Sign in to follow this  
darth_damian_000

PMDG 777. What MCP altitude do you set at Top of Descent?

Recommended Posts

Hello everyone.

 

Life story:

I am struggling with flight simming itself, specifically the landing, and I would like to ask you all for help and advice. My problem is rather simple: I am unable to land manually, and if I am, then my plane is all over the place. I would like to get to the bottom of this issue, and I am getting back to the basics.

 

I was taught to set the MCP altitude before T/D at the G/S intercept altitude. As a result of this, I almost always have to go into vertical speed mode, because I will not be able to reach altitude/speed restrictions along the descent path. The problem THEN becomes I am descending too fast, I am picking up speed, and I have to compensate for that with spoilers, which is undesirable for me as I would prefer to last through a flight with minimal warnings (hah!). 

 

Anyway, I would like to know if my initial altitude setting philosophy is plausible, and if you could identify any issues in my little rant, I would appreciate the criticism of my skills (yup) and even moreso a solution.

 

Secondly, I would like to ask what does what exactly does the MCP altitude selector do? In the instructional video, the narrator set his to 7000 feet, didn't press the button, and the plane started the descent. Upon almost reaching 7000 feet, he reset the MCP altitude to 2000ft WITHOUT pressing the knob. Would it make a difference if he did press it?

 

Is there even a difference between a situation where you set MCP to 7000 and then again to 2000 as opposed to setting it 2000 right off the bat at T/D?

 

Thank you for taking the time to read this, and providing me with any help to improve my flying.

Props to PMDG for making such amazing products.

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

Pretty sure this isn't procedurally correct, but I usually set it too the first altitude restriction in my STAR. Or if I'm feeling lazy, the IAF altitude for my landing. Would be curious to hear how it's really done though.

Share this post


Link to post
Share on other sites

Sup,

 

In the video you are seeing, the airplane is flying in VNAV mode. That is the only mode that departs an altitude with only changing the MCP altitude window. When in VNAV, the FMS calculates your top of descent, but it will not descend unless it gets an altitude restriction to go to. That is what he is setting. And that is also why the airplane just continued down when he turned the MCP window further down to 2000. The VNAV did not have the MCP restriction anymore. There are other restrictions VNAV might have. But for you, that is another lesson.

 

That being said, the 777 almost always finds a way to bring you in hot in VNAV. At 10.000 feet, I'm comfortable with about 45nm to go to touch down (Track miles). This can be read from the progress page. It is the distance remaining to your destination airport's 4 letter ICAO code. Anything less than 45 and you will have to extend flaps early or use speed brakes down low "most probably".

 

As for the landing, the key is to be stable. Follow the flight director and practice without wind.

 

Good luck,

  • Upvote 1

Share this post


Link to post
Share on other sites

 

 


At 10.000 feet, I'm comfortable with about 45nm to go to touch down (Track miles)

 

A good indicator to fly by, thanks!

Share this post


Link to post
Share on other sites

I was taught to set the MCP altitude before T/D at the G/S intercept altitude.

If VNAV is engaged during the flight, the plane will start to descend on profile at the T/D if you have rolled down your altitude on the MCP to an altitude below what your are cruising at. Say you are cruising at FL350, change the MCP altitude to FL240 and the plane will start to descend at T/D. A couple of thousand feet above FL240, roll MCP altitude down to 16000, then 10000, maybe 6000, 4000, and then intercept altitude. In the real world you are never going to be cleared to descend from cruise altitude to intercept altitude in one ATC command. Do be concerned about using speed brakes or manual thrust during descent to maintain your target speed.

Share this post


Link to post
Share on other sites

The problem THEN becomes I am descending too fast, I am picking up speed, and I have to compensate for that with spoilers, which is undesirable for me as I would prefer to last through a flight with minimal warnings (hah!). 

 

the speedbrakes are there for a reason, and the vnav path is not really calculated with the idea that you won't be using them. it's not a warning, it is a planned spot where you will focus on reducing airspeed instead of altitude. i am no expert but as i understand it, it's more efficient to descend at 280 or the econ speed until you reach the 10000/250 restriction and then slow down using the brakes when necessary.

 

now, if you want to minimize the speed difference between your descent speed and the speed you'll be using below 10000 try setting a slower speed in the descent page, if you set it to 250 or 260 you can end up not really needing to use the brakes by the time you reach 10000. you'll also see this is a lot slower, if you spend an extra 5 or 10 minutes on descent, even at idle thrust you are burning more fuel than if you just use the brakes when it's necessary to fly at a slower speed. there are dots that are drawn on the path which indicate where it is expecting a planned deceleration (and that is where the drag required message pops up, along with large deviations above the path in general.)

