Sign in to follow this  
Guest

VNAV ALT

Recommended Posts

Hi guys! I have a quick question about the 737 believe it or not!  :P

 

I've been making some tutorials as you well know and I'm far more familiar with the real thing then PMDG. I've noticed that in VNAV you sometimes get VNAV ALT and I'm not too sure what it is trying to do.

 

After some digging I found out this is optional extra fitted by Boeing and definitely not fitted to our fleet or Level D sims. Is there a way in the FMC settings of PMDG to deactivate it or if someone could explain what it is trying to do that would be greatly appreciated! It's scuppered a few of my NPA tutorials I'm planning!

 

Thanks!

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Sam,

 

Wait... hold on a second....

 

"I'm more familiar with the real thing then[sic] PMDG" and you don't know what/why/how VNAV ALT is?

 

mmmmmmmmmm.....  Okay.  Right.

 

Keep on with it then.  You will need to work quite a bit harder to impress this audience with credentials, however...

  • Upvote 2

Share this post


Link to post
Share on other sites

Sam,

 

Wait... hold on a second....

 

"I'm more familiar with the real thing then[sic] PMDG" and you don't know what/why/how VNAV ALT is?

 

mmmmmmmmmm.....  Okay.  Right.

 

Keep on with it then.  You will need to work quite a bit harder to impress this audience with credentials, however...

I think you may have misunderstood the guy, RR. I do believe he meant he's more familiar with the real airplane as configured for his company than he is with PMDG's version. At least that's how I read it.

  • Like 1

Share this post


Link to post
Share on other sites

I think you may have misunderstood the guy, RR. I do believe he meant he's more familiar with the real airplane as configured for his company than he is with PMDG's version. At least that's how I read it.

 

His statement still stands.  VNAV ALT is not a company option as far as I'm aware.  There has to be some system logic stating you have entered VNAV ALT (hold).

In fact I'm pretty sure VNAV SPD, ALT, and PTH work just about the same in logic no matter which Boeing aircraft is being talked about.

  • Upvote 1

Share this post


Link to post
Share on other sites

His statement still stands.  VNAV ALT is not a company option as far as I'm aware.  There has to be some system logic stating you have entered VNAV ALT (hold).

In fact I'm pretty sure VNAV SPD, ALT, and PTH work just about the same in logic no matter which Boeing aircraft is being talked about.

I don't know. From his YouTube videos, I gather he's been flying these for many years, so I do believe him when he says he's never seen VNAV ALT in his company's fleet. He can of course fend for himself, so I'll leave it at that.

Share this post


Link to post
Share on other sites

Incidentally, the FCOM (p. 4.20.7) defines VNAV ALT thusly:

 

  • VNAV ALT – when a conflict occurs between the VNAV profile and the MCP altitude, the airplane levels at the MCP altitude and the pitch flight mode annunciation becomes VNAV ALT. VNAV ALT maintains altitude.

And it also lists it as an option

 

Edit: I see Gregg got ahead of me :smile:

Share this post


Link to post
Share on other sites

If you are climbing in VNAV with the FMA's saying THR REF | LNAV | VNAV SPD, and ATC assigns a level off at FL220 for instance,

this will then be called an intermediate level off in VNAV. Upon capture of the altitude, the FMA's will say SPD | LNAV | VNAV ALT,

indicating it is an intermediate level off versus if you were climbing in VNAV and you had an altitude constraint/restriction at ABC waypoint to cross it at FL220 on your way to FL350. The FMA's would then say SPD | LNAV | VNAV PTH indicating you are leveling off due to an ATC or procedural constraint on your legs page. Of course, if you are not in VNAV climbing, but in FLCH, and you level off at FL220, then the pitch mode would

be ALT, still indicating an intermediate level off, just not in VNAV. VNAV ALT and ALT are really the same thing, only difference is in the first case you are in VNAV and remain in VNAV during the level off, the second case you level off and the pitch changes from FLCH SPD to ALT.

