gismo
Touchdown! Greaser!
And I suspect the only times you get that "downgraded" to LNAV is when it's too cold or you can't get the local altimeter setting.
Why higher LPV minimums?
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olasek
Pattern Altitude
Yes we know. Again, I was writing from the perspective of a small GA pilot, Captain, sorry, I keep forgetting to add this qualifier ever time I write about it.
Captain, next time I write about WAAS please assume it includes the following:
Warning- DOES NOT APPLY TO CAPTAIN AND HIS AIRPLANE!!!
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aterpster
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aterpster
Not unless you have temperature compensated Baro VNAV. :wink2:
Captain
Final Approach
Yes we know. Again, I was writing from the perspective of a small GA pilot, Captain, sorry, I keep forgetting to add this qualifier ever time I write about it.
Captain, next time I write about WAAS please assume it includes the following:
Warning- DOES NOT APPLY TO CAPTAIN AND HIS AIRPLANE!!!
Well you don't have to be a jerk about it. I wasn't trying to show off or anything. My comment was, I thought, on point.
That's what I was responding to if you care.
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John Collins
En-Route
At your airline, does it support Opspec C073 with the capability to treat a MDA as a DA? If so, when you are conducting an approach that has a LNAV/VNAV minimum that is higher than the MDA of the LNAV, are you permitted to continue to the MDA using your Baro/VNAV guidance IAW the Opspec? What if anything does your equipment annunciate, for example LNAV/VNAV?
Captain
Final Approach
We shoot to LNAV/VNAV mins. We treat it as a DH. We fly the profile the exact same as an ILS. It annunciates FMS for lateral guidance and VGP for vertical guidance and 'RWY' for VNAV altitude capture. (That last one just means the plane on autopilot will fly right to the runway without pilot input...just like an ILS. It's up to the pilot to go missed at the DH if the visual cues aren't present)
olasek
Pattern Altitude
Since we had the same exact conversation before the repetitiveness prompted me to make the comment that I made.
Captain
Final Approach
And then you posted the bold part of my previous post and I answered it. I'll tell you the truth I didn't even notice it was by you. I sorta read the forum like a book and only look to see who the author is if it seems relevant.
In this case it was a specific statement that I had direct experience with so I posted.
In this case it was a specific statement that I had direct experience with so I posted.
John Collins
En-Route
LNAV/VNAV minimums have a DA/DH for all users that are authorized to fly them. Part 91 users with an IFR approved WAAS GPS or a Baro-VNAV system are authorized to fly these approaches to a DA as you describe. If the approach doesn't have LNAV/VNAV minimums, are you authorized to use your VNAV down to the MDA and treat it as a DA? In other words, there are no LNAV/VNAV minimums charted. Part 91 users are not permitted to fly the LNAV approach and treat the MDA as a DA, but Part 121 users can be approved under Opspec C073 to fly these approaches with their VNAV FMS and treat the MDA as a DA.
Captain
Final Approach
Yes, there are rules though. To treat the MDA as a DH we have to meet criteria. We can if: There is an ILS that serves that runway, or there is a VASI or PAPI, or there is a published LNAV/VNAV DA.
John Collins
En-Route
This is a theoretical question. The poster child for this discussion is MDT RNAV RWY 13. There is an ILS approach to this runway, it has a PAPI, and there is a published RNAV/VNAV. The minimums for the LNAV/VNAV are DA of 1572 and 5 SM visibility, the minimums for category C for the LNAV are MDA of 1180 and a visibility of 2 SM. What are your minimums for this approach.
View attachment mdt rnav rwy 13 lnav much lower than lnav vnav.PDF
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Captain
Final Approach
If I shot this approach I'd use dive and drive and shoot the straight LNAV with an MDA if the weather was below 2,000 feet. If the weather was better than 2K then I'd shoot the LNAV/VNAV because it's easier and I know I'll break out.
John Collins
En-Route
Reasonable choices. Since you are authorized to use the LNAV MDA as a DA, why wouldn't you use VNAV if the weather was 1200 overcast and 3 miles. Is this a choice you would be able to make or would the company expect you to do the dive and drive?
poadeleted20
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I'll stick with my interpretation based on the plain language of the AFMS which gives a clear directive.
poadeleted20
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Regardless of the theory or TERPS or DO's or anything else, the plain language of the AFMS is clear, and per 91.9(a), carries regulatory force.
Captain
Final Approach
If the vis is 3 miles then I can't shoot the LNAV/VNAV as the min vis is 5 SM and we all know that visibility is controlling (right?). So right off the bat the 3 miles of vis would drive me to the straight LNAV which requires 2 SM for my plane.