 

also making sure to fill out your descent forecast page can be helpful in ensuring that your TOD is calculated to the ideal spot. a strong tailwind can really make it harder to descend in time and this will compensate for that.

 

cheers

-andy crosby

Share this post


Link to post
Share on other sites

Excellent timing on this question because that's where I'm reading in the FCTM at the moment.  (I'm a noob on the 777 and big iron flying in general so, consider the source.)

 

Just to throw what it says in the FCTM into the discussion...

 

 

Plan the descent to arrive at traffic pattern altitude at flaps up maneuvering speed approximately 12 miles from the runway when proceeding straight-in or about 8 miles out when making an abeam approach. A good crosscheck is to be at 10,000 feet AGL, 30 miles from the airport, at 250 knots.

 

To the OP, have you verified that the only thing you have engaged is VNAV/LNAV?...no speed in the MCP speed window?  AT is engaged all the way down to landing?  Are you minitoring the VNAV path in the ND?  Also, from a bit further up in the FCTM...

 

 

Set all mandatory altitude restrictions and “at or above” constraints in the Mode
Control Panel (MCP) altitude window. The next altitude may be set when the
restriction has been assured or further clearance has been received.

 

Seems to me that setting the FAF altitude wouldn't be a bad idea...less workload if you know ATC isn't going to assign you any altitudes along the way.  On the other hand, even in simpler cases, the MCP can miss altitudes/airspeed restrictions without a bit of help so, putting in the altitudes along the way can help.

Share this post


Link to post
Share on other sites

Hello everyone.

 

Life story:

I am struggling with flight simming itself, specifically the landing, and I would like to ask you all for help and advice. My problem is rather simple: I am unable to land manually, and if I am, then my plane is all over the place. I would like to get to the bottom of this issue, and I am getting back to the basics.

 

I was taught to set the MCP altitude before T/D at the G/S intercept altitude. As a result of this, I almost always have to go into vertical speed mode, because I will not be able to reach altitude/speed restrictions along the descent path. The problem THEN becomes I am descending too fast, I am picking up speed, and I have to compensate for that with spoilers, which is undesirable for me as I would prefer to last through a flight with minimal warnings (hah!). 

 

Anyway, I would like to know if my initial altitude setting philosophy is plausible, and if you could identify any issues in my little rant, I would appreciate the criticism of my skills (yup) and even moreso a solution.

 

Secondly, I would like to ask what does what exactly does the MCP altitude selector do? In the instructional video, the narrator set his to 7000 feet, didn't press the button, and the plane started the descent. Upon almost reaching 7000 feet, he reset the MCP altitude to 2000ft WITHOUT pressing the knob. Would it make a difference if he did press it?

 

Is there even a difference between a situation where you set MCP to 7000 and then again to 2000 as opposed to setting it 2000 right off the bat at T/D?

 

Thank you for taking the time to read this, and providing me with any help to improve my flying.

Props to PMDG for making such amazing products.

What throttle hardware do you have? Are you pulling to idle during descent, or leaving them firewalled?

Share this post


Link to post
Share on other sites

Anyway, I would like to know if my initial altitude setting philosophy is plausible,

 

It is. Even if in real life you wouldn't necessarilly be cleared directly from cruise level to GSIA (glide-slope intercept altitude), it wouldn't be unheard of.

 

In the simulator flying offline or online in uncontrolled airspace, I descend directly to the next altitude restriction by the STAR or approach chart. Sometimes it's a direct descent to GSIA. There's no need of adding unnecessary steps to the descent if nothing else advises against it.

 

And in any case, what's more important, is that this issue is NOT what's preventing you from accomplishing a good landing.

 

 

 

what exactly does the MCP altitude selector do?

 

It sets a target altitude. Also, it's like a "barrier" that the aircraft won't exceed when using the AP. If you're descending, the aircraft won't descend past the value set at the MCP window. When you're climbing, it won't climb past whatever number is set on the MCP.

 

 

 

he reset the MCP altitude to 2000ft WITHOUT pressing the knob. Would it make a difference if he did press it?

 

Pushing the knob does more "advanced" things, related to VNAV and FMC logic:

 

- Deletes altitude constraints that are set in the FMC: Say you're flying level at 2000 feet and ATC clears you to 15000 feet with no constraints. Your SID has a hard constraint at 10000feet. If you set 15000 feet and then push, you're deleting the 10000feet constraint so that VNAV doesn't stop the climb and goes straight to 15000.

 

- Changes the FMC cruise altitude: If your FMC cruise altitude is FL340 but you set 38000 into the MCP and then push, you'll update the cruise altitude in the FMC from 340 to 380.

 

- If you're within 50NM of your top of descent (T/D), set a lower MCP altitude and then PUSH, this would be equivalent to going to the VNAV page of the FMC and hitting the "DES NOW" command.

