Help with GPS (RNAV) approaches

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confusedalot
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Re: Help with GPS (RNAV) approaches

Post by confusedalot »

I guess that I have been spoiled by good equipment, so here is my question out of curiosity.

Could some types of general aviation GPS enroute and non precision approach certified equipment also have vertical (VNAV) guidance that would suffice without having a WAAS platform? it would sure save alot of grief of looking at those CDA constant descent angle charts.

I flew a bizjet for ahwile with a universal fms and it seems to me that it had it, but that was a while ago and my memories of it are fuzzy.
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photofly
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Re: Help with GPS (RNAV) approaches

Post by photofly »

I have tried several times to find a definitive answer to that, and failed.

I have an older GPS, non-WAAS, that gets a barometric altitude from the transponder encoder to improve RAIM availability. Even though it has that, it doesn’t qualify for LNAV/VNAV.

There is a TC document that goes into fearsome detail what kind of equipment and paperwork is required for an OC holder to conduct LNAV/VNAV approaches but it doesn’t say what a privately registered aircraft would need.
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AuxBatOn
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Re: Help with GPS (RNAV) approaches

Post by AuxBatOn »

How does baro altitude help with RAIM availability?!
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photofly
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Re: Help with GPS (RNAV) approaches

Post by photofly »

It reduces the number of satellites required to be in view:

https://www.faa.gov/about/office_org/he ... FSheet.pdf
“Barometric Aiding (Baro-Aiding)
Barometric aiding is an integrity augmentation that allows a GPS system to use a non-satellite input source (e.g. the aircraft pitot-static system) to provide vertical reference and reduces the number of required satellites from five to four. Baro-aiding requires four satellites and a barometric altimeter input to detect an integrity anomaly. The current altimeter setting may need to be entered into the receiver as described in the operating manual. Baro-aiding satisfies the Receiver Autonomous Integrity Monitoring (RAIM) requirement in lieu of a fifth satellite.”

My GPS receiver AFMS says much the same thing, and the unit does indeed require the altimeter setting to be entered prior to commencing an approach.

Note: that FAA document answers some of the other questions posed in this thread, too. The OP should read it.
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Cessna 180
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Re: Help with GPS (RNAV) approaches

Post by Cessna 180 »

AuxBatOn wrote: Thu Dec 14, 2017 9:12 pm How does baro altitude help with RAIM availability?!
I believe the GPS unit needs VNAV ability? I've used VNAV before on older G1000 installations without WAAS (never for an approach however) and I believe this would qualify for an LNAV/VNAV approach. I've also done multiple LNAV/VNAV approaches using non-wass FMS 3000 approaches on older Pro Line 21 King Airs and its similar to the way you shoot an approach on the G1000.
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Re: Help with GPS (RNAV) approaches

Post by CpnCrunch »

ahramin wrote: Wed Dec 13, 2017 3:06 pm Every simulator PPC I have ever done all approaches were at the same airport. I would question the instructor on where this idea came from.
I talked to the examiner who this information came from, and he confirms this. Here is what the examiner's guide says for the instrument rating:

"The candidate will normally perform two different approaches on different approach facilities, where they are available"

According to this examiner, TC (at least here) interprets this as being two different airports, and they want you to do the two approaches at different airports unless it would be difficult to do that. I don't know if PPCs use the same manual, so this might not apply to them. But I would be surprised if you were able to do a regular IPC all at one airport in Pacific region.

Of course like most things this can be interpreted in various ways. Do "facilities" mean different airports? Does "normally" mean you have to? But it's probably just easier to do what TC wants rather than arguing with your examiner.
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Re: Help with GPS (RNAV) approaches

Post by photofly »

First rule of all flight tests: never argue with the examiner. About anything. But in my case the examiner has always been very happy with my choice of approaches, at the same airport. If he wanted somewhere else - no problem, we’ll go there.

My interpretation of different facilities (which as usual is worth nothing) doesn’t extend to different airports: if that was intended, it would say “different airports”. Fewer letters, less ink, easier to read. It suggests to me that you should not, for instance, perform a localizer and an ILS approach to the same runway.

Like almost everything that comes out of TC, there are a lot of ways to read it.
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Last edited by photofly on Fri Dec 15, 2017 2:57 pm, edited 2 times in total.
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Re: Help with GPS (RNAV) approaches

Post by photofly »

Cessna 180 wrote: Fri Dec 15, 2017 11:52 am
AuxBatOn wrote: Thu Dec 14, 2017 9:12 pm How does baro altitude help with RAIM availability?!
I believe the GPS unit needs VNAV ability?
Not to improve RAIM availability, no. My 1998 GPS is baro-aided but offers no vertical guidance at all.
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Aviatard
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Re: Help with GPS (RNAV) approaches

Post by Aviatard »

CpnCrunch wrote: Fri Dec 15, 2017 1:10 pm
I talked to the examiner who this information came from, and he confirms this. Here is what the examiner's guide says for the instrument rating:

"The candidate will normally perform two different approaches on different approach facilities, where they are available"

According to this examiner, TC (at least here) interprets this as being two different airports, and they want you to do the two approaches at different airports unless it would be difficult to do that.r.
Criteria for the Development of Instrument Procedures (TP308/GPH209) refers to facility as being a ground based navigation aid, and refers to aerodromes separately. I believe the different approach facilities restriction is there to disallow a candidate from doing two ILS approaches in a row to the same runway, for example. You might do an ILS, followed by an NDB approach to the same runway, and still meet the different facilities requirement. Examiners we have used have never had a problem doing all the approaches at the same airport, whether on an initial ride, or a renewal.

I think your examiner is wrong, but what do I know?
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Re: Help with GPS (RNAV) approaches

Post by CpnCrunch »

Aviatard wrote: Sat Dec 16, 2017 7:48 am Criteria for the Development of Instrument Procedures (TP308/GPH209) refers to facility as being a ground based navigation aid, and refers to aerodromes separately. I believe the different approach facilities restriction is there to disallow a candidate from doing two ILS approaches in a row to the same runway, for example. You might do an ILS, followed by an NDB approach to the same runway, and still meet the different facilities requirement. Examiners we have used have never had a problem doing all the approaches at the same airport, whether on an initial ride, or a renewal.

I think your examiner is wrong, but what do I know?
That would be my interpretation as well, and it's probably the examiner's interpretation. However this came to him from TC. That's how they expect him to conduct his flight tests, so that's what he does. I was also discussing another very strange interpretation from TC with him that has him baffled.
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