GPS approaches question.

Holocene

Well-Known Member
Are there currently any GPS installations capable of providing vertical guidance during the approach phase, and that are approved for use??? Or is ILS presently the only option for a precision approach?

It's gonna be tough trying to learn about all this stuff after getting my private in a 40 year-old plane.
 

tgrayson

New Member
ILS presently the only option for a precision approach?
There are GPS approaches that provide vertical guidance, but they aren't considered "precision" approaches; they're called "approaches with vertical guidance."

The AIM has comprehensive info on this stuff.
 

jrh

Well-Known Member
Are there currently any GPS installations capable of providing vertical guidance during the approach phase, and that are approved for use??? Or is ILS presently the only option for a precision approach?
Yes, it's a feature of some GPS receivers called "WAAS" (Wide Area Augmentation System) and it's pretty amazing. Almost all new aircraft have this feature now, and a lot of older aircraft are getting retrofitted with it. It is basically receiving extra information that makes the location computation more precise, and therefore allows for vertical guidance as well as horizontal guidance. The idea is that with old receivers, let's say they miscalculated your location by 300 feet...for lateral guidance, that's no big deal. But imagine being 300 feet lower than you're supposed to...that's huge when you're supposed to be 500 feet off the ground, or whatever the approach calls for. WAAS allows a GPS to figure your position in space much more precisely, so maybe it's 10 feet off, but the difference between 240 versus 260 feet is no big deal when you're supposed to be at 250 feet AGL.

It's gonna be tough trying to learn about all this stuff after getting my private in a 40 year-old plane.
No worries, just fly a nicely equipped plane for your instrument training!
 

Holocene

Well-Known Member
Yes, it's a feature of some GPS receivers called "WAAS" (Wide Area Augmentation System) and it's pretty amazing. Almost all new aircraft have this feature now, and a lot of older aircraft are getting retrofitted with it. It is basically receiving extra information that makes the location computation more precise, and therefore allows for vertical guidance as well as horizontal guidance. The idea is that with old receivers, let's say they miscalculated your location by 300 feet...for lateral guidance, that's no big deal. But imagine being 300 feet lower than you're supposed to...that's huge when you're supposed to be 500 feet off the ground, or whatever the approach calls for. WAAS allows a GPS to figure your position in space much more precisely, so maybe it's 10 feet off, but the difference between 240 versus 260 feet is no big deal when you're supposed to be at 250 feet AGL.
Thanks.

So theoretically, this technology would enable you to make an instrument approach into a grass strip?
 

kgflyboy

New Member
Thanks.

So theoretically, this technology would enable you to make an instrument approach into a grass strip?
Yes, and it's pretty useful. Since GPS approaches don't require any expensive ground equipment, it's easy for small rural airports to have instrument approaches that didn't use to.
 

bdhill1979

Gone West
Are there currently any GPS installations capable of providing vertical guidance during the approach phase, and that are approved for use??? Or is ILS presently the only option for a precision approach?

It's gonna be tough trying to learn about all this stuff after getting my private in a 40 year-old plane.
You probably already know this but there are a lot of people out there that think crazy things about GPS, and the wording can mislead a lot of people.

There are no "GPS installations", per se; as in the airport you are flying an approach to needs ZERO equipment on the ground to be WAAS capable. There is no "glideslope" being beamed up into the sky. The "glideslope" is in your GPS database. To have WAAS availability the airport just needs to be within WAAS service area, which is now pretty much the entire US.

There are ground stations that measure atmospheric distortion and send that info up to the two upper orbit satellites that sent out the corrective signal that makes WAAS so accurate. However those stations do not send any signal directly to your receiver(though some publications say they do), they send the signal to a command center, then an uplink station, then up to the satellites, then down to your receiver.
 

Murdoughnut

Well sized member
While we're on the subject ... what is required for enroute navigation using GPS? I have an IFR approved GPS unit in my a/c that does not have WAAS, but does have RAIM integrity monitoring ... can I fly T or Q routes? My understanding is that you can fly them as long as you can use VOR nav as a backup - is that correct?
 

bdhill1979

Gone West
While we're on the subject ... what is required for enroute navigation using GPS? I have an IFR approved GPS unit in my a/c that does not have WAAS, but does have RAIM integrity monitoring ... can I fly T or Q routes? My understanding is that you can fly them as long as you can use VOR nav as a backup - is that correct?
I can't remember the exact paragraph, but the AIM now clearly states that monitoring the VOR is unnecessary if you meet the criteria listed.

Edit:
AIM 1-2-3: A-2

Also check out AC 90-100A U.S. Terminal and En Route Area Navigation (RNAV) Operations
 

kiloalpha

Well-Known Member
Thanks.

So theoretically, this technology would enable you to make an instrument approach into a grass strip?
You could have a non-precision approach into a grass strip but it would have to have LNAV/VNAV or LNAV approach.

In order for a runway to have an WAAS approach with less than 1sm vis (LPV), it needs to have the same qualifications to have an ILS approach, such as runway lighting, parallel taxiway, precision approach markers, ect.
 

bdhill1979

Gone West
You could have a non-precision approach into a grass strip but it would have to have LNAV/VNAV or LNAV approach.

In order for a runway to have an WAAS approach with less than 1sm vis (LPV), it needs to have the same qualifications to have an ILS approach, such as runway lighting, parallel taxiway, precision approach markers, ect.
:yeahthat:Advisory Circular 150/5300-13 spells out the specifics for an airport to meet precision approach requirements.
 

awacs94

Well-Known Member

MidlifeFlyer

Well-Known Member
Garmin LPV = precision approach.
FAA LPV = non precision.

Dunno why.
Strictly a definition issue. A LPV is not a precision approach because it's not a precision approach. I think it may have something to do with ICAO requirements.
 
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