VNAV demo with SID out of Innsbruck

[sagrada737]

Hi Folks,

First off, I'm fairly new to simulators and flying the 737NG.  Just started my 737NG Sim Project in January this year.  I'm using FSX with Sim-Avionics on two separate computers.  Most all of my hardware will be FDS based.  While I'm waiting for my sim hardware, I have been trying to learn as much as possible how to use FSX and Sim-Avionics. 

One of the complexities (among many) that I have discovered is related to the use of VNAV and LNAV as part of flight automation.  Since I had no experience with these funciton prior to this, it has been a challenge to work my way up to this point.

I have to give thanks to Maurice and Scott, and the folks at FDS for their helpful comments on VNAV as well as other issues concerning my Sim Project.   All in all, I'm having a great time pulling the pieces of my Sim Project together.  My FDS MIP package and other items should be arriving in a few day, so that will be another level of interaction I am looking forward to, as I move toward building up a stable 737NG flight deck.

Anyway, here is a short video clip showing a departure out of Innsburck with the aid of VNAM / LNAV following a SID that helps to get out of the deep valley and onto the Route from Innsbruck to Nice.  This is not a tutorial, but rather just sharing what I have learned thus far as I enjoy my Sim experience.  I hope you find it interesting, and if there are constructive comments about properly using VNAV, please chime in.  Thanks.

MVI0435

Mike

[MLeavy737]

Mike,
  Looks great and a nice setup that is to start out with until your hardware arrives!

One thing i noticed is how much work your adding by constantly setting altitudes and using alt intervention.  You should only have to set the highest altitude your cleared to and let the airplane fly itself. As long as the altitudes are in the CDU the airplane will not climb past them until you reach the fix.  In other words the airplane takes the most restrictive altitude and stops there.  Either the MCP altitude or a hardcoded CDU fix. Only in VNAV obviously.  LVLCH will blow past any hardcoded altitude set in CDU.  Hope this helps.

Mike L

[sagrada737]

Hi Mike,

Thanks for your comments and constructive suggestions.  You are the only one that has chimed in.  It's like no one is interested in VNAV or is using it in their Sim operations (can't believe that!).  My looking over the various sites commenting on VNAV clearly shows that there are all kinds of opinions as to how prodedurally and operationally use this VNAV function.  I'm simply wanting to know the "generally accepted way" for using VNAV.  In that regard, your comments have been a BIG help.  Thanks.

I now have a more complete understanding of how the Pilot must consider specific altitudes for Climbs and Descents using VNAV.  As you pointed out, MCP Altitude intervention is more common sense as applied to the Route, the exception perhaps being ATC restrictions/changes in Route and/or altitude.  This is perhaps where the fun comes in, and also the potential danger in real world flying the 737NG - where the Pilot must always "Fly the Aircraft First! - especially when at lower altitudes.

On point-to-point flights in the Los Angeles area for example (eg. Burbank to Orange County airport), Vectors are the norm and the planned Route seems to go out the window.  It's hard to imagine how VNAV could be beneficial in this type of short Route - so manually using the MCP for altitudes and speeds and headings would be a better and safer approach.

Any comments on the above?  Hopefully others will contribute to this discussion so we can ALL learn something.

Mike

[Maurice]

Hi Mike,

Thanks for your comments and constructive suggestions.  You are the only one that has chimed in.

That is very strange indeed. I guess my lengthy explanations via e-mail did not help at all since I believe I told you exactly the same thing and I quote:

"When you are climbing to the cruise altitude, the ALT window in the MCP should be set to the desired cruise altitude. Once you are in cruise, the PFD should be showing VNAV PATH. Then before the T/D, you need to reset the MCP ALT window to whatever lower altitude you want to get to. It can even be set to the destination airport altitude or any altitude restriction given by ATC if any. If you do not reset the MCP altitude to a lower altitude, the plane will NOT start the descent automatically. You do not do that in the CDU but rather in the MCP itself"

Anyway, please stop e-mailing me and continue asking your questions in the forum since my explanation via e-mail needed to be confirmed by others before you could accept it anyway.  I probably would need confirmation as well unless I was communicating with a trained pilot so keeping the communication in the forum instead of private e-mails is the way to go.

