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from a sudden pitchover or pitch up to capture the final approach glidepath.
In these cases the flight director will automatically downmode from VNAV
to PITCH HOLD mode.
NOTE: VNAV will only disconnect if the vertical deviation is greater
than 100 feet relative to the approach glidepath at the time of
approach activation. If it is less than 100 feet, VNAV mode
should stay coupled through the transition. See figure below.
Recommended Operational Procedure
There are several options to fly VNAV during approach mode.
• The pilot can manually fly the aircraft to the approach glidepath and
reselect VNAV mode on the flight director, or,
• The aircraft can be maneuvered (using some other vertical mode) to a
level altitude below the glidepath, and then VNAV mode selected,
which will arm the flight director/autopilot for capture.
Section V
Operations
2423sv602 5-59
Change 1
• VERTICAL WAYPOINT SELECT PAGE - This page is used
to select the flight plan waypoints which are to be used as
reference for defining the VNAV waypoints. Only flight plan
fixes may be used to define vertical waypoints and not floating
terminators. Also, there can be no floating leg types (e.g.,
HDG to ALT, etc.), gaps or *NO LINK* occurrences between
the aircraft position and the selected vertical TO waypoint.
Once the flight plan waypoints are selected, an offset mileage
may be added to define the position of each VNAV waypoint
either prior to or following the flight plan waypoint along the
flight plan route.
• VERTICAL NAVIGATION DESCENT PAGE - This page
becomes active once VNAV is in the Descent mode. Aircraft
deviation from the vertical flight path is displayed.
• VERTICAL TO PAGE - This page provides vertical flight
guidance between the aircraft's present position/altitude and
any of the nine VNAV waypoint position/target altitudes.
VNAV Setup and Activation
VNAV operations are controlled by the vertical speed input by the
pilot for the first waypoint and the vertical speed computed, based on
the altitudes, for second and subsequent vertical waypoints. The
following information describes how vertical speed is used in the
VNAV function.
Section V
Operations
5-60 2423sv602
Change 1
Target Vertical Speed (TGT V/S)
The target vertical speed entry represents a commanded rate of
descent to the first VNAV waypoint from the top of descent (TOD)
(not present position). The VNAV function will lock in the top of
descent point to achieve the flight path angle dictated by the
commanded descent rate. The following figure is a representation of
three scenarios for vertical speed entry and top of descent points.
V/S OK
TOD
V/S HIGH
PPOS
V/S LOW
VWPT
FPA above limit
MAX FPA
Vertical Speed
Required (VSR)
Once Target V/S is entered, then the flight path angle will be
calculated and “locked in”. Subsequent groundspeed changes prior
to TOD will cause the displayed Target V/S to vary proportionately,
in order to maintain the flight path angle.
Section V
Operations
2423sv602 5-61
Change 1
TGT V/S Affects on TOD Point
The marking V/S OK indicates the first scenario in the figure. In this
scenario the TGT V/S entry will be accepted and all values are within
limits. A typical TGT V/S entry would be approximately 5 times
ground speed to result in a 3° descent angle. As a rule of thumb, a
3° descent Flight Path Angle (FPA) will result in a smooth descent
(e.g., @400 kts use 2000 fpm).
In the second scenario V/S HIGH, a high value for TGT V/S has
been entered and the Top Of Descent (TOD) is delayed to achieve
the desired descent rate. As shown in the figure, this results in the
descent angle being increased and the computed change in FPA will
exceed the limit that is configured for FPA. This will occur
independently of the distance between vertical waypoints. When a
high TGT V/S entry causes the calculated path to exceed the FPA
limit, the TGT V/S value will blink and a message will be displayed at
the top of the page. As a rule of thumb, the TGT V/S entry should
be less than 10 times groundspeed for airplanes and less than 16
times groundspeed for rotor craft. The maximum TGT V/S that is
enterable is 6000 fpm. If a higher TGT V/S is entered the TGT V/S
entry will blink.
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