I am preparing for my first ever FMC programmed flight in the PMDG 737 NGX....but I have an issue. When I left click on the VNAV and LNAV buttons on the MCP, they do not turn green, and LNAV and VNAV do not appear (in white) at the top of the FMA roll mode column. Can anyone suggest a reason for this? I have followed all other instructions (as per the Tutorial #1) to the letter. The maiden flight has been delayed until this issue has been resolved

EDIT: Is this because I am starting the flight from the gate, rather than the runway threshold?

1 hour ago, Christopher Low said:

I am preparing for my first ever FMC programmed flight in the PMDG 737 NGX....but I have an issue. When I left click on the VNAV and LNAV buttons on the MCP, they do not turn green, and LNAV and VNAV do not appear (in white) at the top of the FMA roll mode column. Can anyone suggest a reason for this? I have followed all other instructions (as per the Tutorial #1) to the letter. The maiden flight has been delayed until this issue has been resolved

EDIT: Is this because I am starting the flight from the gate, rather than the runway threshold?

Make sure both FD are on, FMS preflight is complete.

There seem to be errors in my flightplan I will need to go back to the drawing board....

1 hour ago, Christopher Low said:

There seem to be errors in my flightplan I will need to go back to the drawing board....

What is your flightplan Chris? What is the error?

1 hour ago, Christopher Low said:

There seem to be errors in my flightplan I will need to go back to the drawing board....

If it is a Discontinuity which is the error, just click the LSK on the next waypoint below the Discontinuity to put it in the scratchpad, then click on the LSK next to Discontinuity and it will close up the error. Don't forget to Execute the flight plan in the FMC if you've changed it.

I have gone through the FMC setup sequence again. I decided to select what appears to be a direct approach to runway 25 at EGAA Belfast Aldergrove (as opposed to an ILS approach), and this time it seems to have worked. I now have the speed and altitude restrictions at each waypoint, so I am hoping that this means that LNAV and VNAV can be set on the MCP. Therefore, the maiden FMC flight has now been set for early tomorrow morning

Some airlines don't arm LNAV until 400 ft in the air, some even higher off the deck than that, but it is the 'Boeing way' to arm it on the ground in the SOP. However, the reason some airlines don't arm it on the ground is because doing so can interfere with some of the other avionics systems, notably any wind shear alerts, which you won't get if LNAV is armed, but, you can always roll open the window, lick your finger and stick it out instead lol.

There are a few things which will prevent you arming LNAV, and one of them catches a lot of people out and that is not having a waypoint on the runway heading in their flight plan. So here are all of the things which will prevent you from arming LNAV if you don't do them...

As noted, you have to have the origin runway you are departing from in your flight plan, you have to have an 'active' route in the FMC (so don't forget to activate your flight plan) and you have to have the track of the first leg of your flight plan be within a few degrees of the runway heading (I think it has to be within 5 degrees, but it might be 10, can't remember, normally a SID will cover this for you anyway). Also, selecting LNAV is inhibited if TO/GA is selected, so select LNAV before you hit TO/GA. That is of course if you actually are using TO/GA, which you probably should, but you can manually throttle it if you like.

The above criteria all apply to when arming it on the ground, but there are some things which will inhibit LNAV in the air too: It won't guide until at least 50 feet off the deck is one of them, the other is you have to be fairly wings level when arming it if you are below 200 feet off the deck, and of course you have to be reasonably on course to do so as well, if you've flown the departure manually. Also watch out for that one if ATC have directed you off the magenta line for some reason.

So you can just fly the take off manually and get on course and then arm it all if you like so long as you are pretty much on the magenta line, after all, you don't want the autopilot to have all the fun do you? 

Don't sweat any of this, everyone cocks this stuff up when they are new to using a proper FMC and MCP, so just take control yourself and fly it if that happens, and when you are in the cruise, you can read up on it.

1 hour ago, Chock said:

some airlines don't arm it on the ground is because doing so can interfere with some of the other avionics systems, notably any wind shear alerts, which you won't get if LNAV is armed, but, you can always roll open the window, lick your finger and stick it out instead lol.

