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 Post subject: GPS Approach Questions
PostPosted: 26 Apr 2012, 20:25 
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Location: Seeley Lake, MT (23S)
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After looking into our local GPS problem and starting to fly with my new panel this brought up a question regarding GPS approaches that I'm not clear on. How do you choose which minimums you will fly to? Is this simply a WAAS/Non WAAS choice? For example why would you pick LNAV/VNAV DA mins vs LNAV MDA mins? Second question is why would the LNAV MDA mins be lower than LNAV/VNAV DA mins as seen here?

http://155.178.201.160/d-tpp/1204/00048R7.PDF

This situation came up last week when I was working the mid shift. Our ILS's were down for maintenance and one of the cargo guys wanted to shoot the GPS but hesitated because the weather didn't allow the approach with some mins but was OK with others. He had to stop and think about which ones he was allowed to use before I could clear him for the approach.

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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 20:29 
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Username Protected wrote:
After looking into our local GPS problem and starting to fly with my new panel this brought up a question regarding GPS approaches that I'm not clear on. How do you choose which minimums you will fly to? Is this simply a WAAS/Non WAAS choice? For example why would you pick LNAV/VNAV DA mins vs LNAV MDA mins? Second question is why would the LNAV MDA mins be lower than LNAV/VNAV DA mins as seen here?

http://155.178.201.160/d-tpp/1204/00048R7.PDF

This situation came up last week when I was working the mid shift. Our ILS's were down for maintenance and one of the cargo guys wanted to shoot the GPS but hesitated because the weather didn't allow the approach with some mins but was OK with others. He had to stop and think about which ones he was allowed to use before I could clear him for the approach.


Scott,

Unless you had Lnav/Vnav capability, which is unlikely, you'd use the Lnav mins, or LPV if it were available, which is it not.

As for your position as a controller, you really don't care what their mins are, you just clear them for the GPS approach to 7... ..... and they figure out their own mins.

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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 20:57 
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Location: Oklahoma City, OK (KPWA)
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You can fly lnav/vnav minimums with waas, it's annunciated as L/VNAV on the GPS.

The answer is you fly to what the box announces. It computes its integrity and announces its capability before the FAF.

If you don't have waas you're stuck with lnav only.

Have you read the pilot guide? There's a ton of good info in there.

I can't answer your TERPS question, but I bet John can.


Last edited on 26 Apr 2012, 21:04, edited 1 time in total.

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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 21:02 
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Username Protected wrote:

As for your position as a controller, you really don't care what their mins are, you just clear them for the GPS approach to 7... ..... and they figure out their own mins.


That part I knew but his indecision got me to thinking about it from the pilots perspective.

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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 21:03 
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Username Protected wrote:
You can fly lnav/vnav minimums with waas, it's annunciated as L/VNAV on the GPS.

The answer is you fly to what the box announces. It computes its integrity and announces its capability before the FAF.

If you don't have waas you're stuck with lnav only.

Have you read the pilot guide? There's a ton of good info in there.


Have not yet read the pilots guide. My 530 has WAAS.

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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 21:08 
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Username Protected wrote:

Have not yet read the pilots guide. My 530 has WAAS.


Start with the quick reference. It will get you 90% of the way there.

http://static.garmincdn.com/pumac/1317_ ... erence.pdf


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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 21:11 
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Username Protected wrote:

Have not yet read the pilots guide. My 530 has WAAS.


I've been meaning to read that myself. Scott if you read yours how about posting the cliff notes version?

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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 21:13 
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Username Protected wrote:
You can fly lnav/vnav minimums with waas, it's annunciated as L/VNAV on the GPS.

The answer is you fly to what the box announces. It computes its integrity and announces its capability before the FAF.

If you don't have waas you're stuck with lnav only.

Have you read the pilot guide? There's a ton of good info in there.


Have not yet read the pilots guide. My 530 has WAAS.


Scott, As Eric said, your 530W will tell you what mins to fly to. It will say LPV/LNAV etc. in the lower left portion of the screen.

My experience has been that if the approach has an LPV option, I have had the 530W give me LPV. Don't count on it, verify as part of your approach procedure prior to the FAF.

Glen
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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 21:19 
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Username Protected wrote:

Have not yet read the pilots guide. My 530 has WAAS.


Start with the quick reference. It will get you 90% of the way there.

http://static.garmincdn.com/pumac/1317_ ... erence.pdf


Oh, that. I thought you were referring to something else. I have looked thru that once but before the radio was installed. I'll go thru it again.
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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 21:21 
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Username Protected wrote:

Scott, As Eric said, your 530W will tell you what mins to fly to. It will say LPV/LNAV etc. in the lower left portion of the screen.

My experience has been that if the approach has an LPV option, I have had the 530W give me LPV. Don't count on it, verify as part of your approach procedure prior to the FAF.

