| Barometric Vertical Navigation (VNAV) Instrument Procedures |
| Terms |
- Barometric Vertical Navigation (BARO VNAV) is a navigation
system which presents computed vertical guidance to the pilot referenced to a
specific Vertical Path Angle (VPA). The onboard avionics computer resolves
vertical guidance data based on barometric altitude and is either computed as
a geometric path between two waypoints or a angle from a single waypoint.
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- Decision Altitude (DA) is a specified
altitude in mean sea level in a approach with vertical guidance at which a
missed approach must be initiated if the required visual reference to continue
the approach has not been established.
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- Decision Altitude (Height) (DA(H)).
The height is used for advisory reference only and does not necessarily
reflect actual height above underlying terrain.
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- Final Approach Segment The final approach
segment for a VNAV approach begins at the final approach fix (FAF) and ends at
the runway threshold. A waypoint is established at the FAF and the runway
threshold.
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- Height Above Threshold (HATh) For VNAV the
HATh is defined as the height above the runway threshold elevation. Also know
as TCH of threshold crossing height.
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- Obstacle Clearance Surface
(OCS) An
imaginary surface in the primary final approach obstacle clearance area
being used for obstacle evaluation.
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- Vertical Path Angle (VPA) Used in connection
with barometric VNAV operations to specify the vertical angle required on a
segment.
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- Waypoint A predetermined geographical
position used for route definition specified in latitude/longitude. For VNAV
the terms waypoint and fix are the same.
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- Fix Displacement Tolerance The rectangular
area formed around and centered on the plotted position of a waypoint. This
describes the region within which the aircraft could be placed when attempting
to over fly the waypoint considering all error components. Its dimensions are
plus-and minute the along-track (ATRK) and cross-track (XTRK) fix displacement
tolerance values found in the applicable lateral RNAV criteria. For VNAV the
ATRK fix displacement error is 0.3 NM.
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| General Criteria |
- The lateral shape of a VNAV instrument procedure is identical
to the LNAV(GPS).
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- The vertical profile provides for an obstacle free area
between the runway and the start of the Obstacle Clearance Surface (OCS)
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- The VNAV Secondary Area Elevation begins at the edge of the
Primary Area and at the elevation of the OCS. and proceeds outward at a 7:1 slope.
For a VPA (GS angle) of 3 degrees the OCS slope is 23.4:1.
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- The distance from the runway threshold where the OCS surface
starts (Section 1) is defined by the formula D = (250-HATh)/.052407779
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- When you draw the VNAV surface (Menu Draw - IAP - RNAV - VNAV)
be sure to extend it 0.3 NM past the FAF waypoint.
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- After you display the procedure and save to the database open
the database, select the procedure using the scroll keys you will need to
regenerate (Re-gen Command Button) the procedure and study (Study Command Button)
the location. The results box will open and display the maximum allowable height.
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- From the Results Form you can select Visual Segment to
automatically build the visual segment and calculate the results if site is inside the visual
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