 

(yes, I checked the FCOM for these, I don't know them all by heart as I don't use this function that often :)

 

 

Is there even a difference between a situation where you set MCP to 7000 and then again to 2000 as opposed to setting it 2000 right off the bat at T/D?

 

If you change the target altitude from 7000 to 2000 BEFORE altitude capture starts (that is, before you're so close to reaching 7000 that the aircraft is leveling out of the descent), then no, there's no difference.

 

 

I would like to get to the bottom of this issue, and I am getting back to the basics.

 

In my humble opinion, the basics are not learning how to descend from cruise to GSIA. You can isolate the descent and the approach/landing phases for training purposes.

 

My advice is to fly touch & goes for landing practice.

 

For approach practice, set the 777 on the runway, take-off, fly to the IAF and start the approach from there.

Share this post


Link to post
Share on other sites

 

 


I am struggling with flight simming itself, specifically the landing, and I would like to ask you all for help and advice. My problem is rather simple: I am unable to land manually, and if I am, then my plane is all over the place. I would like to get to the bottom of this issue, and I am getting back to the basics.

 

Hi, Damian,

 

As Jaime said, setting the altitude targets during descent is not central to accomplishing good landings.   The final approach starts from the IAF.   I suggest that you start a new thread specifically about landing and the issues you are having with manual landings.  You can explain there what is going wrong, beginning at the IAF or GS intercept point.  You will need to explain what type of approach you are doing -- probably best to start with an ILS approach -- and your speed and other MCP settings at the IAF or GS intercept point.  It would also be helpful to give the specific runway and specific airport you are using.  Even with manual landings it is standard to leave the Autothrottle on, so long as the FMC-recommended final approach speed+5 knots is set.  Jaime's suggestion to practice touch and goes is a good one, since it sounds like your major issue is with manual landings.

 

Mike

Share this post


Link to post
Share on other sites

 

 


Pushing the knob does more "advanced" things, related to VNAV and FMC logic:

- Deletes altitude constraints that are set in the FMC: Say you're flying level at 2000 feet and ATC clears you to 15000 feet with no constraints. Your SID has a hard constraint at 10000feet. If you set 15000 feet and then push, you're deleting the 10000feet constraint so that VNAV doesn't stop the climb and goes straight to 15000.

- Changes the FMC cruise altitude: If your FMC cruise altitude is FL340 but you set 38000 into the MCP and then push, you'll update the cruise altitude in the FMC from 340 to 380.

- If you're within 50NM of your top of descent (T/D), set a lower MCP altitude and then PUSH, this would be equivalent to going to the VNAV page of the FMC and hitting the "DES NOW" command.

(yes, I checked the FCOM for these, I don't know them all by heart as I don't use this function that often :)

 

Excellent post.  Just out of curiosity, if someone accidentally pressed the button, how do they return it to the 'unpressed button' barrier mode? 

Share this post


Link to post
Share on other sites

Excellent post.  Just out of curiosity, if someone accidentally pressed the button, how do they return it to the 'unpressed button' barrier mode? 

 

Thanks Gregg!

 

Well, it would depend on the situation.

 

- If you delete a constraint by accident, you'd have to input it again into the FMC. Or if given the workload that's not possible, just "remember" the constraint and act accordingly.

- If you change the cruise altitude, just set the correct cruise FL and push the button again.

- If you push it close to T/D and start descending, I would quickly hit the "ALT HOLD" button. Depending on how much altitude has been lost, you could then set the correct FL and select a climb mode such as V/S (V/S is okay for a small correction of a couple hundred feet at a low climb rate) or if you've just lost say 100 feet and your descent is going to start soon anyway, leave it at ALT HOLD and descend from there.

 

That said, I don't think it's "easy" to push the button by accident. Rotating the knob and pushing it are clearly different "operations" (at least in real life, in FSX yeah, you could screw it up more easily, hehe) :)

By the way: I forgot to mention that each time you push the button, you delete one constraint at a time. So pilots sometimes have the habit of setting the altitude and pushing the button repeatedly a couple of times, to delete all constraints :P

Share this post


Link to post
Share on other sites

 

 


have you verified that the only thing you have engaged is VNAV/LNAV?...no speed in the MCP speed window?  AT is engaged all the way down to landing?  Are you minitoring the VNAV path in the ND?

 

LNAV and VNAV are all ON, speed window in the MCP is blank, AT on at all times (including landing).

 

Yes, I do monitor the vnav path in the ND, and most of the time, I find myself above the glide path. my problems begin when I need to go away from vnav and enable vertical speed mode, which in turn, speeds up the plane. To combat that, I later have to enable speed mode and I attempt to slow down to vref + 80, at which point, plane requires drag. I use say, half full speedbreaks, and I get a caution alert. cool. i arm speedbreaks and...I'm speeding up. That is basically my story. So I am doing something wrong. I do appreciate your input and I will take a look at the FCOM. Thanks for the advice. I will most likely fly again, stress less about it, and see how it goes.


