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IFR Chapter-13-V8_Basic Master Frame.qxd 12/19/2019 5:23 PM Page 18

13-18 Rod Machado’s Instrument Pilot’s Handbook
Flying the Approach to APV Minimums The RNAV Chart Minimums Section
Let’s say we’ve elected to fly the
RNAV (GPS) Z Rwy 31 approach to
Salem’s McNary field (Figure 13). Our
intent is to fly to the lowest possible min-
imums on the chart, which happen to be
the LPV minimums (Figure 13, position
A). We’re approximately a mile south of
GLORR intersection which is an IAF for
this approach (Figure 13, position B).
Using our Garmin 500W WAAS certified
GPS receiver (Figure 14) we’re heading
direct to GLORR and have been cleared
for the approach. Notice that our GPS is
operating in terminal mode as shown in
Figure 14, position C by the letters
TERM (the GPS enters terminal mode
when operating at or within 30 nautical
miles of the airport with the airport
loaded as the destination).
As we cross GLORR, the intermediate
fix (NECIP) becomes the active way-
point (Figure 15, position D). As we con-
tinue towards NECIP, our WAAS unit is
evaluating its horizontal and vertical B
accuracy. The WAAS unit is designed to Fig. 13
allow the lowest minimums possible
based on meeting the required horizon-
tal position limits (HPL) and vertical M
position limits (VPL) for those mini- L
mums. In most cases, you’ll know which
minimums are allowed when reaching
the intermediate fix (IF). At this point,
the approach mode annunciator
(Figure 16, position E) will indicate
the letters for the lowest mini- A
mums allowed. The annunciator
may show LPV (for the lowest min-
imums possible on the RNAV (GPS)
31 approach). If so, then you may
use the LPV minimums and H
descend to a DA of 570 feet
(Figure 13, position F). If LPV J F
minimums are allowed, then the glides-
lope should become active by the time
you reach the IF, meaning that the glideslope warning flag LOTKE (the FAF) and 940 feet once you’re past the step-
on your HSI will disappear. Now let’s examine the other down fix at CUKEY (Figure 13, position L). In case you’re
minimums in Figure 13. wondering why the WAAS unit won’t default to higher
If, for any reason, your WAAS unit was unable to meet LNAV/VNAV DA minimums if the HPL/VPL require-
the HPL/VPL requirements for the LPV minimums, there ments aren’t met for LPV minimums, there’s a good rea-
will be some visual warning on your WAAS unit to alert son. It turns out that the tolerance limits for glideslope
you, and then the unit will default to LNAV minimums generation are basically the same for LPV, LNAV/VNAV
only. In other words, no glideslope is generated for this and LNAV+V glideslopes. If a glideslope can’t be
approach, meaning that no glideslope is available for generated for LPV, then it can’t be generated for
LNAV/VNAV minimums or for LNAV+V advisory purpos- LNAV/VNAV or LNAV+V. The only option left is for
es. You are left with flying a non-glideslope approach. If so, LNAV minimums. You get what you get. Get it?
you’ll see the letters LNAV in the approach annunciator On the other hand, there are approach charts with only
window as shown in Figure 17, position K. This means you one type of APV minima, which is LNAV/VNAV. In other
may descend to an MDA of 1,060 feet once you’re past words, LPV minimums aren’t shown in the chart’s