430 LNAV approach question

[cliffy]

I added the smile at the end of my post for a reason :-)  I'm going to make a prediction and it may not happen for several years but I do think it will eventually come to pass.

The way TERPS are written and the way they are applied to GPS approaches today has increased the complexity of approaches to the point that too much time (for most pilots) is spent trying to figure out just how to fly the approach. Many pilots are never sure that they are actually doing it correctly even when they are. As an example the RNAV GPS 28 above. Many, if not most, will take the bottom mins figure and go with that in real time practice and dump all the info up at the top banner of restrictions. I'm not saying it's correct or safe just that's human nature and the way it will go with most of us PPs doing IFR. In reality, you can put all that "legalese" at the top but it will not get used. It's just too complicated. It's written by layers and CYA backroom geeks to comply with the TERPS.  It's good to talk about this stuff as we do here. It's good training on the desk top but in reality most will "simplify" the numbers in flight. 

Now, my prediction-

       We will see, in the future, a push to "simplify" all approaches in the interest of safety!

Here on this approach we see a difference of what? 29 feet to fly to if one annunciation is different. Can anyone actually fly to 1589'? And, then tell if it;s 1 and 5/8 mile VIS? We have 5 lines of "restrictions with 7 different items to codify at the top and 3 more lines at the bottom. 10 items of info to figure out, maybe on the fly, in weather, single pilot including figuring out if the OAT figures into this procedure. 

SO now we are worst case scenario of single pilot, IMC, night with turbulence and we think everyone or even most will be able to fly to a difference of 29 ft down at mins while looking for the runway or try to go through all the other 'restrictions"? Ain't gonna happen. What if it's a divert for an emergency? These numbers work out fine on the computer, sitting at a desk and when flown by the Flight Check folks in usually CAVU conditions, it's great for a training exercise, but in reality its a joke. Even the difference between 1 mile and 1 and 1/4 mile VIS. Its a joke, period. If you get to mins alt and you see the runway, can you really determine in that instant the difference between 1 and 1 and 1/4 mile VIS? Not hardly. 

In the future we will see mins raised to the next highest 100' increment for a good, easy to fly to marker when the crap hits the fan. The VIS will also be simplified. The amount of missed approaches and not completed landings because of this will be minimal. For the inflight VIS, most pilots are going to land if they see the runway at mins. It's just the way it is. Now they might call the tower after landing and say, "Boy, that approach was right at mins today!" as a CYA. 

[Browncbr1]

i agree, but has the FAA ever actually simplified anything?  

[kortopates]

On 1/13/2017 at 1:12 AM, midlifeflyer said:

I thought I gave the clue with my highlight in your post. Notice that on this approach, the LNAV/VNAV minimums are lower than the LPV minimums (don't ask me why, beats me). But since LNAV/VNAV is a "lower form" of precision those lower minimums can be used. Many pilots don't even look past the LPV line to even see the lower available minimums.

I sure didn't look lower than LPV but your example brings up an excellent point we should be considering when flying an approach. First off though its very rare to ever see an LPV approach minima offered when its higher than LNAV/VNAV - really there is no longer any benefit. But it happens because of a quirk in the different TERPS geometry used between LPV and LNAV/VNAV. Its actually much more common to see this between LNAV/VNAV and LNAV but in this case the two approaches are of course flown differently.

Design criteria for the two VNAV approaches are very different. LNAV/VNAV originated as LNAV with Baro-VNAV - not GPS at all. Using GPS with these is really more like the early GPS overlay approaches years ago; except we get to avoid the cold weather baro limitations. LPV though is designed much like an ILS approach. Both approaches are flown the same way though to DA rather than a MDA, but the geometry quirk that can cause LPV minimum to be above LNAV/VNAV stems from an obstacle near the runway. Close to the threshold, the OCS (Obstacle Clearance Surface) of the usually higher LNAV/VNAV actually passes over or higher than the surface of the LPV, and thus an obstacle right in this pretty brief zone will have a larger impact on the LPV than the LNAV/VNAV since it hits the LPV surface lower. (Eckalbar explains all of these TERPS requirements in detail in his book). But getting back to why it's really a good idea to recognize higher than TERPS minimum DA for LPV and LNAV/VNAV is it also indicates presence of obstacle near the runway that we'll be flying over during the visual segment (after the MAWP). (Obstacles before the missed approach waypoint would have been dealt with higher/steeper glideslope and/or a final course at an angle off center line). LNAV approaches provide the same very important clue in the absence of a VDP which also tells us there is also an obstacle that penetrates the 34:1 visual area. So we need to be extra vigilant not to drop below the visual glide path of the VASI; especially if there is a note that the VGSI is not coincident with GS.