 

VNAV ALT is not an option you can disable, it is part of the logic of VNAV. Maybe that helps...

 

But, then again this is for all Boeing jets I am familiar with (except), but I never flew or was rated on the 737, so some of that logic on certain models could be different.

Share this post


Link to post
Share on other sites

VNAV ALT is an option on the Collins MCP as far as I'm aware, so if you're in a 737 with an old version of the Honeywell MCP, you won't see it. Essentially it will allow you to use VNAV to make altitude changes regardless of the MCP alt setting, instead of doing it (actually in the way which most pilots prefer) via the old school way of switching off VNAV and using V/S and changing the MCP alt. The advantage of doing it the old way via the MCP is that there's a big visual indication of the selected altitude up on the glareshield which is obvious to both pilots and anyone sat in a jumpseat. Of course you could always disengage everything and, you know, actually fly the thing lol. OMG, now I'll be banned from Toulouse! :P

Share this post


Link to post
Share on other sites

In some of the older jets like the 757, if you were in VNAV and you captured the altitude, the jet would come out of VNAV and go into ALT CAP and then ALT HOLD, and there was no staying in VNAV with an intermediate level off. I assume maybe some of the earlier 737's probably did something similar, but later models with newer software probably have the capability of staying in VNAV during an intermediate altitude level off

Share this post


Link to post
Share on other sites

Sam,

 

Wait... hold on a second....

 

"I'm more familiar with the real thing then[sic] PMDG" and you don't know what/why/how VNAV ALT is?

 

mmmmmmmmmm.....  Okay.  Right.

 

Keep on with it then.  You will need to work quite a bit harder to impress this audience with credentials, however...

 

Whilst I have no doubts in your knowledge regarding this excellent product I can assure I genuinely have never seen VNAV ALT installed to any of our aircraft and I've flown to date almost 2/3rds of our almost 400 strong fleet.

 

This is the only reference we have of VNAV ALT after scouring all of our manuals.

 

VNAV%20ALT_zpsikxr648s.png

 

I've checked my original FCOM when I joined the company and our latest which was most recently updated in 2016 and incorporates all the most recent changes to the NG, they both state VNAV ALT (as installed)

 

After speaking to a few colleagues who have a few more than my 4000 measly hours on type VNAV ALT is definitely not installed to our fleet including the NG's we receive on a monthly basis. Our fleet have both Honeywell and Collins MCP.

 

I think you may have misunderstood the guy, RR. I do believe he meant he's more familiar with the real airplane as configured for his company than he is with PMDG's version. At least that's how I read it.

 

That's how I was hoping people read this post and how I think the majority have. I like to think I have quite a reasonable knowledge of the aircraft seeing I'm a Type Rating Instructor!!!!

 

Things like Fail Operational, FLCH, THR REF are not fitted to our aircraft and will not annunciate on the FMA, basically anything which wasn't selected as an option by our company I have NO information on. I make reference to my operators FCOM, FCTM, OPS Manual etc as this is applicable to me. I do not use the one by PMDG so as not to add confusion to myself.

 

I'm instructing in the sim later so will ask a few of the engineers, they know the aircraft back to front but certainly from our fleet whenever we are in VNAV PTH/SPD when reaching the cleared Altitude/Level the aircraft always transitions to ALT ACQ to ALT HLD unless it's an FMC CRZ Altitude and it annunciates VNAV PTH.

 

Also thank you to everyone who contributed, my understanding of VNAV ALT has increased significantly!

Share this post


Link to post
Share on other sites

As mentioned above, VNAV ALT appears when the aircraft has levelled off at some altitude other than that in the MCP (ie because there is a restriction in the LEGS page that is below (climb) or above (descent) what's in the altsel).

 

This may be desirable or not (usually not in my experience), depending on the circumstances. You will need to press ALT INTV (or select another vertical mode) in order to make the aeroplane continue climbing/descending.

