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tkyler

IXEG 737 Progress Update - January 30th

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So here's a small example of what we're doing and where our time is going.  As we chip away on the last part of the FMS, that is the descent phase of the VNAV, we try and capture every scenario and represent it, but then when you begin flight testing as we are now, some sneak by you....like this one that took me half a day to find and fix because I noticed speed and altitude values for this cheeky little waypoint (DF644) didn't match up with common sense...so I knew I was on a bug hunt.

Now when you cross the speed restriction altitude during descent and have to level off and slow down,  this usually happens between waypoints....so most of the time, as you approach and pass a waypoint, you are either descending at a constant rate and speed, OR you level off and decelerate before the waypoint if a speed restriction is in effect at that waypoint.   But what happens if you are decelerating at the speed restriction altitude and you just happen to cross a waypoint at that exact time?  The speed at that waypoint (which you can see on the CDU) should reflect that deceleration and whose value should be somewhere south of the previous waypoints speed and somewhere north of the next waypoints speed.   Well I just happen to come across such a situation....so lucky for you guys and gals ...as that's one less bug you have to find. 

-tkyler

 

 

deceleration.png

Edited by tkyler
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But what happens if you are decelerating at the speed restriction altitude and you just happen to cross a waypoint at that exact time?

But what happen if you get free speed from the approach controller and forget to remove the speed restrictions in the FMS? Does it give you a warning or will the airplane naturally slow down to meet the criteria set in the LEGS page?

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Not sure I understand the question..

You mean like if you exit VNAV mode and use some other vertical AP mode that violates the speed restriction set in the box? My guess is this is one of the reasons real pilots don't use VNAV alot since ATC will mess up your plans sooner or later anyway :P 

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The FMS will do as its told (through key entry only), so in this case, it will still slow down if you don't make a change.  So...If you get a 'free pass' from ATC below the speed restriction altitude, then on the descent page, you simply delete the speed restriction entry per ATC's permission and a new route with new speeds are calculated.  EXEC and be on your way speeding below 10000' like a kid in a Ferrari ;)

-tkyler

Edited by tkyler
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Not sure I understand the question..

Sorry, will try to explain and will use an example

Lets say you are decending from from FL100 inbound BAVAD for an RNAV GNSS RWY 19R (GLS approach) and whilst the speed restrictions states 220 knots at 5000 feet you get a "free speed" clearance from approach while you still need to fly the RNAV with all its "hight restrictions" until you capture the ILS? Will IAS settings on the MCP then override the DES page speed restrictions or any manual added speed limit programmed in the LEGS page for each waypoint on the STAR? Reason for asking is that I have heard many of times to controller say i.e.  "Cleard OVDI at 4000feet no speed restriction" or "maintain high speed approach"..

Perhaps explained already by Tom, but I just wanted to know what happens on the LEGS page and with the navpoint speeds. Will it be calculated by what speed is set on MCP or will it continue to show indicated STAR speeds?

To use the picture Tom posted, if decending on VNAV passing DF644 for DF654 where speed is set to 240 and you get  a  "high speed approach request" due to traffic from ATC making you i.e fly at 280 knots on LNAV, i.e. down to locolizer capture, I take it EFIS will then show FMC SPD, LNAV and on the LEGS PAGE DF654 fix will show /220 calculated hight less you put in a dedicated hight.. So if using my first example again and replacing DF654 with OVDI where /200 at 4000feet is restricted the page will show that and not current IAS???

Hope I managed to explain my self Morten..

and

PS.. Will the aircraft down the line have support for SBAS or EGNOS? I take it Jan and Tom knows it as Wide Area Augmentation System (WAAS)??

 

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6 minutes ago, Tom Knudsen said:

PS.. Will the aircraft down the line have support for SBAS or EGNOS? I take it Jan and Tom knows it as Wide Area Augmentation System (WAAS)??

 

The Wide Area Augmentation System (WAAS) is an air navigation aid developed by the Federal Aviation Administration (prime contractor Raytheon Company) to augment the Global Positioning System (GPS), with the goal of improving its accuracy, integrity, and availability.