As for Cliify's comment that GPS approaches have really added complexity. I agree and see this working with clients that learned in he days of ILS, VORS and NDB's. Or more recently opted to get their IR ticket with the "simpler" VOR ILS only thinking they would catch up on GPS after they got their ticket. There is so much to learn regarding GPS I don't understand why students would want to rob themselves of a good initial training experience but happens. Albeit less and less these days since most training aircraft are equipped with WAAS GPS.

But the complexities of GPS approaches begin with flight planning, understanding the meaning of GPS NOTAMS, alternate airport selection with WAAS vs NON-WAAS GPS etc. And then we should know and expect the changes in CDI tightening and bounds of the protected zones change as we start down a feeder route to an Initial segment to an intermediate segment to the final segment - since this is unique to GPS. But when we're flying the final approach the rules between how we fly to DA and MDA and either continue or go missed have not changed. So I don't see the concern for "flying to a difference of 29'" -we just ensure our altimeter setting is correct and fly to the target altitude. If we do our part, the TERPS guys have provided the obstacle protection.  I am not sure I understand the point on estimating visibility. Its importance was in the ATIS or AWOS reported visibility being hopefully greater than the approach visibility minima before we start (and more important to the commercial ops that can't start the approach without the required vis). But once we start the approach, we know that for a VNAV approach the required minimum visibility is always at least the distance from the DA (on GS) to the threshold. We don't need to estimate visibility, we either see any of the prescribed criteria of 91.175 to continue descent or we must go missed. In contrast, an LNAV visibility minimums can be much less than VNAV minimums and we can also find ourselves much further from the threshold at MDA than our required visibility - whatever it is. But on a LNAV approach we level off at MDA and continue following guidance to MAWP hoping we'll see one of the prescribed criteria of 91.175 in time to allow descent to the runway or we go missed.

Practicality speaking, that is so much easier to do when you have one pilot flying on the gauges with another pilot calling the airport or lights in sight. I really don't want to be doing that to mins single pilot. Thankfully its very rare when I am single pilot.

 

Edited January 15, 2017 by kortopates

[Browncbr1]

what he was getting at is that some IAP plates have become covered up with so much information that it's sometimes difficult to quickly reference and know all the ifs, ands, or buts that dictate a legal approach in a jam.  Many of the different minima are so similar, it is too difficult to really discern the difference anyway, so the minima should be common if calculated difference is less than 100ft or half mile.     

[midlifeflyer]

11 hours ago, kortopates said:

I sure didn't look lower than LPV but your example brings up an excellent point we should be considering when flying an approach. First off though its very rare to ever see an LPV approach minima offered when its higher than LNAV/VNAV - really there is no longer any benefit. But it happens because of a quirk in the different TERPS geometry used between LPV and LNAV/VNAV. Its actually much more common to see this between LNAV/VNAV and LNAV but in this case the two approaches are of course flown differently.

Design criteria for the two VNAV approaches are very different. LNAV/VNAV originated LNAV with Baro-VNAV - not GPS at all. Using GPS with these is really more like the early GPS overlay approaches years ago; except we get to avoid the cold weather baro limitations. LPV though is designed much like an ILS approach. Both approaches are flown the same way though to DA rather than a MDA, but the geometry quirk that can cause LPV minimum to be above LNAV/VNAV stems from an obstacle near the runway. Close to the threshold, the OCS (Obstacle Clearance Surface) of the usually higher LNAV/VNAV actually passes over or higher than the surface of the LPV, and thus an obstacle right in this pretty brief zone will have a larger impact on the LPV than the LNAV/VNAV since it hits the LPV surface lower. (Eckalbar explains all of these TERPS requirements in detail in his book). But getting back to why it's really a good idea to recognize higher than TERPS minimum DA for LPV and LNAV/VNAV is it also points to some obstacle near the runway that we'll be flying over during the visual segment (after the MAWP). (Obstacles before the missed approach waypoint would have been dealt with higher/steeper glideslope and/or a final course at an angle off center line). LNAV approaches provide the same very important clue in the absence of a VDP which also tells us there is also an obstacle that penetrates the 20:1 visual area. So we need to be extra vigilant not to drop below the visual glide path of the VASI; especially if there is a note that the VGSI is not coincident with GS.

Thanks for explaining some of the considerations that go into the "don't ask me why, beats me" comment in my post

Of course, this is not exclusively a GPS thing. There are ILS OR LOC approaches with lower LOC minimums. Again, TERPS requirement are the issue, and sometimes the difference is due to terrain or obstacles on the missed.

i still think the complexity of GPS is overemphasized. There is a bit of technophobia in some folks that hampers learning, but aside from that, I suspect many fledgling instrument students will disagree about how "easy" it is to understand "simpler" approach plates. Heck, some of us have never been able to master the can't-be-simpler-in-concept NDB. 