As I also told you via e-mail, as far as not getting any other answers, maybe other people have a life and don't spend it all in the forums, or maybe they are also still building and not flying much if at all or maybe they just fly VFR in GA planes or maybe they are simply not interested in VNAV and there is nothing wrong with that. You forget that the other place  you were looking at (http://www.pprune.org) is a forum mostly aimed at professional real airline pilots and not at people building various kinds of simulators, so they have a vested interest in VNAV.

I am also beginning to suspect I was not the only one you communicated with via e-mail and maybe they all added their viewpoint as well so as I said, keeping the communication in the forum is the way to go so others can chime in when they are able or willing to do so and confirm or correct erroneous explanations.

Maurice

[sagrada737]

Hello Maurice,

I think there is a bit of confusion and misunderstanding as to my intentions on this thread...

First of all, in my initial post starting this thread, I expressed THANKS to you, Scott, and FDS for all the constructive comments on VNAV issues/questions.

This particular forum thread was intended to share the elementary success I have now with VNAV -- mainly thanks to you!!!

As I mentioned to you via email, you were the only one that came forward with any truly constructive help on VNAV, wth some additional inputs from Scott and FDS.

FOR THE RECORD....   I can't thank you enough for your help you gave me a few days ago, for the "rapid fire" exchange of suggestions and information concerning FMC (CDU) VNAV setup and operation and issues relating to Routes.

WITH REGARD TO THIS THREAD...   My comment to Mike Leavy that "You are the only one that has chimed in."  was not a reference negating your help, but only up to that point, Mike was the only one to comment on the thread - nothing more was intended.  And again, I expressed my thanks to you in my first post on this thread.  Perhaps it was the wrong choice of words, as my intention was to stimulate some feedback on this thread with additional constructive knowledge of VNAV in hopes that folks would "chim in" on this issue, in this thread, on this forum.

***I would like to make an open apology to you on this forum, that I in no way intended to offend you or take your help with the VNAV stuff for granted.***

As far as looking at other sites like the pprune.org site I referenced to you and a few others via email.  It was only intended to share the comments posted by professional pilots concerning VNAV issues, which I thought was highly interesting due to the variation in procedural philosophy for using VNAV in the real world.  As you expressed and appreciate, understanding and implementation of VNAV is all over the map - both in real world flying, and Sim operations.

Anyway, please forgive me Maurice, as I don't take the help you have given on VNAV and other such issues lightly.  I am certainly not one to burn bridges.

What else can I say...

Mike

[Maurice]

Mike,

I wasn't looking for any thanks in the forum. You certainly expressed your gratitude many times via e-mail and I was glad I was able to help you. My comments in this thread were mostly because the tone of your post was such that it left the impression you were left on your own with nobody willing to help.

As I have experienced many times myself, some posts for which I expected a response were not answered for a while but after a few days, there would be a flurries of responses meaning most likely that people were busy with other more pressing matters.

Not everybody here is retired & has the luxury of unlimited free time, so patience is the key. Maybe a friendly reminder from you would have sufficed in a few days rather than a more direct insinuation that nobody cared or was interested enough to respond.

Perhaps I am the only one who felt that way so my response may have been premature & out of line but as I said, dealing with such questions in an open forum rather than by personal email is a better way to communicate so that we can all learn as well, as you said yourself.

Anyway, I'm not holding a grudge and I don't need an apology and I will certainly help again if I can. But I would rather you post your questions in this or other forums. Perhaps what I told you via e-mail would have benefitted others as well or confused them even more if I was full of it, which is certainly not out of the question .

So don't lose sleep over this. I won't either

Maurice

[sagrada737]

Hello Maurice,

I know you were not looking for any special thanks in this forum, but thanks are indeed well deserved for your sharing with others - especially folks like myself that are new to simulators, the 737NG flight deck, and all that goes with trying to build a home cockpit.

To a degree, I have blinders on, as I don't have the range of experience with the culture (meant in a positive manner) of this Forum.  Hence I might seem like a "bull in a china closet" until I sort out how to properly ask questions and properly post information/requests on the forum.  I ask those on this forum to forgive me, as I have no other agenda except to learn about simulators and inform others where I can, such that it might be mutually helpful to everyone interested on the forum.

