737Andi

Changing speed and altitude does not work

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Hello,

I have 2 questions..

1) Sometimes I'm not able to enter a new speed or altitude for a waypoint in the FMC. I'm receiving the message "INVALID ENTRY".
This is happening in flight but also on ground. The entering format is definetely correct. Does someone have an idea why this is happening?

2) Another problem is that the plane is not changing the speed when in LNAV/VNAV mode, although I have changed the speed for the next waypoint.
To explain it more in detail. The plane is on the way to waypoint BAM. The waypoint currently has the speed 250 and the altitude 5000. Before reaching BAM I change the speed to 270 which works fine in the FMC. The plane is however keeping the 250 knots and the 250 knots are still shown on the PFD as set speed limit in magenta.

Thank you very much!

Best regards Andreas
 

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12 minutes ago, 737Andi said:

Does someone have an idea why this is happening?

The entering format - as opposed to the assertion - is incorrect.

...or:

13 minutes ago, 737Andi said:

2) Another problem is that the plane is not changing the speed when in LNAV/VNAV mode, although I have changed the speed for the next waypoint.
To explain it more in detail. The plane is on the way to waypoint BAM. The waypoint currently has the speed 250 and the altitude 5000. Before reaching BAM I change the speed to 270 which works fine in the FMC. The plane is however keeping the 250 knots and the 250 knots are still shown on the PFD as set speed limit in magenta.

Are you using a flight plan that has been exported by some sort of route planner?

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17 minutes ago, 737Andi said:

Hello,

I have 2 questions..

1) Sometimes I'm not able to enter a new speed or altitude for a waypoint in the FMC. I'm receiving the message "INVALID ENTRY".
This is happening in flight but also on ground. The entering format is definetely correct. Does someone have an idea why this is happening?

2) Another problem is that the plane is not changing the speed when in LNAV/VNAV mode, although I have changed the speed for the next waypoint.
To explain it more in detail. The plane is on the way to waypoint BAM. The waypoint currently has the speed 250 and the altitude 5000. Before reaching BAM I change the speed to 270 which works fine in the FMC. The plane is however keeping the 250 knots and the 250 knots are still shown on the PFD as set speed limit in magenta.

Thank you very much!

Best regards Andreas
 

1) In the 747, you cannot enter a speed constraint unless there is also an altitude constraint.

2) I assume you are climbing towards BAM?  Not enough detail.  Also, all speed constraints in the 747 are AT OR BELOW.

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1 hour ago, 737Andi said:

2) Another problem is that the plane is not changing the speed when in LNAV/VNAV mode, although I have changed the speed for the next waypoint.
To explain it more in detail. The plane is on the way to waypoint BAM. The waypoint currently has the speed 250 and the altitude 5000. Before reaching BAM I change the speed to 270 which works fine in the FMC. The plane is however keeping the 250 knots and the 250 knots are still shown on the PFD as set speed limit in magenta.

Check your climb page in the FMC to see if you have a 250 kts limit set below 10'000. (I'm not entirely sure though if the limit is still active when you manually change to a higher speed for a waypoint.)

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Regarding 1...

When reading your answers it seems that one cannot enter any desired number for speed and altitude for the coming waypoints? Why is that?

Regarding 2....

I'm descending towards BAM. BAM has the setting 250 / 5000. The plane has 250 / 6000 5 Nm before BAM. I'm changing 250 to 290 5nm before BAM, which is working in the FMC. However the plane is then not increasing thrust to reach 290 at BAM. Why is that?

 

Thanks!

Edited by 737Andi

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The question about the route file is incredibly important to answer. Please answer it.

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No...I have not used a flight planner for the route. I have chosen the route waypoints myself.

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57 minutes ago, 737Andi said:

No...I have not used a flight planner for the route. I have chosen the route waypoints myself.

Okay, so then it's all down to formatting and monotonic path.

In the descent, you can only set up speeds in a monotonic path: in other words, speed must always decrease. If you set a speed of 250 at one waypoint, then it must be <250 for subsequent waypoints. Additionally, keep in mind that there's a speed restriction set on the descent page, which will affect how the aircraft observes speeds.

Additionally, pay attention to your FMA. It displays what the AP / AT mode is. This will give you an idea of why the AP is doing what it's doing, but again - it won't speed up in VNAV if you've already told it to reduce speed below 290.

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22 hours ago, scandinavian13 said:

Additionally, keep in mind that there's a speed restriction set on the descent page, which will affect how the aircraft observes speeds.

Can you please explain this a little in detail.

