Plan to use LNAV or Circling minimums for RNAV approach at alternate

Mike Gagnon

Mike Gagnon

Pre-Flight
Joined
Jan 19, 2019
Messages
79
Display Name
Display name:
mmkmg
I'm struggling to understand the significance of text in AIM 1-1-18c.9.(a), where it says "When using WAAS at an alternate airport, flight planning must be based on flying RNAV (GPS) LNAV or circling minima line...".

We're already going to be using non-precision alternate minimums (800-2) for the RNAV approach - what are the implications of having to plan to use the LNAV or circling minimums? How might that impact planning?

Note that I understand that if LPV is available, you can fly that when you get there - that's not a question. I'm just trying to understand how this need to use the LNAV minimums for planning purposes changes things.
 
Mike Gagnon said:
I'm struggling to understand the significance of text in AIM 1-1-18c.9.(a), where it says "When using WAAS at an alternate airport, flight planning must be based on flying RNAV (GPS) LNAV or circling minima line...".

We're already going to be using non-precision alternate minimums (800-2) for the RNAV approach - what are the implications of having to plan to use the LNAV or circling minimums? How might that impact planning?

Note that I understand that if LPV is available, you can fly that when you get there - that's not a question. I'm just trying to understand how this need to use the LNAV minimums for planning purposes changes things.
Click to expand...
If the LNAV
or circling MDA/vis is greater than 800&2, you’ll need to adjust the weather minimums for your alternate.
 
This clause probably accounts for LNAV approaches with minima above 800/2, of which are are many, including at my home field.
 
MauleSkinner said:
If the LNAV
or circling MDA/vis is greater than 800&2, you’ll need to adjust the weather minimums for your alternate.
Click to expand...

True, but that will already be published as non-standard alternate minimums for the procedure. So those would be the alternate minimums regardless of which line of minimums he plans to fly.

Like the OP, I am also not sure how to apply the AIM paragraph.
 
RussR said:
True, but that will already be published as non-standard alternate minimums for the procedure. So those would be the alternate minimums regardless of which line of minimums he plans to fly.
Click to expand...

Yes, I should have stated that I have the same assumption here that non-standard minimums would exist and be used in this case.
 
RussR said:
True, but that will already be published as non-standard alternate minimums for the procedure. So those would be the alternate minimums regardless of which line of minimums he plans to fly.

Like the OP, I am also not sure how to apply the AIM paragraph.
Click to expand...
The AIM is explaining why the alternate minimums line exists.

if the AIM statement wasn’t there, the question would probably be why the alternate minimums increase when the approach goes as low as 200 & 1/2.
 
MauleSkinner said:
The AIM is explaining why the alternate minimums line exists.

if the AIM statement wasn’t there, the question would probably be why the alternate minimums increase when the approach goes as low as 200 & 1/2.
Click to expand...
I have a feeling you are correct. It's an explanation, not an admonition. But even so, the sentence structure is pretty abysmal.
 
More importantly, at what point will they allow 600/2 for LPV?
 
N1120A said:
More importantly, at what point will they allow 600/2 for LPV?
Click to expand...
Probably not in our lifetimes.

They’d either have to redefine LPV as a precision approach or change the reg to specifically include LPV for the 600 & 2 alternate minimums. This “problem” isn’t something new or unknown to the FAA, and I haven’t heard any official noises that they’re looking at it, I don’t expect any action on it.
 
Last edited:
MauleSkinner said:
Probably not in our lifetimes.

They’d either have to redefine LPV as a precision approach or change the reg to specifically include LPV for the 600 & 2 alternate minimums. This “problem” isn’t something new or unknown to the FAA, and I haven’t heard any official noises that they’re looking at it, I don’t expect any action on it.
Click to expand...

You'd think they'd do it with MON
 
MauleSkinner said:
MON?
Click to expand...
Either 1) Tuesday would be a better day to do that, or 2) Minimum Operational Network - which I thought was describing reducing VOR towers to a lower number as a GPS back up. Not sure how that factors into re defining LPV as a precision approach to allow it to be used for 600 fee 2mile alternative requirement.
 
N1120A said:
Minimum Operational Network. Some ILS will eventually be scrapped and LPV will be the best alternative.
Click to expand...
I’d be willing to bet that was figured into what defines “minimum”. At least in the FAA’s view.
 
N1120A said:
More importantly, at what point will they allow 600/2 for LPV?
Click to expand...
I think we'll see it within the next 5 years. OTOH, I think it will be a while before we see many ILS approaches go away. When you think how far we've come in such a short time with GPS acceptance, it's really not that big a step.
 
Is there an airport today that doesn’t have an LPV?
 
MauleSkinner said:
I’d be willing to bet that was figured into what defines “minimum”. At least in the FAA’s view.
Click to expand...
"Minimum" refers to the minimum number of enroute VORs (with an expanded service ceiling) needed to allow one to navigate to an airport with an ILS, LOC or VOR approach in case of a GPS system failure.

if you are seeing VORs decommissioned and associated Victor airways being terminated in your area, that's MON.

The widespread removal of VOR approaches is somewhat related since you obviously can't have a VOR approach without a VOR, but is actually part of a separate program. You can see that in my area. We have a nearby VOR which is being retained as part of MON but VOR approaches to at least two airports which used it have been terminated.
 
WDD said:
Is there an airport today that doesn’t have an LPV?
Click to expand...
There are plenty of airports with GPS approaches without LPV minimums. DZJ about 60nm NE of you has only one GPS approach and it's LNAV only.
 
Last edited:
WDD said:
Is there an airport today that doesn’t have an LPV?
Click to expand...

Thousands. Click around to some local airports, you'll find them easily.

Having LPV minimums requires a certain amount of cleared area off the approach end of the runway, called the Vertical Guidance Surface. The most common obstacle penetrating this surface? Trees.
 
You must log in or register to reply here.
Back
Top