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pduck

No VNAV and V Ref Speeds

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Guys, I know it is most likely to be finger trouble, but when I program the FMC the V Speeds are not transfering to the PFD.

Also in the auto pilot VNAV has stopped functioning.

I am programing the FMC the same way I have always done over the last few years and have never had these two problems before.

I am able to set the V Speeds manually, but the VNAV is still inoperable.

Like I said, it is strange that these two functions have all of a sudden stopped working.

All of the 737 models are effected.

 

Don't know if it is worth mentioning, but the 777 is working just fine.

 

Any ideas or help would be very much appreciated.

 

Cheers

Phil Duck

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Like I said, it is strange that these two functions have all of a sudden stopped working.
All of the 737 models are effected.
 
Don't know if it is worth mentioning, but the 777 is working just fine.

 

Sounds like you may be falling victim to the differences between the fleet types, particularly if you've been flying the 777 a lot and are only recently going back to the NG. Are you EXECuting the numbers you entered on the PERF INIT page? This isn't required on the 777, but is required on the 737.

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Hi Kyle,

 

Yes I am executing the numbers on the Perf Init page.

I am using the FMC exactly like I have been since I purchased it.

The other strange thing is that VNAV is now inoperable.

 

I realise in the 777 different and that you don't have to do it.

I know it will most likely be finger trouble but for the life of me I cant figure it out.

 

Cheers

Phil

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Might be  finger  trouble,  suggest  to do the tutorial again   see if  you have the same  issues

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Guys, I know it is most likely to be finger trouble, but when I program the FMC the V Speeds are not transfering to the PFD.

Also in the auto pilot VNAV has stopped functioning.

 

Hi, Phil,

 

If you are using the same saved flight or saved panel state each time, maybe the one you are using got corrupted.  See if you have the same problem with a fresh startup situation and if the problem is still there, try one of the default panel states.

 

Just a thought.

 

Mike

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Just make sure to fill out ALL of the information in the fmc and don't forget to when it gives you the V-Speeds on the take-off page don't forget to push the buttons next to each of the blank lines in order for them to appear there and that should solve it.

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Remember that when using the 737 your VNAV works with certain conditions only. 

 

1. If you are on the ground, and can not engage VNAV, check whether your first waypoint is less than 5deg from your RWY heading, otherwise it will not engage on ground.

2. If you are in the air, and your VNAV is not engaging, make sure that you have completed and EXECuted your PERF INIT page. Post any messages the FMC might give here, I will check back.

 

In any case, you will need to ensure that you correctly calculated your plan fuel and your reserves, which obviously affect your ZWF and GW. Follow these steps on your PERF INIT:

 

1. Manual entry of ZWF.

2. Plan Fuel Entry

3. Reserves Entry

4. Trip/Crz Alt Entry

5. Crz Wind Entry

6. Cost Index

 

If you follow these steps in this exact order, you shouldn't have any trouble activating your VNAV, at least not when airborne. Also, since I don't know how familiar you are, it might seem obvious to state that you only complete your PERF INIT after you have confirmed your payload and fuel on board, but others have forgotten to do this in the correct order before :)

 

If all that has been completed (an it still isn't working, check that you, during your flight, also do as described). Make sure that your T/O is active when taking off, and your PFD shows N1 at first. Aprox. when reaching your transition altitude, you should see a yellow square below your altitude in your PFD, hit the button on your altimeter, then the warning should change to xxx - STD. NOW activate VNAV first, LNAV next and only then hit CMD engage.

 

Just post your outcome here, and tell us if it worked!

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Remember that when using the 737 your VNAV works with certain conditions only. 

 

1. If you are on the ground, and can not engage VNAV, check whether your first waypoint is less than 5deg from your RWY heading, otherwise it will not engage on ground.

 

I don't think VNAV cares about waypoints on the ground to engage. That's more of an LNAV requirement, isn't it?

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I don't think VNAV cares about waypoints on the ground to engage. That's more of an LNAV requirement, isn't it?

 

Granted, thinking that VNAV doesn't care about the 5 degrees between your (hopefully equal to RWY heading) heading and the departure heading is pretty logical. Yet Boeing has issued a Bulletin to the operators of the NG(X) versions of the 737 stating that some operators have reported smaller issues with the arming and engaging of VNAV on ground. It took me quiet long to find the Bulletin, found exactly the one I was looking for somewhere in the internet. Here we go: 

 

 

 

Boeing has received reports of inconsistencies associated with the arming of

VNAV prior to takeoff on 737NG airplanes equipped with FMC Update U10.7.

These inconsistencies can occur even on those airplanes with the configuration

specified in Service Bulletin (...) installed, i.e., FMC Update U10.7,

CDS Blockpoint 06 and Collins Autopilot P4.0.

Additionally, VNAV may incorrectly engage rather than arm if an FCC version

earlier than Collins FCC P4.0 or Honeywell -710 is installed. For FCC P4.0 or

Honeywell -710 or later installations, VNAV may engage rather than arm under

certain conditions when the departure is not aligned within 5 degrees of the

runway. With VNAV engaged on the ground, when TOGA is pressed VNAV will

disengage and the MCP IAS/MACH display will open and display 120 knots

(Collins FCC) or 100 knots (Honeywell FCC).

This anomaly exists only with FMC Update U10.7. It will be corrected in a future

software upgrade of the FMC and/or FCC.

 

Btw, I guess the topic started has actually given up on this issue? 

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The bulletins are in the front of FCOMv1 starting at pg 0.6.1, I think this one is included but without an the TBC number I'm not looking.

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Here we go:

Where did you find this text that is being quoted?

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Where did you find this text that is being quoted?

The bulletins are in the front of FCOMv1 starting at pg 0.6.1, I think this one is included but without an the TBC number I'm not looking.

 

To answer both of your questions, as Dan has suggested, it's part of the FCOM document (although in front of the actual FCOM) for the 737. The exact TBC number is "TBC-70", from June 11, 2007. It's the exact second paragraph of the Background Information section. 

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Hi, Phil,

 

If you are using the same saved flight or saved panel state each time, maybe the one you are using got corrupted.  See if you have the same problem with a fresh startup situation and if the problem is still there, try one of the default panel states.

 

Just a thought.

 

Mike

Mike,

 

I think you have the most likly answer, I also experienced this issue yesterday afternoon for the very first time.  I had everything set up correctly in the FMC and the  VREF speeds would not transfer to the tape no matter how many times I clicked them.  Just to satisfy my own curiosity I departed, since I knew what the references already were, and found that VNAV would not intate either.  I closed everything out and re-started and flew 3 more consecutive flights without the error re-occuring.  I use my preferred panel state for each flight and think that something just hiccuped in this particular case and a reset did the trick for me.

 

Cheers,

Jeff

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Apologies for the delay in getting back to this topic, work beckoned so no fly time.

However I have now had the chance to revisit and get back flying.

 

Just a couple of notes, I never save my flights and always started with a fresh flight.

I always completed my FMC entries as per Jens list/order above.

I never engaged the autopilot, LNAV or VNAV, until over 1,000ft and established in the climb and tracking on the planned route.

 

What I have done is as suggested and gone back to one of the default panel states and started from scratch again.

Low and behold, VRef speeds are now back and VNAV engaging as it should.

 

As I previously said, I have been entering data into the FMC the same way since day 1, and after going back to a default panel state, entered the data as I always had.

Anyway, having everything back to how it should be is extreemly pleasing and I would like to just thank you all for your help and suggestions, very much appreciated.

This sort of help is what makes this a great forum.

 

Cheers

Phil Duck

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