Can't engage LNAV

[bob755 1]

I was practicing some DME arcs, flying manually without any flight plan in the FMC, only the same departure and arrival airports and a SID were entered.   After flying manually close to the airport, I entered an arrival runway and then entered and an ILS approach.

I set the heading to intercept the first waypoint for the approach but even when I was on the path I couldn't engage LNAV. Am I missing something?

 

[pracines 823]

Well, I don't know about anybody else, but I would not attempt that landing from that position even in a flight sim. Some sort of course reversal procedure would normally solve this situation.

-too fast 

-too tight a turn 

-too high 

-likely a tail wind landing

Its a good thing LNAV does not engage, its saying "try it yourself!".😂

If you want a technical reason as to why LNAV does not engage, you may want to ask at the official PMDG forum for the 737: https://forum.pmdg.com/

[bob755 1]

Well I actually did land but without LNAV but that's not the issue as I was just experimenting.

Had time too reduce speed even with the tail wind.

Not too high. The plane is currently at 3000ft. LAPMO is 3000ft, and MAXDEV 2500 to intercept the glide path.

 

 

 

 

Edited April 13, 2019 by bob755

[pracines 823]

2 hours ago, bob755 said:

Well I actually did land but without LNAV but that's not the issue as I was just experimenting.

Had time too reduce speed even with the tail wind.

Not too high. The plane is currently at 3000ft. LAPMO is 3000ft, and MAXDEV 2500 to intercept the glide path.

 

 

 

 

Glad you were able to land, good job!

You asked if you were missing something and I let you know what was missing - a course reversal procedure.🤓

The point I was making is, though a 737 may go through an experimental/rigorous flight test process, you setting up a sudden "unpublished" and very unconventional approach like you tried to, is your issue. LNAV is designed to provide passenger safety and comfort, not to "experiment". 👨‍🏫

There are good reasons why Instrument approaches have coarse reversal procedures, and many approaches have different (WIDER) procedures for Cat C and D aircraft.👨‍🎓 

For the record - I could have landed it easy too. 👨‍✈️

Bottom line, there is nothing wrong, in this context, with LNAV in the NGX.👨‍⚖️

 

[BlueStar 323]

6 hours ago, pracines said:

Well, I don't know about anybody else, but I would not attempt that landing from that position even in a flight sim. Some sort of course reversal procedure would normally solve this situation.

-too fast 

-too tight a turn 

-too high 

-likely a tail wind landing

I'm guessing you haven't done a lot of H-TACANs in KC-135s.  🤣

[pracines 823]

1 hour ago, BlueStar said:

I'm guessing you haven't done a lot of H-TACANs in KC-135s.  🤣

What, with 144 United Airlines customers on board?😂 Not lately 🤢🤮😵😄

Edited April 13, 2019 by pracines

[BlueStar 323]

9 minutes ago, pracines said:

What, with a 144 United Airlines customers on board?😂 Not lately 🤢🤮😵😄

Those folks with the 82nd don't mind. 🙂

 

[MarkJHarris 128]

Nope. I can't see why it wouldn't engage either. It appears to be an active leg. You're at the right altitude too, though that shouldn't be an issue.  Wind is nothing special. 

No idea. Did you have all the perf info entered in that page? That is the usual no-go for LNAV. You need the zero-fuel weight entered so it can work out it's VREF speeds and stuff. It can't calculate otherwise. It does appear to have speeds in the legs page so just a guess at the usual suspects.