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Driver170

Overlay approaches

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My understanding of an overlay approach is when you use the GPS when doing a NPA. Ie the VOR APCH is selected from the DB

 

But then i found this -

 

Note: What is an “overlay” approach? If the approach to be flown is not in the FMC database, another approach having the same profile and plan view may be selected.

 

That note sounds alot different to what i think it is? Can anyone clear this up?

 

Thanks.

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That note sounds alot different to what i think it is? Can anyone clear this up?

 

This is what happens when someone spends too much time in "real world pilot" forums where either the "pilots" don't know what they're talking about, or are poor at communicating it.

 

Ignore what that person said, honestly.

 

An overlay approach is an approach that is designed off of an "old nav" non-precision approach. By and large, most of these approaches are gone (or being phased out), in favor of newer procedures specifically developed as RNAV approaches. They were essentially a stopgap between the old style VOR/NDB-based approaches and tailored RNAV approaches: instead of waiting to introduce RNAV/GPS approaches as their own thing, the administration created a "GPS" version by simply using the existing procedure.

 

In the case of the 737, different airline SOPs require different things when selecting VOR or NDB approaches from the database (often noting that the raw data must be displayed, and the waypoints/path display on the ND is for situational awareness). If an RNAV approach is available, though, then that should be used (again, most airline SOPs will state that the "most precise" option be used, and RNAV is more precise than VOR/NDB).

 

This is an example:

gps_overlay.jpg

 

Note the "[Old Style Nav] or GPS." This is an overlay. Everything else is a dedicated approach.

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I got that NOTE from a PDF on smartcockpit.

 

Thanks for that explanation and a bit of history learning there.

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I got that NOTE from a PDF on smartcockpit.

 

Weird. It sounds so very...awkward as a note. Then again, SmartCockpit has some odd stuff up there because it can't be the actual, licensed stuff.

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Yeh exactly, weird! Thats why i brought it on here.

 

Well, thanks for doing that, and sorry for assuming it was another PPRuNe pull. I'd assumed someone was responding directly to one of your questions like that...

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Haha no worrys!

 

If your doing a VOR apch out of the FMS do you need the navaid to be seviceable?

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If your doing a VOR apch out of the FMS do you need the navaid to be seviceable?

 

Yes, and it should be displayed, too. The loaded procedure should be used for secondary reference only.

 

Think of it like an ILS. You can load the ILS and use the data on the ND for cross-reference, but the actual approach is flown off of the raw data. The GPS data for the fixes can be used in lieu of DME, or cross radial data, however, so that additional data/reception is not required.

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Haha no worrys!

 

If your doing a VOR apch out of the FMS do you need the navaid to be seviceable?

 

If there is no reference to GPS in the approach title than yes, the navid needs to be operational and the raw data needs to be monitored.  An overlay approach will have "or GPS" in the approach title, for example "VOR or GPS RWY 27".  If that is the case the navid does not need to be operational because the approach can be flown by GPS alone.

 

VOR RWY 27 - the navaids must be operational and monitored

VOR or GPS RWY 27 - the navaids do not need to be operational.

 

I'd have to check but I'm almost certain both examples would only show up as VOR 27 in the FMC database so you need to look at the approach plate to determine if you need the navaid or not.

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Well that sounds right joe ;) well of course you are the pilot !

 

Does the NGX or the NG fly DME arcs or RF legs ?

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Well that sounds right joe ;) well of course you are the pilot !

 

Does the NGX or the NG fly DME arcs or RF legs ?

The real plane can fly RF legs.  It's been a long time since I've flown an ARC and have never tried it in the 737.  I'd have to look and see if the ARC transitions are coded in the database.  If they are then the plane could fly them.

 

I don't know if the NGX can do it.  I don't think RF legs are supported.  You can always fly a poor man's arc by putting a circle around the navid on the fix page and use that to guide yourself around while monitoring the DME raw data to keep it legal.

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Cheers joe its okay don't worry! All my addon airports don't have those arcs so i'll never do it.

1 other thing i just watched a 737 NG video on youtube they were cruising at FL400 but on the ND during descent they had T/D-FL260 why did they renter another cruise ALT

 

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why did they renter another cruise ALT

 

 

They didn't. They had a FL260 crossing restriction at NOS01 and the T/D is saying where the plane will continue the descent from FL260.

 

The plane will do DME arcs, as well, you just select the correct transition if it's available. I've done them in Korea quite a few times and in Mexico, as well. I don't think I've done any in the US in the 737.

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Just guessing, but I would presume the difference is because the aircraft in the video is set up to calculate idle descent paths from each crossing altitude, whereas the NGX calculates a continuous geometric descent path (and therefore there is no intermediate T/D point).

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Just guessing, but I would presume the difference is because the aircraft in the video is set up to calculate idle descent paths from each crossing altitude, whereas the NGX calculates a continuous geometric descent path (and therefore there is no intermediate T/D point).

 

That was my guess, too.

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A slight spin on the overlay approaches already mentioned is where the crew 'create' FMS waypoints commensurate with the desired approach and fly them in sequence, with reference to the primary aid.

 

For example, a straight in VOR could easily be coded by the crew and flown using the FMS - but to be legal the aircraft must be navigated by the required navaid - probably goes without saying it can be fraught to do it this way, but its an option if you ever need it I suppose.