As for the reference of being "retired"...   It is true that I am retired, but please don't hold that against me.   I have worked hard all my life and only desire to fulfill some dreams at this point in my life - one of which is to build up a full-scale 737NG simulator. 

I tell you...   I don't know where the time goes these days.  Like everyone else, I have personal responsibilities and demands on my life that are not suitable to share on this forum, but I too feel the pressure of life and desire like everyone else, to spend my time in good and productive ways.  It is only in that light that I get a little impatient sometimes.  This trait is not an attribute in me, as I struggle with the complexity of building a simulator, and I desire to make as much progress as possible - both in building and flying, learning proper cockpit management procedures and flight deck operations - all of it.

I greatly appreciate your statement of not holding a grudge - it means a lot.

I have found in life that there are "movers and shakers" in any field of endeavor.  With respect to home cockpits, you are one of a few that have excelled in this interest.  My hat is off to you, and I wish you well in all your future efforts.  May they continue to be a guiding light for those climbing the learning curve of this very interesting and satisfying hobby.

By the way...   I just purchased and loaded up Ultimate Terrain X - Europe.  My test flight from Innsbruck to Nice has taken on a new visual experience!  Even thought it's in its early stages, I love flying my Sim!

Take care, and keep your airspeed up!

Mike

[Sean]

Great thread!

If I may, I have a few questions regarding vertical navigation in general, rather than the specific use of VNAV.

In VNAV, what might be typical climb and descent rates? And what would be classed as absurd values?

Would these figures be the same in LVL CHG?

When I watch other people fly (sims), I notice that V/S is used for descents, I would say more than VNAV or LVL CHG. They simply dial the V/S until the green arc is over where they want to be at a given height. Now I remember when I first picked up Bill Bulfer's FMC Users Guide, as early as page 5 (Hot Buttons), item 13:

"Think of Vertical Speed as "Very Special". With the exception of three specific situations, some mode of autoflight other than V/S is probably more appropriate".

I have yet to discover what these 3 situations are! Does anyone know?

Sean

[sagrada737]

Thanks for your comments Sean.  I too am interested feedback on your questions.

From what I understand about LVL CHG, if you don't set a vertical descent/climb rate in the MCP, then the aircraft seems to climb/descend to its max ability, depending if in A/T or manual mode.

I have ordered, but not yet received Bill Bulfer's FMC guide, but I understand it is an "interesting read", possibly yeilding more questions than it answers :-)

The Green ARC (must have a name) seems to be a tool whereby it displays the target end-point of a climb or descent based on the FMC calculations.  I'm hoping to learn more about its function and proper use.

Mike

[Maurice]

Hi Sean,

First let me qualify my answers by stating categorically I'm no expert and what I am about to tell you refers only to my own experiences, so I may well be full of it.

First, the reason why a lot of simmers use V/S instead of VNAV may well be due to the fact that VNAV is a notoriously complicated software to program and it may not work very well under many conditions so you get fed up and switch to V/S which is definitely more accurate and gets you to a specific altitude at a specific waypoint every time.

But when VNAV works well, it works much better than V/S as it maintains a steady best economical climb or descent all the way up or down. Unless you are very good at doing the calculations required to achieve the best economical flight path, VNAV would be much better at it. Can anybody say with reasonable certainty that they can pick the correct T.O.D. to achieve maximum fuel economy?

Of course, in a sim, most of us don't care about saving fuel, so it's a moot point. But I still maintain that most simmers do not trust or do not know how to use VNAV and are fed up to see it misbehave. I have to say that based on my own experience, the latest version of the SimAvionics software does a great job with VNAV (not being paid to say that . It's not perfect but certainly good enough for my limited experience. I'm sure PMDG software may be even better for those desktop simmers not using a separate avionics software package.

While you can do the whole flight just using V/S and/or LVL CHG, I think the trouble with V/S may be that it is so damn good at maintaining V/S. So if you slow down by reducing the speed in the MCP or if you start extending flaps, the plane will pitch further down to try & maintain the desired V/S.

