whatever else). If you leave that set, the sim starts to trim internally, and then whenever the hardware sends a signal (or spikes) it conflicts with the sim's internal signaling and causes massive pitch changes.

 

The fix? Don't use an external/hardware trim axis, or make sure to zero it out before switching the AP on.

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