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IXEG 737 Progress Update - December 12th FMS VNAV


tkyler
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Once you are 'out of bounds' of the route parameters, you are right that things go bad very fast.  The most difficult situation is when you are past the Top of Descent point and you simply cannot make it to the runway following the procedure without flying too steep and with flight spoilers deployed and even then there is no guarantee depending on how "late" you are past the T/D point.  Simply said, in such a case, you can NOT recover and still fly the given procedure, you have to extend your descent distance somehow by flying off route.  Jan does this in one of his videos where he "circles back" and rejoins a procedure leg.  (ala pattern work)  Also, It could be your arrival procedure has some restrictions that cause you to fly level segments and if you can get ATC permission to bust the restrictions, you could make up some ground and descend on those legs.

I have actually spent the last few weeks working on these more difficult scenarios...what to do "IF".  As Jan mentioned...as a professional pilot, he has never seen some of these situations, but for newbies like us, we get into trouble all the time and so the FMS has to handle really odd inputs sometimes.  There is one thing to note...and that is that the flight profile does have bounds....and the FMS is not a "save all".  You get too far out of bounds and the FMS will do no good or give you bad results.     BUT, I can say firsthand, that is why I myself keep at it....to get it right.  It is addicting.

I flew my very first completely automated flight yesterday, takeoff to touchdown with speed and altitude restrictions on climb and descent...all the way down to minimums, the ultimate milestone.  All I did was raise/lower gear and flaps after engaging LNAV/VNAV.  So whats left?  There are still other scenarios we have to punch in to see what happens. Short routes, half routes, changed routes, changed destinations etc.  Of course we have coded for these, but we are testing them now for stability and patching holes as they arise.  Good news is the bugs are getting much fewer and far between.  Stability testing with a broader group is up next.

-tkyler

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6 hours ago, tkyler said:

Once you are 'out of bounds' of the route parameters, you are right that things go bad very fast.  The most difficult situation is when you are past the Top of Descent point and you simply cannot make it to the runway following the procedure without flying too steep and with flight spoilers deployed and even then there is no guarantee depending on how "late" you are past the T/D point.  Simply said, in such a case, you can NOT recover and still fly the given procedure, you have to extend your descent distance somehow by flying off route.  Jan does this in one of his videos where he "circles back" and rejoins a procedure leg.  (ala pattern work)  Also, It could be your arrival procedure has some restrictions that cause you to fly level segments and if you can get ATC permission to bust the restrictions, you could make up some ground and descend on those legs.

I have actually spent the last few weeks working on these more difficult scenarios...what to do "IF".  As Jan mentioned...as a professional pilot, he has never seen some of these situations, but for newbies like us, we get into trouble all the time and so the FMS has to handle really odd inputs sometimes.  There is one thing to note...and that is that the flight profile does have bounds....and the FMS is not a "save all".  You get too far out of bounds and the FMS will do no good or give you bad results.     BUT, I can say firsthand, that is why I myself keep at it....to get it right.  It is addicting.

I flew my very first completely automated flight yesterday, takeoff to touchdown with speed and altitude restrictions on climb and descent...all the way down to minimums, the ultimate milestone.  All I did was raise/lower gear and flaps after engaging LNAV/VNAV.  So whats left?  There are still other scenarios we have to punch in to see what happens. Short routes, half routes, changed routes, changed destinations etc.  Of course we have coded for these, but we are testing them now for stability and patching holes as they arise.  Good news is the bugs are getting much fewer and far between.  Stability testing with a broader group is up next.

-tkyler

That sounds very nice. Sounds like you are getting the work done! This is great. Keep up the great work. The end is near :D Hopefully :)

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30 minutes ago, cmbaviator said:

Dcl: decelerate??

Why is there 2 TD and 2 DCL?

I suspect the release to be mid-end March

Envoyé de mon iPhone en utilisant Tapatalk

 

This is symbology we have in there for now to help with debugging. Later on there will be only one T/D. DCL means "decelerate" and denotes points where a speed-change is scheduled.

Jan

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As Jan says, DCL is for debug only; however, I think other FMS systems may utilize it. (Hrm..small bug uncovered.  The wrong waypoint is Magenta :P)  See...still a tiny bit of work to do ;)

NOTE:  Before we get in too deep....theses points are not absolutes.....except maybe the first T/D.  You cross that first T/D circle and the plane enters the decent phase.  The other green dots are "estimated" of course and depending on lots of things...like our performance database, winds and such, the plane may respond a bit on "either side" of these markers...but they are, in general, close....or should be.  Its one of those things we expect users to help refine if we missed anything.

Here's the correlation.

 

vnav.png

Edited by tkyler
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6 hours ago, tkyler said:

As Jan says, DCL is for debug only; however, I think other FMS systems may utilize it. (Hrm..small bug uncovered.  The wrong waypoint is Magenta :P)  See...still a tiny bit of work to do ;)

Yeah the NG FMS/Avionics stick a 'DECEL' on the route line where it anticipates the VNAV will need to slow for a lower speed planned at a subsequent fix.

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On 19/2/2016 at 0:57 PM, tkyler said:

As Jan says, DCL is for debug only; however, I think other FMS systems may utilize it. (Hrm..small bug uncovered.  The wrong waypoint is Magenta :P)  See...still a tiny bit of work to do ;)

NOTE:  Before we get in too deep....theses points are not absolutes.....except maybe the first T/D.  You cross that first T/D circle and the plane enters the decent phase.  The other green dots are "estimated" of course and depending on lots of things...like our performance database, winds and such, the plane may respond a bit on "either side" of these markers...but they are, in general, close....or should be.  Its one of those things we expect users to help refine if we missed anything.

Here's the correlation.

 

vnav.png

Outstanding...and really useful image.

Thanks a lot tkyler...such post/image helps a lot a newbye like me, in the effort to understand/learn navigation using FMS and so on...

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