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Driver170

Few Questions

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Ok on the ground i can't select LNAV or VNAV but after takeoff i can? I have set up the FMC correctly.

 

Second, taking off from EGKK rnav SID rwy 8r there are speed and alt rest my aircraft holds me and gets me at my alt restrictions ok but not my speed it holds me at 250 and the waypoints are 210 so i get an FMC message saying unable to do 210 blah blah why doesn't it reduce speed?


Vernon Howells

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You can't "engage" them on the ground, but you can "arm" them, it's different things.

 

About your speeds, I'd have to see what you were doing. On the LEGs page you could input any values you want while on the ground, the FMC won't complain because he doesn't know whether he'll be able to meet those restrictions (up to a certain point, if it's too obvious he'll complain). Once airborne the computers are calculating the aircraft's performance in real time and they decide that the restrictions you inputted on the ground can't be met, hence the "unable" messages.

 

However, if you KNOW the aircraft SHOULD be at a particular speed, but it IS NOT. Then your DUTY as a pilot in command is using all means on your disposition to make it happen. That is: Disconnect the A/T and slow the engines down if you must, or "speed intervene" or something. But don't just stare at the screens and ask yourself "What the hell is HE doing? Oh well..."


Jaime Beneyto

My real life aviation and flight simulation videos [English and Spanish]

System: i9 9900k OC 5.0 GHz | RTX 2080 Super | 32GB DDR4 3200MHz | Asus Z390-F

 

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Well i couldn't arm them on this flight? Well i thought thats what the fmc are for it was an auto hard mand restriction of 210 kias over london and it failed to reduce its speed !!


Vernon Howells

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Well i couldn't arm them on this flight? Well i thought thats what the fmc are for it was an auto hard mand restriction of 210 kias over london and it failed to reduce its speed !!

Hi Dave, tell me the SID you were flying, I'll have a look and come back to you, 

 

Enrico

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Well i couldn't arm them on this flight?

 

There are tolerances that must be met.  They're mentioned in either the intro manual, or the tutorials.  Do those and it'll probably answer a bunch of the questions you've been posting lately (specifically the reserves one from yesterday).

 

Remember that this is a simulation of the real plane.  People spend quite a few days from 8-5 learning the inner workings of this aircraft to do it daily.  From all of your posting of late, it seems like you just need to sit back and take a stab at a few things at a time.  You're gonna burn yourself out and just confuse yourself even more if you keep trying to learn everything at once.  Relax.  It isn't a race.

 

...and if it was, I've already beaten you anyway :P

 

 

 


Well i thought thats what the fmc are for

 

I'll spare you my rant, but I'll answer that with a resounding NO.

 

First, you're the one flying plane.  Always.  The FMC is a tool.  It is not in charge, and you should not rely on it to be.  Second, you have to know how to operate the plane pretty well for it to behave like you expect it to.  You have to treat it like it's expecting to be treated (that's the case with anything automated, really).  My bet is that you didn't do something properly.


Kyle Rodgers

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Very true buddy lol but i'm just so eager to learn it all !!!


Vernon Howells

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Hi Vernon, pardon me for calling you Driver, I had not noticed your name below your replies...anyways, here is what you have to do, to fly the BIG 1Z SID:

 

You have three speed restrictions: one at KKE02 at MAX 250 KIAS, and two at KKE23 and at BIG VOR, both MAX AT 210 KIAS. First off, those speed and altitude restrictions are there because EGKK  is close to Heathrow, and the controllers need to make sure there are no traffic conflicts between the two airports. 

 

When you download the latest AIRAC into the PMDG NGX and call up this SID via the FMC, very likely at KKE02, Legs Page, you'll see a magenta 250, as if the NGX has to meet that speed. In effect, the procedure wants you at or below 250 kias, not at 250 kias. How do you deal with it? in the FMC scratchpad you type 250Band then line select it next to KKE02 line. By doing this, you are telling the system to fly at that waypoint max at 250, once you do that, the FMC recalculates the climb profile, and you won't see any message like: unable to meet speed restriction. 

 

Same thing for the next two restrictions, at or below 210 kias. You'll see this in many procedures, all you have to do is add a for "at or below" next to the speed, and off you go. Not every Boeing works this way, the 777 for example is a little different, I believe, and there is another workaround for speed restrictions like these. 

 

Enrico  :wink:

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Hi enrico thats correct i looked at the SID and understood it very well, speed and alt rest. I did type in 250B but no for the other waypoints for 210 kias as i thought Vnav would deal with that! So you are saying i should type in 210B and the 737 will slow down for those speeds? So why did it not slow down for the 210 hard mandatory speed rest thats in the legs?

Just confused why it didn't slow down for the normal 210 thats already there? You know what i mean? I have been looking at manuals tutorials but nothing explains that


Vernon Howells

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Most SIDS (in the US, anyways) are all coded for the correct speeds. You really shouldn't have to monkey with the box other than to select the correct SID and arm the LNAV/VNAV.

 

Try a few screen shots so we can do some diagnosis.

 

One thing for 210B is you might need to stay at Flaps 1 or maybe Flaps 5, depending on your weight. The FMC won't go below your minimum airspeed for your configuration. If you need to be at 6000' at 210knots, then you might need to wait to clean up.


Matt Cee

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Ok i'll do the flight again and do some screenshots really don't know why its not holding at 210 but 250 instead.


Vernon Howells

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Ok i'll do the flight again and do some screenshots really don't know why its not holding at 210 but 250 instead.

 

You should be looking at your FMA, your magenta commanded speeds on the speedtape, and your LEGs page on the FMC to see what's happening.


Jaime Beneyto

My real life aviation and flight simulation videos [English and Spanish]

System: i9 9900k OC 5.0 GHz | RTX 2080 Super | 32GB DDR4 3200MHz | Asus Z390-F

 

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Ok i'll do the flight again and do some screenshots really don't know why its not holding at 210 but 250 instead.

What's your configuration at this point? Like Alpha Floor said, what does your FMA say?


Matt Cee

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Also, look at your FMC, under the LEGS page, and let us know what speed number is there next to those two waypoints, and if it is a white or magenta one,

 

Enrico

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