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For example, a straight in VOR could easily be coded by the crew and flown using the FMS - but to be legal the aircraft must be navigated by the required navaid - probably goes without saying it can be fraught to do it this way, but its an option if you ever need it I suppose.

 

Every airline I have worked for prohibits this.  Approaches flown with RNAV are required to be selected from the database.  Pilot created approaches are not allowed.

 

There may be operators that allow this but it would be rare indeed.

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Every airline I have worked for prohibits this.  Approaches flown with RNAV are required to be selected from the database.  Pilot created approaches are not allowed.

 

Its in the FCTM black and white

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Procedures must be in the database; this is not only an airline or manufacturer requirement but is a regulatory requirement.  Very simply, a clearance is required for an approach and unless the approach is published (or otherwise vetted) there is no clearance.  To stretch it, if you are cleared to a VOR approach and you used a pilot-created overlay to take advantage of GPS tracking and do not track the raw-VOR signal then you'll illegally flying an approach.  I cannot imagine a qualified pilot ever doing this.  There's just too many pitfalls.

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A slight spin on the overlay approaches already mentioned is where the crew 'create' FMS waypoints commensurate with the desired approach and fly them in sequence, with reference to the primary aid.

 

For example, a straight in VOR could easily be coded by the crew and flown using the FMS - but to be legal the aircraft must be navigated by the required navaid - probably goes without saying it can be fraught to do it this way, but its an option if you ever need it I suppose.

 

 

Every airline I have worked for prohibits this.  Approaches flown with RNAV are required to be selected from the database.  Pilot created approaches are not allowed.

 

There may be operators that allow this but it would be rare indeed.

 

 

Its in the FCTM black and white

 

 

Procedures must be in the database; this is not only an airline or manufacturer requirement but is a regulatory requirement.  Very simply, a clearance is required for an approach and unless the approach is published (or otherwise vetted) there is no clearance.  To stretch it, if you are cleared to a VOR approach and you used a pilot-created overlay to take advantage of GPS tracking and do not track the raw-VOR signal then you'll illegally flying an approach.  I cannot imagine a qualified pilot ever doing this.  There's just too many pitfalls.

 

This one, as mentioned by Joe is one of those parts of what I call 'greyviation,' where this issue is addressed by regulation, but not directly. The FAA stance on the matter is that any approach to be flown must be loadable from the database directly. No exceptions are made for where the actual reference is: AIM 1-1-19f1(B) Equipment and Database Requirements - For IFR Operations "All approach procedures to be flown must be retrievable from the current airborne navigation database..."

 

I'm sure company OPSpecs make that even more clear. A good example of why this is required is that it's far more common to have pilots fat-finger waypoints than you'd think. That, or they misinterpret their spelling. I was flying around with my old college roommate and good pilot friend one day, shooting the RNAV approach into Harford County (0W3, if anyone is interested in attempting to land a smaller plane on a 40x2000 foot runway). In order to skirt some airspace, he told me to fly to "Lindsay." I translated this to LINZE, when the fix intended was LINSE. Luckily, I knew that I needed to go ENE, and noticed that the GPS wanted to take me due south (LINZE is in Florida). I tried the alternate spelling just as he looked up and realized he should probably spell it out. Stuff like this is actually a big issue on the NATs, too, particularly with the ARINC 424 lat/lon points: N4240 versus 4240N. Which one do you need? Don't know? If you fly across the NATs without knowing, a report of it will likely come across my desk...

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Stuff like this is actually a big issue on the NATs, too, particularly with the ARINC 424 lat/lon points: N4240 versus 4240N. Which one do you need? Don't know? If you fly across the NATs without knowing, a report of it will likely come across my desk...

 

Indeed -- and one of the reasons why I would always recommend entering the long-format lat/long (N42W040) rather than the abbreviated waypoints!

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This one, as mentioned by Joe is one of those parts of what I call 'greyviation,' where this issue is addressed by regulation, but not directly. The FAA stance on the matter is that any approach to be flown must be loadable from the database directly. No exceptions are made for where the actual reference is: AIM 1-1-19f1(B) Equipment and Database Requirements - For IFR Operations "All approach procedures to be flown must be retrievable from the current airborne navigation database..."

 

I'm sure company OPSpecs make that even more clear. A good example of why this is required is that it's far more common to have pilots fat-finger waypoints than you'd think. That, or they misinterpret their spelling. I was flying around with my old college roommate and good pilot friend one day, shooting the RNAV approach into Harford County (0W3, if anyone is interested in attempting to land a smaller plane on a 40x2000 foot runway). In order to skirt some airspace, he told me to fly to "Lindsay." I translated this to LINZE, when the fix intended was LINSE. Luckily, I knew that I needed to go ENE, and noticed that the GPS wanted to take me due south (LINZE is in Florida). I tried the alternate spelling just as he looked up and realized he should probably spell it out. Stuff like this is actually a big issue on the NATs, too, particularly with the ARINC 424 lat/lon points: N4240 versus 4240N. Which one do you need? Don't know? If you fly across the NATs without knowing, a report of it will likely come across my desk...

Mmm. Greyvi.

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