Jump to content

VNAV not calculating V/S correctly, wrong ALT in MCDU


Recommended Posts

I have experienced this several times now and I'm not quite sure as to what I'm doing wrong or if there is an actual problem.

 

I usually depart not knowing the arrival procedure (no RW at this point), the FMS essentially only ends with Altitudes that are my cruizing altitude as it should be I suppose. But when I get closer to the Airport and have my ATIS available (Vatsim) I will program accordingly and the FMS (in Legs page) shows the respective altitude restrictions and calculates V speeds for each altitude.

 

Here comes the issue: when given an altitude to reach at a certain waypoint (that has no restrictions assigned to it) I am overwriting the altitude calculated in the Legs page. That altitude is displayed correctly in my PFD, but the FMS shows the "old" altitude and calculates the V speeds accordingly.

 

In my screenshot you can clearly see, that when descending with 1kft/min I will reach the dialed in altitude (FL230) at this speed at or around the waypoint (which also shows FL230). BUT: the MCDU still shows FL319 (essentially giving the FL I should be at to meet the first published restriction on the arrival) and VNAV says my vertical speed should be way lower.

 

1) What am I doing wrong? 2) Is there something wrong?

1.jpg

  • Upvote 1
Link to post
Share on other sites

The VNAV doesn't work unless an approach is loaded early. If you look at the Come Fly With Me tutorials, the pilot loads an approach before take-off to cover up for the issue. Definitely not real life SOP. There's apparently also an issue where the snowflake doesn't indicate the actual VPATH when vnav is on, reported in another thread. You'll have to do the math on Vatsim to get a 3 degree VPA. 

  • Downvote 2
Link to post
Share on other sites

Thanks! I figured it's not actual SOP. But interestingly even when I add the approach during my flight (in this case it was KPHN - VALRE5 and then Vectors to ILS) it wasn't re-calculating the path correctly (didn't update restrictions at all and was consistently giving me a rate of descend of 700ftm)

I feel there's something buggy programming the FMS during the flight.

  • Upvote 1
Link to post
Share on other sites
  • Root Admin
6 hours ago, mynolix said:

I feel there's something buggy programming the FMS during the flight.

 

Okay, if you give us examples we gladly check them!

Link to post
Share on other sites
On 5/15/2021 at 4:26 AM, BobbyFeta1021 said:

The VNAV doesn't work unless an approach is loaded early. If you look at the Come Fly With Me tutorials, the pilot loads an approach before take-off to cover up for the issue. Definitely not real life SOP. There's apparently also an issue where the snowflake doesn't indicate the actual VPATH when vnav is on, reported in another thread. You'll have to do the math on Vatsim to get a 3 degree VPA. 

 

Not sure where you get your "definitely not real life SOP" from, I must be doing something wrong on the real plane then. You enter your flightplan and you can take an educated guess at the arrival and approach you are likely to get, even at multiple runway airports. There is nothing wrong with entering those before takeoff. In fact, I'd recommend doing so as it will give you much better predictions regarding VNAV, ETA and fuel use on the real plane. And it is easy to change should your expected arrival/approach not pan out.

  • Upvote 3
Link to post
Share on other sites
3 hours ago, CRJay said:

 

Not sure where you get your "definitely not real life SOP" from, I must be doing something wrong on the real plane then. You enter your flightplan and you can take an educated guess at the arrival and approach you are likely to get, even at multiple runway airports. There is nothing wrong with entering those before takeoff. In fact, I'd recommend doing so as it will give you much better predictions regarding VNAV, ETA and fuel use on the real plane. And it is easy to change should your expected arrival/approach not pan out.

Ditto, I always put in an educated guess as to an arrival runway and approach when programming the FMS preflight.

Link to post
Share on other sites
6 hours ago, CRJay said:

 

Not sure where you get your "definitely not real life SOP" from, I must be doing something wrong on the real plane then. You enter your flightplan and you can take an educated guess at the arrival and approach you are likely to get, even at multiple runway airports. There is nothing wrong with entering those before takeoff. In fact, I'd recommend doing so as it will give you much better predictions regarding VNAV, ETA and fuel use on the real plane. And it is easy to change should your expected arrival/approach not pan out.

