Question PMDG 737 NGX NDB approach on Skiathos using LNAV/VNAV

[rene2004 0]

In the underlying link you will see a LNAV/VNAV approach on Skiathos (LGSK). What I don't understand is the fact that at the end of the approach the plane will leave the magenta line and moves to track 001 and that both the LNAV- and VNAV-knobs are activated.

 

https://www.youtube.com/watch?v=ZcGpbp52K01

 

Is there anyone who can explane to me how this is done. If so, I will be very grateful.

 

 

[rene2004 0]

I am sorry, the link was not correct. Another try:

 

 

https://www.youtube.com/watch?v=ZcGpbp52k0I

[Overload 91]

Not sure I understand the question - but the NDB approach track is 008 degrees, the runway direction is 015 degrees, so there is a final manual or heading select turn required towards the end.

The minima are quite high - 1600ft, so the aircraft needs to be visual around 5 miles out to fly a normal decent profile.

On touchdown the blue dotted missed approach track changes to magenta so if the aircraft does a last second go-around, this now becomes the active leg.

Although LNAV and VNAV are active, the autopilot is disconnected around 4.5 miles out, the aircraft is being flown manually, but following the flight director commands, which seem to bring it in on a rather low profile, the VASI lights red most of the time, but that could just be an imperfection of the sim.

Any of the above useful, or have I misunderstood the question?

Eugene

[pschlute 37]

As Eugine pointed out at 4.5 nm out and at DH the pilot turned off the autopilot to fly the final approach manually. All normal so far.

 

I think (I am not a pilot), he should also have turned off the FD as he was now flying a non-precision approach below minimums. Maybe someone else can chip in.

[Overload 91]

I think (I am not a pilot), he should also have turned off the FD as he was now flying a non-precision approach below minimums.

 

The Flight director will continue to give vertical guidence down to the runway threshold, so can still be useful. Laterally it will direct towards the procedures inbound track of 008 degrees, but as the pilot flying will be aligning with the runway visually, I don't see that it's much of a problem, I think it just a matter of pilot preference.

Eugene

[pschlute 37]

Thanks for that Eugene.

 

I recall some videos of Concorde pilots turning off the FD once reaching DH, and tend to follow that procedure myself. I guess in the video in this post he should have turned off LNAV so that he only gets vertical guidance (VNAV) fron the FD. I am sure different airlines will each have their own procedures.

[skelsey 765]

 

 

The Flight director will continue to give vertical guidence down to the runway threshold

 

Not in all aeroplanes, in all modes or all types of approach -- it depends how the approach is coded in the database as well.

 

In some types there are some very serious 'gotchas' that one might encounter. The golden rule is that in any event, if you are not going to follow the guidance then you should and must turn the FDs off: if nothing else they are distracting, and at worst could lead to some serious dangers (for example, a FLCH descent where you are pitching above the FD guidance).

[Overload 91]

Not in all aeroplanes

 

Of course - but I believe the 737NG in the video provides this function.

 

 

In some types there are some very serious 'gotchas' that one might encounter

 

 

I'm not sure this example is "Gotcha" territory, as the approach has to be conducted visually below 1600 feet.

 

Eugene

[rene2004 0]

Dear Simmers,

 

as far as I can see, VNAV is on, LNAV is on and there is no heading select. When I do this approach myself  the plane will stay on the magenta line. Could it be possible that the pilot made use of the rudder?

[Overload 91]

VNAV is on, LNAV is on

 

 

But the autopilot is disconnected at 4.5 miles and the aircraft positioned manually towards the runway centre line, diverging from the magenta line, no rudder required!

Eugene

[pschlute 37]

 

 

as the approach has to be conducted visually below 1600 feet

 

Exactly the reason for not having FD cues telling the pilot what he does not need to know.

[rene2004 0]

Dear Eugene,

 

thank you for your replys. I still have the question what action of the pilot moves the aircraft to the runway centre line. Because even if I disconnect the autopilot, the aircraft remains on the magenta line! I hope you have an answer to me!

[pschlute 37]

Dear Eugene,

 

thank you for your replys. I still have the question what action of the pilot moves the aircraft to the runway centre line. Because even if I disconnect the autopilot, the aircraft remains on the magenta line! I hope you have an answer to me!

 

The autopilot is off.

 

The pilot is flying the aircraft.

 

What do you think causes the aircraft to line up with the runway?  The pilot moves the bloody control yoke.

[rene2004 0]

Peter,

 

You are bloody wright. My problem was that if I used my yoke the lnav disengaged. Unfortunely I did it before disengaging the autopilot. Anyway, I thank everybody who was so kind to spend time to reply to someone who likes to fly but is not very expirienced.

 

René

[pschlute 37]

On this approach , below 1600 feet you are flying a visual approach, so disengage the A/P and disengage LNAV/VNAV. Do not follow the magenta line. Just fly the aircraft to the runway.