777 VS Mode Fluctation

[777simmer 117]

Like in :

 

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

I like that one :-)

 

The V/S thing being an ok mode or not is an endless discussion I am afraid. I work for a real airline flying real 777 and for years V/S mode was so unwanted....it was almost forbidden.

I am not kidding nor exagerating!

 

Today it is accepted as a normal mode again and you dont get into trouble for using it anymore.

 

Those in favour of V/S mode and those opposed to it still do not agree ofcourse.

 

What I am trying to say

I dont think we are going to solve this discussion here on the forums if the pros dont even agree in real life.

And, since this is FSX, we can all make our own SOPs and not get fired whatever we do.

 

My personal opinion is that BOEING would not have given us a mode if it is not practicable in at least some situations.

There is a right time for V/S mode and a wrong (or less appropriate) time for it, just like there is a right (and wrong) time for Vnav and Flch.

[Paul_Smith 92]

Paul, you post here a lot,...

You post here even more often than I do so there is no excuse for you not knowing the rules regarding personal comments. In my opinion, you are getting very close to crossing the line in your last post. Nobody here gives a damn what you think of me as a person, what you think my experience is, or what you think my motives are. If you think I something I say is factually mistaken, say what and why, preferably with slightly more supporting evidence then "I try to speak from either first hand experience or from knowledge gained speaking to actual type rated guys...".

 

Now, back to the facts.

 

V/S is considered 'uncontrolled' because it is a reactive mechanism using only internal factors for decision making. The AP will adjust pitch to met the targeted rate of climb regardless of the consequence and without consideration of external factors. If misued, it will fail in an unsafe way which means it requires close monitoring, and therefore does not significantly reduce the pilots workload. Two quick thought experiments; what happens when you set your fpm to +3000 and don't change your throttle position? What happens when you set it to -3000 and don't change your throttle position? That said, it is a tool in the pilots arsenal and it has its uses. I have never suggested otherwise.

 

VNAV, FLCH and even FPA all use thrust in their calculations and, if AT is enabled, will control the thrust to acheive the desired outcome, and in the case of misconfiguration, will fail in a manner that does not put the airframe in jeopardy. All three modes also all use external factors such as position to acheive the desired results and so will automatically account for the movement of the airmass. 

 

You commented on the fact that I quoted from the manuals, but you forgot to read the quote I gave. FLCH (as implemented on the T7) has logic to allow shallow climbs and descents for small altitude changes, so you are mistaken in suggesting it only provides climb power or idle thrust. Are you sure you are not confusing the SOPS you referred to (but didn't specify) regarding low energy state usage of FLCH with the SOPs for airframes other then the T7? Perhaps I am not the only one who needs educating? 

 

If a pilot (or more importantly, a simmer) is using V/S to acheive a desired result because, in their considered opinion, it is the best tool for the job (and they know and understand the other tools available) then more power to them. I would like to hear the circumstances of that situation so I can improve my own piloting skills. However, if a simmer is using V/S because thats the way they did it in the default cessna, or because they simply don't know about the other tools available, (or worse they think they know and are wrong) then it can hardly be considered the most 'appropriate' tool. Yes it will still work, but so does VOR to VOR navigation, which was my original point.

[Don t moderate me this way 882]

I like that one :-)

 

 

(...)

I dont think we are going to solve this discussion here on the forums if the pros dont even agree in real life.

And, since this is FSX, we can all make our own SOPs and not get fired whatever we do.

(...)

 

 

And I like those! Sorry, if my post came across offensive. I didn't intend to "degrade" RW piloting and airmanship. Guess, I'm one of the worst "just button pushers" myself.

[Manny 1,293]

 

 

V/S is considered 'uncontrolled' because it is a reactive mechanism using only internal factors for decision making.

 

What does that mean?

[777simmer 117]

And I like those! Sorry, if my post came across offensive. I didn't intend to "degrade" RW piloting and airmanship. Guess, I'm one of the worst "just button pushers" myself.

No no, I thought it was funny :-) And I might be able to use it now and then!

[FLEX1978 373]

What does that mean?