Share this post


Link to post
Share on other sites

Thanks Skelsey

 

Our fleet transition from VNAV PTH/SPD - ALT ACQ -ALT HLD or VNAV PTH if at a restriction in the FMC. You then have to re-select VNAV or an appropriate mode AND push ALT INTV to continue to the cleared level to clear any applicable FMC restriction.

Making reference to that last post from 2011 I'm guessing not all Boeing aircraft are fitted with this option!

 

His statement still stands.  VNAV ALT is not a company option as far as I'm aware.  There has to be some system logic stating you have entered VNAV ALT (hold).

In fact I'm pretty sure VNAV SPD, ALT, and PTH work just about the same in logic no matter which Boeing aircraft is being talked about.

My best guess is our system logic is to engage ALT HLD or VNAV PTH if at the FMC cleared Altitude. I can only go as far as guessing this was an option selected by my Operator.

Share this post


Link to post
Share on other sites

VNAV ALT is an option on the Collins MCP as far as I'm aware, so if you're in a 737 with an old version of the Honeywell MCP, you won't see it. Essentially it will allow you to use VNAV to make altitude changes regardless of the MCP alt setting, instead of doing it (actually in the way which most pilots prefer) via the old school way of switching off VNAV and using V/S and changing the MCP alt. The advantage of doing it the old way via the MCP is that there's a big visual indication of the selected altitude up on the glareshield which is obvious to both pilots and anyone sat in a jumpseat. Of course you could always disengage everything and, you know, actually fly the thing lol. OMG, now I'll be banned from Toulouse! :P

With PMDG is the only way to essentially "deselect" VNAV ALT to choose the Honeywell MCP? Certainly with all our new NG's with the Collins MCP there is no change to the logic of the system! Either way it's not going to be no scarbus!

 

Sorry if I offended anyone regarding my question. I had a genuine curiosity about VNAV ALT and feel like I've had to defend myself about asking about said question, something akin to the real life pilots forum!

 

I'm not here to boast or show off, I'm here to simply help with anyone who is passionate about flight simulation and aviation. The reason I made my channel is to share one way of operating this extremely accurate rendition of the aircraft and I love every minute of making content. Its's something, with some support from you guys, I will continue to do for the foreseeable future!

 

If I have a question in the future I will be more specific with my wording to ensure I'm looking for differences between my operator setup and PMDG.

 

Once again thank you to all who took the time to answer my question.

 

Happy Landings!

Share this post


Link to post
Share on other sites

Genuine question mate don't think you have offended anyone or this PMDG desktop sim. Keep up the good work and focus on the real thing ;)

Share this post


Link to post
Share on other sites

 

 


I'm not here to boast or show off, I'm here to simply help with anyone who is passionate about flight simulation and aviation. The reason I made my channel is to share one way of operating this extremely accurate rendition of the aircraft and I love every minute of making content. Its's something, with some support from you guys, I will continue to do for the foreseeable future!

 

Love the videos you make!  Very detailed and thoroughly thought out.

Share this post


Link to post
Share on other sites

 

 

Love the videos you make! Very detailed and thoroughly thought out.

Thanks a lot Gregg! Glad I could help.

 

Spoke to the engineers and 100% VNAV ALT is not fitted to our fleet.

 

VNAV%20PTH_zpsg4jyi5ys.png

 

Thanks for the feedback anyway! I will try and deactivate VNAV ALT by switching to the other MCP panel!

 

Fly Safe.

Share this post


Link to post
Share on other sites

With PMDG is the only way to essentially "deselect" VNAV ALT to choose the Honeywell MCP? Certainly with all our new NG's with the Collins MCP there is no change to the logic of the system! Either way it's not going to be no scarbus!

 

 

Not sure. When talking about the real 737, I tend to go off what I've learned from this book:

 

http://www.b737.org.uk/book.htm

 

Which is worth getting, particularly if you drive the things for real, but also if you are a simmer with any 'study sim' version of a 737. Along with help from a couple of real world B737 pilots, I know I found that book invaluable when attempting to come across as authoratitive (yeah, right) when I was reviewing a 'proper' 737 sim aeroplane for Avsim, since in the real world, the fancy aeroplanes I fly are the ones which have a fully working radio lol (I'm not joking).