This would probably result in an excessive & maybe uncomfortable nose down attitude and may no longer take you to the correct altitude at the specific waypoint you were aiming for unless you keep re-adjusting the vertical speed which each change of speed or flap setting.

If VNAV worked perfectly, it could take you down to short final without any intervention if you were flying an RNAV approach. This may work well in commercial airliners but in the sim world, it seldom works flawlessly. I have tried one RNAV approach which worked almost perfectly but I don't count on it. And besides, do you really want to just sit there & monitor the A/P? I don't, so even though I use VNAV a lot, I still switch to V/S once I get down below 10,000 ft or lower.

Also, if you are on VATSIM or other ATC program, VNAV will cease to be useful once you start getting vectors. I take the liberty to post a link that Steve posted in the FDS forum which talks about flight automation in general. Great video which should be a must see for any pilot:

Children of Magenta

I don't think that VNAV or LVH CHG give you the same rate of climb or descent since VNAV will adjust these rates based on the FMC programming meaning such things as temperature, derate function or cost factor to name a few. LVL CHG would keep the same rate whatever it may be depending on the avionics software or FSX behaviour or both.

No idea what is considered as a 'normal' climb or descent rate in the real world. I suspect there is a wide variation.

Regarding the Bulfer FMC guide, it's a great resource but it certainly gives way too much information which is not applicable to us simmers. It is written for real world operations and covers many topics you will never experience unless you own a CAE simulator 

Again, this is just the way I see & do things and I'm sure that Mike Leavy or any other real pilot may have a totally different take on this, so hopefully they will grace us with their more accurate knowledge.

I almost did not post this reply as I feel it is almost presumptuous for me to do so and explain things for which I have a very limited understanding... the blind leading the blind sort of thing. But maybe I can convey useful information in a more simplistic manner which may help someone rather that a more detailed & complicated real explanation. Anyway, take it for what it's worth 

Maurice

[KyleH]

LVL CHG mode operates by holding the speed set in the Speed window of the MCP climbing/descending to the altitude set in the ALT window at what ever vertical speed results for that airspeed.

Basically functions as follows (assuming A/T is engaged):

During climb: Auto throttle is set to climb thrust, and the aircraft pitches for the speed set in the Speed window of the MCP.

During Descent: Auto throttle is set to flight idle, and the aircraft pitches for the speed set in the MCP.


With Vertical Speed mode, the throttle is not left in one position. Basically The aircraft will attempt to pitch for the descent/climb rate set in the V/S window, and the throttle will try to maintain the airspeed set in the MCP Speed window. V/S is the driving control mode here though, so if the demanded vertical speed is outside the possibility of maintain the set airspeed, the aircraft will descent at whatever airspeed results from that V/S setting.

[sagrada737]

Thanks Maurice for posting that video.   This "Children Magenta" video is quite sobering.  Even in our Sims, we can even get distracted playing around with the automation, and I'm guessing that some would agree that trying to sort out the "automation" in flight can result in "situational awareness" issues to say the least - not to mention the major issue the video speaks to - being Controlled Flight Into terrain (CFIT).  Fortunately, we just turn OFF the power switch and go have lunch, then give it another try later.  However, the presenter in this video is dead-serious.

Along the lines of using automation like VNAV, I found an interesting blog comment from a 757 pilot (in answer to some questions) as to how he handles vertical descent.  I thought it would be of interest here, as it certainly echos Maurice's comments for operations below 10,000 ft.  Here it is...

1. ATC will often clear me to a lower altitude even before the FMC shows the top-of-descent point. Tell me if I'm wrong, but this seems to be the correct procedure: (1) set the new altitude in the MCP and (2) set a VERT SPD to begin the descent. This disengages VNAV mode.

Correct, and if ATC is telling you an alt or speed restriction at a fix, you need to adjust your speed and VS to place the trend indicator (green banana on the ND) just prior to that restriction.




2. What is a good vertical speed rate to use during the cruise descent phase? I've been using 1000-1500.

1500 is a good starting point as it allows the plane to slow if necessary without normally using the speed brakes. Of course it all depends on ATC and what they are asking of you. As you get lower and your speed changes, you will have to adjust the VS to keep the green arc where you want it.