To each their own. From my personal exprience I've learned not to rely on crutches like that because they prevent developing a deep understanding of an aircraft and its flight systems. To give an example just in the context of this forum, loading an early approach prevents identification of the flight system problem in the Aerosoft CRJ that VNAV doesn't work until an approach is loaded. It should be able to advise to the bottom of a STAR regardless.   
Over the last few decades, it's become a concerning trend that pilots are expected to be operators rather than experts that question what they see. We've now reached a point where pilots are not even fully trained in particular flight systems anymore, sometimes deliberately unfortunately. So maybe you're right that SOP is no longer relevant.   

  • Upvote 1
  • Downvote 1
Link to post
Share on other sites
3 hours ago, BobbyFeta1021 said:

To each their own. From my personal exprience I've learned not to rely on crutches like that because they prevent developing a deep understanding of an aircraft and its flight systems. To give an example just in the context of this forum, loading an early approach prevents identification of the flight system problem in the Aerosoft CRJ that VNAV doesn't work until an approach is loaded. It should be able to advise to the bottom of a STAR regardless.   
Over the last few decades, it's become a concerning trend that pilots are expected to be operators rather than experts that question what they see. We've now reached a point where pilots are not even fully trained in particular flight systems anymore, sometimes deliberately unfortunately. So maybe you're right that SOP is no longer relevant.   

Does your personal experience involve flying a CRJ-550/700/900/1000 in the real thing? 

  • Upvote 2
Link to post
Share on other sites
9 hours ago, BobbyFeta1021 said:

To each their own. From my personal exprience I've learned not to rely on crutches like that because they prevent developing a deep understanding of an aircraft and its flight systems. 

 

Thank you for implying I do not understand the aircraft I am typerated on and have thousands of hours on in both seats. I will take your worthy advice under consideration. Let me hop along now with my crutches :P. But I take it your personal experience is mostly in finding flaws with sim addons and then proclaiming opinions as facts ;).

  • Upvote 2
Link to post
Share on other sites
6 hours ago, CRJay said:

 

Thank you for implying I do not understand the aircraft I am typerated on and have thousands of hours on in both seats. I will take your worthy advice under consideration. Let me hop along now with my crutches :P. But I take it your personal experience is mostly in finding flaws with sim addons and then proclaiming opinions as facts ;).

So besides the distractions you bring to the OP post, there is no problem then? 

  • Downvote 1
Link to post
Share on other sites
12 hours ago, LesOReilly said:

Does your personal experience involve flying a CRJ-550/700/900/1000 in the real thing? 

Thanks for asking politely. It's in bigger and smaller craft. Smaller is usually a private gig, knowing people through other people in the area. Time is money for those :) 

 

  • Downvote 1
Link to post
Share on other sites
2 hours ago, BobbyFeta1021 said:

Thanks for asking politely. It's in bigger and smaller craft. Smaller is usually a private gig, knowing people through other people in the area. Time is money for those :) 

 

That does not actually answer the question?  If you do not have actual experience in a CRJ-5/7/9 etc...  Then it is hard to make "authoritative" statements to SOPs and how the operation does work in that aircraft...

 

I have no idea if the advisory VNAV requires this in the real CRJ or not...  

  • Upvote 1
Link to post
Share on other sites
On 5/14/2021 at 9:26 PM, BobbyFeta1021 said:

The VNAV doesn't work unless an approach is loaded early. If you look at the Come Fly With Me tutorials, the pilot loads an approach before take-off to cover up for the issue. Definitely not real life SOP. There's apparently also an issue where the snowflake doesn't indicate the actual VPATH when vnav is on, reported in another thread. You'll have to do the math on Vatsim to get a 3 degree VPA. 

It may not be real life siting at a computer SOP for you, but it definitely is in a real airplane.  Why would you file a flight plan that includes an arrival if you are not going to enter it in an fms?  Why file a flight plan with an arrival, many of which are runway specific, if you are going to enter a runway and expected approach? 

 

Saying something is not real because it does not fit into your knowledge base is very misleading. 