The other things are clear to me now 🙂

Thanks!

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21 minutes ago, 737Andi said:

Can you please explain this a little in detail.

Explain "this?" If you are asking about the speed restriction on the descent page, you could be asking about the value that defaults to 240/10000.  In most places in the world, a speed constraint exists below 10000 regardless of the TL.  Every field on every page of the FMS is described in the FCOM.

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I you need to fly a different speed other than what’s published on an approach or STAR the easiest and most reliable method is to just speed intervene. That’s what it is there for. 

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Kind of a funny story, but I was jumpseating to work years ago in an old 737-500. The Captain was attempting to put every new speed that was assigned into the FMC while on approach for some reason, and the airplane just wasn’t doing what he wanted it to do. It got pretty messy. He finally threw his hands in the air, turned around to myself and the other regional jet guy in the other jumpseat, and said “I give up, you guys want to come give this a try??”

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Why not just be the pilot and do a speed intervention...manually set 250 on the MCP, or disconnect the a/t and do it yourself.  Don’t rely on a computer to fly your plane...

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41 minutes ago, Jetlinker said:

Kind of a funny story, but I was jumpseating to work years ago in an old 737-500. The Captain was attempting to put every new speed that was assigned into the FMC while on approach for some reason, and the airplane just wasn’t doing what he wanted it to do. It got pretty messy. He finally threw his hands in the air, turned around to myself and the other regional jet guy in the other jumpseat, and said “I give up, you guys want to come give this a try??” 

This isn't kind of a funny story; it is actually very worrying.  I hope the Captain was having a bit of fun with you - or you with us - otherwise how on earth did he pass his final checkout on the aircraft and get it validated on his pilot's licence?

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9 minutes ago, berts said:

This isn't kind of a funny story; it is actually very worrying.  I hope the Captain was having a bit of fun with you - or you with us - otherwise how on earth did he pass his final checkout on the aircraft and get it validated on his pilot's licence?

If I remember right he was trying to prove to the FO that he could get the aircraft all the way onto final by inputting speeds in the FMC and staying in VNAV. It just didn’t work out as he planned. I don’t know, wasn’t my company or an airplane that I had any experience with, but his comment to us was tongue in cheek obviously. He eventually gave up and took over manually. 

Edited by Jetlinker

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Clearly this was a non-standard way to operate below 10,000ft, which is how aircraft accidents can happen.  I suppose it was a good job you were there to keep an eye on them both..   

  • Upvote 1

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3 minutes ago, berts said:

Clearly this was a non-standard way to operate below 10,000ft, which is how aircraft accidents can happen.  I suppose it was a good job you were there to keep an eye on them both..   

This was 15 years ago when us lowly RJ drivers were considered to be the enemy. It was always enlightening to see how the “professionals” did it. 😅

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18 hours ago, downscc said:

Explain "this?" If you are asking about the speed restriction on the descent page, you could be asking about the value that defaults to 240/10000.  In most places in the world, a speed constraint exists below 10000 regardless of the TL.  

I am actually aware of this 240/10000 rule. But is this setting in the fmc actively preventing the plane from reaching higher speeds below 10000?

 

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7 minutes ago, 737Andi said:

I am actually aware of this 240/10000 rule. But is this setting in the fmc actively preventing the plane from reaching higher speeds below 10000?

I would think so, yes.

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The rule 250/10000. This also mentioned on the charts. But pmdg coded 240/10000. As that is below the max speed which is 250.

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40 minutes ago, ph-cxz said:

The rule 250/10000. This also mentioned on the charts. But pmdg coded 240/10000. As that is below the max speed which is 250.

Yup, and this is noted in the FCOM.  The speed is normally 10 kts lower than regulated speed.

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13 hours ago, 737Andi said:

I am actually aware of this 240/10000 rule. But is this setting in the fmc actively preventing the plane from reaching higher speeds below 10000?

 

Yes. Why else would it be there?

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On 1/22/2019 at 3:18 PM, 737Andi said:

I am actually aware of this 240/10000 rule. But is this setting in the fmc actively preventing the plane from reaching higher speeds below 10000?

 

If you want to ignore this speed restriction in the FMC then simply delete it; or alternativley disconnect the autopilot, turn the Flight Directors off and then fly the aircraft manually. More often than not it is cancelled after takeoff by ATC; especially if you ask them nicely!

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33 minutes ago, berts said:

More often than not it is cancelled after takeoff by ATC; especially if you ask them nicely!

Except the 240/10000 is for the approach, not the departure.

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