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Top of Descent


dresoccer4
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Hello! I'm trying to follow along with the tutorial and it's showing how the TOP OF DESCENT display is shown in the MFD, however mine seems to be missing. I believe I have all of the correct FMS data (of course not 100% sure). 

Is there something else I need to press to get the T.O.D shown?

 

Thanks

 

1-tod.thumb.jpg.a7e8f30db382b168f231dcb22b16a8fb.jpg

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8 minutes ago, dresoccer4 said:

Hello! I'm trying to follow along with the tutorial and it's showing how the TOP OF DESCENT display is shown in the MFD, however mine seems to be missing. I believe I have all of the correct FMS data (of course not 100% sure). 

Is there something else I need to press to get the T.O.D shown?

 

Thanks

 

1-tod.thumb.jpg.a7e8f30db382b168f231dcb22b16a8fb.jpg

I had the same problem on my last flight from Nice to Vienna this evening. Never experienced that before. Also made a fix 90nm from Vienna but that didn't appear either, and at what I believe should've been the TOD I suddenly got a seatbelt announcement out of the blue. A lot of strange things happening.

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6 minutes ago, TomAce said:

I had the same problem on my last flight from Nice to Vienna this evening. Never experienced that before. Also made a fix 90nm from Vienna but that didn't appear either, and at what I believe should've been the TOD I suddenly got a seatbelt announcement out of the blue. A lot of strange things happening.

 

*thumbs up*

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I am not sure if this is correct behavior -- it seems to me that it should be able to calculate TOD without knowing the arrival runway -- but in my experience it will only give you a TOD if you enter both a cruising altitude and arrival runway. I always look for my TOD by clicking the MFD data button and looking on there though as the VNAV display otherwise stops updating sometimes which is a problem.

 

Also, the snowflake will not appear until you have passed your TOD, even if you start your descent slightly early. Once again this seems odd to me but I'm not sure if that's a bug or just designed differently than I would expect.

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7 minutes ago, Aplato said:

I am not sure if this is correct behavior -- it seems to me that it should be able to calculate TOD without knowing the arrival runway -- but in my experience it will only give you a TOD if you enter both a cruising altitude and arrival runway. I always look for my TOD by clicking the MFD data button and looking on there though as the VNAV display otherwise stops updating sometimes which is a problem.

 

Also, the snowflake will not appear until you have passed your TOD, even if you start your descent slightly early. Once again this seems odd to me but I'm not sure if that's a bug or just designed differently than I would expect.

 

the tutorial states the opposite though. it says the snowflake appears before the top of descent

 

1-sortly.thumb.jpg.4b21e88e8142ba457f76cdf4b39effdc.jpg

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2 minutes ago, dresoccer4 said:

 

the tutorial states the opposite though. it says the snowflake appears before the top of descent

 

1-sortly.thumb.jpg.4b21e88e8142ba457f76cdf4b39effdc.jpg

 

Interesting. I'm not convinced it actually does that as I don't think that's been my experience, but I was actually thinking of the little blue circle on the vertical speed section of the PFD rather than the snowflake. I believe that appears at the same time as the snowflake but I could be wrong. In any case, I tend to not use either -- I wait until I reach my TOD and then follow the vertical speeds on the DIRECT screen for whichever waypoints make the most sense on my arrival.

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1 hour ago, Danny Vincken said:

few things:

 

1: in your first screenshot you are to far away to see the TOD (or to low pfd range setting)

2: in your 2nd screenshot you have not passed TOD yet, the snowflake becomes visible after passing TOD.

 

More like:

Quote

 

DEVIATION SCALE AND POINTERS

A unique FMS deviation pointer shows the vertical deviation from the descent path on the same scale as the glideslope deviation (when in VPATH or VGP mode, or when close to the planned descent path). When VNAV is active, the vertical deviation scale and pointer show on the display 60 seconds before the aircraft arrives at the Top of Descent (TOD). If advisory VNAV is selected, the vertical deviation scale and pointer show when the vertical deviation is within 1000 feet of the descent path.