   
3. How do I manage speeds during descent? Let the FMC calculate speeds, or manually set the SPD using the autopilot? Above 10,000 ft, I usually just set the SPD to 250 kts and use the speedbrake as needed to slow down. But from 10,000 ft. to ~ 1,700 ft., I'm not sure what speeds to use.

Again, it depends on what ATC wants. VNAV uses the programmed speeds in the FMC, FLCH uses your current speed, SPEED uses the manually set speed in the MCP. Personally I let VNAV start the descent, then once established and stabilized I switch to SPEED and VS modes so I can control them manually through the MCP. It gives a smoother ride, no chasing speed/profiles, and allows me to make any adjustments needed to conform to ATC instructions.

250kts is a bit slow from altitude, in the US below 10K that is the speed restriction, above 10k I usually use 290kts. Typical speed reductions for me are:

Above 10K, 290kts or as instructed by ATC
Below 10K, 240kts so I can deploy flaps 1 as needed
30nm from the approach, begin to slow to 200kts
20nm from approach, at 200kts
10nm from approach, 180kts, lower flaps according to speed card
10nm from the airport, 170kts, lower flaps according to speed card
Crossing the outer marker, 150kts, lower flaps according to speed card
Over the  fence, 140kts
Of course these are just general speeds as your weight will figure in.

Mike

[MLeavy737]

Hey all,
  I intend to write another post here as soon as I'm well enough. Ill clarify a bunch of things and make it easy, it's not as bad as y'all think.  I've spent the last 8 days in the hospital from some kinda extreme food poison or bacteria. Just got out yesterday and still nowhere near normal. Doing better though.

Give me a little bit and I'll get back to this.  Just letting y'all know I didn't forget!

Mike L

[Maurice]

Hey all,
  I intend to write another post here as soon as I'm well enough. Ill clarify a bunch of things and make it easy, it's not as bad as y'all think.  I've spent the last 8 days in the hospital from some kinda extreme food poison or bacteria. Just got out yesterday and still nowhere near normal. Doing better though.

Give me a little bit and I'll get back to this.  Just letting y'all know I didn't forget!

Mike L

Was that from airline food?  . Hope you fully recover very soon. The natives apparently need you

Maurice

[MLeavy737]

Was that from airline food?  . Hope you fully recover very soon. The natives apparently need you

Maurice

No not airline food, it was actually from a shithole restaurant called Friendly's.. Obviously never eating there again. Some kind of crazy chicken poison. literally almost killed me. 104.5 temp, extreme dehydration that led to kidney failure, stage 4 hypoglycemic shock, and blood pressure of 80 over 50 something with my heart racing.. Doctor's said another hour like that if I didn't respond to multiple full blast IV's and I was toast.. lost 25 lbs..its been over 3 weeks and im only really feeling 99% last few days.. bit of a life changing event to say the least!  crazy shit..

So about this VNAV stuff.. are there any specific questions that I can help with instead of getting into every aspect of it? I will if you ask but im not exactly sure what you peeps are missing

let me know..

Mike L

[sagrada737]

Hi Mike,

Welcome back to the world !  I know what it is like having extreme food poisoning, as I had a bout with that a few decades ago while stationed in Germany - turned out to be tainted chocolate milk locally brewed.  Never again!  Anyway, glad to hear you are on the mend - sounds like it could have been life changing.

Regarding the whole VNAV / LNAV thing...   I don't want to make a big deal out of this.  I was originally only trying to sort out how these functions were used and how they are being emulated in with our Sims.  Maurice helped to get me off the ground on VNAV, and now that I have received my FDS MIP package, there is a whole lot more that makes sense now that I can use the hardware vs. mouse clicks.

If I had a question for you at this time concerning this thread, it would be on the issue of proper procedure (how you do it) for transition from VNAV/LNAV to an ILS Approach. 

For example, if you decided to allow VNAV/LNAV to control the aircraft down to the IF on the ILS, how would you then make a transition to the ILS Approach? I am assuming that you would simply press "APP" on the MCP and fly it down to either an AutoLand, or cancel AutoPilot and A/T Disconnect then land manually.