I am authorized to use VNAV if there is an ILS, or LNAV/VNAV, or PAPI/VASI...but if the LNAV/VNAV is published then i must comply. In this case it is published and requires 5 SM. So, I'd shoot the LNAV if the weather was 1200 and 3.
olasek
Pattern Altitude
After studying this chart closer I came to conclusion that the reason for this unusual situation is a solitaire obstacle right underneath the approach path and less than 2 miles from the runway. But it is ultimately a bit paradoxical that you will be able to fly over this obstacle lower while on LNAV then on LPV approach. So I understand it bolis down to some technicality but still it is interesting and perhaps counterintuitive that LNAV will let you be closer to such obstacles.
John Collins
En-Route
So, according to you, if LPV is annunciated, you are not permitted to fly the approach to the LNAV MDA minimums if they are lower than the LPV DA. You could if the approach downgraded, because it LNAV would be annunciated, and you could if your number 2 GPS was a non WAAS TSO C129 GPS in the aircraft and used it for the approach guidance or if you turned off the SBAS setting in your WAAS GPS. Makes perfect sense.
John Collins
En-Route
Thanks, you got at the point I was trying to discover. At your airline, if the LNAV/VNAV is published, they require you to use it, even if using the LNAV with your VNAV capability C073 would be more advantageous. The notes in the IPG-ACF suggest that some airline crews may have the option.
John Collins
En-Route
These kind of anomalies exist. They are more prevalent with a LNAV/VNAV approach. In this case, a remote altimeter setting is required, which pushes up the MDA and the DA. The MDA gets pushed up 1 foot for 1 foot higher of obstacle, whereas the LPV DA gets pushed up more than 1 for 1 for the same obstacle. On the LNAV, the obstacle is below the MDA and is therefore in the visual segment (see and avoid it). To get the obstacle in the visual segment for the LPV, the MAP (DA) has to be moved back away from the obstacle, which means that at the same time it is being moved up along the glideslope. The distance it is moved back from the obstacle location is determined by projecting the height of the obstacle back along the approach course to the point where it is intersects the sloped Obstacle Clearance Surface (OCS) that it penetrated in the first instance. The DA is fixed to be above this position.
Brad Z
Final Approach
Wow, you guys are still arguing about this? 
It's my opinion that they should not have published LPV minima on this approach. Back in the day, there was policy only to publish lines of minima if it had some sort of operational advantage. For example, LNAV/VNAV offers vertical guidance (which may be an opspec requirement of some operators) over LNAV, even if the minima am be higher.
In the case of the Sanford RNAV approach we are discussing here, there is absolutely no operational advantage to publish the LPV minima. Every WAAS equipped box that can fly LPV can also fly LNAV/VNAV.
The sole reason the LPV minima is published on this chart is to meet an internal FAA "Flightplan" goal for the number of WAAS approaches each year. It's also the same reason they're publishing LP minima even when it adds no value.
I understand Ron's reluctance to fly minima lower than LPV. I don't necessary agree with him based on my experience, as well as factors mentioned by John Collins here, but I will never chastise him for taking a more conservative approach to instrument flying. Thankfully, this is a very rare thing and is really only controversial in the world of aviation forums.
It's my opinion that they should not have published LPV minima on this approach. Back in the day, there was policy only to publish lines of minima if it had some sort of operational advantage. For example, LNAV/VNAV offers vertical guidance (which may be an opspec requirement of some operators) over LNAV, even if the minima am be higher.
In the case of the Sanford RNAV approach we are discussing here, there is absolutely no operational advantage to publish the LPV minima. Every WAAS equipped box that can fly LPV can also fly LNAV/VNAV.
The sole reason the LPV minima is published on this chart is to meet an internal FAA "Flightplan" goal for the number of WAAS approaches each year. It's also the same reason they're publishing LP minima even when it adds no value.
I understand Ron's reluctance to fly minima lower than LPV. I don't necessary agree with him based on my experience, as well as factors mentioned by John Collins here, but I will never chastise him for taking a more conservative approach to instrument flying. Thankfully, this is a very rare thing and is really only controversial in the world of aviation forums.
Captain
Final Approach
Not true. I can fly whatever I want. I was speaking to what I'd do. If the LNAV is more advantageous then I'd shoot that if needed. Straight LNAV is dive and drive.
John Collins
En-Route
Thanks for the clarification.
John Collins
En-Route
Wow, you guys are still arguing about this?
It's my opinion that they should not have published LPV minima on this approach. Back in the day, there was policy only to publish lines of minima if it had some sort of operational advantage. For example, LNAV/VNAV offers vertical guidance (which may be an opspec requirement of some operators) over LNAV, even if the minima am be higher.
In the case of the Sanford RNAV approach we are discussing here, there is absolutely no operational advantage to publish the LPV minima. Every WAAS equipped box that can fly LPV can also fly LNAV/VNAV.
The sole reason the LPV minima is published on this chart is to meet an internal FAA "Flightplan" goal for the number of WAAS approaches each year. It's also the same reason they're publishing LP minima even when it adds no value.