 

 

Or at least, that is how it should function :D.

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It's become habit now for me to reassign a hard coded altitude restriction to properly display the TOD indicator. Eg. On a star where you already have a pre determined restraint i just retype one of them in. ( usually one which is a single alt, not a between shelf. Once i do that and press exec, then wula the tod is now present. Takes two seconds.

Dave.

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On 9/11/2021 at 6:32 PM, Aplato said:

I am not sure if this is correct behavior -- it seems to me that it should be able to calculate TOD without knowing the arrival runway -- but in my experience it will only give you a TOD if you enter both a cruising altitude and arrival runway. I always look for my TOD by clicking the MFD data button and looking on there though as the VNAV display otherwise stops updating sometimes which is a problem.

 

Also, the snowflake will not appear until you have passed your TOD, even if you start your descent slightly early. Once again this seems odd to me but I'm not sure if that's a bug or just designed differently than I would expect.

How would the FMC be able to calculate TOD without a selected arrival runway?  If you are landing on a south runway and flying north to get there, your TOD will be closer to the airport than if you were on the same flight path and landing north.  This is because you have to fly a greater distance to hit a way point that is north of the airport.  Also, if you are flying the CRJ with the realistic ADVISORY vnav enabled, then any TOD is just a suggestion.  It is up to you to calculate and fly the descent to get where you are going at the altitude you want/need to be at.  I use the fix function on the FMC to set 3 range rings around my arrival airport.  The first is set at a distance equal to 3x my cruise altitude.  The second is set to 30 miles and the last is set to 5 miles.  Unless instructed otherwise by ATC or limited by charts, I begin a descent to 10000 at the first ring.  Normally this will be a +/-1800 fpm descent to hit the 30nm ring at 10,000 feet.  The 5 mile ring is where I want to be in final approach configuration. 

 

Think of it this way.  If I live in Texas and you live in Nebraska and I want you to come visit but I don't tell you what city I live in.  You want to know how long the trip will be.  It may only be 4-5 hours to the border of Texas but if I live in Brownsville that is at least another 8 hours.  So you leave Nebraska without knowing how long the trip is because you don't know your actual final destination.

 

So when programming the FMC you should ALWAYS put in an arrival runway and procedure while at the DEPARTURE gate.  This is the way it is done in real life.  Yes, weather/wind can change during a flight and therefore arrival runways and even STARS can be altered.  That is why you can change them in the FMC.  If the computer knows what the expected entire route is, it can compute the things you want as a pilot.

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16 minutes ago, Crabby said:

How would the FMC be able to calculate TOD without a selected arrival runway?  If you are landing on a south runway and flying north to get there, your TOD will be closer to the airport than if you were on the same flight path and landing north.  This is because you have to fly a greater distance to hit a way point that is north of the airport.  Also, if you are flying the CRJ with the realistic ADVISORY vnav enabled, then any TOD is just a suggestion.  It is up to you to calculate and fly the descent to get where you are going at the altitude you want/need to be at.  I use the fix function on the FMC to set 3 range rings around my arrival airport.  The first is set at a distance equal to 3x my cruise altitude.  The second is set to 30 miles and the last is set to 5 miles.  Unless instructed otherwise by ATC or limited by charts, I begin a descent to 10000 at the first ring.  Normally this will be a +/-1800 fpm descent to hit the 30nm ring at 10,000 feet.  The 5 mile ring is where I want to be in final approach configuration. 

 

Think of it this way.  If I live in Texas and you live in Nebraska and I want you to come visit but I don't tell you what city I live in.  You want to know how long the trip will be.  It may only be 4-5 hours to the border of Texas but if I live in Brownsville that is at least another 8 hours.  So you leave Nebraska without knowing how long the trip is because you don't know your actual final destination.