The bigger problem is we tell people it's really complicated, that they are bound to have trouble understanding it. That becomes a self-fulfilling prophesy, We do it throughout instrument training. We manage to poorly teach or overcomplicate procedures as basically simple as holding patterns or DME arcs and they continue to strike fear into some otherwise excellent instrument pilots. And, now we do it with GPS. SSDD.

For those who learned on paper VORs in 100% hand flown aircraft that did not even have DME (like me), there is definitely going to be a learning curve moving to GPS or from round dials to glass or paper to tablet. But, to me at least, that's about effective training, not some intrinsic limitation in the technology.

Edited January 14, 2017 by midlifeflyer

[PTK]

On 1/12/2017 at 1:35 PM, Browncbr1 said:

I understand the difference between what waas and non waas allows.. i'm just trying to discern if a non waas box provides a glideslope just for reference...   similar to how a glideslope will come alive if you are flying a LOC approach if there is also an ILS.    

Brian has confirmed that the GS does NOT come alive on LNAV approaches, but I am unclear if he is saying the GS does not come alive universally, or if it just for LNAV approaches.    

For example, I understand that the GS does not come alive for RNAV RWY 10 below, but does it come alive on the RNAV RAY 28 below?  (understanding that you still must fly the LNAV minima)

 

This is an excellent discussion.

Interestingly enough there are also cases when MDA are lower than DA. Here's an article on how they're calculated:

http://www.boldmethod.com/learn-to-fly/navigation/when-your-lnav-minimums-are-lower-than-vnav-which-should-you-choose/

Another concept that's related to which minima is that of the MAP.  Where is the MAP and more importantly when has the airplane reached it. On the profile view there's only one MAP shown and it corresponds to the first minima listed. But there may be more than one. For LNAV and circling the MAP is the last wpt which is typically the runway. This is clear on the rwy 10 above because that's all the minima listed. It may not be so clear on the rwy 28. For the LPV to rwy 28 the MAP is depicted as the point where the glide slope intercepts the DA of 1398 msl and missed approach course is shown with the dotted line. The missed approach course for LNAV is not depicted. This is significant especially for LNAV because if have to go missed early no turns are allowed until JAVNE. 

On some np approaches the FAA gives us the luxury of a VDP (visual descent point). (Yes...the FAA is simplifying it for us!) With a VDP depicted the decision becomes simpler because no turns are allowed after the VDP and also not allowed to drop below the mda before reaching the VDP. And a normal landing becomes increasingly more difficult from MDA the more we go beyond the VDP. So there's no reason to continue to fly along at MDA searching for the runway and waiting for MAP. If runway environment is not visible at the VDP initiate missed.

http://155.178.201.160/d-tpp/1701/00669RY31.PDF

[kortopates]

 

16 hours ago, midlifeflyer said:

Thanks for explaining some of the considerations that go into the "don't ask me why, beats me" comment in my post

Of course, this is not exclusively a GPS thing. There are ILS OR LOC approaches with lower LOC minimums. Again, TERPS requirement are the issue, and sometimes the difference is due to terrain or obstacles on the missed.

i still think the complexity of GPS is overemphasized. There is a bit of technophobia in some folks that hampers learning, but aside from that, I suspect many fledgling instrument students will disagree about how "easy" it is to understand "simpler" approach plates. Heck, some of us have never been able to master the can't-be-simpler-in-concept NDB. 

The bigger problem is we tell people it's really complicated, that they are bound to have trouble understanding it. That becomes a self-fulfilling prophesy, We do it throughout instrument training. We manage to poorly teach or overcomplicate procedures as basically simple as holding patterns or DME arcs and they continue to strike fear into some otherwise excellent instrument pilots. And, now we do it with GPS. SSDD.

For those who learned on paper VORs in 100% hand flown aircraft that did not even have DME (like me), there is definitely going to be a learning curve moving to GPS or from round dials to glass or paper to tablet. But, to me at least, that's about effective training, not some intrinsic limitation in the technology.