(quote from; https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System )

 

Given that the X-Plane default GPS system is accurate down to about, oh, i dunno.... some fraction of a millimeter (it's a double precision float), what exactly do you hope to improve by "implementing WAAS" ?

It takes work to remove accuracy from the X-Plane GPS coordinate system. It takes no effort what-so-ever to have unrealistically precise positioning data.

 

Do you know what WAAS is for?

Edited by Ben Russell
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I think he's asking will the FMS be capable of loading and flying WAAS-aided approaches, namely RNAV LPV with vertical guidance.

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I asked another developer a few weeks ago about LPV approaches seeing that the plane he develops uses Honeywell Primus in most cases.

I was also wondering whether it could be implemented in X-Plane seeing that, as Ben pointed out, GPS data in XPX is highly accurate and basically the plane has to follow the decent path from the chart.

It's more of a novelty to be honest and maybe Jan can comment on LPV approaches in real life from a professional point of view?

 

 

 

 

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Dudes im like a hungry kid watching a chicken cook in the oven, really looking forwards to this now xD. It's going to be quite interesting to see the difference in characterisics between this and the old 200 model in X-plane, I'm wondering if I will see a difference in fule consumption and costs on the VA I am with :D.

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8 hours ago, Tom Knudsen said:

Sorry, will try to explain and will use an example

Lets say you are decending from from FL100 inbound BAVAD for an RNAV GNSS RWY 19R (GLS approach) and whilst the speed restrictions states 220 knots at 5000 feet you get a "free speed" clearance from approach while you still need to fly the RNAV with all its "hight restrictions" until you capture the ILS? Will IAS settings on the MCP then override the DES page speed restrictions or any manual added speed limit programmed in the LEGS page for each waypoint on the STAR? Reason for asking is that I have heard many of times to controller say i.e.  "Cleard OVDI at 4000feet no speed restriction" or "maintain high speed approach"..

Perhaps explained already by Tom, but I just wanted to know what happens on the LEGS page and with the navpoint speeds. Will it be calculated by what speed is set on MCP or will it continue to show indicated STAR speeds?

To use the picture Tom posted, if decending on VNAV passing DF644 for DF654 where speed is set to 240 and you get  a  "high speed approach request" due to traffic from ATC making you i.e fly at 280 knots on LNAV, i.e. down to locolizer capture, I take it EFIS will then show FMC SPD, LNAV and on the LEGS PAGE DF654 fix will show /220 calculated hight less you put in a dedicated hight.. So if using my first example again and replacing DF654 with OVDI where /200 at 4000feet is restricted the page will show that and not current IAS???

Hope I managed to explain my self Morten..

and

PS.. Will the aircraft down the line have support for SBAS or EGNOS? I take it Jan and Tom knows it as Wide Area Augmentation System (WAAS)??

 

The MCP speed window is blanked whenever VNAV is engaged. The FMC will plan and fly the descent at the speed programmed into the DESCENT page except for legs where there is a speed or altitude restriction, in which case the currently applicable restriction is displayed on the DESCENT page. The pilot can delete any such restrictions if cleared by ATC and he can also enter a desired speed for a specific waypoint on the LEGS page if he knows in advance that a particular speed is required.

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12 hours ago, Nils said:

The MCP speed window is blanked whenever VNAV is engaged. The FMC will plan and fly the descent at the speed programmed into the DESCENT page except for legs where there is a speed or altitude restriction, in which case the currently applicable restriction is displayed on the DESCENT page. The pilot can delete any such restrictions if cleared by ATC and he can also enter a desired speed for a specific waypoint on the LEGS page if he knows in advance that a particular speed is required.

Could we use SPD INTV button on MCP?

Edited by ETOPS-330
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4 hours ago, ETOPS-330 said:

Could we use SPD INTV button on MCP?

The aircraft we model does not have the altitude or speed intervention buttons, just like many of the real 737-300s out there.

But you are correct, if it had, using it would clear the next limiting speed restriction, which is the same as erasing it manually on the LEGs page.

