VNAV ALT

[Guest]

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

 

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!

[rsrandazzo 6,353]

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...

[cannonplug 126]

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.

[thibodba57 462]

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.

[cannonplug 126]

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.

[Gregg_Seipp 568]

Found this in a thread from 2011...

 

http://www.avsim.com/topic/356238-vnav-alt-hold-what-is-it/?p=2188223

[cannonplug 126]

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:

[Captain_Al 66]

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.

[Chock 17,769]

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!

[Captain_Al 66]

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

[Guest]

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.

 

 

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!

[skelsey 765]

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.

[Guest]

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.

Found this in a thread from 2011...

 

http://www.avsim.com/topic/356238-vnav-alt-hold-what-is-it/?p=2188223

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.

[Guest]

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!

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!

[Driver170 42]

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