Add-drag messages in FMC

[Paul12 2]

I wonder if those messages also appear in the real world FMC or if it is only a FlightSim function ?

Same with Reset Alt when reaching the point of descent ?

 

Anybody knows ?

 

Hubert Werni

 

 

[Sam 68]

Real

[LeeL 272]

All real

 

Sent from my Nexus 4 using Tapatalk

 

 

[PHXMD-11 86]

 

 

I wonder if those messages also appear in the real world FMC or if it is only a FlightSim function ?

Same with Reset Alt when reaching the point of descent ?

 

"ADD DRAG" will appear when the FMC is having difficulty maintaining the descent path to meet a speed constraint.

 

"RESET ALT" is a reminder that the top of descent point is approaching.

[scandinavian13 5,192]

...and this is all information contained in the tutorials.

[Paul12 2]

...and this is all information contained in the tutorials.

 

Where exactly ???

 

Hubert Werni

[hopskip 253]

Open the manuals

 

Hold down the Ctrl and F key together

 

Type Reset Alt

 

Press Enter a few times

 

the PDF reader will show you any and every time the text "Reset Alt" appears in the document.

[Vagabondo 23]

 

 

"ADD DRAG" will appear when the FMC is having difficulty maintaining the descent path to meet a speed constraint.

The message in the real aircraft is "DRAG REQUIRED". I can't recall exactly what it is in NGX.

[SierraHotel 974]

...and this is all information contained in the tutorials.

 I would be too embarrassed to ask any questions, especially those relating to PMDG, without first reading all the info at my disposal, it's simply a matter of pride! Pride, which along with "civility" seems to be evaporating like water in a desert in this "so-called" modern World in which we all live!  

[Paul12 2]

 I would be too embarrassed to ask any questions, especially those relating to PMDG, without first reading all the info at my disposal, it's simply a matter of pride! Pride, which along with "civility" seems to be evaporating like water in a desert in this "so-called" modern World in which we all live!  

 

May be you should first read my question  of the post which was: does " the message add drag" show in the real world or only on Flight Simulator.

 

Regards

 

Hubert Werni

[Don t moderate me this way 882]

No offence intended: The addon was developed according to the real-world aircraft and a number of genuine Boeing manuals are included in the addon documentation.

 

Still this may be a valid question as flightsim addons may offer a number of "cheats" to help the simmer fly the plane. ("autofill" of certain FMC entries, for example)

[Paul12 2]

 I would be too embarrassed to ask any questions, especially those relating to PMDG, without first reading all the info at my disposal, it's simply a matter of pride! Pride, which along with "civility" seems to be evaporating like water in a desert in this "so-called" modern World in which we all live!  

 

Me,I  would be embarrased to issue dumb remarks before having read and understood  the content of a post.

As to asking questions which may be somewhere in a manual : may be I am not as intelligent as you - or as you think you are -

and therefore  I sometimes do not understand the manual.

This is the reason I am in the Forum and by the way I make contributions.

 

Cheers

 

Hubert Werni

[hopskip 253]

Reset MCP Altitude

 

This means you are within about 5nm of your Top of Decent point and your MCP (Mode Control Panel) altitude is set to the altitude you are currently at. This means you are only authorizing the autopilot to descend no feet to the altitude it is already maintaining.

 

When you reach the Top of descent point, the aircraft will slow down, hoping that by the time you allow it to descend, it can use the acceleration back to normal speed to get back onto profile.

 

You may need to do this if ATC don't clear you to descend, for instance to avoid hitting the aircraft that is under you or about to pass under you. In this case you will not be able to reach the IAP in LNAV/VNAV and will need to add track miles to get down.

 

It is quite possible to fly overhead your destination at FL410 and then run out of route. The autopilot will NEVER descend below the altitude you have set in the MCP (Because if it did, you might collide in middair and kill everyone on board both your plane and the one you hit).

 

 

 

Add Drag

 

 This is the FMC asking you to add drag. Drag can be added by

1. Deploying the speedbreak
2. Deploying flap
3. Lowering the Landing Gear

There are other unapproved methods of adding drag such as side-slipping, but these are potentially dangerous and may cause damage to the aircraft in some cases.

 

Drag may be required if you are close to the vertical profile, but have too much energy. This is usually caused by an unforecast (See Descent Forecast Page) tailwind.

 

It can also be caused by being slow on the MCP altitude, or by a VNAV profile that is too steep (This may happen in some locations due to the STAR profile being steeper than the most efficient profile, but is more likely to be due to the unforecast tailwind, or a forecast headwind that doesn't eventuate).

 

To avoid seeing this - Always add a descent forecast wind profile. However sometimes the forecast isn't exactly what actually happens, and in those situations you may need to add a bit of drag.

 

Before you reach down and grab the speedbrake handle though, have a look at the trending information. The FMC will immediately go "Drag Required" on you the minute it detects that it's going a bit too fast, but if you notice your speed decreasing anyway (especially if you are near the 10,000ft mark) you may find that the aircraft can still make the restriction, but may just be slowing down a little too slowly for the FMC to like it. I have often ignored the profile if it means we will be 250kts by 9500ft anyway. No point pulling brakes now and then adding thrust later.

