LNAV, VNAV and LPV

Andrew Sarangan wrote:

Is there a formal discussion of these various approach minimums? I
looked through all the obvious places (AIM, GPS manuals, AOPA
articles), but I haven't found a comprehensive discussion of these.

1.1.20 of the AIM has a fair discussion.

LPV (localizer performance with vertical guidance)


With the TSO C-129 spec, VNAV was generated with the proper air data
computer and adjunct equipment. It is an expensive solution although
the price is coming down (called BARO VNAV).

With the TSO C-146 all kinds of new "magic" is possible. Like the other
responder says, you spend $1,500 to convert your 430 to a 430W and you
will have it all. (You need a new antenna, too, which will have the
same footprint as your present antenna unless you want XM weather.)

Of course, you will be able to fly LPV approaches whenever WAAS is
available (SBAS in genertic terms, for space based augmentation system).

You will also be able to fly to VNAV minimums on RNAV IAPs with
LNAV/VNAV minimums, although it is unclear to me at present whether you
can use the DA concept (I suspect you can because what's the difference
at that point on the IAP). This will not require BARO VNAV.

Further, you will be provided vertical guidance on some LNAV IAPs
without an LNAV/VNAV line of minima. Garmin calls this LNAV+V. This
would seem to not permit the DA concept, though.

The vertical component of LNAV/VNAV and LNAV+V require that WAAS be
available.

The final segment scaling is much different than you're used to. Also,
the en route mode is 2.0 n.m, rather than 5.0 n.m. You can select and
fly parallel offsets en route.

The final approach scaling starts 2 miles from the PFAF most of the time
(unlike all the time for your present 430). It starts a lot further out
if you select VTF (vectors to final). The width on your 430 reduces to
+ or - 0.3 over two miles so it is 0.3 at the PFAF. With the 430W is
keeps reducing to +/- 350 feet at the MAP and remains at +/- 350 feet
until you terminate suspend with the OBS button. But, then it jumps to
0.3 n.m, rather than 1.0 mile and displays MAPR. MAPR drops out at the
first waypoint after the MAP, and returns scaling to the familiar
terminal 1.0 n.m. If the second waypoint is a long ways out you can
force MAPR to drop out by hitting OBS again unless the track is within 3
degrees of runway centerline, in which case you're stuck with 0.3
scaling until reaching the second waypoint (this is to support tighter
LPV missed approach criteria in the future.

Procedure turns and charted holds are far better displayed and computed.

I recommend you download the 430W trainer, which includes the full manual.

Garmin has chosen its own terminology for all these modes, which is
different than what is set forth in the AIM, but it all complies with
the requirements. And, as usual, Garmin has done it smarter than the
feds did. ;-)