 

 


What throttle hardware do you have? Are you pulling to idle during descent, or leaving them firewalled?

 

I use F1-F4 to control throttles. I am not doing anything, as A/T is on at all times.

Share this post


Link to post
Share on other sites

 

 


Yes, I do monitor the vnav path in the ND, and most of the time, I find myself above the glide path. my problems begin when I need to go away from vnav and enable vertical speed mode, which in turn, speeds up the plane. To combat that, I later have to enable speed mode and I attempt to slow down to vref + 80, at which point, plane requires drag. I use say, half full speedbreaks, and I get a caution alert. cool. i arm speedbreaks and...I'm speeding up. That is basically my story. So I am doing something wrong. I do appreciate your input and I will take a look at the FCOM. Thanks for the advice. I will most likely fly again, stress less about it, and see how it goes.

 

I think you would do better to remain in VNAV.  VNAV will raise the pitch to decrease speed, while V/S is more passive and won't adjust for speed.   V/S won't solve your overspeeding problem -- it will make it worse. 

 

When your speed is too high in a descent in VNAV, you should see a message on the CDU (FMC screen) "drag required."  Try using full speed brake -- nothing wrong with that.  Your autothrottle should go into Idle or HOLD -- make sure your hardware throttle controls are at minimum, as in HOLD they may prevent the Autothrottle from minimizing thrust (depending on how your hardware is set up).  Keep an eye on the N1 indications and make sure they are going to minimum when your speed is too high or you are above the descent profile. 

 

Another thing to take into account is wind.  If you have a tail wind the FMC will calculate your initial descent point too late and you will be too high and too fast. 

 

You may get a cautionary message at some point that the speed brake is on -- this is not necessarily bad.  You can decide then to retract it if your speed and vertical profile look good.

 

Mike

Share this post


Link to post
Share on other sites

Hello everyone.

 

Life story:

I am struggling with flight simming itself, specifically the landing, and I would like to ask you all for help and advice. My problem is rather simple: I am unable to land manually, and if I am, then my plane is all over the place. I would like to get to the bottom of this issue, and I am getting back to the basics.

 

I was taught to set the MCP altitude before T/D at the G/S intercept altitude. As a result of this, I almost always have to go into vertical speed mode, because I will not be able to reach altitude/speed restrictions along the descent path. The problem THEN becomes I am descending too fast, I am picking up speed, and I have to compensate for that with spoilers, which is undesirable for me as I would prefer to last through a flight with minimal warnings (hah!). 

 

Anyway, I would like to know if my initial altitude setting philosophy is plausible, and if you could identify any issues in my little rant, I would appreciate the criticism of my skills (yup) and even moreso a solution.

 

Secondly, I would like to ask what does what exactly does the MCP altitude selector do? In the instructional video, the narrator set his to 7000 feet, didn't press the button, and the plane started the descent. Upon almost reaching 7000 feet, he reset the MCP altitude to 2000ft WITHOUT pressing the knob. Would it make a difference if he did press it?

 

Is there even a difference between a situation where you set MCP to 7000 and then again to 2000 as opposed to setting it 2000 right off the bat at T/D?

 

Thank you for taking the time to read this, and providing me with any help to improve my flying.

Props to PMDG for making such amazing products.

 

Not sure if this would help but, I'll explain what I do within the sim:

 

EMKAM.jpg

 

I usually set the MCP ALT to the first "fix" on the approach chart. For example: If I'm landing ILS 08L at CYVR, I would set 3000' since EMKAM is the first fix on that approach. (This is only if I am flying offline "Vatsim" and have no ATC restrictions. I dont usually fly with the default ATC).

 

All of this is setup before reaching T/D. Once I reach T/D, The aircraft will manage the decent on it's own. The 777 calculates the speed restrictions properly as well. I rarely have to intervene with speed brakes, unless I have a strong tail wind. If the PFD is showing [HOLD] mode, I use the throttle to manually adjust the speed when required. Once I reach EMKAM, The aircraft will maintain 3000' until glide-slope is captured with APP mode enabled. 

 

Another tip: I usually set a 7nm ring by entering the arrival ICAO within the FIX page of the FMC. This gives me a distance marker of when I should have the aircraft fully configured for landing. I've always had great landings once I started doing that. I guess the main thing is, try to be "ahead" of the aircraft and everything else will follow. 

 

It may not be "real world" at all but, it does help with what I have to accomplish. Hope this helps.

 

Cheers,

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this