I understand Ron's reluctance to fly minima lower than LPV. I don't necessary agree with him based on my experience, as well as factors mentioned by John Collins here, but I will never chastise him for taking a more conservative approach to instrument flying. Thankfully, this is a very rare thing and is really only controversial in the world of aviation forums.
I have no problem with Ron being conservative, my issue is with the logic of his analysis.
aterpster
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aterpster
Speaking in terms (pre-LPV and pre-LNAV/VNAV) ILS has always provided you with far more protection than a NPA.
poadeleted20
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Yes, that's how I read the AFMS. I'm not saying it wouldn't be safe, just that as the AFMS is written, it wouldn't be legal.
aterpster
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aterpster
I have made a request to OKC to remove the LPV procedure from this particular runway. I provided the argument that the lower LNAV/VNAV minimums will be denied to all WAAS equipped operators.
If there is resistance they may set forth the premise that it is okay to fly the LPV to the LNAV/VNAV minimums. If so, then I'll request a reference.
poadeleted20
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Be careful what you wish for -- removing the LPV procedure also removes the ability to fly it as an LPV approach, and I think most people would trade 24 feet for the added precision laterally plus the vertical guidance.
They'd have to change the Garmins AFMS's, too, since a more restrictive AFMS requirement takes precedence over less restrictive regulations.
poadeleted20
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That seems legit to me, although I'd need more research into the AFMS to be sure, and mine's in the airplane. Of course, you give up the LPV precision, but if an extra 24 feet of descent is worth that to you, you go right ahead.
John Collins
En-Route
You misquoted me in post 111. You edited my quote and incorrectly labeled it as being from the "GNS530W AFMS Text:", when in fact it wasn't. In my text, I clearly noted that it was from the "GNS530W Pilot Guide:". The AFMS does not have the wording you quoted and the Pilot Guide is not an FAA approved document. I assume your edit was accidental and not a deliberate falsification to prove your point.
aterpster
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aterpster
Redo your math. It's 45 feet and 1/8 mile. There is no added precision laterally; it's an issue of integrity and alerting. At least with Garmin units LNAV/VNAV ramps down to +/- 350 at the runway. And, what's the practical difference in vertical accuracy?
Obviously, lateral obstacles are not an issue for this runway's final approach segment.
They'd have to change the Garmins AFMS's, too, since a more restrictive AFMS requirement takes precedence over less restrictive regulations.[/QUOTE]
Nonetheless, it will be interesting whether they go down that path. If they do, can you provide me with a copy of the pertinent AFMS page?
John Collins
En-Route
I have made a request to OKC to remove the LPV procedure from this particular runway. I provided the argument that the lower LNAV/VNAV minimums will be denied to all WAAS equipped operators.
If there is resistance they may set forth the premise that it is okay to fly the LPV to the LNAV/VNAV minimums. If so, then I'll request a reference.
Although I did not get a reference, I discussed this with an individual at AFS420 who was referred to me by the manager of AFS420 as the local expert and it was his opinion that the annunciation of LPV was annunciating a level of service available, and one would be permitted to fly the approach to any charted minima the equipment was approved to fly and that was charted on the approach, in this case, the LNAV/VNAV or LNAV. Of course, this is just his opinion and doesn't carry any force of regulation.
aterpster
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aterpster
Thus, a copy of the AFMS becomes important.
John Collins
En-Route
What Ron quoted is not in the GNS530W AFMS, it was a misquote. I have attached a copy of the AFMS.
View attachment GNS530W AFMS SW Ver 3 30 Rev B.pdf
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poadeleted20
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If that's so, I misread it. No falsification intended. I'll have to dig my AFMS out of the plane and see exactly what it says.
poadeleted20
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There is a very big difference between in lateral precision between the LPV and LNAV modes, and if the LPV procedure is removed, the unit will only go to LNAV.
poadeleted20
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The AFMS says the Pilot's Guide must be immediately available during flight, and Section 4 of the AFMS starts out saying that the Pilot's Guide is to be referred to for normal operating procedures. That suggests that the procedures in the Guide must be followed, and the only time it says anything about using LNAV procedures/mins after starting with the LPV is when the system downgrades. However, from a regulatory perspective, that is probably a question only answerable by the Chief Counsel.
aterpster
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No there is not. It is an issue of alerting and integrity.
So, you are saying that those RNAV IAPs with no LPV but both LNAV/VNAV and LNAV actually don't have LNAV/VNAV?
poadeleted20
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I thought you were talking about LPV versus plain LNAV. LNAV/VNAV (L/VNAV in Garmin annunciation-speak) is another story entirely. So now you're talking about leaving the LNAV/VNAV up but killing the LPV, so you get L/VNAV when the system brings it up? I don't see an issue there.