Yep, I am also still trying to figure out exactly what is he on about.....

 

Paul, if I was getting personal you would know about it. I was pointing out a blatant obvious fact regarding the bulk of your posts round here, including the mods having enough and eventually banning you. I have personally had to point out multiple times over the years huge inaccuracies in your posts (not just simple things like a misunderstanding, plenty of stuff I don't know and still have to learn) I'm talking about trying to call people out with far more experience than you, hence why I don't normally reply anymore if I see your name.

 

Now let's please get something straight, I have nothing against you as a person, I don't know you in the real world, you could be the greatest guy on earth, help little old lady's cross the road and be a genius that belongs to Mensa. All I comment on is your posts on this little corner of the internet.

 

So, (And I'm not trying to call you out) can you explain who in the industry calls V/S uncontrolled? I understand exactly how V/S works, just confused as to where you came up with that terminology.

 

Of course V/s has no protection, who in their right mind would set +3000 or -3000 and not adjust thrust to compensate? this is basic stuff here so I don't see what you are getting at.

 

I could list a whole bunch of other modes including FLCH that are potentially dangerous if not monitored correctly, there is a reason you have humans on the flight deck... Take a look at the FLCH trap, A/T going to HOLD and not monitored.. EVERY mode requires close monitoring, to get complacent and think FLCH or VNAV requires any less monitoring because it has built in protections is what gets people killed.

 

I am fully aware of the 125 second FLCH logic regarding target altitudes. My comment regarding energy states and FLCH is pretty simple, so here's a basic example. You are at 5000 ft 210 knots,select FLCH and 2000ft target altitude, and increase the airspeed to 250knots or even more, watch what the machine does.

 

Now the last part of your post makes more sense, if a simmer is just using V/S to get from A to B because they don't understand the other modes than fair enough, not the best way to operate the aircraft, however I don't see anyone around here stating that is how they purely operate the PMDG 777

[scandinavian13 5,192]

 

 

You post here even more often than I do so there is no excuse for you not knowing the rules regarding personal comments. In my opinion, you are getting very close to crossing the line in your last post.

 

No offense Paul, but I'm not seeing it.  That's not me taking sides; rather, I'm just saying perhaps you read it and took it the wrong way.  I don't see anything personal, honestly, but let's be real...I don't take much personally.

 

 

 

V/S is considered 'uncontrolled' because it is a reactive mechanism using only internal factors for decision making. The AP will adjust pitch to met the targeted rate of climb regardless of the consequence and without consideration of external factors. If misued, it will fail in an unsafe way which means it requires close monitoring, and therefore does not significantly reduce the pilots workload. Two quick thought experiments; what happens when you set your fpm to +3000 and don't change your throttle position? What happens when you set it to -3000 and don't change your throttle position? That said, it is a tool in the pilots arsenal and it has its uses. I have never suggested otherwise.

 

I, like the others, am confused by that first sentence, but I'll comment more on the rest.

 

While you're right that V/S mode doesn't offer speed protection, the whole reason we have pilots up front is to ensure the safe operation of the aircraft.  If the pilot determines V/S is the best course of action, he or she will adjust the MCP (or throttles if applicable) accordingly to manage the "increased" risk (which is quite minimal anyway).  Additionally, V/S is the only vertical mode that a lot of the lighter aircraft out there have.  This would lend a hand to the idea that the pilots would have a decent amount of time using the mode, and be keenly aware of its shortcomings (again, really only speed protection).  In many modern aircraft, kicking the aircraft into V/S from a "higher order" mode like VNAV will dump the A/T mode into speed hold anyway.  So, while it's true that V/S could force you to out climb the available thrust, or over run the idle thrust (and potentially overspeed), that would take some pretty negligent behavior by the crew to: 1) set a high enough V/S to put themselves in the situation, and 2) not monitor the situation adequately enough to recognize the impending stall/overspeed and react accordingly.

 

 

 

VNAV, FLCH and even FPA all use thrust in their calculations and, if AT is enabled, will control the thrust to acheive the desired outcome, and in the case of misconfiguration, will fail in a manner that does not put the airframe in jeopardy. All three modes also all use external factors such as position to acheive the desired results and so will automatically account for the movement of the airmass. 