  • Upvote 1
  • Downvote 1
Link to post
Share on other sites
  • Deputy Sheriffs

 

On 5/15/2021 at 4:26 AM, BobbyFeta1021 said:

If you look at the Come Fly With Me tutorials, the pilot loads an approach before take-off to cover up for the issue. Definitely not real life SOP

 

Funny how you seem to know why I did something and even more interesting to know that many RW airlines seem to live in some sort of parallel universe where they apply SOPs that are not used in "real life". 

 

Please, stick to stuff you know ok? No need to make things up or post opinion as fact. The AS CRJ has bugs and you can report or comment on them without telling fairytales.

 

Thanks.

  • Thanks 1
  • Upvote 3
Link to post
Share on other sites

Just wanted to chime back in to the topic. So yesterday I took  a flight from CYUL to KLGA. Obviously I knew the STAR so I put it in the FMS. I did leave out the Approach though as I was expecting it to change anyways. On the arrival (HAARP3) there is just one advisory Altitude at BASYE (expect 8000ft). The FMS however (after eventually adding the approach) gave me roughly 11000 (possibly accounting for a steady 3deg descent angle). Now I'm not sure if this is the way in the actual aircraft (I'm a mere PPL holder) but when I tried to change it to the said 8000ft in the Legs page it did show the new 'restriction' in both the MCDU and the MFD. But looking at the Dir page the VNAV advisory said it would need 1800ft/min to reach it from my FL (please don't educate my as I know it's an early descent, but I was given the instruction to start the descent and reach 8000ft at BASYE - not to my discretion). However, when selecting 1800ft/min the magenta VNAV radial (what's it actually called?) on my MFD showed I would reach 8000ft waaayyyy beyond the waypoint (like almost 40mls out). I had to dial it down even more and with approx 2600ft/min I reached 8000ft almost exactly at the Waypoint (I have also cross checked my VNAV page and made sure that my descend speeds were ok, I held 290kts above 10k and 250 below - plus I had about 5kts crosswind so that theoretically doesn't have a big effect on the calculation I suppose)

  • Upvote 1
Link to post
Share on other sites
On 5/19/2021 at 10:37 PM, Crabby said:

Why file a flight plan with an arrival, many of which are runway specific

That's the thing, most Arrivals I fly are not at all RW specific or they fork depending on the landing direction, hence, I'll leave out the RW selection until my descent so I can pull the most current ATIS.

  • Upvote 1
Link to post
Share on other sites

Encountered another instance: CLIPR2 into DCA. Programmed the STAR before departure, leaving out the approach.

 

It has two advisory ALTs on the Arrival which are TRISH at 12k and BAL VOR at 10000. The FMS had odd numbers in it. I tried to correct the numbers but still the advisory VNAV would indicate the wrong Vertical speed.

 

Apparently this will not be acknowledged as an issue or explained why it isn't an issue if nobody else reports it. So I ask anyone reading this to kindly try literally any Arrival and report back what happens when you change the Altitude in the Legs page.

  • Upvote 1
Link to post
Share on other sites
  • CRJ Forum Moderator
36 minutes ago, mynolix said:

Encountered another instance: CLIPR2 into DCA. Programmed the STAR before departure, leaving out the approach.

 

It has two advisory ALTs on the Arrival which are TRISH at 12k and BAL VOR at 10000. The FMS had odd numbers in it. I tried to correct the numbers but still the advisory VNAV would indicate the wrong Vertical speed.

 

Apparently this will not be acknowledged as an issue or explained why it isn't an issue if nobody else reports it. So I ask anyone reading this to kindly try literally any Arrival and report back what happens when you change the Altitude in the Legs page.

The nav database will not contain hard-coded altitude constraints for “expect” waypoints, since those are assigned by ATC. The altitude shown on the legs page (before entering a manual constraint) is the initial prediction of where the aircraft will cross an “expect” waypoint.

 

The advisory VNAV system still needs additional work, and in general, VNAV changes were not part of the upcoming update, as there were more critical problems to address, but it will be looked at.

 

I have found that in general, choosing a 2000 FPM rate of descent in VS mode at TOD generally works well. If you set the altitude selector to the next upcoming constraint (rather than the final altitude), the magenta arc will give a more accurate indication of whether you will meet the constraint or not.

  • Like 1
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
×
×
  • Create New...