 

Remember the FMC has a programmed profile it wants. It is based on computer models and predictions, but sometimes the atmosphere of planet earth does things like change wind direction without the FMC expecting it Use your judgement to figure out if you need to do something to get back on profile, and then do that thing. Obey ATC, don't hit any traffic or cause breakdowns of separation (Especially unauthorized things that ATC don't want you to do)

 

The FMC messages are telling you "If you don't change something, we will be high and/or fast"

 

There's one more similar message related, something like "Descent path unachievable"

 

This is basically the FMC saying "Your telling me you want to go from 300kts at FL180 to "on the ground and stopped" in 15 miles? That's not possible."

The FMC will try to do what it's been told to do, but it can't break the laws of physics.

[Paul12 2]

Reset MCP Altitude

 

This means you are within about 5nm of your Top of Decent point and your MCP (Mode Control Panel) altitude is set to the altitude you are currently at. This means you are only authorizing the autopilot to descend no feet to the altitude it is already maintaining.

 

When you reach the Top of descent point, the aircraft will slow down, hoping that by the time you allow it to descend, it can use the acceleration back to normal speed to get back onto profile.

 

You may need to do this if ATC don't clear you to descend, for instance to avoid hitting the aircraft that is under you or about to pass under you. In this case you will not be able to reach the IAP in LNAV/VNAV and will need to add track miles to get down.

 

It is quite possible to fly overhead your destination at FL410 and then run out of route. The autopilot will NEVER descend below the altitude you have set in the MCP (Because if it did, you might collide in middair and kill everyone on board both your plane and the one you hit).

 

 

 

Add Drag

 

 This is the FMC asking you to add drag. Drag can be added by

1. Deploying the speedbreak
2. Deploying flap
3. Lowering the Landing Gear

There are other unapproved methods of adding drag such as side-slipping, but these are potentially dangerous and may cause damage to the aircraft in some cases.

 

Drag may be required if you are close to the vertical profile, but have too much energy. This is usually caused by an unforecast (See Descent Forecast Page) tailwind.

 

It can also be caused by being slow on the MCP altitude, or by a VNAV profile that is too steep (This may happen in some locations due to the STAR profile being steeper than the most efficient profile, but is more likely to be due to the unforecast tailwind, or a forecast headwind that doesn't eventuate).

 

To avoid seeing this - Always add a descent forecast wind profile. However sometimes the forecast isn't exactly what actually happens, and in those situations you may need to add a bit of drag.

 

Before you reach down and grab the speedbrake handle though, have a look at the trending information. The FMC will immediately go "Drag Required" on you the minute it detects that it's going a bit too fast, but if you notice your speed decreasing anyway (especially if you are near the 10,000ft mark) you may find that the aircraft can still make the restriction, but may just be slowing down a little too slowly for the FMC to like it. I have often ignored the profile if it means we will be 250kts by 9500ft anyway. No point pulling brakes now and then adding thrust later.

 

Remember the FMC has a programmed profile it wants. It is based on computer models and predictions, but sometimes the atmosphere of planet earth does things like change wind direction without the FMC expecting it Use your judgement to figure out if you need to do something to get back on profile, and then do that thing. Obey ATC, don't hit any traffic or cause breakdowns of separation (Especially unauthorized things that ATC don't want you to do)

 

The FMC messages are telling you "If you don't change something, we will be high and/or fast"

 

There's one more similar message related, something like "Descent path unachievable"

 

This is basically the FMC saying "Your telling me you want to go from 300kts at FL180 to "on the ground and stopped" in 15 miles? That's not possible."

 

The FMC will try to do what it's been told to do, but it can't break the laws of physics.

  

  Thank you very much for your superb answer and explanation.

 As I mentioned before I wanted to know if those CDU messages appear in the real world airplanes.I assumed that is the case

 but wanted it confirmed.

I am surprised how certain people freak out because a question asked my be found somewhere in manuals,google,YouTube etc etc

First: As I am convinced that any question can be found somewhere else then why having a Forum ?

  Second: nobody asked them to answer.

 Third: I support this superb forum with small donations.

 

 Cheers

 

Hubert Werni

[scandinavian13 5,192]

 

 

First: As I am convinced that any question can be found somewhere else then why having a Forum ?

 

The forum could actually be discussing more interesting things than the same things over and over again if people actually read the answer.  A lot of people equate forum with Help Desk for some reason.  Clearly, if we weren't here answering the same 12 questions over and over, we'd all be sitting here with nothing to talk about, right?  Wrong.  We could be discussing why the AP has so many different modes, or different techniques to fly the plane better.  Heck, if everyone at least glanced at the intro manual and tutorials, we could at least answer the more detailed questions where people have to e

 

Also, you have to admit, it kinda grates your nerves when you've written it somewhere and someone ignores the help you've provided by writing it and asks the question again.  This, of course, forces someone to write it all over again.

 

It also introduces human error into the information.  Each time someone repeats the original information from the manual, certain aspects of the original info may be compromised.  See: Chinese Whispers.

 

In pictures and diagrams:

 

 

 

Second: nobody asked them to answer.

 

Sure, but you can't blame them for jumping in and saying where the information is.  Contrary to popular forum belief, it is actually helpful to point out where the information is.  It's just more work for the recipient than they wanted.

 

Maybe I'm just a mean old cuss because my parents always just told me to go look things up in our set of encyclopedias.  I was brutally forced to go learn things on my own, and ended up learning about more things in the process.

 

Repressed childhood memories eventually made me into the RTFM guy.

 

 

 

Third: I support this superb forum with small donations.

 

None of those donations make it to the people who are actually providing answers or the location of the information (not that they should).  So, while I'm glad you support AVSIM, a donation to them doesn't mean you're entitled to have people find the information for you.