4-4
Approach Procedures
must be pressed. If it is not manually changed to NAV, then
an automatic switch will occur when/if a GPS glide slope
signal is received. In either the manual or automatic case,
the AP switches to NAV APPR. Then fly coupled to MDA. If
a level off at the MDA is desired, the ALT button must be
pressed on the autopilot.
LNAV/VNAV (Lateral Navigation with Vertical
Navigation)
In this mode, the GPS provides lateral
navigation, providing more accurate guidance than regular
LNAV but easier to follow indications than a localizer. The
vertical navigation is driven by GPS signals. LNAV/VNAV
approaches are operationally different from LNAV+V in that
the glide path is protected from obstructions but attention
still must be applied to step down fixes. Also, the minimum
altitude presented is a decision altitude/height (DA/DH)
– DA
being what is on the altimeter, and DH being the height of
the DA above the touchdown zone elevation. This is not a
MDA, thus, fly it just as though it were a precision approach.
Follow the glide slope needle just as though it were an ILS
GS and continue all the way to DA before initiating a missed
approach, if appropriate.
This type of approach is automatically coupled to the
autopilot meaning that somewhere in the vicinity of the FAF,
the system will automatically toggle the autopilot mode from
GPSS to NAV APPR and GS will arm.
LPV (Localizer Precision with Vertical Guidance)
The
lateral guidance is significantly more precise than LNAV,
and equivalent to that of a localizer, except easier to fly.
Vertical guidance is provided to minimums as low as 20
0’
AGL above the touchdown zone. Lateral tolerance starts out
at 0.3 NM full-scale (slightly tighter than a localizer at the
FAF), transitioning to 350 feet either side at the runway
threshold (slightly looser than a localizer). The steering
remains linear all the way so you don’t get the difficult to
follow swings of a real localizer close in. The vertical
guidance is precise and has a DA/DH (shown as “DA(H)” on
approach charts) rather than a MDA.
This type of approach is also automatically coupled to
your autopilot. This means, in the vicinity of the FAF, the
system will automatically toggle the autopilot mode from
GPSS to NAV APPR and GS will arm.
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