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Driver170

level change problem

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I was following my STAR untill i got vectored off, so i selected LVL CHG. But the aircraft wouldn't descend it was decending really shallow like 600 fpm and it would level off for a while then slowly descend. i only had a crosswind at that time as you can see by the pict below that i have provided. only way i could descend to meet my FAF ALT is by selecting V/S

 

This is not the first time this has happened to me. any idea folks?

 

 

 

 

 

https://www.dropbox.com/s/ecbmx9cv8oqaqh2/2014-10-15_22-10-11-728.BMP?dl=0


Vernon Howells

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Right ok what does that mean matt? Should it be at a different N1 %


Vernon Howells

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Right ok what does that mean matt? Should it be at a different N1 %

 

That means that you've left your hardware throttles at above IDLE.  FL CH and VNAV DES are both pitch for speed modes.  What this means is that the AP will command a descent at a particular speed, given the current throttle setting.

 

In other words, without moving the throttle, set the airspeed to X by adjusting the pitch of the plane.  As we all know, pitching down more makes you go faster.  Conversely, if you have the throttle at idle, it requires more nose down pitch (and therefore higher vertical speed) to hit the same speed as it would if your throttles are at 55% (which would require less nose down pitch, and less vertical speed to hit that same speed).

 

Prior to T/D, place your throttles at IDLE.  This is where VNAV expects them to be.  If you watch carefully, prior to T/D, VNAV will command throttles IDLE and roll the throttle back appropriately.  Soon thereafter, that IDLE mode drops to ARM/HOLD, which means the crew is able to manually adjust the throttle while A/T remains active.  Given your settings, this is allowing your hardware to re-set the throttle to 55% (where I'm guessing you've left it since takeoff), which kills your descent.

 

This is all information from the tutorial.  Again, you're getting so mixed up with inane stuff (like that CI and FI mean for pseudo-fixes thread) that you're either not paying attention to basic core knowledge, or just forgetting it.  Slow down.  Pay attention to what you're reading/doing.  As always, I applaud the effort to seek knowledge, but take time to let it sink in.


Kyle Rodgers

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Hi, i place my throttles to idle every time i press DES NOW prior to my TOD. I could of advanced them on my intermediate app to about a 1/4 the way up, so when i disengage the A/T on final roughly - 500 RA, my N1 doesn't drop and therefor the throttles don't require much N1 % change!

 

Next time i will pay more attention and make sure my throttles are idle up untill i disengage the A/T and report back!

 

But the last time this happened my throttles on my hardware where at idle thats why i'm questioning this again!

The reason for the N1 being high is because my AC level off at 8k so the throttles advanced forward MATT


Vernon Howells

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This is not the first time this has happened to me. any idea folks?

Vernon

 

Your screenshot is useless you are zoomed out so far. How can anyone have any ideas when they can't even see what your FMA shows?

 

If I got vectored off of a STAR, I would use V/S, speedbrakes, speed knob and the banana to make sure I ended up where I should be.


Michael Cubine
xVxT6x.jpg

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Hi, i place my throttles to idle every time i press DES NOW prior to my TOD. I could of advanced them on my intermediate app to about a 1/4 the way up, so when i disengage the A/T on final roughly - 500 RA, my N1 doesn't drop and therefor the throttles don't require much N1 % change!

 

Next time i will pay more attention and make sure my throttles are idle up untill i disengage the A/T and report back!

 

But the last time this happened my throttles on my hardware where at idle thats why i'm questioning this again!

The reason for the N1 being high is because my AC level off at 8k so the throttles advanced forward MATT

 

If you have your throttle at the idle stop, your N1 shouldn't be up in the 50% range.  I would check your hardware calibration, or set your A/T Override Settings to NEVER in the PMDG SETUP> menu.  Additionally, you might also want to look into the SHOW THROTTLE POSITION option.  This helps you sync the position right before you disconnect A/T.


Kyle Rodgers

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Michael i'm sorry about the pict i just took a screenshot and copy/paste to dropbox! Maybe if you download it you will have a full screen shot.

 

Extend the centerline and use the path deviation on the ND to get an idea how high you are.

 

Kyle i have that option checked - show throttle position. On my next flight i will double check my throttles and then select LVL CHG and let you guys know what happens


Vernon Howells

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Extend the centerline and use the path deviation on the ND to get an idea how high you are.

Vernon

 

Extending the centerline is a good idea. Do it in both directions for the runway for reference in case you become disoriented. Here's how. Assume the runway is 34R with a heading of 343 degrees. On the legs page select 34R to the scratchpad Go to the fix page and select 34R up as a fix. Then on line one enter 343/20 and on line 2 enter 163/20. Now you have a centerline in both directions with a circle around the runway  at a distance of 20 miles and the line is right thru the center of the runway not the center of the airport as if you used KSEA as the fix. The NGX is the only airplane that I believe that does this.


Michael Cubine
xVxT6x.jpg

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Tangent:

 

 

 


Extend the centerline and use the path deviation on the ND to get an idea how high you are.
Unfortunately, that only works if you're on the extended centerline or on an LNAV course (NOT heading) to intercept.

 

Let's say you are on a 90deg intercept with 6 miles to intercept a final at point 6 miles out from the runway (12 miles travel). The vertical deviation will simply infer that you are actually on final at 6 miles. At 12 miles of travel, you could be somewhere around 3600 AGL and be on profile. The FMC doesn't account for that 6 miles of base and mathematically is thinking you're really on final at 3600. The vertical deviation will show you 1800 feet high.

 

2 ways to fix that. Ignore the vertical deviation or use the LNAV to let the FMC calculate the path. Personally, I ignore the vertical deviation but I use the vertical bearing on the DESC PAGE.

 

For example, ILS16R SEA. I'll put FINKA/1900 in the DESC page and check the vertical bearing. 3=good. <3 decrease your ROD. >3 increase your ROD.


Matt Cee

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Interesting! I found these -

 

http://www.pprune.org/tech-log/489412-fmc-intc-crs-question.html

 

http://www.pprune.org/tech-log/435247-737ng-fms-question.html

 

 

About this V bearing matt, thats new for me can you explain more? What is FINKA/1900

A typical G/S is 3deg. Vertical Bearing tells you what your degrees to whatever fix is on the DESC page. So, if your vertical bearing is 3deg to FINKA at 1900 (the appropriate height for the ILS), then you're on a good profile if you're pointing at FINKA.

 

Some guys I fly with force the runway RW16R/ into the DESC page (scratch pad RW16R from LEGS add the "/" and put it in the DESC 4R (?5R?)). I prefer the FAF.

It'd be easier if we were flying and I could just draw it out on the paperwork. :P


Matt Cee

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