I've never heard that before. That sounds bad. Where did you find that?

 

1 hour ago, Chock said:

 That is of course if you actually are using TO/GA, which you probably should, but you can manually throttle it if you like.

You can also use TO/GA without the autothrottles. You still hit the TO/GA button, but you just push the T/L until it gives you the N1 you need.

I noted the comment about making sure the initial leg is within 5 degrees of the runway heading (my first waypoint is ADN; almost straight ahead after take off on runway 34). I will be using TO/GA, and the LNAV and VNAV buttons will be activated prior to this. I was more concerned with the fact that neither of them appeared at the top of the FMA roll mode column, but I suspect that they will "arm" properly this time. I should know around 7 AM tomorrow morning (the estimated time when I will be starting the flight).

On 10/23/2017 at 8:42 AM, Ralgh said:

If you want to see an example of this look at the flight I flew yesterday, AAL 265. You can look up the route on FlightAware. There is no STAR to LIhue so they file us to MORKE which is on the approach. When we get back on radar near DENNS the controllers usually clear us direct NAPUA which is also on the approach. When we get close we typically get cleared to cross NAPUA at 3,000 feet and cleared for the approach to runway 35. 

And watch out for ships and the lighthouse. ;)

9 hours ago, Chock said:

However, the reason some airlines don't arm it on the ground is because doing so can interfere with some of the other avionics systems, notably any wind shear alerts, which you won't get if LNAV is armed

That is the case with VNAV and is the reason we no longer arm VNAV on the ground prior to takeoff.  LNAV being a lateral mode has no affect on wind shear escape guidance which is a vertical mode.

3 hours ago, JoeDiamond said:

That is the case with VNAV and is the reason we no longer arm VNAV on the ground prior to takeoff.  LNAV being a lateral mode has no affect on wind shear escape guidance which is a vertical mode.

Yup, my mistake, was having a brain fade moment lol, knew it was one of em which screwed with W/S. Makes sense it would be a vertical mode.

Four attempts, and four failures. I can get the plane to take off and follow the waypoints to the destination airport just fine. However, it refuses to start descending on approach. I do not get the RESET MCP ALTITUDE warning message shortly before the aircraft reaches the T/D marker on the ND, which probably means that something is not set properly. Would this have anything to do with restricting the altitude to no more than 5000 feet for the entire duration of the flight?

During the first three attempts (trial and error is a wonderful thing) I had the approach to runway 25 set incorrectly, but I was hopeful that the fourth attempt would work, because the ILS25 y approach looked like it had been set up properly this time (with reduced airspeeds and altitudes, and also slight course adjustments to line up with the runway).

Damn, I wish I had one of you guys sitting next to me. I could probably solve this problem in seconds

EDIT: I assume that forgetting to switch the BARO knob from "InHg" to "hPa" would not affect this?

2 hours ago, Christopher Low said:

Four attempts, and four failures. I can get the plane to take off and follow the waypoints to the destination airport just fine. However, it refuses to start descending on approach. I do not get the RESET MCP ALTITUDE warning message shortly before the aircraft reaches the T/D marker on the ND, which probably means that something is not set properly. Would this have anything to do with restricting the altitude to no more than 5000 feet for the entire duration of the flight?

During the first three attempts (trial and error is a wonderful thing) I had the approach to runway 25 set incorrectly, but I was hopeful that the fourth attempt would work, because the ILS25 y approach looked like it had been set up properly this time (with reduced airspeeds and altitudes, and also slight course adjustments to line up with the runway).

Damn, I wish I had one of you guys sitting next to me. I could probably solve this problem in seconds

EDIT: I assume that forgetting to switch the BARO knob from "InHg" to "hPa" would not affect this?

What does your FMA say at cruise? What is your cruise altitude in the FMC?

The cruise altitude is only 5000 feet. I have just made another attempt (and clicked on the "Alt Inv" button to try and force the plane to descend; based on something I read in a similar thread here on AVSIM), but it failed again. I am extremely puzzled