 

While you're right that FLCH and FPA measure resultant performance, they do not measure external position.  FLCH and FPA don't know if you're over WV, PA, FL, or CA.  Additionally, VNAV doesn't technically pay attention to your position directly, either.  It simply judges your performance on the calculated vertical path.  Granted, I'm sure you could argue that the calculated vertical path is related to the lateral path (based on geographic position, of course), and could therefore infer position.  Still, it's not like VNAV is taking you actual measured position into account directly.  You need only look as far as the fact that OFFPATH DESC exists.  OFFPATH DESC is there to address the fact that VNAV doesn't work well if you're off the lateral path.  This wouldn't be a problem if VNAV took current position into account.

 

I'm not entirely sure what you mean by "fail" upon misconfiguration.  I'm guessing you're referring to FLCH not climbing if there isn't enough thrust to maintain a climb, or similar, though.

 

 

 

If a pilot (or more importantly, a simmer) is using V/S to acheive a desired result because, in their considered opinion, it is the best tool for the job (and they know and understand the other tools available) then more power to them. I would like to hear the circumstances of that situation so I can improve my own piloting skills.

 

I mentioned the slow-go-and-go-down earlier.  That would be one case.  Additionally, you could use V/S to fly a stepped non-precision approach without wondering how FLCH would handle the descent, specifically.

 

VNAV and FPA would be better used where an RNAV approach is certed for vertical guidance, as those generally have some sort of published glide path angle.

 

 

 

However, if a simmer is using V/S because thats the way they did it in the default cessna, or because they simply don't know about the other tools available, (or worse they think they know and are wrong) then it can hardly be considered the most 'appropriate' tool. Yes it will still work, but so does VOR to VOR navigation, which was my original point.

 

Again, I'll agree and disagree.

 

It's not the most appropriate because it's being used as a crutch to not learn a new mode.

It is the most appropriate because the pilot is not using modes that are unfamiliar.  I'd argue that using an unfamiliar autopilot mode is more dangerous than the shortcomings of VS.

[Flamin_Squirrel 71]

V/S is considered 'uncontrolled' because it is a reactive mechanism using only internal factors for decision making. The AP will adjust pitch to met the targeted rate of climb regardless of the consequence and without consideration of external factors. If misued, it will fail in an unsafe way which means it requires close monitoring, and therefore does not significantly reduce the pilots workload. Two quick thought experiments; what happens when you set your fpm to +3000 and don't change your throttle position? What happens when you set it to -3000 and don't change your throttle position? That said, it is a tool in the pilots arsenal and it has its uses. I have never suggested otherwise.

 

VNAV, FLCH and even FPA all use thrust in their calculations and, if AT is enabled, will control the thrust to acheive the desired outcome, and in the case of misconfiguration, will fail in a manner that does not put the airframe in jeopardy.

 

...

 

If a pilot (or more importantly, a simmer) is using V/S to acheive a desired result because, in their considered opinion, it is the best tool for the job (and they know and understand the other tools available) then more power to them. I would like to hear the circumstances of that situation so I can improve my own piloting skills.

Those on Asiana flight 214 May disagree with your first statement. FLCH is implicated as a contributory factor to the crash.

 

In ITVV's 747, Virgin 19 fight deck video, the captain makes a comment about how US ATC prefer pilots to descend at best rate to 1,000 above then reduce to -500ft/min so they can see you won't bust your level.

[mjd7419 2]

OK guys, back to the original topic of VS mode fluctuation.  Has anybody seen this and found the root cause yet, or have suggestions as to what is causing it.

 

(and no, I have not tried to re-install... not sure how that would clean this up)

[tcas_climb 45]

 

 

OK guys, back to the original topic of VS mode fluctuation.  Has anybody seen this and found the root cause yet, or have suggestions as to what is causing it.

 

I submitted a ticket to PMDG about it, they said they were looking into it.

