Approach Procedures
4-3
WAAS approaches are intended to flown in NAV APPR mode in
the DFC90 system and thus the “Primary Nav” LSK must be set
to GPS1/2. Roll commands are issued by the GPS Nav-Com in
GPSS mode instead of the DFC90 and proper vertical guidance
cannot be assured, hence the need to fly WAAS approaches in
NAV APPR modes. Glide slope will not arm if the autopilot mode
is GPSS.
If the autopilot were left in GPSS mode and the “Primary Nav”
LSK is set to GPS1/2, then the autopilot will automatically switch
from GPSS to NAV mode if/when a valid glide slope signal is
received.
If the autopilot were left in GPSS mode and the “Primary Nav”
LSK is set to VLOC1/2, then the glide slope will not arm and the
autopilot will not automatically switch from GPSS to NAV mode.
There are several types of WAAS approaches:
LNAV (Lateral Navigation):
Provides lateral (horizontal)
guidance only, with standard GPS precision of 0.3 NM full-
scale deflection. This is essentially the same as a non-
WAAS GPS approach. It is flown as any other non-precision
approach
– descend to MDA, fly at MDA altitude to the
MAP, and execute the missed approach procedure if
appropriate.
For this approach type, a manual coupling to the autopilot is
permitted.
Prior to FAF the “NAV” (or “APPR”) button on AP
must be pressed. There is no glide slope in a LNAV
approach so a manual means to accomplish the vertical
component of this approach needs to be enabled (VS and
ALT). Then fly coupled to MDA.
LNAV+V (Lateral Navigation with Vertical Information)
This mode provides the same lateral navigation as LNAV,
but presents an ILS GS-like presentation on the VDI. The
GPS draws a 3-D picture of the approach based on crossing
the FAF at the depicted altitude. Then it follows a glidepath
from the published approach, which is typically a 3 degree
angle to the touchdown zone. This type of approach remains
a non-precision approach and does not consider any step-
down limitations.
For this approach type, a manual coupling to the autopilot is
permitted.
Prior to FAF the “NAV” (or “APPR”) button on AP
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