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H. Simpson
Topic Author
Posts: 933
Joined: Sat Mar 10, 2001 7:30 am

GPS = Nonprecision App?

Thu Aug 30, 2001 4:56 am

Hi everybody!

i was wondering is GPS consider a non-precision approach? Since it does not provide glide slope information and localizer. Only the heading to fly...

What about RNAV, is it also like GPS? using longitude and latitude...
 
Ralgha
Posts: 1589
Joined: Tue Nov 09, 1999 6:20 pm

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 5:13 am

Yes, both GPS and RNAV are non-precison approaches.

Actually, GPS can be considered a form of RNAV (Area Navigation), but most RNAV computers use VOR radials and DME distances to define waypoints, which it uses to form the route.  Big thumbs up
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Sunken_Lunken
Posts: 87
Joined: Sat Jul 07, 2001 2:48 am

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 5:27 am

Hey Homer!

An approach has to provide vertical guidance (usually the glideslope of an ILS) in order to be a precision approach. So, technically the way a runway is equipped determines if it has a precision approach or not.

As far as an airplane's capabilities are concerned, I believe you can dial in a localizer freq. on some GPS units, and have the CDI driven by the GPS.

However, I think most published GPS approaches are non-precision approaches (if glideslope were available, it would probably be published as an ILS).

Hope this helps!  Smile
 
XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 6:00 am

Actually.. there are newer VNAV GPS approaches now that have vertical profile guidance. I havent researched much into them, but they may be precision type approaches.
Chicks dig winglets.
 
cv640
Posts: 843
Joined: Wed Aug 30, 2000 8:10 pm

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 6:33 am

Right now GPS approaches are non poresicions. I know they are working on allowing some precision approcahes, but that is still a few years away. Be advised though that not all GPS's are approved for approaches, and even if they are they must be kept up to date. Also there must be a published approach(GPS) in order to shoot one.
 
Guest

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 12:54 pm

We are able to fly the new GPS-RNAV approaches, but I've only done them in actual conditions once or twice. They seem to work extremely well. The ones at Phillips, WI wil get you down to about 450' AGL and 1-3/4 mile for our Category C aircraft. I remember seeing one that had minimums of 250' or 300' and 3/4 mile which, for all intents and purposes puts it right in there with an ILS. As far as accuracy goes, they're pretty amazing - I'm our company's FMS and EFIS training captain and one of the demonstrations that I give our people is to set up the ILS on one pilot's instruments and the GPS (with VNAV) on the other pilot's side. The needles never get more than 1/4 dot away from each other and usually they're right on. That's pretty good. As accurate as the new GPS approaches are, I foresee the day when ILS approaches will be a thing of the past. The ground equipment is very costly to install and maintain.
 
Guest

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 1:30 pm

Like Jetguy says the GPS is amazingly accurate and even for today, its accuracy could arguably be used for a precision type (say CAT I) approach. However, it will never be approved by the FAA in its current form (GPS navigator or GPS-inputted FMS).

It's not the accuracy that is the main issue, it is the integrity (say against jamming, interference, etc.) and the availability (signal coverage, RAIM) that is of concern.

The FAA has been working for several years on the LAAS system (see http://avstop.com/GPS/laas.html).

LAAS is basically a differential GPS system (use of a ground station to measure GPS errors, send to airborne receivers for filtering out errors, thus resulting in super accurate data). The accuracy demonstrated during tests was phenomenal, except the current LAAS comes up short of the integrity goal so it will be a while before this is fielded.

BTW, the FAA had approved at least one SCAT1 (special category CAT1) differential GPS system, built by Honeywell for Northwest I believe; which is the forefather of LAAS. Except this system was never used beyond trial periods. I suppose it is more expensive to operate than ILS given stringent requirements for maintaining the airborne equipment as well as the differential GPS ground station -- custom tailored to each airport.

Regards,
Nut
 
Guest

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 2:25 pm

They were going to instal a glideslope at YKA but they figured the mountains would interfere. Since the airport is trying to get westjet here(they require an ILS) the airport authority said the people responsible for airport navigation will look into other alternatives, the most likely being a GPS, which quote "Will be cheaper and faster to instal" then the glidepath.

Could they be refering to the SCAT1? If not, is Canada subjected to the FAA's approvences(sp?.....is there even such a word?....you know what I mean)?
 