Jan

 

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This is what I love about the whole project.

In science, a theory is not valid unless it's impossible to disprove. I see this same kind of attitude with IXEG concerning complex systems like the FMC, it's not complete until it's proven to be robust and "unbreakable".

I'm not a programmer but I'm assuming IXEG dedicate more/as much work into the rare or abnormal scenarios than normal situations, because the normal situations are only a quarter of the story. This is what has been lacking with other products, I feel like other developers have worked on their aircraft to get it to a stage where it can fly and perform, PROVIDED everything is done/entered correctly, resulting in a very glitchy and shallow product that does not respond correctly to the slightest abnormal input.

Wonderful stuff :)

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2 hours ago, MadMckMax said:

This is what I love about the whole project.

In science, a theory is not valid unless it's impossible to disprove. I see this same kind of attitude with IXEG concerning complex systems like the FMC, it's not complete until it's proven to be robust and "unbreakable".

I'm not a programmer but I'm assuming IXEG dedicate more/as much work into the rare or abnormal scenarios than normal situations, because the normal situations are only a quarter of the story. This is what has been lacking with other products, I feel like other developers have worked on their aircraft to get it to a stage where it can fly and perform, PROVIDED everything is done/entered correctly, resulting in a very glitchy and shallow product that does not respond correctly to the slightest abnormal input.

Wonderful stuff :)

 

That is the idea - Tom made an architecture for the FMS that is designed to take abuse without faltering. Now it´s not omniscent, and it´s still a computer - garbage in, garbage out. But at least we don´t want it to crash in those scenarios. We want you to be able to change your mind, edit, delete, enter again - all without folding up. This takes a very "robust" code, and that´s what we have been hammering at the last months.

Jan

 

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On 2/1/2016 at 10:30 PM, Litjan said:

The aircraft we model does not have the altitude or speed intervention buttons, just like many of the real 737-300s out there.

But you are correct, if it had, using it would clear the next limiting speed restriction, which is the same as erasing it manually on the LEGs page.

Jan

 

I'm probably going to sound like an idiot here, but how would you perform a step climb enroute without those buttons? I've always either used ALT INTV or "pressing in the knob", depending on the aircraft in question, and I'm unsure how to do so with the Honeywell MCP without the buttons. 

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Set new alt into the MCP, then FMC? I'm not sure if the aircraft will start to climb or if it needs to be nudged via FLCH or V/S. Or if its done any other way for that matter. 

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Set the MCP to the new target. Then change the CRZ ALT on the CRZ page, execute. Plane starts climbing (or descending).

Jan

 

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Set the MCP to the new target. Then change the CRZ ALT on the CRZ page, execute. Plane starts climbing (or descending).

Jan

 

Can you add a planned SC on the cdu where it would give you the fuel saving in %

CMB

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Not quite decided, yet. It depends on wether we can slip it in before release, but I don´t think we will delay release for it.

Jan

 

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Not quite decided, yet. It depends on wether we can slip it in before release, but I don´t think we will delay release for it.

Jan

 

Ah sorry maybe I should have rephrased my question. Initially I was asking if you could add a planned SC in the classic, I know you can do this in the ng but wasn't sure about the classic.

I wasn't giving you an order to implement it for 1.0. Anyway I got my answer :)

Envoyé de mon iPhone en utilisant Tapatalk

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2 hours ago, cmbaviator said:

Ah sorry maybe I should have rephrased my question. Initially I was asking if you could add a planned SC in the classic, I know you can do this in the ng but wasn't sure about the classic.

I wasn't giving you an order to implement it for 1.0. Anyway I got my answer :)

Envoyé de mon iPhone en utilisant Tapatalk

 

Yes, it is possible to enter a step altitude on the CRZ page (in the real plane). The FMC will calculate the optimum step point (when to climb), allow entry of estimated wind at the new step altitude (for fuel penalty/benefit calculation) and also show the prospective savings as a percentage.

It shouldn´t be hard to implement that, I can almost do the calculation in my head... but it will need some time that we don´t have right now ;).

Jan

 

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