I too am having the issue with VNAV causing a rapid descent upon engaging, but I recall that someone (I believe it was Mark) had found a temporary work-around to get VNAV to properly engage until the next SP. What was the process, and does VNAV otherwise work in the current version?

Thanks!

I use FL CH until above 10,000 feet. I have had VNAV work fine from as low as 3,000 feet! VNAV has worked at below 10,000 feet on my last 3 flights, at progressively lower altitudes, with 3,000 feet being the last one.

With that last flight, I'm pretty sure that I had the Altitude Hold indicator set to 10,000 feet, while all the others have been set to FL300 or above.

boeing247 wrote on Jan 31^st, 2013 at 12:31am:

I too am having the issue with VNAV causing a rapid descent upon engaging, but I recall that someone (I believe it was Mark) had found a temporary work-around to get VNAV to properly engage until the next SP. What was the process, and does VNAV otherwise work in the current version? Thanks!

Yes, there is a fix that makes the FMC revert from VNAV DES to VNAV CLB as it should be. But FMS-speed control in VNAV (both CLB and DES) is screwed up, too, in v1.0.

So I changed my mind and went to FLCH, too. I wouldn't use V/S, because there's no speed protection in that mode.

olli4740 wrote on Jan 31^st, 2013 at 10:02am:

boeing247 wrote on Jan 31st, 2013 at 12:31am: I too am having the issue with VNAV causing a rapid descent upon engaging, but I recall that someone (I believe it was Mark) had found a temporary work-around to get VNAV to properly engage until the next SP. What was the process, and does VNAV otherwise work in the current version? Thanks! Yes, there is a fix that makes the FMC revert from VNAV DES to VNAV CLB as it should be. But FMS-speed control in VNAV (both CLB and DES) is screwed up, too, in v1.0. So I changed my mind and went to FLCH, too. I wouldn't use V/S, because there's no speed protection in that mode.

So is the problem that that the FMC is actually going directly to DES mode? I've only had one chance to try out the 777 since 1.0 came out, and I didn't check that.

boeing247 wrote on Feb 1^st, 2013 at 2:05am:

olli4740 wrote on Jan 31st, 2013 at 10:02am: boeing247 wrote on Jan 31st, 2013 at 12:31am: I too am having the issue with VNAV causing a rapid descent upon engaging, but I recall that someone (I believe it was Mark) had found a temporary work-around to get VNAV to properly engage until the next SP. What was the process, and does VNAV otherwise work in the current version? Thanks! Yes, there is a fix that makes the FMC revert from VNAV DES to VNAV CLB as it should be. But FMS-speed control in VNAV (both CLB and DES) is screwed up, too, in v1.0. So I changed my mind and went to FLCH, too. I wouldn't use V/S, because there's no speed protection in that mode. So is the problem that that the FMC is actually going directly to DES mode? I've only had one chance to try out the 777 since 1.0 came out, and I didn't check that.

I checked this again and I can confirm: The FMC changes to DES after engaging VNAV manually. You can check this for yourself by pushing the VNAV button on the CDU: The CDU will show the DES page, indicating the current submode is VNAV DES.  8-)

But I have to edit my former posts: After re-entering the initial cruise level into the CDU (don't forget that EXEC button!), the FMC does NOT change to CLB, it changes to CRZ instead. This gives an explanation for not adhering to the speed restriction (250/10000). The restriction is only valid for submode CLB, not for the CRZ.  :-/

But please check Mark's ('Markoz') posts in this forum, too: He's the CS 777-wizard around here ...  ;)

(selection of smilies made by my younger daughter, helping me on this post)

What we have here is a classic snafu, Me thinks they might have programmed the VNAV backwards when the transferred everything to the installer. Just Giving my benefit of the doubt. Now in all fairness I just want a working VNAV, I can tolerate pretty much everything else. It's been a little over a week and the natives are getting restless.  :D

olli4740 wrote on Feb 1^st, 2013 at 3:42pm:

boeing247 wrote on Feb 1st, 2013 at 2:05am: olli4740 wrote on Jan 31st, 2013 at 10:02am: boeing247 wrote on Jan 31st, 2013 at 12:31am: I too am having the issue with VNAV causing a rapid descent upon engaging, but I recall that someone (I believe it was Mark) had found a temporary work-around to get VNAV to properly engage until the next SP. What was the process, and does VNAV otherwise work in the current version? Thanks! Yes, there is a fix that makes the FMC revert from VNAV DES to VNAV CLB as it should be. But FMS-speed control in VNAV (both CLB and DES) is screwed up, too, in v1.0. So I changed my mind and went to FLCH, too. I wouldn't use V/S, because there's no speed protection in that mode. So is the problem that that the FMC is actually going directly to DES mode? I've only had one chance to try out the 777 since 1.0 came out, and I didn't check that. I checked this again and I can confirm: The FMC changes to DES after engaging VNAV manually. You can check this for yourself by pushing the VNAV button on the CDU: The CDU will show the DES page, indicating the current submode is VNAV DES.  8-) But I have to edit my former posts: After re-entering the initial cruise level into the CDU (don't forget that EXEC button!), the FMC does NOT change to CLB, it changes to CRZ instead. This gives an explanation for not adhering to the speed restriction (250/10000). The restriction is only valid for submode CLB, not for the CRZ.  :-/ But please check Mark's ('Markoz') posts in this forum, too: He's the CS 777-wizard around here ...  ;) (selection of smilies made by my younger daughter, helping me on this post)

