Despite having gone through some different tutorials, etc, I am having a hard time trying to fully understand the different hand flying options in the 737NGX.  Assuming I’ve loaded a flight plan into the FMC so I have a course line to follow, my "understanding" is as follows (please correct as needed):

1. If I don’t turn on LNAV, VNAV, AT, CMD A, etc, all pitch, roll, IAS and N1 settings are under my control, and there is no FD display even if the FD switches are on.
2. If I now turn on LNAV and VNAV, I will have FD roll and pitch guidance (if the FD switches are on), and power (N1 settings) and IAS are still under my control.
3. If I then turn on AT, and the autopilot with CMD A, (with LNAV and VNAV still on) the autopilot is flying the plane with regard to pitch, roll, and IAS ( not hand flying  anymore).
4. I could now turn off LNAV and VNAV and instead use HDG SEL, ALT HLD, and VS inputs to the autopilot (no yoke inputs).

 

Some additional issues:

 What happens when hand flying if you do something that conflicts with the FMC flight plan with regard to heading, altitude or IAS? I ask because I found that when using HDG SEL and ALT HLD with the autopilot on, the FD pitch bar did not ask for a pitch setting that resulted in a climb even though ALT HLD was set at a much higher altitude then the plane was currently at. In fact, the FD pitch setting produced a loss of altitude. In other words, if CMD A is on, do the FD pitch and roll indications reflect the flight plan stored in the FMC rather than the current HDG SEL and ALT HLD settings?

 

I don’t understand the appropriate use of the N1, SPEED and LVL CHG buttons on the speed control.

 

Thx,

Al

Your four point understanding is basically correct.

 

ALT HLD will simply stop the aircraft climb or descent where ever you pressed it regardless of what is in the altitude window. You will notice that initially the aircraft will go through the altitude at the time of pressing ALT HLD, but will return to it in a short space of time.

 

The FD bars reflect the mode of automation selected. If you have LNAV/VNAV then the FD bars command pitch and roll according to the FMC. When you select HDG SEL, LVL CHG, ALT HLD or VS you are overriding the FMC inputs with specific headings, altitudes, speeds and rates of the climb and the FD will command pitch and roll to match your MCP inputs.

 

LNAV/VNAV should be thought of as high level automation functions.

 

Direct MCP input (HDG SEL, LVL CHG, ALT HLD, VS) are lower level and more basic automation functions.

 

When you engage AT and/or AP you are engaging the aircraft to automatically follow MCP SPD/N1 settings and the FD command bars.

 

If you disengage the AT/AP the level of automation remains the same, you are just requires to follow the FD command bars manually.

 

If you don't wish to follow the FD command bars, simply turn the FDs off. The is standard practice. Deselecting automation modes is not the normal way to remove the FD command bars.

 

Hope that helps!

The FD will always show you whatever is programmed into the FMC, which is LNAV and VNAV basically. It also depends on the autoflight modes that you set via the MCP (Modes like LVL CH, VS etc.). 

 

A golden rule is to not just blindly follow the magenta lines and cross, instead you should always have raw-data backups for critical phases like takeoff or landing and be aware of what's ahead of you (situational awareness). The FD might be helpful for hand flying SID's or STAR's in low vis. conditions but if the visibility is good enough your eyes should be outside. 

 

To come back to your original question: Most of the time the FD will show you whatever is set on the MCP, which in the case of LNAV/VNAV depends on the data that you have entered into the FMC. 

 

 

he FD will always show you whatever is programmed into the FMC, which is LNAV and VNAV basically.

 

This is not true.

 

 

 

It also depends on the autoflight modes that you set via the MCP (Modes like LVL CH, VS etc.). 

 

This is more like it.

 

 

 

 What happens when hand flying if you do something that conflicts with the FMC flight plan with regard to heading, altitude or IAS?

 

The bars will show you how to get back to the plan (if you use LNAV/VNAV - i'll get back to this in a moment)

 

 

I ask because I found that when using HDG SEL and ALT HLD with the autopilot on, the FD pitch bar did not ask for a pitch setting that resulted in a climb even though ALT HLD was set at a much higher altitude then the plane was currently at. In fact, the FD pitch setting produced a loss of altitude.

 

Yes, as was mentioned, ALT HLD means hold altitude the button was pressed at. THe correct mode to go for the altitude in the window would be ALT SEL, except the Boeing AFDS works a bit different - you don't have ALT SEL but you have a couple modes that get you to selected altitude via different means.

 

 

I don’t understand the appropriate use of the N1, SPEED and LVL CHG buttons on the speed control.

 

LVL CHG is not, strictly speaking, a speed control mode.

N1 - will have A/T run the engine on current limit (CRZ, MCT, CLB or derated CLB)

Speed - will have A/T try to maintan selected speed as best as it can (with regard to vertical mode, speed limits...)

