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Nevian

A few approach wonderings

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I'm having great fun with the NGX package, but I can't seem to understand some of the aspects of the different approaches. Reading the FCOM didn't give me any eureka moments either, and so I'm here. A few questions:

  • In a VOR approach, if your route is already programed into the FMC, what good does it do to dial in the VOR-frequency when the FMC is going to line you up with the runway anyway? And if I do use the LOC/VOR button, does the VOR course preside the FMC's programed waypoints?
  • I've found that LAND 3 only appears in ILS approaches. What about LAND 2? I don't think I've ever seen it. And if we have Land 2 and 3, what ever happened to 1?
  • How exactly does an NDB approach work? I know how to work the ADF itself, but how does the APP-button come into play? I'm getting the SINGLE CH message - sometimes in amber, sometimes in green. What's the difference here?

Thanks :)

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In a VOR approach, if your route is already programed into the FMC, what good does it do to dial in the VOR-frequency when the FMC is going to line you up with the runway anyway?

 

One probably that VOR and LNAV may have different MDA or there is some authorised way of flying this approach. Thought NGX mostly have good ANP so LNAV is very precise you can stay in it for the approach.

 

 

 


And if I do use the LOC/VOR button, does the VOR course preside the FMC's programed waypoints?

 

Yes.

 

 

 


I've found that LAND 3 only appears in ILS approaches. What about LAND 2? I don't think I've ever seen it. And if we have Land 2 and 3, what ever happened to 1?

 

There is no LAND 1. Land 3 and 2 show capabilities of the autopilot. Land 3 shows maximum availability of the aircraft systems and functions. LAND 2 and NO AUTOLAND show the degradated status caused by some failures.

 

 

 


but how does the APP-button come into play? I'm getting the SINGLE CH message - sometimes in amber, sometimes in green. What's the difference here?

 

Green single channel means that you're flying itegrated approach navigation. It's FMC-calculated lateral and vertical path for the approach shown in ILS format. You can use it with non-presision, non-offset, constant-angle approaches. Search "IAN" in FCOM and FCTM for details.

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In a VOR approach, if your route is already programed into the FMC, what good does it do to dial in the VOR-frequency when the FMC is going to line you up with the runway anyway? And if I do use the LOC/VOR button, does the VOR course preside the FMC's programed waypoints?

 

If it is a VOR approach, you must use the VOR signal, unless it is an RNAV overlay approach, where it will have both in the title.  In any case where the approach does not include some form of RNAV or GPS in the title, RNAV data data displayed on the ND may only be used to identify progress on the approach.  The approach itself must be flown using the "raw data" or the signal from the navaid itself.

 

The reason for this is that the approach was written to be flown using the signal from the navaid.

 

Additionally, if your aircraft's initial position was entered incorrectly, you could have a position shift, where the plane thinks it's in a different location than it really is.  This would affect any tracking on LNAV, relying on the IRS/GPS, but it would not affect your VOR/ADF/ILS tracking capabilities.  Even if the plane is physically sitting at IAD, I can key in the coordinates for MIA for the initial position, and the plane will believe it's is sunny south Florida, instead of right outside the Nation's Capital.  Try flying an RNAV approach after that kind of blunder.

 

 

 


I've found that LAND 3 only appears in ILS approaches.

 

ILS approaches are the only approaches from which you can conduct an autoland (and only a select few are approved, at that).  These planes do not always land themselves, despite the belief of all too many simmers out there...

 

 

 


How exactly does an NDB approach work? I know how to work the ADF itself, but how does the APP-button come into play?

 

The ADF is not linked into the autopilot in any way.  If you want to fly an NDB approach using the autopilot, you would have to use HDG SEL with V/S.

 

I'm getting the feeling you don't like flying the plane with your hands.  It's not really that scary.

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Even if the plane is physically sitting at IAD, I can key in the coordinates for MIA for the initial position, and the plane will believe it's is sunny south Florida, instead of right outside the Nation's Capital. Try flying an RNAV approach after that kind of blunder.

 

People already tried something along those lines, and predictably it didn't end well. See https://en.wikipedia.org/wiki/Aeroflot_Flight_821 (although a lot more went wrong on that flight than just a misaligned inertial reference system, and you'll have to delve into the actual accident report to learn how that factored into the sorry chain of events that led to the flight's demise).

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People already tried something along those lines, and predictably it didn't end well. See https://en.wikipedia.org/wiki/Aeroflot_Flight_821 (although a lot more went wrong on that flight than just a misaligned inertial reference system, and you'll have to delve into the actual accident report to learn how that factored into the sorry chain of events that led to the flight's demise).

 

Interesting.  I'll have to take a look.  Thanks!

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If it is a VOR approach, you must use the VOR signal, unless it is an RNAV overlay approach, where it will have both in the title.  In any case where the approach does not include some form of RNAV or GPS in the title, RNAV data data displayed on the ND may only be used to identify progress on the approach.  The approach itself must be flown using the "raw data" or the signal from the navaid itself.

 

That is not neccessarilly true. You can often fly the approach in LNAV/VNAV or IAN overlay with raw data monitoring. Sometimes even without monitoring.  A lot depends on what the airline got certified for.

 

 

 


Additionally, if your aircraft's initial position was entered incorrectly, you could have a position shift, where the plane thinks it's in a different location than it really is.  This would affect any tracking on LNAV, relying on the IRS/GPS, but it would not affect your VOR/ADF/ILS tracking capabilities.

 

If the shift is small, the airplane should update itself to correct position using GPS and DME/DME updating. Still, not really a good idea without at least monitoring raw data.

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That is not neccessarilly true. You can often fly the approach in LNAV/VNAV or IAN overlay with raw data monitoring. Sometimes even without monitoring.  A lot depends on what the airline got certified for.

 

You're right.  I was answering for GPS instead of VOR, and not to IAN.  Thanks for the correction!

 

As far as IAN procedures/certifications go, you're saying it's tied to the OpSpec?

 

 

 


If the shift is small, the airplane should update itself to correct position using GPS and DME/DME updating. Still, not really a good idea without at least monitoring raw data.

 

True.  That's why used such a large deviation, though I could've made that a little more clear.

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As far as IAN procedures/certifications go, you're saying it's tied to the OpSpec?

 

As I am told, you can fly it in LNAV/VNAV overlay without any specific cert, if you are cross-checking with raw data.

You need cert to fly it without raw data display (might need NPS though?)

This is not 100% confirmed true and in Europe.

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As I am told, you can fly it in LNAV/VNAV overlay without any specific cert, if you are cross-checking with raw data.

You need cert to fly it without raw data display (might need NPS though?)

This is not 100% confirmed true and in Europe.

 

Fair enough.  That's better information than I've been able to pull out of the official sources over here in FAA land.  It makes sense.

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