 

So when programming the FMC you should ALWAYS put in an arrival runway and procedure while at the DEPARTURE gate.  This is the way it is done in real life.  Yes, weather/wind can change during a flight and therefore arrival runways and even STARS can be altered.  That is why you can change them in the FMC.  If the computer knows what the expected entire route is, it can compute the things you want as a pilot.

 

I have approach and arrival runways programmed in but no TOD timer or snowflake

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14 minutes ago, Crabby said:

If you are landing on a south runway and flying north to get there, your TOD will be closer to the airport than if you were on the same flight path and landing north.  This is because you have to fly a greater distance to hit a way point that is north of the airport.

 

That is a fair point that I hadn't considered -- with this in mind it makes sense. I was just thinking that it knows the airport elevation so it could calculate at least a rough TOD based on a direct path, but again I wasn't sure if that was a bug or a design decision by Bombardier. In any case I typically do enter a runway and approach prior to departure with the understanding that I may have to change that mid-flight, was just curious to know how it's supposed to work if you don't.

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Just now, dresoccer4 said:

 

I have approach and arrival runways programmed in but no TOD timer or snowflake

Do you have your cruise altitude set (under PERF INIT)? Do you see a TOD appear if you click the MFD DATA button (you may have to move to the next page if it's a long flight plan)?

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4 minutes ago, Aplato said:

Do you have your cruise altitude set (under PERF INIT)? Do you see a TOD appear if you click the MFD DATA button (you may have to move to the next page if it's a long flight plan)?

 

yep, cruise is there. If you look at my second screenshot you can see the TOD green circle appears on the moving map, so the correct TOD is calculated and shown, however the TOD timer that's supposed to appear above the word "DESCENT" as well as the snowflake are absent.

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11 minutes ago, dresoccer4 said:

 

I have approach and arrival runways programmed in but no TOD timer or snowflake

Well, my only guess is that something else is missing.  The only other thing I can think of is when I import a flightplan from Sim Brief and then enter all the data on the departure and arrival pages, I check the Legs page all the way through.  There is always a discontinuity at the STAR transition to clear.  If I do not clear all DISCOs then I do not see a TOD/Snowflake.  Other than forgetting that, I have never seen them missing with over 125+ hours in the cockpit.   

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1 minute ago, Crabby said:

Well, my only guess is that something else is missing.  The only other thing I can think of is when I import a flightplan from Sim Brief and then enter all the data on the departure and arrival pages, I check the Legs page all the way through.  There is always a discontinuity at the STAR transition to clear.  If I do not clear all DISCOs then I do not see a TOD/Snowflake.  Other than forgetting that, I have never seen them missing with over 125+ hours in the cockpit.   

 

yeah i'm guessing it's something missing, but question is what. it does't make sense to me that the TOD circle is there but not the TOD timer. next time i fly it and it happens ill post more screenshots of my FMC pages

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vor 21 Stunden , JetNoise sagte:

Works every time. You're probably missing something, but without any further info/screenshot/we have to have our glasbowls set-up 😉  

 

Oliver

Makes sense. I have the flightplan programmed in the FMS, that is, departure and arrival runway, SID, STAR, airways and waypoints, cruising and transition altitudes are all set and there‘s no discontinuities. I usually fly with Nav and Speed mode. The TOD is shown on the map display. Before reaching the TOD, I set the new altitude and activate vertical speed mode without changing it. When I reach the TOD I change the vspeed according to what the Dir/Int page suggests. Everything seems to work except I don‘t have a snowflake. The nav display looks like in Dresoccer4‘s screenshot. Is there anything I have forgotten? I can‘t remember having done anything differently before the last update. 

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3 hours ago, Crabby said:

How would the FMC be able to calculate TOD without a selected arrival runway?

 

It should calculate a path to get you to 1500ft AGL at 10nm from the destination airport. Same when you have no altitude restrictions at all along your path. It will generate an advisory DES point.

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