 

If I get time later today, I'll see what I can find in that book, although I should probably buy it again as my copy is a few years old and I daresay its been revised to remain completely up to date. Worth a look too, is the author's website:

 

http://www.b737.org.uk/

 

In any case, I always appreciate anyone's efforts to make tutorials. Being a software trainer myself (CGI, movie effects etc), I know how valuable the efforts of a decent teacher with some real world experience can be. So thanks for taking the trouble to pass on your knowledge.

Share this post


Link to post
Share on other sites

Sam,

 

Wait... hold on a second....

 

"I'm more familiar with the real thing then[sic] PMDG" and you don't know what/why/how VNAV ALT is?

 

mmmmmmmmmm.....  Okay.  Right.

 

Keep on with it then.  You will need to work quite a bit harder to impress this audience with credentials, however...

 

It's an option. I've flown both types.

 

Line pilots, instructors, and designated examiners at my current outfit with tens of thousands of hours in the plane would look at you cross-eyed if you mentioned VNAV ALT.

 

<cough cough>

Share this post


Link to post
Share on other sites

As long as we are at it Filch or FL Ch is same as LVL CHG or level change. I believe all MCPs have one of the two. Important thing is the function where descent is at idle power while maintaining MCP SPD. Thrust goes to ARM mode, meaning you can add power manually if you wish. In climbs MCP SPD is maintained at N1 power.

 

Now a question, what is this Thrust Ref ? I have Thrust Hold but is only used on takeoff. I have never flown the Honeywell MCP.

Share this post


Link to post
Share on other sites

Had a play around this evening, switching to the Honeywell MCP and I still have VNAV ALT annunciate if the aircraft levels off at an intermediate altitude set in the MCP window. I'm use to ALT ACQ then ALT HLD or VNAV PTH.

 

It's a bit of a pain when flying circling approaches in the PMDG based on our SOP's. With our old school non VNAV ALT fitted fleet we descend using VNAV to the circling minima rounded up to the nearest 100ft which is set in the MCP panel. Approaching the cleared Altitude we get ALT ACQ then ALT HLD, we break left or right using HDG SEL and set the MISAP ALT whist the aircraft stays in ALT HLD at the circling minima.

 

At the moment I'm getting ALT ACQ, VNAV ALT and when I set the MISAP the aircraft continues to descend on the VNAV profile. A quick fix is to select ALT HOLD but would rather have the aircraft in PMDG do it for me (I'm lazy) and it's what I'm used to.

 

I guess I'll ask PMDG directly and see if it's all setup this way or if I can somehow disable VNAV ALT! 

Share this post


Link to post
Share on other sites

Very interesting discussion. VNAV ALT is pretty standard across a lot of aircraft with VNAV capability.  VNAV ALT is a very simple and benign annunciation. It something that you should expect. As stated before, it's basically a simple annunciation to tell you that the plane is going to level off at a procedural altitude. Say for example you are at airport x and flying the dixie one departure.

 

Your clearance is the dixie one departure, climb and maintain 10,000ft. Let's say the dixie one departure has you level off at 3000ft for one mile after departure. In this case, if you flew the departure in LNAV/VNAV, you should expect see VNAV ALT if you have your MCP set to your cleared altitude. Now in my old school days without VNAV, we would set 3000ft in the MCP and then 10,000ft after the mile. Same thing if you are flying an arrival and given the "descend VIA" clearance. If you were cleared down to 2000ft and the arrival had some level offs on the way down, you would expect to see VNAV ALT at those specific altitudes while in LNAV/VNAV.

 

Now that's a basic description. It's similar to the jets I currently fly. In my aircraft, we get VASL, VALT and the constraint altitude below the VASL/VALT on the PFD. It works the same as the Boeings. If I have a constraint altitude on the way up or down in VNAV, I will get a VASL(VNAV altitude select) annunciation on the PFD with the altitude right below. The altitude will have a hashed symbol in front of it meaning it's armed. Over the altitude tape, I would have my MCP selected altitude annunciation. Once the airplane captures the VNAV constrain altitude, the VASL will switch to VALT(VNAV ALT) and the constraint altitude will turn blue.

