曝光台 注意防骗
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MA26 Missed Approach Point for the specified approach to
Runway 26
MA123 The missed approach point for a circling procedure, lying
on the 123 degree radial from (or bearing to) the
referenced navaid.
Previously, these waypoints were not identified by name on the
approach charts. GPS overlay approaches now include reference to
the database names for these approach waypoints.
Approach Guidance
The approach guidance furnished by the FMS is intended to provide
a stabilized approach to an appropriate runway threshold crossing
height. No “level-off” is provided at MDA, since MDA will often vary
as a function of the aircraft approach speed category. The data
base altitudes provide for a threshold crossing height of 30 to 50 feet
above the touchdown zone of the runway. It is the pilot’s
responsibility to terminate the descent at MDA if visual contact with
the runway environment has not been established.
Section V
Operations
2423sv602 5-85
Change 1
Non-Precision Approach Glidepath
The FMS calculates a glidepath between the Final Approach Fix
(FAF) and Missed Approach Point (MAP) altitudes. When approach
is active, vertical deviation is calculated using aircraft position and
baro-corrected altitude relative to this glidepath.
In some approaches a step-down fix is depicted on the chart, but this
point is not specifically coded in the navigation data base electronic
data base.
The figure below depicts a direct glidepath from FAF to MAP as
calculated by the FMS. Notice that this glidepath passes under the
860’ step-down fix approximately 80’.
FMS calculated glidepath from FAF to MAP
A Flight Path Angle (FPA) is coded in the Navigation data base,
which takes into account the step-down fix location. This FPA will
always be greater than a computed FPA between the FAF and MAP
when a step-down fix is present.
Section V
Operations
5-86 2423sv602
Change 1
When the database FPA is greater than the FMS computed FPA
between FAF and MAP, the FAF altitude will be recalculated to a
higher altitude using the data base supplied FPA, such that a single
glidepath will be generated which clears all step-down fixes in the
approach procedure.
NOTE: There are instances in the database where the FPA is
higher than the computed FPA between the FAF and
MAP, but there is no step-down fix depicted on the chart.
This is due to coding rules that were in effect in the past in
which the FPA was not allowed to be less than -3.0
degrees. The data base supplier is working to change
these FPAs to match the computed FAF/MAP FPA
when a stepdown fix is not present.
In this case, the glidepath intercept point will be some distance past
the FAF. When you link an approach, the FAF altitude displayed by
the FMS may be higher than the charted FAF altitude. The correct
procedure will be to continue level flight past the FAF until the
vertical deviation indicator indicates glidepath capture, and then
descend.
As always, it is the pilot’s responsibility to observe and assure that
the published MDA is not violated.
Section V
Operations
2423sv602 5-87
Change 1
Refer to the following diagram of a typical approach profile with a
stepdown fix:
Recalculated glidepath using the Navigation data base coded
FPA
In this example (KBXA GPS 36 approach at Bogalusa LA), there is a
stepdown fix at 860 feet, 2.0 nm from the MAP. In this case the
navigation data base coded FPA of -3.3° will be used to recalculate
the FAF altitude of 1919 feet, which will replace the database FAF
altitude of 1700 feet. The FAF will still be crossed at 1700’ but the
new glidepath intercept point will now be approximately 0.6 nm past
the FAF. Note that the new glidepath will cause the aircraft to be at
exactly 860 feet when 2.0 nm from the MAP.
Section V
Operations
5-88 2423sv602
Change 1
Approach Types
NOTE: Refer to DATA BASE Section for details of creating Pilot
Defined Approaches.
ILS Approaches
ILS approaches are included in some data base part numbers.
Depending upon the installation, these approaches may or may not
be coupled to the flight director/autopilot. Refer to “ILS and RNAV
Approaches with and without Advanced EFIS Configuration” later in
this section for more detailed information. In aircraft that do not
allow coupling to the FGS, the FMS will provide guidance up to the
point where the ILS localizer signal becomes active, and then the
pilot must manually transition to ILS guidance using the FGS.
LOC and LOC-BC Approaches
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