EDIT: The v1.0 doesn't adhere to the DES speed restriction either (240/10000). So it's not a case of omitting the CLB. It rather seems to me a case of CS not having implemented speed restrictions in the FMS logic yet. (Despite of displaying them on the VNAV CLB page; VNAV DES page respectively.)

Hello all,

I am a new member of these forums.  I am a real pilot, based in Australia, flying for the Royal Flying Doctor Service.

Don't fly the B777 and never have, but have enough general understanding of aircraft systems and automation to be of some help here.

Congratulations, Captain Sim!  Your B777 is a magnificent piece of work.  I know it is still a work in progress, but already is bringing great enjoyment to myself and my 10 year old son.  We make flights together.

By signing up here, and helping others out, I hope to be showing my appreciation to Captain Sim and thanking them.

The VNAV is mostly working for me.  In about half a dozen fully-automated flights, I have not experienced the "immediate descent" that others are reporting upon VNAV engage.

I am still yet to fully explore the VNAV, but so far, the only thing I have found thus far that doesn't work is the crossing altitudes for each waypoint in the flight plan.

As an experiment, I set different flight levels for several consecutive waypoints to see if the VNAV would climb/descend the aircraft accordingly.  It didn't, but that could just be my misunderstanding of how it is all supposed to work.

What it definitely does do, is climb and descend the aircraft to the level set on the VNAV page 2 screen - and maintains the speeds set on those pages.

More experimentation to come.

One thing I have found essential to getting VNAV to engage is to have a "cost index" value set on the performance page.  I don't know what the value should be, but I just enter 1 (one).  I believe the entered value is not used in any way at this stage (apart from preventing VNAV engagement).

For those having problems with VNAV engagement, can you please confirm that:

1. You have a route loaded and it is active;
2. You have some value entered for the "cost index";
3. You have an altitude (or flight level) entered into the VNAV pages;

Welcome to CS, I'm sure you will enjoy this product (and others) as much as I.

I, for one, always welcome the knowledge and experience of real time pilots no matter what class and my heritage comes out of Broken Hill so very familiar with you operations.

Yes the cost index is a mystery to me, I believe a figure between 1 and 1000 is acceptable. I normally use 100.

Daddns wrote on Feb 2^nd, 2013 at 5:54am:

The VNAV is mostly working for me.  In about half a dozen fully-automated flights, I have not experienced the "immediate descent" that others are reporting upon VNAV engage. I am still yet to fully explore the VNAV, but so far, the only thing I have found thus far that doesn't work is the crossing altitudes for each waypoint in the flight plan. As an experiment, I set different flight levels for several consecutive waypoints to see if the VNAV would climb/descend the aircraft accordingly.  It didn't, but that could just be my misunderstanding of how it is all supposed to work. What it definitely does do, is climb and descend the aircraft to the level set on the VNAV page 2 screen - and maintains the speeds set on those pages. More experimentation to come. One thing I have found essential to getting VNAV to engage is to have a "cost index" value set on the performance page.  I don't know what the value should be, but I just enter 1 (one).  I believe the entered value is not used in any way at this stage (apart from preventing VNAV engagement). For those having problems with VNAV engagement, can you please confirm that: 1. You have a route loaded and it is active; 2. You have some value entered for the "cost index"; 3. You have an altitude (or flight level) entered into the VNAV pages;

Testing again, this time paying even more attention to the CI. Yes, I had put it in there (values between 25 and 90 for me), route had been loaded and activated, preflight seemed pretty much complete.

I had this "VNAV DES" thing happening again. I re-entered and EXECuted my cruise level, so VNAV reverted to CLB.

New test: After VNAV engaging in CLB, I re-entered the CLB speed restriction (250/10000 by default) and EXECuted that, hoping for the best. No, the FMC still ignored the restriction; putting me at ECON CRZ speed even in the climb, when still under 10.000 ft ...

I'm getting used to my own mistakes: With my fix, VNAV goes into CRZ mode, but CLimBing the A/C anyway ...