 

So again, the annunciation is the airplanes way of telling you it will level off to an altitude other than what you have selected on the MCP. It's a good thing.

 

As for your circle issue, interesting. In the jets I fly, we don't set missed approach altitude on a circle until on the go. We leave the minima in the MCP and once we change the lateral mode to heading select, it cancels VNAV and holds the MCP altitude. The only issue is when you go missed, the pilot not flying gets busy. You have to get the flaps, reach over and set a lateral source and or lateral mode for the pilot flying, dial 180 in the speed window, set a heading if not following LNAV, set missed approach altitude and come back to the gear awaiting the gear up call. It's all done in a couple of seconds. In your case, I don't know why it descends if you have minima set in the MCP, altitude captured and you entered heading select. We operate a couple BBJs, let me see what our SOPs say for circling for our Boeing guys.

Share this post


Link to post
Share on other sites

Had a play around this evening, switching to the Honeywell MCP and I still have VNAV ALT annunciate if the aircraft levels off at an intermediate altitude set in the MCP window. I'm use to ALT ACQ then ALT HLD or VNAV PTH.

 

It's a bit of a pain when flying circling approaches in the PMDG based on our SOP's. With our old school non VNAV ALT fitted fleet we descend using VNAV to the circling minima rounded up to the nearest 100ft which is set in the MCP panel. Approaching the cleared Altitude we get ALT ACQ then ALT HLD, we break left or right using HDG SEL and set the MISAP ALT whist the aircraft stays in ALT HLD at the circling minima.

 

At the moment I'm getting ALT ACQ, VNAV ALT and when I set the MISAP the aircraft continues to descend on the VNAV profile. A quick fix is to select ALT HOLD but would rather have the aircraft in PMDG do it for me (I'm lazy) and it's what I'm used to.

 

I guess I'll ask PMDG directly and see if it's all setup this way or if I can somehow disable VNAV ALT! 

 

We do not have an option to disable VNAV ALT - not going to be a way to do it unless we add it in a future update. Can you say which airline you're with? I'm curious...

Share this post


Link to post
Share on other sites

I looked at our BBJ SOPs. They are letting the altitude capture at the 100ft increment above MDA or selecting Altitude hold at MDA if the MDA is a odd number. They then set missed approach altitude and heading select. That should keep the aircraft from descending once you are in ALT HOLD.

Share this post


Link to post
Share on other sites

We do not have an option to disable VNAV ALT - not going to be a way to do it unless we add it in a future update. Can you say which airline you're with? I'm curious...

 

Hi Ryan,
 
A very big one in with almost 400 737-800's (I'll send a PM)
 
None of them are fitted with VNAV ALT. Am I right in thinking you could deselect VNAV ALT with previous versions of NGX? If that could be reinstated that would be great! 
 

 

I looked at our BBJ SOPs. They are letting the altitude capture at the 100ft increment above MDA or selecting Altitude hold at MDA if the MDA is a odd number. They then set missed approach altitude and heading select. That should keep the aircraft from descending once you are in ALT HOLD.

 

Really interesting Rick thanks for sharing. We always round the MDA up to the nearest 100ft which we set as our minima and the MCP ALT. When ALT HLD annunciates we use HDG SEL, break L OR R and then set the MISAP so in a slightly different order to how your guys do it on the BBJ.

 

Then if we go around at any point we just have to push TO/GA and go from there, the MISAP is already set so the PM is just having to configure as he would on and go-around. Depending on the MISAP you can either use HDG SEL or LNAV once established on an intercept for the missed approach track. I'm not sure about the BBJ but usually in the -800 you have to hold F15 to comply with the 180kts which causes the warning horn to go off! 

 

Really nice to see how other operators manage it.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this