JulianUK
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NDB/VOR Vs GPS Approaches

Wed May 17, 2006 7:23 am

If you are flying to an airport with only an NDB or an NDB/VOR would you now choose GPS for the approach and would GPS give you lower minimums than a typical NDB or VOR approach? I would be very interested in learning exactly what happens for a modern airliner on an NDB or VOR only available at an airport, and whether GPS comes into play at all - and also what the minimums are in terms of weather/visibility for these kind of approaches.

J
 
Ralgha
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RE: NDB/VOR Vs GPS Approaches

Wed May 17, 2006 7:40 am

Quoting Julianuk (Thread starter):
If you are flying to an airport with only an NDB or an NDB/VOR would you now choose GPS for the approach

You can only do that if the NDB or VOR approach has a GPS overlay on it, and your GPS has the approach in its database. If both conditions are met, then I'd probably do the GPS approach.

Quoting Julianuk (Thread starter):
would GPS give you lower minimums than a typical NDB or VOR approach?

If it's an overlay, no. A stand alone basic GPS approach gives minimums that are generally comperable to VOR approaches. Usually lower than NDB approaches.

Quoting Julianuk (Thread starter):
I would be very interested in learning exactly what happens for a modern airliner on an NDB or VOR only available at an airport, and whether GPS comes into play at allIf you are flying to an airport with only an NDB or an NDB/VOR would you now choose GPS for the approach and would GPS give you lower minimums than a typical NDB or VOR approach? I would be very interested in learning exactly what happens for a modern airliner on an NDB or VOR only available at an airport, and whether GPS comes into play at all - and also what the minimums are in terms of weather/visibility for these kind of approaches.

Legally the GPS can only come into play if the approach is a GPS approach (whether overlay or standalone). However, it's not uncommon to find the GPS used for situational awareness when flying a VOR or NDB approach. It's not primary navigation data though. Flying a VOR or NDB approach in an airliner is a bit more work than an ILS since you have to keep track of the stepdowns, but it's nothing too exciting.

The minimums depend on the individual approach and vary widely depending on terrain and other factors. Some may leave you as high as 1500 feet above the ground, others may get you down within 500 feet of the ground.
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KELPkid
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RE: NDB/VOR Vs GPS Approaches

Wed May 17, 2006 7:45 am

Quoting Julianuk (Thread starter):
If you are flying to an airport with only an NDB or an NDB/VOR would you now choose GPS for the approach

Depends on the GPS installation (for me at least). Some GPS'es make setting up an approach a piece of cake, others make you enter an entire frickin' flight plan just to shoot an approach. GPS approaches, once set up, are much more forgiving to fly, and you have the added benefit of a two dimensional "video game" display to show you where you are-makes things MUCH nicer.

Quoting Julianuk (Thread starter):
would GPS give you lower minimums than a typical NDB or VOR approach?

Depends. In the US, many GPS approaches are overlays for an existing NDB or VOR approach, and the minimums are the same. A dedicated GPS approach (one with no equivalent NDB, VOR, or LOC procedure), IIRC, do have lower minumums, but not as low as a precision approach (ILS). However, with WAAS in the US, vertical guidance will now be a part of many GPS approaches, and we will start seeing ILS-like minumums for WAAS-equipped aircraft.

Brent
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JulianUK
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RE: NDB/VOR Vs GPS Approaches

Wed May 17, 2006 8:02 am

Interesting are there any approaches that use GPS coupled with a VNAV profile and do the whole thing themselves both vertically and horizontally or is that still in the future?
 
KELPkid
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RE: NDB/VOR Vs GPS Approaches

Wed May 17, 2006 9:23 am

Quoting JulianUK (Reply 3):
Interesting are there any approaches that use GPS coupled with a VNAV profile and do the whole thing themselves both vertically and horizontally or is that still in the future?

You mean like this one  Wink http://204.108.4.16/d-tpp/0604/00361RZ31.PDF

There is a story behind that-Apollo Avionics (now a division of Garmin) is located at SLE, and yes, they certified the first WAAS-enabled VNAV capable GPS for GA aircraft...the Apollo CNX80. The Cessna 172 I regularly rent for my instrument currency happens to have one of those, along with an MX20 moving map display.
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Mir
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RE: NDB/VOR Vs GPS Approaches

Wed May 17, 2006 2:12 pm

If a VOR approach had an overlay, I'd probably still fly the VOR - it's much less work to put in the right frequency and radial than deal with the GPS, and the accuracy is pretty much the same unless you're really far away from the VOR. If it was an NDB approach with an overlay, however, I'd sure as hell do the GPS, since the GPS is going to be noticably more accurate than the NDB.

Of course, my GPS has to be IFR certified with a current database, etc.

-Mir
7 billion, one nation, imagination...it's a beautiful day
 
Tom12
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RE: NDB/VOR Vs GPS Approaches

Thu May 18, 2006 11:59 pm

I was under the impression that GPS wasn't permited. I thought airlines couldn't use it as it was Uncle Sam's sattelite's?
"Per noctem volamus" - Royal Air Force Bomber Squadron IX
 
JulianUK
Posts: 105
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RE: NDB/VOR Vs GPS Approaches

Fri May 19, 2006 4:41 am

I believe it is all down to minimums. GPS systems used in modern aircraft have a cross check method that continually take a dip sample from 3 then 4 then 5 then 6 satellites and so on. If it finds by bringing in one satellite that its position calculation varies dramatically it cuts out the information from that satellite deciding it is transmitting incorrectly. So it is quite clever.

However perhaps some pilots out there would take us through an approach to say a Greek Island or somewhere that only has NDB/VOR approaches available and how they would do it..
 
Mir
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RE: NDB/VOR Vs GPS Approaches

Fri May 19, 2006 6:13 am

Quoting JulianUK (Reply 7):
However perhaps some pilots out there would take us through an approach to say a Greek Island or somewhere that only has NDB/VOR approaches available and how they would do it..

It's really not that difficult. If you're getting vectors to final, just put in the right frequency and course, intercept it just like an ILS, and follow it in just like an ILS. The only difference is that the minimums are higher, and you have to follow the stepdown altitudes - try to get down to each one as soon as possible so that you have the best chance of seeing the runway (within reason, obviously you want a stable, controllable descent rate).

If you're not getting vectors, there's generally a procedure turn or DME arc somewhere in there, but that's not too difficult either - worst case scenario you'll have to do some fiddling around with frequencies while flying the approach, which can mess around with your situational awareness if you don't plan for it.

-Mir
7 billion, one nation, imagination...it's a beautiful day

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