[xkoote 57]

Hi,

 

As a real life pilot, may I also add that not only is V/S a tool. It is so much more than that. Given that my ride's FMC technology is from the early 90's and the VNAV function sometimes doesn't get along too well with the autothrottle it still performs respectably. And when I fly PMDG's 777 I can sometimes see the similarities with the plane I fly. (e.g. crossing speed/altitude constraints in descents).

If you regularly use V/S you will get to know your aircraft. You can intervene and make a choppy level off and further descent into a smooth transition. You can adjust V/S when going off path to still meet your targets. And when you do, you will be endlessly more satisfied that you know your aircraft, that you are connected to it and that you are able to make a flight so much more pleasant with this simple mode.

Personally not one of my 777 approaches have seen VNAV below 5000 HAA, and very few below 10000 HAA. Some airlines still have a policy on some aircraft types of not using FLCH or VNAV below certain Flight Levels.

 

Try using it sometimes when there's no ATC when you are arriving (or disconnect VATSIM). Try reducing to a speed of less than 250 and see how you get above the projected VNAV path (better glide), accelerate to barber pole -10 and see how you can correct for an above path situation. Just play with it. The A/T is still in SPD/MCH mode, and the altitude is still armed. So you won't crash. I guarantee you'll appreciate it's function.

 

Back on topic, I also have the fluctuations around a set V/S. But it's the same in real life so it doesn't matter much to me.

 

 

Cheers,

 

Xander

[mjd7419 2]

Xander - Maybe the MD80 fluctuates in VS mode, but the 777 does not (and I'll bet the MD80 does not fluctuate as much as I'm seeing.  If so, you'd have sick passengers on your hands).  I can attest to that as a Boeing engineer who has been on many 777 flights and have taken note of this... paying particulare attention during actual flights since I've noticed this on my sim.  I've also had time in our company sims, and did not see this phenomena.

[777simmer 117]

Xander - Maybe the MD80 fluctuates in VS mode, but the 777 does not (and I'll bet the MD80 does not fluctuate as much as I'm seeing.  If so, you'd have sick passengers on your hands).  I can attest to that as a Boeing engineer who has been on many 777 flights and have taken note of this... paying particulare attention during actual flights since I've noticed this on my sim.  I've also had time in our company sims, and did not see this phenomena.

I have submitted a ticket a while ago about go around causing fluctuating pitch. Can you try an automatic (AP engaged) go around (press TOGA at around 200ft or so) and see if that is the kind of pitch fluctuation you mean?

 

If so, then this up-down-up-down behavior could be something that is caused by the flight model rather then a single AFDS mode like TOGA or VS

 

I have not noticed it in VS mode but will do some tests.

[kevinh 409]

Of course VS is there to be used, but it is a secondary mode. VNAV and FLCH provide most of the control you need. VS provides additional control if required, especially during departures and arrivals. I think criticism of its use is justified when it's being used as the primary mode for climb and descent. This is especially true for simmers mainly used to default airliner autopilots. They tend to try and use VS in the same way, i.e. as the only mode for climb and descent. I think people should get used to using VNAV and FLCH first and then learn to use VS properly later, once they've lost their old default autopilot habits.

 

I only rarely use VS so I've not encountered the problem people are reporting. I certainly wouldn't use VS for an extended climb or descent, only for "tactical" adjustments where VNAV or FLCH weren't doing what I wanted. However, no doubt it is more used under real conditions.

 

Are people perhaps expecting the AP to be perfect in all conditions? Especially as thrust changes to control airspeed will cause pitch changes too and therefore VS changes. In the 777 the FBW should take care of this, but it's a lot to expect all this to work perfectly all the time in a desktop simulator. If you use VS for extended climb or descent A/T speed control is much more of an issue than it is in level flight, since even though IAS or Mach is constant, TAS is not so the aircraft is always having to change speed. Using pitch for speed control (as in FLCH or VNAV) much more direct and therefore more stable than using thrust.

[Paul_Smith 92]

You are familiar with the term 'unprotected' in this context? I would suggest that even a protected mode that does not reference external factors is uncontrolled, and that is all I was trying to say. Sorry for the confusion this has caused.