I don't disagree with you at all. Maybe complexity isn't the best word to describe it. I think there is lot to learn coming from VOR & ILS only as we both did - but none of it what I would really describe as adding operational complexity than what we already had with ILS & VOR - in fact I feel GPS simplifies things greatly from before GPS. What I find is clients/students being overwhelmed about using the GPS properly. But as CFII we know the avionics really well, or should, and can show how to simply usage of the box and break down when to do what so as to stay ahead of the plane. For example, having the expected approach loaded but not activated before we leave the enroute portion, then activating the approach as soon as we are on our first vector for the approach. The GPS is especially valuable when we get to partial panel training. I still require my students to know how to use the compass per ACS standards, but partial panel approaches are done using TRK and DTK GPS data (not following the magenta line) which allows them to fly partial panel to ATP standards.  Very little understanding of TERPS complexities are needed to be safe. But I really stress survival tactics, and an example one important one is VDP. But what I stress is its the absence of a VDP which is so important since it means we have obstacles to avoid in the visual segment. There are additional survival aspects of the VDP which include recognizing when flying an LNAV approach to minimums that there is no TERPS requirement that the charted required approach visibility is enough to see the threshold from the VDP at minimums - so what will be our plan? To sum it up, rather than harp on complexity, I try to stress how to use the box to simplify our workload, rather than be consumed by it, and then do my best to make sure they understand the important gotcha's and survival tactics that at least I've learned over the past 27 years of flying and still learning. 

[Marauder]

 
I don't disagree with you at all. Maybe complexity isn't the best word to describe it. I think there is lot to learn coming from VOR & ILS only as we both did - but none of it what I would really describe as adding operational complexity than what we already had with ILS & VOR - in fact I feel GPS simplifies things greatly from before GPS. What I find is clients/students being overwhelmed about using the GPS properly. But as CFII we know the avionics really well, or should, and can show how to simply usage of the box and break down when to do what so as to stay ahead of the plane. For example, having the expected approach loaded but not activated before we leave the enroute portion, then activating the approach as soon as we are on our first vector for the approach. The GPS is especially valuable when we get to partial panel training. I still require my students to know how to use the compass per ACS standards, but partial panel approaches are done using TRK and DTK GPS data (not following the magenta line) which allows them to fly partial panel to ATP standards.  Very little understanding of TERPS complexities are needed to be safe. But I really stress survival tactics, and an example one important one is VDP. But what I stress is its the absence of a VDP which is so important since it means we have obstacles to avoid in the visual segment. There are additional survival aspects of the VDP which include recognizing when flying an LNAV approach to minimums that there is no TERPS requirement that the charted required approach visibility is enough to see the threshold from the VDP at minimums - so what will be our plan? To sum it up, rather than harp on complexity, I try to stress how to use the box to simplify our workload, rather than be consumed by it, and then do my best to make sure they understand the important gotcha's and survival tactics that at least I've learned over the past 27 years of flying and still learning. 

I think one of the challenges of GPS is the programming of the box to setup the approach. As a "late" bloomer to the world of GPS (at least for approaches), I found that ILS/VORs were simple in what was expected out of the box in front of you. The frequency needed to be tuned, identified and the correct course set on the CDI. You relied on the paper in front of you and your ability to interpret and fly analog needles.

When I moved to the GPS approach world after flying IFR for 22 years using strictly VOR, ILS and heaven forbid, the occasional NDB, it was challenging. The concept of loading an approach and selecting a transition was just different and took some time getting used to. Knowing what an LPV meant versus an LNAV/VNAV as well as all those little notes about barometric settings all added more complexity.

Now after flying GPS approaches for the past 5 years in my plane, I do find these approaches easier. Especially when you are fed additional information such as waypoints on the approach, cross track, ground speed and distance. I also appreciate the rock solid needles. I'm reminded of that every time I fly the VOR approach to my home airport.


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[midlifeflyer]

6 hours ago, Marauder said:

When I moved to the GPS approach world after flying IFR for 22 years using strictly VOR, ILS and heaven forbid, the occasional NDB, it was challenging. The concept of loading an approach and selecting a transition was just different and took some time getting used to. Knowing what an LPV meant versus an LNAV/VNAV as well as all those little notes about barometric settings all added more complexity.
 

 

Absoluteky. But one I got the hang of it, wow. I'm not talking about following magenta lines, but the situational awareness created by the act of loading an approach and, especially, selecting a transition. 

Consider: you are a half hour out from your destination nontowered airport. You are going to be telling ATC what you want. First, you need the know the weather, especially the wind direction to even select which approach to which runway; the days of a single off airport VOR or sole ILS or LOC option are gone. Once you choose the approach, choosing a transition requires you to know exactly where you are coming from and how your approach fits into the enroute environment.

Done right, it's quite the opposite of "magenta line" mentality. The options provided by GPS approaches require us to know where we are, where we are going, and how to best get there. To know what the weather is doing. That, in turn, forces us to stay way ahead of the airplane. And to manage our time. Those are, of course, important for any approach or phase of flight, but I think they are forced in us by these extra options.