777 VS Mode Fluctation

[mjd7419 2]

The following link is the only thread I can find where VS Mode fluctuation is discussed.

 

 http://forum.avsim.net/topic/419461-777-rocking-problem/page-2?hl=mode

 

I'm still having this problem after testing different weather conditions, different VS settings, disconnecting my input devices etc...

Will this be addressed in the SP1 update?  Has PMDG even acknowledged this as a problem to go fix?

 

(My LD767 can hold a VS, as can my PMDG MD11)

 

 

Mike Dessero

[scandinavian13 5,192]

 

 

Will this be addressed in the SP1 update?

 

Is it in the pinned thread?  If yes, then yes; if no, then no.

 

 

 

Has PMDG even acknowledged this as a problem to go fix?

 

See above.

 

Either way, your post doesn't explain the issue you're having at all.  If you want anyone to look at it, you're going to need to be more specific so that it can be recreated and tested.

[mjd7419 2]

When in VS hold mode on the MCP, the flight control system cannot hold that specific VS.  It fluctuates +- 150 fpm.  For instance, setting 2000 fpm will result in a fluctuation between 1850 and 2150, both climing and descending.  No wind or turbulance.  I've tried it with A/T engaged and speed hold mode and with A/T off and holding a constant N1 speed manually.  Same problem.

[scandinavian13 5,192]

 

 

Same problem.

 

I'm not sure what the tolerance is, but I wouldn't expect it to hit the set V/S 100% of the time.  If you believe this is a bug, you should submit a ticket at support.precisionmanuals.com

[mjd7419 2]

Kyle - Have you seen this phenomonon also?

[scandinavian13 5,192]

 

 

Have you seen this phenomonon also?

 

Looking back at my videos, not really.  It's always right around the selected VS.

[777simmer 117]

Mine does pretty good as well in fair weather.

I will try in some other weather scenarios.

 

It is possible/normal that weather changes throw it off a bit and then it corrects again.

 

Now if it seems to be constantly chasing/overcorrecting and thereby go from +150 to -150 to +150 etc endlessly....then that would not be normal.

[Werner747 107]

Don't have this issue at all, doesn't matter if I use weather or not.   Have you tried to re-install the product?

 

Kind regards.

[Don t moderate me this way 882]

I contributed to the other thread by stating that my V/S in clear/fair weather is dynamically unstable: Fluctuations increase slightly over time.

[Paul_Smith 92]

I am curious about when and why you would use VS mode flying the T7? I could be mistaken but I would have thought it is a bit like flying the T7 VOR to VOR. It can be done and will get you from A to B, but it is the hard way to do it.

[FLEX1978 373]

You are mistaken, In descent... In a shallow climb.... Step climbing.... Off path and being vectored at low altitude etc

 

It is another tool at your disposal, FLCH,VNAV and V/S all have a place, you decide the best tool while operating in a dynamic environment.

[Paul_Smith 92]

As I said, it can be done and it does work (or at least it should), however, it is rarely the most appropriate way to fly a T7.

 

FCTM, 1.35 

 

FLCH has logic to allow shallow climbs and descents for small altitude changes. There is no need to us V/S mode for passenger comfort.

If unplanned speed or altitude restrictions are imposed [...] use FLCH or V/S as appropriate.

So yes, V/S is another tool at the pilots disposal and should be understood as such, however, it should also be remembered that it is an uncontrolled tool and has been superceeded by tools such as FLCH which provide considerably more control and protection. Even FPA is going to give a pilot more control with a lower workload since it will automatically compensate for head and tail wind components, and is less sensitive to vertical movement of the airmass.

FCTM, 5.13

 

...VNAV is the preferred descent mode when the FMS flight plan is programmed for the intended arrival. When VNAV is not available, FLCH is the preferred descent mode for altitude changes.

[scandinavian13 5,192]

 

 

As I said, it can be done and it does work (or at least it should), however, it is rarely the most appropriate way to fly a T7.

 

"Ooh. Yeah. Um... I'm going to have to go ahead and sort of disagree with you there."

(Sorry - not trying to use it as an image to troll.  The movie line just popped into my head as I was thinking of a response)

 

The "most appropriate" way to fly a T7 is the way that follows what you and ATC need you to do.  You could hand fly the entire leg if you wanted to and it would still be an appropriate way to fly the plane.  I'd would've agreed with you if you had said that it wasn't the most efficient or least work intensive solution, because both of those are definitely true.

 

The quotes from the FCTM are definitely valid, but again, there's a time and place for V/S.  If a pilot wants to use it, then he or she can certainly use it.  Honestly, I really only use it when I'm trying to force a slow-down-and-go-down, but if someone wanted to climb in the mode, that's their prerogative.  They should know they're sacrificing speed protection, but it doesn't make it not acceptable.

 

So...I agree with the idea that there are better ways, but I don't agree that it's not "most acceptable."

[FLEX1978 373]

Paul, you post here a lot, I also see you like to argue with type rated guys.. Even managed to get yourself a ban once.

 

It is not an uncontrolled tool. Let me be clear, when I post here 99% of time I try to speak from either first hand experience or from knowledge gained speaking to actual type rated guys or trainers through either work or a general chat as friends.

 

What I notice is you like to read manuals and quote, adding your own interpretation. Not a bad thing to a certain extent however in a discussion like this regarding real world operation it becomes clear that your knowledge does not consist of any real world experience.

 

So, to clarify and once again answer your original question, yes there is a need to use V/S at times in the 777 and all other commercial airliners for a multitude of reasons that I have already explained.

 

VNAV is great when everything is plugged in correctly and you are flying the magenta path, FLCH is also great when you require full climb thrust or idle thrust in descent.

 

VNAV is not so good when you are off the magenta path and require a specific descent rate. IDLE thrust in FLCH is not so good when you do not require the maximum descent rate from IDLE thrust, at low altitude many SOPS prohibit the use of FLCH, if you do not understand the potential dangers of FLCH at low altitude and energy states then please educate yourself.

 

Flying in a constantly changing terminal area requires you to think outside the box and use all tools at your disposal.

 

I could go on however it's pointless, I already know what you are like. Just keep in mind that the most powerful computer on the flightdeck is between your ears, doesn't matter if you are PF or PNF you should always be evaluating which of all the available tools will get the job done for a given situation.. That is why you Have LNAV VNAV FLCH FPA & V/S at your disposal.

[Don t moderate me this way 882]

Like in :

 

"Pilots don't get paid for pushing buttons - they get paid for knowing when to push which one."