 

Do I think Rob is getting personal? Yes. Maybe Kyle is right and I am over reacting, but when Rob's his follow up starts with

 

Paul, if I was getting personal you would know about it...

followed by two more paragraphs on his thoughts about me, and his thoughts about what he thinks others think about me, with neither evidence nor reference, then I have to think that either Rob cant tell the difference between being personal and being insulting, or he really doesn't care, or in the worst case, he thinks that denigrating a person will denigrate their arguments.

 

Rob, just so you know, this is me being personal to you (not insulting, just personal); Do you really think that twice mentioning the fact that I have been banned somehow weakens my argument that V/S mode is rarely (not never, rarely) the most appropriate mode to use on a T7? You do know all the facts behind my being banned, don't you? No? What a surprise. Instead of saying that you could list other modes that do stuff, why don't you actually list them? Instead of telling us that you know stuff, why not tell us the stuff you know, but, and this is quite important, when you tell us something is true, or is a fact, or is a SOP, please back it up with references or evidence. Just because you claim you spoke to someone who claimed to know something does not, in itself, make it true, it just makes it 'hearsay'.

 

I am glad that you now seem to be aware of the FLCH logic as implemented on the T7, as the comments you made earlier in this thread about max speed climbs and idle descents for small changes, along with the comments you made about unspecified SOPs, suggested (perhaps incorrectly) that you were not, as the politician put it, "in full command of the facts at that time". Finally, the FSX experiment you suggested? Perhaps it would be worth trying if you could suggest any valid reason for accelerating a plane as slippery as a T7 from 210 to 250 knots while descending from 5000 to 2000ft. Why don't you tell us what happened when you tried it, and then you could tell us what the advantages of doing the same thing with V/S mode are.

 

Kyle, you are correct about FPA mode. Flight Path Angle is measured relative to inertial and barometric readings and not external references as I had mistakenly thought.

 

When I talked about failing through misconfiguration, what I meant (as you guessed) was what state would the aircraft be in if the pilot either failed to correctly complete the configuration or failed to appropriately monitor the progress. Being unprotected, the first warning that things are not right with V/S will be stall warning or over speed. FLCH will simply not reach your target altitude, and I am going to have to try FPA again to find out what it will do.

 

It is the most appropriate because the pilot is not using modes that are unfamiliar. I'd argue that using an unfamiliar autopilot mode is more dangerous than the shortcomings of VS.

I would agree that a pilot using V/S because they do not know about more appropriate modes is safer, but I would argue that it does not make it an more appropriate.

 

I have said from the outset that V/S does (should) work and it will get the job done, all I am suggesting now is that, in the case of a T7, other ways to do the job exist, and in most cases, can do it better. Despite the furore, no one has actually described a scenario where the use of V/S will get the job done best. Jordan (Flamin_Squirrel) did suggest one possible situation (below) and you can tell me if you think the way I have suggested handling it is better then using V/S or not.

 

Those on Asiana flight 214 May disagree with your first statement. FLCH is implicated as a contributory factor to the crash.

In ITVV's 747, Virgin 19 fight deck video, the captain makes a comment about how US ATC prefer pilots to descend at best rate to 1,000 above then reduce to -500ft/min so they can see you won't bust your level.

I could be wrong (again) but I believe that the current state of the investigation is focused on the selection of numerous A/P and A/T modes in the last two and a half miles of the flight while a pilot under instruction was in command. I don't wish to prejudge the outcome but that is the sort of thing I have often done when I fly head down and get behind the plane and it rarely ended well for me.

 

As for pleasing the US ATC, of course you can do it with V/S. That is the way it has been done for many years and it is tried and tested and everyone knows it works. However, if I was flying a T7 with the additional tools it provides, then the way I would fly it would be to set the target 500 to 1000 high and use FLCH. This would give me most efficient descent and a warning when I get close in case I have been distracted. It would also soften the descent before target without needing my explicit input so keeping the ATC happy. I would then reset target and reengage FLCH to drift in gently. In other words, dial, button, wake up, dial, button and I am at target altitude at target speed without scaring ATC. The same procedure flown with V/S requires a much higher workload from the pilot.