Guest

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 2:34 pm

Now it came to me, the word is "approvals"....cant belive I couldnt remember it.
 
Guest

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 3:17 pm

Hi CYKA,
Canada has its own aviation authority. The FAA and the Canadian authority has a bilateral agreement, basically honoring each other's certifications.

I know of at least 2 countries (Norway and Canada) who can't wait for LAAS to be fielded and are trying to get SCAT-1 installed, especially for the Dash-8s that operate in pretty demanding airports. The US FAA has all but abandoned SCAT-1 in favor of LAAS.

Regards,
Nut
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: GPS = Nonprecision App?

Thu Aug 30, 2001 11:38 pm

You don't need "glideslope" for precision approaches. There are plenty of "localizer only" precision approches out there.

Also, if an aircraft has a GPS system or FMS system that allows the display of glideslope vertical guidance coincidentily with GPS lateral guidance, it doesn't meet the regulatory requirements (It isn't legal) as far as the FAA and Transport Canada are concerned. There are a few out there though. The dangerous thing is that all approved published GPS approaches DO NOT give you guidance down the centeline of the runway. They give you guidance to the fina approach fix (FAF). Relatively few GPS approaches leave the aircraft lined up with the runway at the FAF, so following the associated glideslope could lead the aircraft to local obstructions off of the ILS path.

 
H. Simpson
Topic Author
Posts: 933
Joined: Sat Mar 10, 2001 7:30 am

RE: GPS = Nonprecision App?

Fri Aug 31, 2001 12:01 am

Ok, thanks...DOH!
 
Guest

RE: GPS = Nonprecision App?

Fri Aug 31, 2001 12:39 am

Airplay...
I thought that, by definition, LOC approaches were non-precision. As far as I know, there are only three types of precision approaches in common usage - ILS, MLS, and PAR. And out of those three, only the ILS is normally used - MLS never really caught on and the PAR is usually only available at military airfields. Our Universal UNS1-C FMSes are approved for both lateral and vertical approach guidance and have been for years. This equipment is in all of the corporate jets that have been sold for the past 10 or 15 years. It isn't anything new. The FMSes simply overlay a "psuedo-glideslope" over the non-precision approach path. Very reliable and much, much safer since it allows the crew to fly a stabilized approach without the "dive and drive" requirements of the typical non precision approach profile. It's been a long time since I've flown a VOR, LOC, GPS, or NDB approach without vertical guidance. It's very nice and very easy - for all intents and purposes every approach is flown as if it were an ILS. As far as centerline alignment is concerned offset localizer approaches as well as SDF approaches are not uncommon - in those cases the minimums are simply increased accordingly.
Jetguy
 
XFSUgimpLB41X
Posts: 3961
Joined: Fri Aug 25, 2000 1:18 am

RE: GPS = Nonprecision App?

Fri Aug 31, 2001 12:51 am

Airplay.. that is incorrect... A localizer only approach drops you down into the non-precision category.
Chicks dig winglets.
 
airplay
Posts: 3369
Joined: Sat Oct 25, 2003 1:58 am

RE: GPS = Nonprecision App?

Fri Aug 31, 2001 11:55 pm

Whoops....yes I am wrong

Thanks for the correction. I was using the word "precision" in the engineering context and not the pilot context and wrongly assuming they were interchangeable.

A localizer offers lateral "precision" that the GPS cannot offer reliably, but a localizer only approach is not a "precision approach".

Sorry for the mis-information.

 
iwantanL1011
Posts: 148
Joined: Thu Jul 27, 2000 12:24 am

RE: GPS = Nonprecision App?

Mon Sep 03, 2001 10:49 am

no, gps isnt precision by definition, but I honestly am more comfortable shooting a GPS approach down to minimums than a localizer approach, certainly more than a VOR/NDB approach.. Many GPS approaches now have lower minimums than any other approach on the field. I'm talking about GPS approaches designed for GPS,not ndb overlays. These approaches are extremely precise. I like them better than LOC because the sensitivity remains constant throughout the approach (with my unit, after crossing FAF)

the LOC is very insensitive at FAF, and sooooo sensitive near DH. the GPS just seems very consistent.

the other benefit is situational awareness from the moving map. the downside: can be tricky if your unit decides not to cooperate with the instructions you gave it. GPS units talk back sometimes... LOC/GS receivers dont.

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