I know that some folks have commented that they don't even bother with VNAV below 10,000 ft. - let alone allowing the automation to take you down to a landing.   But I am curious how this would be done.   Anyway, your comments on what you typically would do would be interesting and appreciated.

Good to have you back among the living :-)

Mike

[MLeavy737]

Hey Mike, thanks for the well wishes

Transitioning to an ILS from LNAV/VNAV is exactly how you mentioned. Just hit the APP button and assuming your on course and path it will capture. I did exactly that last week into KSFO. We fly the FMS Bridge Visual to 28R. Its coded as an RNAV approach for us. Once the airplane is on that last heading to intercept I usually then join the ILS by just pressing APP. Not necessary as it is a visual approach but that doesn't stop you from using it There are no disconnects or any other button pressing. Usually there is a slight correction because as you know the ILS receiver coupled to the autopilot is a bit more precise and sensitive. Mexico City has an arrival that joins an ILS approach into 5R. The Approach is armed as you pass a certain radial I believe and it captures perfectly.

As far as VNAV below 10000.. The main reason I don't use VNAV below 10k is because generally your being vectored for some type of approach and the arrival you were just on is over. Its much easier to conform to assigned speeds and altitude changes using LVLCH or VS. Also keep in mind that that if you are in VNAV, as soon as you start extending flaps the airplane will then slow to the maneuvering speed for the flap setting. Not good when ATC wants specific speeds. Its possible to override that using SPD Intervention however you then have other problems with descent rates and VNAV SPD or VNAV PATH...  Either way.. See what works for you, that's just the way I like to do it. Im sure you can find others that stay in VNAV the whole time..  BTW, there are arrivals and approaches where they join up and you do stay in LNAV/VNAV all the way till the ground.

Hope that helps, let me know if you have any other questions..

Mike L

[sagrada737]

Hello Mike,

Thanks for the detailed post, and thank you for you kindness to share some basics regarding VNAV/LNAV procedures.  What you have described is very understandable.

I'm guessing that for certain hubs, the congestion is so unpredictable, that you can always count on ATC giving you vectors below 10,000 ft., the So Ca area comes to mind depending on the route and destination, or a short maintenance hop from KOAK to KSFO.   

I do have a couple of other question re. FMC operations, but I'll post them in a separate thread.

Have a great weekend!

Mike

[MLeavy737]

Mike,
Anytime! Just ask.. Funny you should mention California area because that's some of the places where your in VNAV all the way from cruise to the runway.. actually from the gate to the destination runway.. lol    The point is that it depends on the situation really. Some arrivals join up perfectly with an approach and others conclude with a heading to fly after a fix. Generally you get to stay in LNAV/VNAV when the arrival and approach join. When your on a heading to fly after a fix ATC is then responsible for you and LNAV/VNAV become more trouble than its worth. Myself and everyone else who fly's the 737 here seem to think the same way.. could be that were all doing it wrong however

Mike L

[Sean]

I've been reading a bit on this since you started the thread Mike. And it's great to get 'real' input from the other Mike too (incidentally, I have a friend who has flown 757's for the last 15 or so years, but his Company has just retired them and this last week he had his final line check in the 737-800. Now I can pester him too)!

Back to the books... A couple of paragraphs stick in my mind which relate to what we are talking about here...

From Bill Bulfers guide...

"At some point during the descent, only the most necessary FMC entries are made. This point may vary, and is the subject of lively debate among standardisation weenies. They will advocate points anywhere from TOD to the traffic pattern. Our view is that when you get busy, that's the time to spend less time with the FMC. That point might be TOD at ORD, but 5000ft at DSM. At that point, airplane control is changed to LVL CH and HDG SEL when the path and track deviate from that which is programmed in the FMC".

And from the FCOM itself...

"During high workload times, for example, departure or arrival, try to reduce the need for CDU entries. Do this by using the MCP altitude, heading and speed modes. The MCP can be easier to use than entering complex route modifications into the CDU".

So you need to stop being a standardisation weenie  , and get your eyes out of the window! Also from Bills guide...

"One pilot always flies the airplane. Sounds obvious, but it is surprising how often both pilots will have their heads down during an FMC modification".

A bit difficult when your'e flying alone!

Great debate.

Sean