Glen


OK, thanks. I'll have a lot of questions as I get to flying it. I'm sure others are in the same boat.

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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 21:37 
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I've always taken all the options, LPV, LNAV/VNAV, LNAV, CIRCLING, as either an operational limitation or an equipment limitation. For 91 folks, the operational considerations is not the same as air carriers, like your freight guy. I have a 530W in the King Air, but we JUST got the LPV approval for our OPSPECS. I have not completed the LPV training program since the approval. Therefore, on a 135 flight, I cannot fly that approach. I cannot stop the unit from displaying the glide path, but I cannot descend below the LNAV MDA. Period.

As for picking the appraoch, we (my current 135 carrier) are not authorized for all approaches. For instance, we can't do a PRM or an LDA/GS. To come up with those two, I had to think about it for a minute. My last job was not allowed to do NDB approaches -- the CP didn't want to do one with the FAA. :thumbup: So, it was removed from the OPSPECS.

As for equipment, I believe there are some older FMS systems that are not WAAS, but will display a derived glidepath. So, it's better than LNAV only, but not as good as the LPV.

EDIT: Has anybody come across a note similar to "If local altimeter not available LPV NA"? I thought I had, but cannot find it.


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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 21:45 
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Username Protected wrote:

As for equipment, I believe there are some older FMS systems that are not WAAS, but will display a derived glidepath. So, it's better than LNAV only, but not as good as the LPV..


I think that might be what's called baro vnav, or what the lnav/vnav minima was designed for.


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 Post subject: Re: GPS Approach Questions
PostPosted: 26 Apr 2012, 23:44 
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Location: Minneapolis, MN (KFCM)
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Username Protected wrote:
After looking into our local GPS problem and starting to fly with my new panel this brought up a question regarding GPS approaches that I'm not clear on. How do you choose which minimums you will fly to? Is this simply a WAAS/Non WAAS choice? For example why would you pick LNAV/VNAV DA mins vs LNAV MDA mins? Second question is why would the LNAV MDA mins be lower than LNAV/VNAV DA mins as seen here?

http://155.178.201.160/d-tpp/1204/00048R7.PDF

This situation came up last week when I was working the mid shift. Our ILS's were down for maintenance and one of the cargo guys wanted to shoot the GPS but hesitated because the weather didn't allow the approach with some mins but was OK with others. He had to stop and think about which ones he was allowed to use before I could clear him for the approach.


There's a pretty good thread on this at PoA. Due to the different geometry of the TERPS mandated obstruction clearance zones for each type of approach it's possible but rare to have higher mins for LPV than LNAV/VNAV, and higher mins for LNAV/VNAV vs LNAV (or it's cousin LNAV+V) is more common. As a pilot you can use the lowest mins on the chart for the type of approach the GPS decides is acceptable regardless of which one is lower. IOW if the GPS says it's good with LPV mins you can use the LNAV/VNAV mins if they happen to be lower and you always have the option of going with the LNAV mins as long as you fly the approach in accordance with the altitude restrictions on the chart for that.

I recommend John Eckalbar's book "Instrument Flying Update" as a good source for this kind of information along with some other useful stuff relevant to today's IFR navigation issues. In addition to explaining what a pilot needs to do, he does a pretty good job of explaining the underlying reasons for the unusual scenarios and what their existence should imply to a pilot.

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 Post subject: Re: GPS Approach Questions
PostPosted: 27 Apr 2012, 06:23 
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Username Protected wrote:
...Has anybody come across a note similar to "If local altimeter not available LPV NA"? I thought I had, but cannot find it.
are you thinking of "Only Authorized Operators may ..." ?

And ... here's a pretty nice checklist. I saw it somewhere and tweaked it.

IFR PROCEDURE → NAME, TYPE
How Low? How Far? Which Way? Obstacle.
S - Source (GPS/VLOC), Sequencing
C - Course and Needle
A - Altitude – Assigned & Next
M - Modes - FD/AP & GPSS

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 Post subject: Re: GPS Approach Questions
PostPosted: 27 Apr 2012, 08:41 
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Location: Charlotte, NC (KUZA)
Aircraft: 1968 Bonanza V35A
Username Protected wrote:
You can fly lnav/vnav minimums with waas, it's annunciated as L/VNAV on the GPS.

The answer is you fly to what the box announces. It computes its integrity and announces its capability before the FAF.

If you don't have waas you're stuck with lnav only.

Have you read the pilot guide? There's a ton of good info in there.

I can't answer your TERPS question, but I bet John can.


Eric,

I believe the annunciation on the GPS annunciates the highest service that a part 91 operator may use with the equipment, it does not preclude using a lower level of service. For example if LPV is annunciated, nothing prevents you from flying the dive and drive to the LNAV MDA if it is on the chart and is advantageous to the pilot. A good example when you might use a MDA is when circling is desired.

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