 

LVL CHG - is a vertical mode, which will maintan the selected speed, while A/T is either in N1, or IDLE mode, depending whether you are climbing or descending. (if A/T is off, it will maintan the speed, while you control the rate manually by throttle levers).

 

 

note: all vertical modes will level off when reaching preselected MCP altitude.

 

 

 

Now, to the FD.

To really "get" the whole F/D / AP interaction thing, you will have to think a bit different.

 

Consider it like this: the whole AFDS system controls not the airplane, rather FD. It will move FD to the point it want the airplane symbol on the PFD to aim to. Depending on what AFDS modes are selected via MCP (shown on FMA).

 

All the actual autopilot does, is follow the FDs.

When you hide the FD, but keep the AP on, it still "sees" them - it's just from the display they are hidden.

Thanks all for the insight, viewpoints and explanations -- a great help and much appreciated!

Al

I always find another point of view can sometimes help (maybe sometimes not lol). Fabo seems to have a good grasp of the MCP modes. I'd like to add my 2 cents worth.

 

There are three levels that the MCP can be operated in:

 

1. Flight Director (FD) only-mode. This means the pilot is hand flying the plane and HDG inputs (for example) will cause the FD bars to give the pilot steering commands to fly the selected heading. When a pilot has the airplane symbol in the PFD centered with the FD vertical and horizontal bars (or tucked in tight into the v-bars or bow-tie FD type as configured in the CDU as there are two different kinds of FD bars you can choose to see) then one of two things are happening: the pilot is either on the heading and maintaining it as long as he has the FD bars centered -- or -- he is correcting to get to the desired heading. So, to summarize: when you are flying the FD bars centered you are either on your mark or correcting to get on your mark.

 

So, in this FD only-mode, you can press HDG select or V/S and climb and descend using these MCP knobs and all they will do is feed steering commands to the flight director command bars. It's up to the pilot to follow the cues and manually fly the plane to the desired results.

 

2. The next level is with an auto pilot on and using the MCP itself. What I mean by this, is that if you turn an auto pilot on, select a given HDG and the AP will fly the aircraft to that heading (right?). Then you dial in a lower altitude and press V/S and dial down a descent of say, 500 FPM and the AP will descend and capture that lower altitude.

 

At this level, the flight directors may or may not be on, but I strongly recommend them to always be on. They will still provide their steering commands but in this case, the AP will fly the plane and 'follow' the FD command bars instead of the pilot.

 

So, in this level of MCP operation, the AP is flying but you don't care about what's in the FMC or in fact weather or not you even have a route in the FMC. In other words, at this level you are operating the MCP without being connected to your FMC route.

 

At this second level you can use everything on the MCP panel except for LNAV, VNAV, ALT INTV and SPD INTV. Altitude intervention and Speed intervention are for the third and last MCP level of use which is when you have LNAV and VNAV engaged (and thus the AP is flying your FMC route) and you want to make a speed or altitude change.

 

So, to re-state, at this second level of MCP operation, you have the AP and A/T on and you can select HDG to make heading changes, V/S to climb and descend and LVL CHG to climb and descend, you can select APP or VOR/LOC or ALT HOLD or SPEED or N1. In other words, you can select anything except for LNAV, VNAV, ALT INTV and SPD INTV.

 

3. The third and last level in which the MCP can be operated is when it is 'married' or 'coupled' to the FMC route. To tie the MCP panel to the FMC we use LNAV and VNAV (you may use one only but we never train that way and encourage both to be used at the same time if they are going to be used at all).

 

Once you are using LNAV and VNAV, your use of the MCP buttons and knobs reduce dramatically. In fact, in normal operation, you mostly just use the altitude knob to make altitude adjustments. SPD INTV and ALT INTV are not used as much but they are used.

 

So there are your three levels of MCP usage.

I always find another point of view can sometimes help...There are three levels that the MCP can be operated in:

I kinda wrote that already, maybe not quite as comprehensively though

Yes you did...and that's exactly why I prefaced my post by saying my 2 cents was just from another point of view. Many times when someone can read what 3 different people have written on the same subject matter, they finally 'get it'...reading basically the same thing written in 3 different ways, often helps someone to finally understand the topic. I know it does for me.

 

 

reading basically the same thing written in 3 different ways, often helps someone to finally understand the topic. I know it does for me.

 

Exactly.  Fundamentals of teaching, really.

 

You can clearly explain something for one person, and another person may still be confused.  By re-stating something in a different way, it may clear it up for that person.  People learn differently.

 

Some people pick up the knowledge as it's stated, while others require visuals.

 

 

I always find another point of view can sometimes help (maybe sometimes not lol). Fabo seems to have a good grasp of the MCP modes. I'd like to add my 2 cents worth.

What a deal for 2 cents! Very informative summary post, thanks much rfresh737.

Al